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post #1 of 54 Old 05-03-2020, 12:29 AM - Thread Starter
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Gearhead Garage Theater - HVAC Design



Overview
The overall design relied heavily on the Rod Gervais book, Home Recording Studios - Build It Like the Pros. Additional inspiration came from this forum, as well. The theater consists of a Main Room ("MR") and a Lobby. The MR will be built as a room-in-room with a small attic space which will house all of the HVAC equipment suspended from the rafters. The Lobby outside the MR includes a bathroom, a small snack area and a Rack Space or AV closet ("AV"). Cooling will be provided by a Mitsubishi minisplit system with a combination of a ducted air handler as well as two wall mounted ductless units. The system will also include additional dehumidification as well as a fresh air source. Submittal sheets for most of the components will be attached below.
Lobby
The Lobby will have a dedicated 9,000Btu minisplit wall unit near the entry door to provide cooling (or heating). At one end of the Lobby will be a small bathroom with a dedicated Panasonic ERV (FV-04EV1). This is an all-in-one 40cfm Energy Recovery Ventilator ("ERV"). It's not super efficient, but it is pretty quiet and it only needs to vent the bathroom while it is in use. There is also the option to run the bathroom ERV unit continuously at 20-40cfm if the Lobby needs additional fresh air. At this point, I'm not planning on sharing the MR fresh air system with the Lobby.

The Lobby will also house a small drink refrigerator and a popcorn machine in the Snack Area and will have a dedicated vent hood with a makeup air supply to match the vent hood exhaust flow, although this has not yet been specified. The plan is to connect the vent hood to a timer. A motorized damper will also be connected to the timer which will open a duct to the outside to allow makeup air to enter the Lobby near the popcorn machine while the vent hood is in use. Without the makeup air, the vent hood effectiveness would gradually diminish as the vent hood depressurizes the Lobby. At some point the negative pressure in the Lobby would match the pressure differential achieved by the vent hood and no more exhaust flow would occur. I have no idea how long this would take and whether makeup air is really needed or if this is just overkill. Adding the makeup air ducting with a motorized damper would be relatively inexpensive, but I'm not sure what the routing might entail....

Near the entrance to the MR will be the AV closet which will house equipment racks. I have room for two racks and a small entrance door, but I have not decided whether I want a door or a simple false wall or some other design. At the far end of the AV closet will be an electrical sub-panel and the area around the panel will be relatively open. Above the racks, inside the AV closet, I plan to install a second 9,000Btu ductless minisplit wall unit. I'm still not sure whether I need 9,000 Btu or if 6,000Btu would be sufficient (I've never done this before). If you look at the attached spreadsheet, I'm anticipating around 7,000Btu of heat generation during peak use, but this is highly dependent on how much heat my amplifiers produce during normal listening vs. reference vs. play time...I just don't have a good feel for this. For now, I've plugged in a 10% power usage to determine my Btu output. The amplifier capacity was determined by the watts needed to play at reference plus 3dB of headroom based on Titan mains, HTM12s for surrounds and Concentric 8s for Atmos. I've allotted 6 channels for subwoofers at 2,000 Watts per channel to play 6-10dB hot over reference.

Main Room
The spreadsheet has been pretty handy for determining duct size and air handler sizing as well as providing a double check for grille sizing. For example, I had originally planned in a 12,000Btu air handler, but the fan capacity would be maxed out meeting the room air exchange requirements. Also, at the highest airflow, the noise produced would also be increased, requiring more extensive duct silencing. Lastly, the smaller unit did not have any reserve capacity to overcome airflow resistance introduced by ducting and filtration. Moving up to the next larger air handler, 18,000Btu, would then overtax the planned outdoor unit, so I had to increase the size of the outdoor unit as well. While normally you can install 130-150% greater capacity of the indoor units with a minisplit system, there was a small footnote that said you should only install indoor units up to 100% of rated outdoor capacity when you are using a ducted air handler. Sooo, I was forced to increase the outdoor unit Btu capacity yet again, especially when you take into account derating factors such as outside air temperatures and piping lengths. All things considered, my total cooling derating is 94%.

One aspect of the Gervais design that was new to me was the need for a barometric pressure relief valve. Basically, if we have truly built an airtight room, and we are constantly supplying it with fresh air from the outside, we will eventually reach a point where the positive pressure inside the theater exceeds the fresh air fan's ability to force more air into the room. Thus we need some sort of pressure relief system to vent stale air out of the room as new fresh air is brought into the room.

As I researched systems that utilize Barometric Pressure Relief Dampers ("BPRD"), I soon realized that there really aren't any BPRDs sized for home use. Furthermore, most commercial BPRDs operate in a higher differential pressure range than I expect to have inside my theater. As a result, I decided I would just use a common backdraft damper, with the hope that the opening pressure is sufficiently low as to not impede fresh air circulation into the MR. Since the Stale Air vent creates a direct connection between the MR and the outside, I felt it would be necessary to introduce some sort of muffler to minimize sound escaping outside and defeating the whole purpose of the room-in-room.

On the other hand, the Fresh Air vent enters the return air plenum close to the air handler and does not create a direct path between the room and the outside. I've elected to use a passive Fresh Air system to take advantage of the relatively negative air pressure near the mouth of the air handler on the return side. My hope is that the pressure differential will be sufficient to entrain an adequate volume of fresh air into the room to meet the calculated fresh air volume. Ever the optimist, I'm planning an air flow regulator to limit the fresh air flow to the maximum needed for a full house in the MR. The CAR-II-LP is a clever passive device that continuously varies its orifice size to maintain a constant air flow over a reasonable range of differential pressures. The Fresh Air circuit will include a large air filter for minimal flow resistance. A motorized damper will also be incorporated to prevent back-flow when the system is not operating (this connection is shown as a>>a in the schematic). In the event the passive system fails to work as expected, I can always add a small inline fan to ensure positive fresh air flow.

I've sized all of the grilles to achieve airflow velocities of less than 200fpm, and many are closer to 100fpm. Grille placement is shown in the drawing below. 8"x48" Linear bar grilles are placed up front with a 15° bar angle to direct the airflow away from the screen and toward the seats. 16"x25" filter intake grilles are placed in the rear of the MR in outboard positions. The remaining two grilles in the rear are 14"x14" and one serves the dehumidifier and the other is for the Stale Air / BPRD system. I plan to maximize duct size to minimize velocity within the ducts to limit aerodynamic noise and I plan to line all of the ducts with insulation to absorb as much noise as possible. In addition, both the supply and return ducts will incorporate 90° bends to try to attenuate HVAC-based noise transmission into the MR as well as to prevent theater sound from escaping the MR into the attic space and thus flanking into the rest of the house.

Lastly, I plan to use a single wired controller in the MR to control all of the minisplit units. I also plan to have a humidistat in the MR for controlling the MR humidity.
Discussion
All of this is new to me, and I may have overlooked something incredibly basic. Regardless, I am really looking forward to your comments and constructive criticism on this design. I plan to install most of this system early during the construction so I can take advantage of a comfortable room while I complete the interior. Therefore I thought it would be prudent to start this discussion early. My thinking right now is to do the majority of the mechanical and electrical installation and have a technician come out and perform the system checkout, evacuation and charging. I'm not sure how this impacts the equipment warranty, and this is one area I still need to investigate.

Thanks in advance for all your time and assistance,
Mike



Here are links to the files or web pages that are too large for me to attach to this post:
MXZ-4C36NA2-U1
SVZ-KP18NA
MSZ-GL09NA-U1
MD6
CFB-6
RSK6
Attached Thumbnails
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Attached Files
File Type: pdf HVAC Calcs.pdf (231.1 KB, 17 views)
File Type: pdf Panasonic fv-04ve1_submittal.pdf (603.1 KB, 6 views)
File Type: pdf car-ii-lp_spec.pdf (338.0 KB, 7 views)
File Type: pdf Ultra-Aire-70H-Spec-Sheet.pdf (505.5 KB, 7 views)
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Last edited by mhutchins; 05-04-2020 at 04:43 PM. Reason: Updated the two inline drawings to reflect new component placement
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post #2 of 54 Old 05-04-2020, 02:52 PM
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Great start to your HVAC plan, thank you for sharing -- a quick comment below as I haven't had time to review your documents in detail (particularly how you calculated the heat load for the equipment):

Quote:
Originally Posted by mhutchins View Post
At the far end of the AV closet will be an electrical sub-panel and the area around the panel will be relatively open. Above the racks, inside the AV closet, I plan to install a second 9,000Btu ductless minisplit wall unit.
Make sure you have the appropriate clear area around the subpanel, if memory serves its 30" clear area (total) along the wall and 36" in front of the panel.

I don't have first-hand experience with ductless minisplits but I would be wary of mounting it directly above any electronics -- in case the unit starts dripping due to some dehumidification draining failure.
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post #3 of 54 Old 05-04-2020, 04:25 PM - Thread Starter
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Quote:
Originally Posted by jjcook View Post
Great start to your HVAC plan, thank you for sharing -- a quick comment below as I haven't had time to review your documents in detail (particularly how you calculated the heat load for the equipment):



Make sure you have the appropriate clear area around the subpanel, if memory serves its 30" clear area (total) along the wall and 36" in front of the panel.

I don't have first-hand experience with ductless minisplits but I would be wary of mounting it directly above any electronics -- in case the unit starts dripping due to some dehumidification draining failure.
Thanks jj!

The panel wall will be 36" wide, so the 30" requirement is met. So long as I only have 1 rack in the Rack Space/AV Closet, there will be plenty of room to comply with the required 36" in front of the panel.

Great comment about possible leakage from the minisplit! I initially planned to have it behind the racks, but that area is pretty tight. I ended up centering the minisplit in the Rack Space/AV closet, but I am concerned about inadequate air circulation near the racks. Your comment has me rethinking this decision. With the minisplit mounted high in the space, there shouldn't be any problem drawing in warm air. My principal concern was supplying enough cool air to the equipment without creating a cooling "short circuit" where the minisplit circulates a limited volume of air leaving the racks untouched in their own bubble of poorly cooled air. Maybe I'm just worrying too much...I'll give some more thought to offsetting the minisplit towards the panel (staying out of the 3'x6' exclusion zone, of course).

Equipment heat load calcs is the biggest area of uncertainty for me with regards to audio amplifiers. I determined the watts per channel needed to achieve reference +3dB head room at the main listening position ("MLP") based on speaker distance and sensitivity. I used -4dB/per distance doubling rather than -6dB as I have read this is more representative in a reverberant room vs. an anechoic space where -6dB is appropriate. I then took the total watts for the bed layer and Atmos speakers and then guessed the normal wattage would only be 10% of the total (also because they will all be Class D topology), and that is the value I converted to Btu. For the subwoofers, I did a similar calc, but planned for heat output based on +6dB over reference + 3dB of head room. I did not factor amplifier efficiency or any other factors since my guess was likely wildly inaccurate. I then guessed that I would have another 500W worth of equipment such as a 16ch pre/pro, router, UPS, NAS server, DVD player, PS V, etc., and that is how I ended up with 7000+Btu of heat generation from the Rack Space.

I am very receptive to anybody's comments with regards to any of these calculations as I have no experience in this area.

Thanks again,
Mike

ps. If anyone can tell me how to post a MS Excel spreadsheet via this forum without resorting to some 3rd party hosting service, I would be happy to share my spreadsheet.

Last edited by mhutchins; 05-04-2020 at 04:29 PM. Reason: added ps about sharing Excel spreadsheet
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post #4 of 54 Old 05-04-2020, 08:28 PM
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If you have your amplifiers picked out already you can look at the data sheets to find the thermal dissipation in BTU/hr. Typically these are specified at Idle and also at 1/8th Power Pink Noise and 1/3rd Power Pink noise. Overall you should and will not use your amplifier for any sustained load higher than the 1/8th Power level so that is a safe upper limit re BTU/hr. Unfortunately many of the other components don't come with such complete specifications.
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post #5 of 54 Old 05-04-2020, 09:44 PM - Thread Starter
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I have waaaaayyyy underestimated the potential heat load from the amplifiers. Currently I'm dreaming of a full compliment of QSC DCA series amps. At 1/8 power, which QSC says represents maximum power with rare clipping of program material, the audio amps would draw ~70amps!......that's almost 30,000Btu!!!

After I regained consciousness I began to talk myself down off the precipice. OK, my amplifiers are spec'ed with 3dB headroom, so now reference would be half that power, or ~15,000 Btu. OK, now we are back into a realm where I think I can manage the heat. A typical movie won't demand reference volume levels the whole time, so worse case scenario is 3dB below reference, and now I'm down to ~7500Btu. This is getting uncomfortably close to the maximum cooling capacity of <9,000 Btu (I think the derated capacity came in at 8,600Btu, but I don't have the figures handy for that). Based on jj's suggestion to check the manufacturer's spec sheets (why didn't I think of that?!?) I may need to reconfigure my cooling distribution in the Lobby. I can drop the Lobby minisplit down to 6,000Btu and up the Rack Space minisplit to 12,000Btu and have a comfortable margin for the equipment cooling. Since the Lobby will only be occupied for brief periods, its cooling demands will be fairly minimal, so I should be safe with the smaller minisplit...famous last words.

Thanks to @jjcook ! This is just one example of why posts like this can be so helpful. It's so much easier to change a spec on paper than after the fact when your equipment is overheating>

Mike
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post #6 of 54 Old 05-04-2020, 10:04 PM
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I understand that realization -- at first I was going to use all QSC CXD-Q amplifiers for fronts, surrounds, and subs for my 13.x.8 but found that the heat load (at idle) would be too high so I backed off to use Crown CT8150 & CT875 amplifiers for the surrounds -- as those at 150W/75W per channel it will be cutting wattage close for reference peaks but my room is super small and the surrounds reasonably efficient. Gear is all bought second hand but the room is still down to studs so I can't speak to the real world heat load.

I suspect that even the 1/8th Power load is much higher than the average load -- given that reference is 20dB peaks over 85dB average program level that is ~64-128x less power. But then add in your house curve in the mid-bass and below octaves...

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Excellent work thus far in your planning. It looks like you are using very high end equipment. The inverter driven Mitsubishi minis are probably the best on the market. I installed an Ultra Aire 70H in my home a few weeks ago. This unit is extremely well engineered and built in the USA. It is a compact unit easily installed and the manual was written in only 1 language....english.

The Ultra Aire might be able to handle your fresh air intake more efficiently than using the air handler blower. It has the ability to walk and chew gum at the same time. You can wye the fresh air duct into the dehu intake duct, still need the damper and filter, and that duct needs to be insulated, but would be a good way to control Texas humidity during the times the HT is unoccupied. The controls are already set up to run fan only, dehumidifier, and has a damper control built in. Per their documentation, it can supply about 55 CFM of fresh air in this configuration. The best way to introduce fresh air is low and slow, like a Texas BBQ. The set up you diagrammed are exactly per their recommendations; central intake separate from the air handler and discharging into the supply plenum using a back draft damper.

As far as how much fresh air you need, all of those recommendations you read are pretty much just educated guesses based on average infiltration, average number of occupants, average barometric pressure, etc. If you don't measure you're just guessing, residential HVAC controls are pretty much all based on anticipation and assumptions. The best way to control the fresh air is with a carbon dioxide sensor. Honeywell model C7232A1008 or Dwyer instruments CDTR series will do the trick. Carbon dioxide gives you a measure of how much oxygen is in the space. The level obtainable will be different based on where you live; if you live in a rural area with a lot of green grass and vegetation it should be lower than an urban area. The lower the level, the better. The ideal range is between 450ppm to 700ppm, the lower the better. Both of these devices are transmitters with analog outputs, but can be configured with relay contacts which is what you would need. You can use the low voltage controls on the 70H to power the sensor.

I would highly recommend a small return duct (4") located near the projector to remove the heat it generates and needs to be dissipated.

There has to be a better way to control over pressuring the room, let me think about that a bit. It seems a bit crude to add to the system you've designed. Are you comparing pressure to the outdoors, or other parts of the building?

Having the air handler and dehumidifier located in an attic, make sure they have emergency overflow pans installed and properly interlocked overflow switches. If done correctly it will shut the unit down before it can generate enough condensate to cause any major damage.
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post #8 of 54 Old 05-06-2020, 09:57 PM - Thread Starter
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As always, Bourbon, your HVAC advice is well considered. Let me respond to each section below, so I don't miss any important information.

Quote:
Originally Posted by Bourbon County View Post
Excellent work thus far in your planning. It looks like you are using very high end equipment. The inverter driven Mitsubishi minis are probably the best on the market. I installed an Ultra Aire 70H in my home a few weeks ago. This unit is extremely well engineered and built in the USA. It is a compact unit easily installed and the manual was written in only 1 language....english.
My goal is to build the room right the first time, then I can upgrade AV equipment for years to come without having to tear the room apart. It's reassuring you hold both brands in high regard. They may be a bit pricey, but I hope to get decades of use out of them.

The Ultra Aire might be able to handle your fresh air intake more efficiently than using the air handler blower. It has the ability to walk and chew gum at the same time. You can wye the fresh air duct into the dehu intake duct, still need the damper and filter, and that duct needs to be insulated, but would be a good way to control Texas humidity during the times the HT is unoccupied. The controls are already set up to run fan only, dehumidifier, and has a damper control built in. Per their documentation, it can supply about 55 CFM of fresh air in this configuration. The best way to introduce fresh air is low and slow, like a Texas BBQ. The set up you diagrammed are exactly per their recommendations; central intake separate from the air handler and discharging into the supply plenum using a back draft damper.
I had originally designed this system with a larger model, the 98H, with the integral fresh air duct. As I thought about it however, I was concerned that the dehumidifier may not run the whole time the theater is occupied, whereas I plan to run the air handler anytime the theater is occupied. Once I considered that point, I reasoned I could use a smaller dehumidifier and pull the fresh air into the room via the negative pressure in the return plenum of the air handler.

As far as how much fresh air you need, all of those recommendations you read are pretty much just educated guesses based on average infiltration, average number of occupants, average barometric pressure, etc. If you don't measure you're just guessing, residential HVAC controls are pretty much all based on anticipation and assumptions. The best way to control the fresh air is with a carbon dioxide sensor. Honeywell model C7232A1008 or Dwyer instruments CDTR series will do the trick. Carbon dioxide gives you a measure of how much oxygen is in the space. The level obtainable will be different based on where you live; if you live in a rural area with a lot of green grass and vegetation it should be lower than an urban area. The lower the level, the better. The ideal range is between 450ppm to 700ppm, the lower the better. Both of these devices are transmitters with analog outputs, but can be configured with relay contacts which is what you would need. You can use the low voltage controls on the 70H to power the sensor.
I'm going to have to think about CO2 modulated Demand Control Ventilation ("DCV") for my theater. My first reaction is that this may be overly complicated for a simple home theater HVAC system. Part of the attraction of the current system design is that the fresh air system is completely passive and thus as close to maintenance free as I can get (except for changing the air filter). I can understand the argument for energy savings by only introducing the volume of fresh air that is actually needed to maintain a reasonable CO2 level (600-800ppm). But I also wonder if the energy savings is worth the cost, both in terms of expense and complexity? Maybe the answer is to simply buy and install the meter and see what happens. I can install conduit from the meter to the attic space so that if an improved Fresh Air system is required, I at least have access to the meter for control purposes.

I would highly recommend a small return duct (4") located near the projector to remove the heat it generates and needs to be dissipated.
I'm planning on some form of hush box that ties into the air handler, but I haven't fleshed this out yet. It sounds like I need to sort this detail out and get it designed into the system schematic so that it doesn't become some sort of hack, later.

There has to be a better way to control over pressuring the room, let me think about that a bit. It seems a bit crude to add to the system you've designed. Are you comparing pressure to the outdoors, or other parts of the building?
The system does not share any air with the rest of the home, so the barometric pressure differential is relative to outdoors. Since I am designing all of the ducting and filtration oversize for low velocities, I assumed that also meant there would be equally low pressure differentials. When I researched Barometric Pressure Relief Dampers ("BPRD"), most of them didn't actuate until .4" W.G. or higher. My guess is that would be near the upper limit of the pressure differential across the air handler and therefore the pressure difference to the outside would be half that and would be insufficient to open the BPRD before incoming fresh air ceased to flow. I assumed that a backdraft damper would function at a lower pressure differential than .4" W.G. but I had trouble finding any data to support my assumption. The alternative is to pressurize the room with a boost fan in the Fresh Air duct and operate the entire room at a higher pressure differential to the outside but still a low differential across the air handler. Again, this is where my ignorance and lack of experience may be leading me down a false path.

Having the air handler and dehumidifier located in an attic, make sure they have emergency overflow pans installed and properly interlocked overflow switches. If done correctly it will shut the unit down before it can generate enough condensate to cause any major damage.
I'll have to look into that. I hadn't considered a back up drain pan, but now that you mention it, it makes perfect sense. Do you have any recommendations on how to accomplish the interlock/emergency shut down function?

Thanks again for your thoughtful comments. It was your reply in another thread that opened my eyes to ventilating dehumidifiers and their relative advantages over more costly Energy Recovery Ventilators.

Mike
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post #9 of 54 Old 05-08-2020, 12:55 PM
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I went back and reviewed your original post and documents a little closer and have some additional comments and will attempt to answer your questions from your last post.

To start with, do a load calculation on the building/structure itself. There are several on the web that are free or a small cost for a 1 time use. loadcalc.net is one I've used. The standard for sizing HVAC equipment is ACCA manual J. It takes many factors into consideration such as your location, insulation values of walls ceilings and rooms below if applicable, size of windows and exterior doors and the compass direction they face, some factor roof material and color which we'll discuss later, air infiltration, Your electronics should not factor into this since all but projector will be isolated in a separate room. After determining this, you can add for occupants and other otherwise abnormal conditions. You need to determine the heat gain of the building before moving on.

After looking at your spread sheet, I agree about the bathroom. Only being roughly 6' X 6' I'm assuming it's only a toilet and sink, no shower or tub. A 20 second hand wash won't produce much heat or humidity, you basically only need the proverbial "fart fan". I would switch the light(s) and fan separately, There are a number of timers on the market both spring wound or digital that will fit in a standard switch box if you wanted to set up a fan overrun for 10-15 min. The 40 CFM will be quite adequate for that. I think that the 400 CFM exhaust hood for a popcorn maker is absurd. Just roughing the area for your snack bar and media storage/theater entrance looks to be about 6' X 15'. With 8' ceilings that would exhaust every molecule of air in that area in <2 minutes. Put that in perspective, if you supply make up air for that kind of exhaust which is good thinking, and brought in that much hot humid Texas air it would take >1 ton of A/C just offset that heat gain, and that's not even considering the building heat gain. Not to mention that as soon as you open the door to the theater that air is going to rush into that room. I'm thinking something in the range of an 80-100 CFM bath exhaust fan would be quite enough. A good experiment would be move the popcorn maker into your bathroom and make a batch of popcorn, see how long it takes to exhaust the steam and heat. This setup would not require any make up air since they are only used infrequently and for short periods of time.

Part of my thinking for using the Ultra Aire for fresh air is only partially for energy savings. Look up the install manual and look on page 10 where it explains how to accomplish this. I believe all of the other models of their dehumidifiers have a designated fresh air duct inlet. I believe Ultra Aire designed this model to compete with Aprilaire and Honeywell who make similar size units that can be used in crawl spaces. The extra duct inlet makes the overall size of the unit much larger. Connecting the fresh air supply to the inlet duct as opposed to the unit takes the air to the same place ultimately. In fact, by connecting to the fresh air to the intake duct will only help mix with the conditioned air before it gets to the blower. I can't find the exact specs, but I'm assuming the blower on the Ultra Aire is 1/3 the size of the air handler or less. The other part of my thinking was for times the theater is unoccupied. A lot of thermostats have dehumidification settings, but they accomplish by letting the air conditioning to go lower than set point by as much as 3 degrees which can be very costly. During the times the theater is unoccupied, you can turn the temperature up to say 80 deg or so, but leave the humidity set at 45% and carbon dioxide to your desired level. When you do use the theater, it will be fresh and there will be little if any latent load for the A/C to remove, it will cool quickly. A/C provides comfort for occupied spaces, proper humidity levels also provide comfort but also help to remove fertilizer for mold and mildew, it's just more healthy.

I have to run out and pick up dinner, will continue later this evening.
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post #10 of 54 Old 05-08-2020, 05:47 PM
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For the fresh air control, it won't be a modulated system but can be done fairly simply and there is a way to set it up so you could switch from the Ultra Aire to the air handler pretty simply and quickly. I'm building a demand driven modulating system for my house and I've chosen Dwyer Instruments for all of my sensors, they seemed to have a sensor for everything I want to monitor. I bought their model CDTR-2N4A2-LCD-RLY for my carbon dioxide sensors, the outputs for temp and humidity are analog but on this model it has relay contacts for the carbon dioxide which is what you would need. I liked these over the Honeywell because the range is programmable on these where the Honeywell had a bunch of dip switches to select one of their ranges which none fell near where I wanted. You will get some overshoot with these but it's just more of a good thing. These devices cost about $225 each as I recall. To make this possible, it would require a little extra work and low cost parts for the electrical and ducting.

For the ducting, run the 6" line from the intake point damper and branch off to the dehu as well as running it to the air handler return. Keep it full 6" the whole run. Install a manual damper just before it connects to the dehu inlet duct and another before the air handler return. They are a little more expensive, but I would use an iris damper as opposed to a balancing damper. The blades on an iris damper work like an SLR camera aperture and will close completely. They have ports on both sides so you can connect a manometer and measure your airflow. Pay close attention to the power damper you choose and don't buy a damper for zoning, they don't close completely, they actually want them to leak a little to keep static pressure lower. Buy one that closes 100% and has rubber seals around the blade when closed. This needs to be physically located as close to the building entrance point as you can get but allow access for service, they do fail from time to time. Buy an exterior intake hood that has some screen material over the opening to prevent birds from nesting in the duct, and it should have a hood to help keep rain from entering.

For the controls, buy and install a junction box somewhere midway between the air handler and dehu, preferably one big enough to mount a 10-12 point terminal strip in. Buy and mount the Dwyer CDTR in the theater area, and run a 4 or 5 conductor thermostat cable from it to the junction box. A word of caution, don't mount the sensor until all drywall, painting are done and room is thoroughly cleaned. This is a pretty delicate device and you don't want it filled with dust. Run a 2 wire thermostat cable to the power damper from the junction box. Run a 5 wire thermostat cable from the junction box to the dehu and another to the air handler. Make sure the wires are clearly marked. Once you get to this point, email me and I'll tell you how to connect. These are all 24 volt sourced and won't hurt you, when you start to interconnect devices powered from different power sources (transformers) is where you get in trouble. This will give you the flexibility to switch from the air handler to the dehu by moving a few wires and opening one iris damper and closing another. If you find one method works better than the other just leave it connected to that one. This is not complex at all.

As far as becoming over pressurized, I'm going to throw out a couple of ideas. Dwyer (again) makes a sensor made to control a modulating damper BYDS series, this could be used with a modulating damper such as Honeywell MARD series. The only thing I noticed was the range on these is between 2.0 and 10.0" WC which seems a bit high. There is another Dwyer sensor, the APDS series that is field settable and comes in a variety of ranges. These are <$25 and will require a small poly tube to be run to a static probe inside the theater and another to the outside. When you decide what pressure you want to maintain, you can use this switch to open another powered damper. I don't know just how well a barometric damper will work and have no idea how to simulate pressure differential to set it up. By the way, that Mitsubishi air handler is rated at 0.3", 0.5", and 0.8" of static based on what speed it's running. Normally 0.5" is the design standard for the duct system which in this case includes the filter and evaporator coil. That is the static pressure the air handler sees, not necessarily the difference between indoor and outdoors.

Diversitech and many other manufacturers make overflow pans, some plastic, some sheet metal. I personally like the Diversitech plastic ones, they have ribs that the unit sits on so if it were ever to get water in it, your unit won't start rusting. These are required by code anywhere equipment that can produce condensate is located above living spaces. Rectorseal and other manufacturers make the switches, they are basically a float switch inside a 3/4" PVC pipe fitting. The switches are always normally closed so you just series the common wire for the unit through the switch so if the switch ever opens, your unit will shut down. They also make water sensors that can be installed in the pan that can sense a very small amount of water and operate the same way. There should be a switch on the evaporator coil and the emergency pan.You could easily wire a relay and an alarm to these, but it's rarely ever done, you just notice the unit won't work. In most cases it's just a clogged drain line.

This loft area where you are installing the equipment, is it a somewhat conditioned space or just an attic space. The reason I'm asking is because installing air handlers and/or ducts in an unconditioned space is not a really good idea. Think about how hot it can get in that space, I'm thinking in Austin possibly 130-140 degrees? You will be pushing hopefully 55 degree air through ducting in that space and no matter how well you insulate the duct, the heat will win that battle, or cause some inefficiency at minimum. I realize there are times it has to be done, but there are a few things you can do to the space to help with that situation. Look at Florida where almost all houses are built on a slab and the attic is about the only place to install the air handler.
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I went back and reviewed your original post and documents a little closer and have some additional comments and will attempt to answer your questions from your last post.

To start with, do a load calculation on the building/structure itself. There are several on the web that are free or a small cost for a 1 time use. loadcalc.net is one I've used. The standard for sizing HVAC equipment is ACCA manual J. It takes many factors into consideration such as your location, insulation values of walls ceilings and rooms below if applicable, size of windows and exterior doors and the compass direction they face, some factor roof material and color which we'll discuss later, air infiltration, Your electronics should not factor into this since all but projector will be isolated in a separate room. After determining this, you can add for occupants and other otherwise abnormal conditions. You need to determine the heat gain of the building before moving on.
I was more than a little unsure how to enter my wall values for a room-in-room construction with both walls consisting of 2 x 6 construction and 1" airgap between walls and triple layer drywall, so I chose a wall type that I thought would have the least amount of heat flux. For the attic space above the theater, I have no idea what it takes to accomplish a given R-value or what impact triple layer 5/8" drywall would have, so I arbitrarily chose R-30. Likewise for the floor, I wasn't sure what to use. From top to bottom the floor will consist of: Carpet and pad, 3" layer of Gypcrete, 1" subfloor, 3" airgap with insulation, 1" subfloor, ~12" Engineered I Joists w/ 7.5" insulation, 2 x 5/8" Type-X drywall, garage.

Here is the result of the calculation for just the theater space with 7 people, without the lobby or the projector heat load:


After looking at your spread sheet, I agree about the bathroom. Only being roughly 6' X 6' I'm assuming it's only a toilet and sink, no shower or tub. Correct. A 20 second hand wash won't produce much heat or humidity, you basically only need the proverbial "fart fan". I would switch the light(s) and fan separately, There are a number of timers on the market both spring wound or digital that will fit in a standard switch box if you wanted to set up a fan overrun for 10-15 min. The 40 CFM will be quite adequate for that.
Cool, thanks!


I think that the 400 CFM exhaust hood for a popcorn maker is absurd. Just roughing the area for your snack bar and media storage/theater entrance looks to be about 6' X 15'. With 8' ceilings that would exhaust every molecule of air in that area in <2 minutes. Put that in perspective, if you supply make up air for that kind of exhaust which is good thinking, and brought in that much hot humid Texas air it would take >1 ton of A/C just offset that heat gain, and that's not even considering the building heat gain. Not to mention that as soon as you open the door to the theater that air is going to rush into that room. I'm thinking something in the range of an 80-100 CFM bath exhaust fan would be quite enough. A good experiment would be move the popcorn maker into your bathroom and make a batch of popcorn, see how long it takes to exhaust the steam and heat. This setup would not require any make up air since they are only used infrequently and for short periods of time.
In my defense, I had planned to bring in the makeup air just beneath the popcorn maker to minimize the path between inlet and exhaust to try to avoid the exact scenario you describe. Regardless, your point is well taken! Based on what you are saying, maybe a 50-110cfm ceiling mounted bathroom fan such as the Panasonic FV-0511VQ1 is all I really need. It would certainly simplify things not having to deal with makeup air. I just didn't want the lobby area to be covered in a layer of coconut oil grime after a few years of use, but I guess I went a little overboard....

Part of my thinking for using the Ultra Aire for fresh air is only partially for energy savings. Look up the install manual and look on page 10 where it explains how to accomplish this. I believe all of the other models of their dehumidifiers have a designated fresh air duct inlet. I believe Ultra Aire designed this model to compete with Aprilaire and Honeywell who make similar size units that can be used in crawl spaces. The extra duct inlet makes the overall size of the unit much larger. Connecting the fresh air supply to the inlet duct as opposed to the unit takes the air to the same place ultimately. In fact, by connecting to the fresh air to the intake duct will only help mix with the conditioned air before it gets to the blower. I can't find the exact specs, but I'm assuming the blower on the Ultra Aire is 1/3 the size of the air handler or less. The other part of my thinking was for times the theater is unoccupied. A lot of thermostats have dehumidification settings, but they accomplish by letting the air conditioning to go lower than set point by as much as 3 degrees which can be very costly. Yah, I don't like doing that because it gets too cold! During the times the theater is unoccupied, you can turn the temperature up to say 80 deg or so, but leave the humidity set at 45% and carbon dioxide to your desired level. When you do use the theater, it will be fresh and there will be little if any latent load for the A/C to remove, it will cool quickly. A/C provides comfort for occupied spaces, proper humidity levels also provide comfort but also help to remove fertilizer for mold and mildew, it's just more healthy.
I think all of this is within the control functionality of the Ultra-Aire controller. I need to do more research on the CO2 sensor/controllers you linked previously. From my preliminary look, I think I might be able to control the Ultra-Aire with the two controllers in parallel, so long as they both use the 24vac from the Ultra-Aire for power.

I have to run out and pick up dinner, will continue later this evening.


Here is the updated schematic with the new fresh air circuit as well as the resized wall units:


Thanks again @Bourbon County for helping me with this. I really appreciate it!
Mike
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For the fresh air control, it won't be a modulated system but can be done fairly simply and there is a way to set it up so you could switch from the Ultra Aire to the air handler pretty simply and quickly. I'm building a demand driven modulating system for my house and I've chosen Dwyer Instruments for all of my sensors, they seemed to have a sensor for everything I want to monitor. I bought their model CDTR-2N4A2-LCD-RLY for my carbon dioxide sensors, the outputs for temp and humidity are analog but on this model it has relay contacts for the carbon dioxide which is what you would need. I liked these over the Honeywell because the range is programmable on these where the Honeywell had a bunch of dip switches to select one of their ranges which none fell near where I wanted. You will get some overshoot with these but it's just more of a good thing. These devices cost about $225 each as I recall. To make this possible, it would require a little extra work and low cost parts for the electrical and ducting. Yep, I liked the Dwyer better as well for the same reasons.

For the ducting, run the 6" line from the intake point damper and branch off to the dehu as well as running it to the air handler return. Keep it full 6" the whole run. Install a manual damper just before it connects to the dehu inlet duct and another before the air handler return. They are a little more expensive, but I would use an iris damper as opposed to a balancing damper. The blades on an iris damper work like an SLR camera aperture and will close completely. They have ports on both sides so you can connect a manometer and measure your airflow. Pay close attention to the power damper you choose and don't buy a damper for zoning, they don't close completely, they actually want them to leak a little to keep static pressure lower. Buy one that closes 100% and has rubber seals around the blade when closed. This needs to be physically located as close to the building entrance point as you can get (yep, that's why I have it drawn close to the line separating indoors and outdoors) but allow access for service, they do fail from time to time. Buy an exterior intake hood that has some screen material over the opening to prevent birds from nesting in the duct, and it should have a hood to help keep rain from entering.
In this area it has to be screened to keep the mud dauber wasps out!

For the controls, buy and install a junction box somewhere midway between the air handler and dehu, preferably one big enough to mount a 10-12 point terminal strip in. Buy and mount the Dwyer CDTR in the theater area, and run a 4 or 5 conductor thermostat cable from it to the junction box. A word of caution, don't mount the sensor until all drywall, painting are done and room is thoroughly cleaned. This is a pretty delicate device and you don't want it filled with dust. Run a 2 wire thermostat cable to the power damper from the junction box. Run a 5 wire thermostat cable from the junction box to the dehu and another to the air handler. Make sure the wires are clearly marked. Once you get to this point, email me and I'll tell you how to connect. These are all 24 volt sourced and won't hurt you, when you start to interconnect devices powered from different power sources (transformers) is where you get in trouble. This will give you the flexibility to switch from the air handler to the dehu by moving a few wires and opening one iris damper and closing another. If you find one method works better than the other just leave it connected to that one. This is not complex at all.
I also considered connecting to both units as you mentioned, but without the iris dampers. If I leave the flow controller in the circuit, I can easily limit the maximum fresh air flow into the system, regardless of how many intake ducts it is connected to. The Ultra-Aire install manual mentioned a fresh air flow around 50cfm with a simple 6" Tee, and mentioned higher airflow with 8" ducting. In all honesty, I doubt I will ever have more than 3 people in the theater for longer than 2 hours, so I think the 105cfm fresh air flow target is excessive. 50cfm of fresh air should be more than enough for 99.9% of the usage this theater will ever see.

If I power all of the sensor/controllers from the Ultra-Aire 24vac circuit (other than the centralized thermostat for the whole minisplit system), I should be able to avoid any issues with phase/neutral mismatch, shouldn't I???

As far as becoming over pressurized, I'm going to throw out a couple of ideas. Dwyer (again) makes a sensor made to control a modulating damper BYDS series, this could be used with a modulating damper such as Honeywell MARD series. The only thing I noticed was the range on these is between 2.0 and 10.0" WC which seems a bit high. There is another Dwyer sensor, the APDS series that is field settable and comes in a variety of ranges. These are <$25 and will require a small poly tube to be run to a static probe inside the theater and another to the outside. When you decide what pressure you want to maintain, you can use this switch to open another powered damper. I don't know just how well a barometric damper will work and have no idea how to simulate pressure differential to set it up. By the way, that Mitsubishi air handler is rated at 0.3", 0.5", and 0.8" of static based on what speed it's running. Normally 0.5" is the design standard for the duct system which in this case includes the filter and evaporator coil. That is the static pressure the air handler sees, not necessarily the difference between indoor and outdoors.
I found a datasheet for the Fantech backdraft dampers and the 8" dampers open at ~.2" (I had to convert from pascals and cubic meters/hour), the 6" open a little higher, but not by a whole lot. I think that opening pressure relative to outside should work well with the system as designed. If my CO2 levels can't be managed with the passive system, I can always add a boost fan in the fresh air circuit and use the Dwyer CO2 sensor to control the boost fan.

Diversitech and many other manufacturers make overflow pans, some plastic, some sheet metal. I personally like the Diversitech plastic ones, they have ribs that the unit sits on so if it were ever to get water in it, your unit won't start rusting. These are required by code anywhere equipment that can produce condensate is located above living spaces. Rectorseal and other manufacturers make the switches, they are basically a float switch inside a 3/4" PVC pipe fitting. The switches are always normally closed so you just series the common wire for the unit through the switch so if the switch ever opens, your unit will shut down. They also make water sensors that can be installed in the pan that can sense a very small amount of water and operate the same way. There should be a switch on the evaporator coil and the emergency pan.You could easily wire a relay and an alarm to these, but it's rarely ever done, you just notice the unit won't work. In most cases it's just a clogged drain line.
Great info, I'll look into adding these for the installation!

This loft area where you are installing the equipment, is it a somewhat conditioned space or just an attic space. Just attic space. The reason I'm asking is because installing air handlers and/or ducts in an unconditioned space is not a really good idea. Think about how hot it can get in that space, I'm thinking in Austin possibly 130-140 degrees? You will be pushing hopefully 55 degree air through ducting in that space and no matter how well you insulate the duct, the heat will win that battle, or cause some inefficiency at minimum. I realize there are times it has to be done, but there are a few things you can do to the space to help with that situation. Look at Florida where almost all houses are built on a slab and the attic is about the only place to install the air handler.
Well, I am thinking about linacoustic lined ducts built from OSB, Green Glue and double 5/8" Type-X drywall. Not sure of the R-value for that combo, but I could always add a layer of rigid iso foam with a radiant barrier. I need to talk to Nyal Mellor about the duct requirements to control bass leakage outside the room. I'll see what the builders in Florida are doing for their attics to minimize heat gain and I'll talk to my architect as well.


Wow! You are a wealth of information. I hope others benefit from this discussion as much as I have!!

Mike


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First of all, thanks for your compliments. Did you post the results of your load calculation? I didn't see it. It's interesting how these calculations work out, try punching in your structure's information and use a Minneapolis or Denver zip code and see how different they are. Even in a housing development with identical houses built across the street from each other and 1 has a large amount of west facing glass and the other has the same glass expanse only facing east, it will be different. The old "rule of thumb" sizing norms are ancient history even though a lot of contractors use 500 to 600 sq. ft. per ton. Size does matter in A/C and oversizing is probably the worst mistake. You are paying for the larger equipment to start with, it will have bigger motors that are more expensive to run, they will cool to set point too fast and cycle too often which will shorten the lifespan of the equipment. Since they run for short cycles they don't do a very good job of dehumidifying and even though the house is cool, it's not comfortable. The variable speed units will hide a multitude of sins of oversizing but you're still paying more for the equipment.

Yes, you can use the power supply on the Ultra-Aire to control the fresh air system. They have oversized the controls transformer and set up the terminal strip just for that reason. I'm telling you this is a very well designed and engineered product. This won't be complex at all and if you should need assistance, I'll be glad to sketch it out and send it to you. There is one more wrinkle I would like you to consider that will make it a little more complicated. The more airtight we build buildings, the more we need to bring in fresh air by mechanical means for reasons we have previously discussed. You do pay a price for that fresh air in a few ways, first the labor and materials to install the intake, the energy required to run the intake system, and the energy required to condition the air you brought in. Obviously much of this is very much climate driven. I'll bet you have many days that are >96 degrees and you will have to cool the amount of that air to 72 deg or whatever your comfort level is. The point I'm getting to is there is a point where it no longer makes sense to bring in outdoor air. If outdoor temps drop below 30 degrees,which should not be a concern for you, don't bring it in. If you aren't familiar with dew point, read up on it. Dew point is a factor of temperature, humidity, and barometric pressure and is where the discomfort lies. If you know anyone living in Houston, ask them about dew point. Houston is probably the most uncomfortable city in the nation. Anyway, if the outdoor dew point gets too high, you probably don't want to bring it in. I found a really cool little Honeywell device I'm using on my system. The model is DG115EZIAQ it can control a humidifier, dehumidifier, ventilation system, most everything but the main unit. It has a wired (2 wire) remote outdoor sensor and will calculate dew point. It has a number of dry contacts (no power supplied) and I'm only using 2 of them that close one when the dew point reaches 65 deg and another that closes when dew point reaches 75 deg. If you are interested in this option, let me know and I'll detail it a little more. I believe this sells for about $50 and would not be very complex to hook up.

The pressure relief you talked about has really puzzled me, it makes good sense and a lot of the energy gurus I read all say you should maintain a slight positive pressure inside. Many talk about the benefits, but it was hard to find anyone that said by how much and how to control it. As it turns out, you were on the right track but pressures were too high. I found an article Rob Falke wrote that explained a lot. Rob is the president of National Comfort Institute, and considered the godfather of HVAC performance and air balancing. I had the pleasure of meeting him at an energy conference a few years ago and he is extremely knowledgable and very funny. I attended a few of their classes and they really know their stuff. Their message is that air movement is king. Any unit regardless of brand, country of origin, SEER rating can make the air warm or cool the real key is to get the right amount of air to the right location with minimal duct loss. There is more value in a properly sized, designed, and installed duct system than in equipment. In Rob's article he says that 0.02 to 0.04 in WC is a good pressure difference between indoor and outdoor pressures. Those are lab level measurements and you were off by a factor of 10X according to that. He went on to say if you were only bringing in between 55-75 CFM of outdoor air it should not be a problem.

All buildings leak, yours will likely be extremely low but you don't know unless you measure. There should be some BPI or RESNET raters in your area, if you want to make the investment have them do a blower test when your theater is finished. The going rate used to be about $300 and you certainly don't need a full energy audit. This would be of some value for acoustics too, if air will leak through a gap so will sound. If you aren't familiar with the process, they set up a dummy door on your front door that holds a calibrated fan, they lower the pressure in your house to 50 pa which supposedly emulates a 20 mph wind hitting the side of your house. They go around with a thermal camera and try to find anywhere air is leaking in. The 50 pa standard they use equals about 0.2 in WC which is still 10X what you are looking for. I don't know if you could divide their number by 10 and still be accurate, I don't know if that scale would be linear or not. I suppose you could ask them to set the fan for 5 pa and see what the natural leakage is. This would confuse most of them to a great degree, they have a very rigid set of standards and most that I've met are very OCD about them. They also seem to have a standardized list of explanations for things they really don't understand. If there isn't enough natural leakage, I don't have any ideas better than yours. One concern is that duct will be a conduit for sound coming in from outside and vice versa.

What is the model of the Mitsubishi thermostat you are going to use? The upside to using their thermostats is they do a great job of controlling the variable speed motors and metering valve, the downside they don't give you much versatility in controlling other devices. I'm curious to see if they have a set of dry contacts to control the dehumidifier without having to mount a separate control just for that.

One other device to consider is a UV lamp in the evaporator coil. Their main function is to prevent mold growth on the coil. That coil will be the only part of your system that will be damp. After an A/C call it takes a few minutes for all of the condensate to drip off, but that film of water while it's running gives it higher efficiency. They are made by a number of manufacturers: Aprilaire, Field Controls, Honeywell, Sanuvox one to fit your unit is about $200 and the lamps have to be replaced every couple of years which are pretty costly. This would be an easy add on down the road, very simple install.

I'll do another post on duct design and some ideas about the attic later.
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First of all, thanks for your compliments. Did you post the results of your load calculation? I didn't see it.
Not sure what happened, it was there at one point. I reran the calcs since I'm at work and I used slightly different conditions, but the results came out within 10% of my previous run.
Here is the result:


Here are my comments from an earlier post regarding my choices when I ran the above load calc:
Quote:
I was more than a little unsure how to enter my wall values for a room-in-room construction with both walls consisting of 2 x 6 construction and 1" airgap between walls and triple layer drywall, so I chose a wall type that I thought would have the least amount of heat flux. For the attic space above the theater, I have no idea what it takes to accomplish a given R-value or what impact triple layer 5/8" drywall would have, so I arbitrarily chose R-30. Likewise for the floor, I wasn't sure what to use. From top to bottom the floor will consist of: Carpet and pad, 3" layer of Gypcrete, 1" subfloor, 3" airgap with insulation, 1" subfloor, ~12" Engineered I Joists w/ 7.5" insulation, 2 x 5/8" Type-X drywall, garage.
.
.
.
Yes, you can use the power supply on the Ultra-Aire to control the fresh air system. They have oversized the controls transformer and set up the terminal strip just for that reason. I'm telling you this is a very well designed and engineered product. This won't be complex at all and if you should need assistance, I'll be glad to sketch it out and send it to you. There is one more wrinkle I would like you to consider that will make it a little more complicated. The more airtight we build buildings, the more we need to bring in fresh air by mechanical means for reasons we have previously discussed. You do pay a price for that fresh air in a few ways, first the labor and materials to install the intake, the energy required to run the intake system, and the energy required to condition the air you brought in. Obviously much of this is very much climate driven. I'll bet you have many days that are >96 degrees and you will have to cool the amount of that air to 72 deg or whatever your comfort level is. The point I'm getting to is there is a point where it no longer makes sense to bring in outdoor air.
I just got a quote for a whole home dehumidifier install and the technician that came out said that they don't use the fresh air option for the very reasons you stated above. Obviously, for an air tight room such as a well constructed home theater, fresh air is a requirement to prevent CO2 buildup, unlike in the typical home that has a much larger air volume per person than the average home theater.

If outdoor temps drop below 30 degrees,which should not be a concern for you, don't bring it in. If you aren't familiar with dew point, read up on it. Dew point is a factor of temperature, humidity, and barometric pressure and is where the discomfort lies. If you know anyone living in Houston, ask them about dew point. Houston is probably the most uncomfortable city in the nation. I'm quite familiar with dew point from an aviation standpoint and I lived in Houston for several years and a hurricane ago. Anyway, if the outdoor dew point gets too high, you probably don't want to bring it in. I found a really cool little Honeywell device I'm using on my system. The model is DG115EZIAQ it can control a humidifier, dehumidifier, ventilation system, most everything but the main unit. It has a wired (2 wire) remote outdoor sensor and will calculate dew point. It has a number of dry contacts (no power supplied) and I'm only using 2 of them that close one when the dew point reaches 65 deg and another that closes when dew point reaches 75 deg. If you are interested in this option, let me know and I'll detail it a little more. I believe this sells for about $50 and would not be very complex to hook up.
Last year where I live on Lake Travis, the dew point was over 65° for nearly 6 months and it rose into the mid 70s almost daily for most of the summer.

The pressure relief you talked about has really puzzled me, it makes good sense and a lot of the energy gurus I read all say you should maintain a slight positive pressure inside. Many talk about the benefits, but it was hard to find anyone that said by how much and how to control it. As it turns out, you were on the right track but pressures were too high. I found an article Rob Falke wrote that explained a lot. Rob is the president of National Comfort Institute, and considered the godfather of HVAC performance and air balancing. I had the pleasure of meeting him at an energy conference a few years ago and he is extremely knowledgable and very funny. I attended a few of their classes and they really know their stuff. Their message is that air movement is king. Any unit regardless of brand, country of origin, SEER rating can make the air warm or cool the real key is to get the right amount of air to the right location with minimal duct loss. There is more value in a properly sized, designed, and installed duct system than in equipment. In Rob's article he says that 0.02 to 0.04 in WC is a good pressure difference between indoor and outdoor pressures. Those are lab level measurements and you were off by a factor of 10X according to that. He went on to say if you were only bringing in between 55-75 CFM of outdoor air it should not be a problem.
I'm not sure where or how residential HVAC engineers are maintaining such a low indoor/outdoor pressure differential when all of the barometric controls I can find often have a lower limit of 0.2 in. WC. If I go to an 8" Fantech backdraft damper, I think the opening pressure was down around 0.12-0.16 in. WC. I did find some large 12-24" barometric dampers that could be adjusted lower, but their installation in my system would be impractical, at best.

All buildings leak, yours will likely be extremely low but you don't know unless you measure. . . . . One concern is that duct will be a conduit for sound coming in from outside and vice versa.
That is why I have a "muffler" shown in the schematic for the Barometric Pressure Relief circuit. That is the only part of the HVAC system where there is a straight path between the indoors and the outdoors, and I am very concerned about sound leakage in both directions. This will certainly be an area that I address with Nyal to limit sound transmission as much as possible.

What is the model of the Mitsubishi thermostat you are going to use? The upside to using their thermostats is they do a great job of controlling the variable speed motors and metering valve, the downside they don't give you much versatility in controlling other devices. I'm curious to see if they have a set of dry contacts to control the dehumidifier without having to mount a separate control just for that.
I don't have that info available right now. I have been using the Mitsubishi "Diamond System Builder" ("DSB") at home to assist me with defining my system and modeling performance. According to DSB, I can control all three indoor units with a single wall-mounted control, but I haven't looked any further into the features of that controller or the cost. I was planning on using the optional Ultra-Aire controller, the DEH3000, as it looked like it had the extra functionality I needed, but I can't say right now what that was beyond just controlling the humidity setpoint.

One other device to consider is a UV lamp in the evaporator coil. Their main function is to prevent mold growth on the coil. That coil will be the only part of your system that will be damp. After an A/C call it takes a few minutes for all of the condensate to drip off, but that film of water while it's running gives it higher efficiency. They are made by a number of manufacturers: Aprilaire, Field Controls, Honeywell, Sanuvox one to fit your unit is about $200 and the lamps have to be replaced every couple of years which are pretty costly. This would be an easy add on down the road, very simple install.

I'll do another post on duct design and some ideas about the attic later.
I can't thank you enough Bourbon!
Mike
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Wow to the wow on that loadcalc! Just think the 7 occupants you entered represent nearly half of that load. I imagine the insulation values you used are probably a little low, and the calculation does have some "fudge factor" built in.You're basically building a big Yeti cooler. Less than a half ton load in Austin! Not that you would use one, but I don't know if anyone even makes a window unit that small.

As far as residential HVAC engineers concerned about pressure differential with outdoors, I sincerely doubt it's ever crossed their minds, that is purely a sales driven market and most of their money is made on new equipment. They most always want to replace same size with same size and unless a manual J is required in their locale or a customer demands it before they buy. There is always natural leakage and exterior doors being opened off and on during the day, probably not an issue.

Now that you you have seen what size equipment you need, what are your ideas going forward? I have some ideas about the dehu and fresh air that somewhat work around the excessive dew points if you are interested. The advantage you have is it's not a space that will be occupied round the clock. Humans are about the only thing that can put humidity in that space and absolutely the only thing that can put CO2 in there.
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Wow to the wow on that loadcalc! Just think the 7 occupants you entered represent nearly half of that load. . . .
Yep, and the projector and lights add about as many Btu's as the people, which wasn't part of the load calc performed by the online calculator!

Now that you you have seen what size equipment you need, what are your ideas going forward? I have some ideas about the dehu and fresh air that somewhat work around the excessive dew points if you are interested. The advantage you have is it's not a space that will be occupied round the clock. Humans are about the only thing that can put humidity in that space and absolutely the only thing that can put CO2 in there.
Well, I think the 6K Btu unit for the Lobby and the 12K Btu unit for the Rack Space are the right choices, although the Rack Space may never operate for prolonged periods at full capacity (otherwise that closet will be HOT even with 12K Btu cooling capacity!!). The choice of the air handler was driven more by blower capacity to meet room exchange requirements than Btu capacity. Also, the larger blower is quieter for any given cfm of air flow vs. the next smaller sized air handler. The smaller, 78 pint Ultra-Aire dehumidifier should be sufficient for the room, especially combined with the additional dehumidification provided by the air handler. I think I will Tee the fresh air into the dehumidifier return for two reasons: 1) the dehumidifier has greater capacity for humidity reduction of the fresh air than the air handler; and 2) it should be a simpler installation than Teeing into the main air handler from an acoustic and mechanical standpoint.

Right now I'm working on all the HVAC controller and sensor integration and how that all fits together. I'll post an electrical schematic once I get that figured out. There is a lot of overlap in functionality between these controllers so I am trying to find the most rational design while not overloading any transformers or mismatching 24Vac hot and neutral in any circuit. Earlier you asked which Mitsubishi thermostat/controller I was planning for the various spaces and I replied I only needed one for all three indoor units. After more careful review, I believe that only would work if all three indoor units shared the same temperature setpoints. Sooo, whether I use one or three, it will likely be the same controller, the PAC-YT53CRAU (operation manual attached). It's just a basic controller, but it should do everything I need.

I hope to have more later tonight or tomorrow.

Mike

PAC-YT53CRAU Operations Manual

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I'm not sure where you got your air exchange requirements or what you are calling an air exchange. My definition for an air exchange is exchanging indoor air with outdoor fresh air. Circulating room air across the evap coil is not an exchange in my book. The proper way to design an HVAC system is by doing an ACCA manual J which you have already done. The ACCA manual S helps with equipment selection, and the ACCA manual D is for duct design. The fan speed setting on a traditional air handler is somewhat regional, the higher the average humidity is the lower the fan speed, the typical selection choices are between 350-400 CFM per ton (in cooling mode). On the variable speed systems it will likely set the speed/CMF in the firmware and you will have little or no ability to adjust. Once equipment, fan speed, and ducting is selected you adjust the airflow going to each supply with balancing dampers. Designing by CFM is kinda doing it backwards.

I believe what your book calls air exchanges is swapping indoor with outdoor air. Remember what I said about being educated guesses? There are also local climate conditions to consider such as your extreme dew points. The CO2 control method will supply exactly what you need, no more, no less, and you are still light years ahead of most other homes and theaters. Proper CO2 levels are only a creature comfort, the audio and video gear doesn't care. Ironically humans are the only thing that can raise the CO2 levels in that room. To take air exchange to the next level you would need an energy recovery ventilator. If you want to see a really high end ERV look up Ultimateaire. They make what is considered to be the best in the industry, variable speed and they offer an add on accessory pressure regulator system. It's an analog system made to work with their controls. Warning: this ERV and the pressure regulator will likely cost more than the Ultra Aire and Mitsubishi together. There are 4 different ducts to install with any ERV, and they can work in harmony with a central dehumidifier.

I looked at the thermostat you linked and I believe that's just for a wall mount head. It has a setting for the vanes and that's only on the wall mounts, I'll bet there is a different one for an air handler. I also saw that it was a 12 vdc system, so it's not going to be good about sharing it's toys with the Ultra Aire. You will have to install a stat in each area.
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I'm not sure where you got your air exchange requirements or what you are calling an air exchange. My definition for an air exchange is exchanging indoor air with outdoor fresh air. Circulating room air across the evap coil is not an exchange in my book. OK, my bad for not using proper nomenclature. By "air exchange", I was referring to recirculation of room air volume through the air handler. The proper way to design an HVAC system is by doing an ACCA manual J which you have already done. The ACCA manual S helps with equipment selection, and the ACCA manual D is for duct design. The fan speed setting on a traditional air handler is somewhat regional, the higher the average humidity is the lower the fan speed, the typical selection choices are between 350-400 CFM per ton (in cooling mode). On the variable speed systems it will likely set the speed/CMF in the firmware and you will have little or no ability to adjust. Once equipment, fan speed, and ducting is selected you adjust the airflow going to each supply with balancing dampers. Designing by CFM is kinda doing it backwards.

I believe what your book calls air exchanges is swapping indoor with outdoor air. Remember what I said about being educated guesses? There are also local climate conditions to consider such as your extreme dew points. The CO2 control method will supply exactly what you need, no more, no less, and you are still light years ahead of most other homes and theaters. Proper CO2 levels are only a creature comfort, the audio and video gear doesn't care. Ironically humans are the only thing that can raise the CO2 levels in that room. To take air exchange to the next level you would need an energy recovery ventilator. If you want to see a really high end ERV look up Ultimateaire. They make what is considered to be the best in the industry, variable speed and they offer an add on accessory pressure regulator system. It's an analog system made to work with their controls. Warning: this ERV and the pressure regulator will likely cost more than the Ultra Aire and Mitsubishi together. There are 4 different ducts to install with any ERV, and they can work in harmony with a central dehumidifier. I think I'll pass on that ERV system based on the $$$$ alone.

I looked at the thermostat you linked and I believe that's just for a wall mount head. It has a setting for the vanes and that's only on the wall mounts, I'll bet there is a different one for an air handler. This may be the better choice for the main space, PAR-40MAAU. It looks to be compatible, but I will verify before I purchase, of course. The Mitsubishi indoor units all use a simple 2-wire interface for the thermostat and there are no options for making other connections inside the thermostat. I also saw that it was a 12 vdc system, so it's not going to be good about sharing it's toys with the Ultra Aire. This won't be a problem with the way I've configured the system below. You will have to install a stat in each area. Yah, as I read more about these systems, that started to become apparent. It wasn't clear to me what constituted a "Group" within the Mitsubishi ecosystem, but I now believe it means that all the indoor units in a group share the same setpoints and other settings.

Here is the schematic for the HVAC control system. I have only shown the 24Vac connections and not the line voltage connections.




Overview

The main theater system will have 3 controllers: 1) a Thermostat for the control of heating and cooling of the room; 2) a Humidistat to control the relative humidity in the room; and 3) A CO2 sensor to control the CO2 levels in the room via introduction of fresh air from outside. This control system should optimize interior comfort while minimizing energy usage through the use of the most efficient equipment for the intended task. The equipment will consist of a Mitsubishi SVZ-KP18NA air handler connected to a Mitsubishi minisplit compressor outdoors, an Ultra-Aire 70H dehumidifier with a fresh air inlet controlled by a motorized damper. Stale air will be exhausted from the room via a passive Barometric Pressure Relief system.

Heating and Cooling - The air handler will be controlled by a programmable thermostat with a 2-wire, nonpolarized connection (either a Mitsubishi PAC-YT53CRAU, PAR-40MAAU or similar). When the room is occupied, the target temps will be selected, otherwise, wider range "setback" temperatures will be maintained while the theater is unoccupied. The air handler will have a secondary condensate pan equipped with a moisture sensor. If the secondary condensate pan begins to fill with water, the condensate sensor will prevent further cooling and its associated condensate production via the connections labeled "CN4F". This condition will also trigger a flashing alarm condition on the thermostat screen. The air handler will also provide some degree of dehumidification, however there may be conditions where this ability is limited without overcooling the room.

Dehumidification - An Ultra-Aire dehumidifier will perform the bulk of the dehumidification chores for the room. It will be controlled by an Ultra-Aire humidistat. When the humidistat senses high relative humidity ("RH") in the room, it will energize the COMP(ressor) signal which is connected to the DEHU(midify) control on the dehumidifier, thus putting the unit in dehumidify mode. The COMP signal is run through a condensate sensor mounted in a secondary condensate pan. When moisture is detected, the COMP signal is interrupted and the dehumidifier will turn off. This state will also cause an alarm device to signal, so long as moisture is detected in the secondary pan and the COMP signal is active. Whenever the humidistat energizes the COMP signal, it will also energize a fan relay which is used as an interlock with the air handler to ensure the air handler fan will run to circulate the dry air in the room. This function is accomplished via the "CNER" connections on the air handler.
Here in Austin we can have routinely high RH for the six months of summer and in the fall and spring we can have occasional days with near 100% RH but with temperatures in the mid 60-70's where normal AC would not be in use.

CO2 Control - A Dwyer instruments CO2 controller will be used to control theater CO2 levels by introducing fresh air into the room when CO2 exceeds it's set point. Normal atmospheric CO2 is in the range of 350-400 parts per million ("ppm"). Studies show performance degradation at levels above 800-1000ppm. When CO2 levels above a threshold are detected, the Dwyer controller will energize a relay that will be wired to the FAN input on the dehumidifier and it is also connected to a motorized damper which will open and allow fresh air to flow into the Ultra-Aire inlet duct via a Tee connection. As the dehumidifier draws in outside air, it will likely trigger the internal humidistat in the dehumidifier and dry the incoming fresh air if needed. The internal humidistat will be set for a higher RH than the wall mounted controller. When the dehumidifier is triggered by the Dwyer sensor, it is not interlocked with the air handler fan, so only the dehumidifier fan will be circulating the air to reduce the CO2 levels. On the other hand, since only people can raise the CO2 (under normal circumstances), it is quite likely that the air handler will already be running.

The benefit of using a controller to introduce fresh air only as needed, rather than bringing in fresh air continuously at a rate sufficient to cover maximum occupancy, should result in substantial energy savings. Here in Austin, AC is needed for much of the year and when it is not required, substantial dehumidification is often needed. I also plan to check the CO2 display during hi occupancy periods to verify that my fresh air ducting arrangement is sufficient.

Any time additional air volume is introduced into a closed space, the pressure must increase. If the pressure vessel (theater)
doesn't leak, the pressure will continue to build until a point is reached where no additional air volume can be introduce into the room. Unless a door or window is opened, CO2 will continue to rise, since there is no fresh air introduced to dilute the CO2 and there is no vent to exhaust the CO2 saturated air. This is where the Pressure Relief Damper system ("PRDS") comes into play. In this installation, the PRDS consists of a simple backdraft damper that is exposed to room pressure on one side and outside air pressure on the other. When the pressure differential across the backdraft damper is in the range of 0.16-0.2" WC, the damper begins to open and releases the pressure in the room, thus venting stale indoor air, making room for fresh outdoor air. In this manner, CO2 levels are controlled within the target range. That's the plan, at least....

Mike
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You're pretty much there. You will need 2 float switches each on both the air handler and the dehumidifier, a primary installed on the unit, and an emergency installed on the overflow pan. I've never seen one that had a double throw switch, that's not to say they don't make one though. Since the dehu can turn on via the internal dehumidistat while bringing in fresh air which will produce condensate, the Dwyer will need to be in series also. Probably easier to series the 2 float switches in before you branch off to the 2 devices on either the 24v or com wires. Being located in an attic that is rarely checked, you want all of the protection you can get, it could be leaking for a long time before you ever noticed it inside the room.

The spec on the Dwyer sensor says the contacts are rated for 2 amps, check the damper you buy for it's current rating, if it's too high you might need to add a relay. A normally closed damper stays energized the entire time it's supposed to be open. These dampers have some really small motors and a lot of gear reduction, they can take up to 30 seconds to fully open.

Normal atmospheric CO2 levels and what you have might not necessarily be the same, there are a number of things that can affect it. I ran a data logger outdoors for 48 hours and the lowest I saw it go was around 350 PPM and I live in a rural area with lots of vegetation around. Don't set it to a level it can't achieve, you can never get it lower than outdoor conditions at your house. I'm setting mine for a 450 to 700 PPM range. This is easily adjustable on the sensor if you need to change. Remember you will have to condition the air you bring in.

Running the air handler blower during dehu cycle only is optional, the Ultra Aire blower will be enough.
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You're pretty much there. You will need 2 float switches each on both the air handler and the dehumidifier, a primary installed on the unit, and an emergency installed on the overflow pan. I've never seen one that had a double throw switch, that's not to say they don't make one though. Since the dehu can turn on via the internal dehumidistat while bringing in fresh air which will produce condensate, the Dwyer will need to be in series also. Probably easier to series the 2 float switches in before you branch off to the 2 devices on either the 24v or com wires. Being located in an attic that is rarely checked, you want all of the protection you can get, it could be leaking for a long time before you ever noticed it inside the room.
Great catch on the Dwyer needing to be interrupted as well if there is a condensate overflow situation with the dehumidifier! I remember thinking that dehumidification would likely be needed with fresh air flow and that the internal humidistat would engage in most situations where fresh air was demanded, but I never connected the dots that that was also a failure mode in the event of a blocked condensate drain. In their manual, Ultra-Aire mentions connecting a float switch mounted in a secondary drain pan to interrupt the common/neutral side of the 24Vac supply to the control board. If I rewire the condensate sensor in this fashion, it will preclude the need for a second float switch for the Dwyer CO2 fresh air control circuit. I will make this change on the schematic tomorrow when I get home from work.

I don't understand why you say I will need 2 float switches for the air handler. The primary drain pan on the air handler will always be wet and/or have a water level present, so placing a float switch in the primary drain pan would always result in the air handler shutting down after a short period of use. Mounting a float switch/condensate sensor in the secondary drain pan makes absolute sense, and I fully intend to include that feature.

On this topic I have yet another question. The Mitsubishi air handler has two drains for each orientation; a primary drain and an overflow drain. If I have a condensate sensor in the secondary drain pan, can I just run the overflow drain into the secondary drain pan, or should this be routed outside with the primary drain? Of course the secondary drain pan will have its own drain to the outside.


The spec on the Dwyer sensor says the contacts are rated for 2 amps, check the damper you buy for it's current rating, if it's too high you might need to add a relay. A normally closed damper stays energized the entire time it's supposed to be open. These dampers have some really small motors and a lot of gear reduction, they can take up to 30 seconds to fully open. The MD6 motorized damper sold by HVACQuick.com is rated at 0.3A (24Vac), so current draw from the damper should be handled easily by the Dwyer CO2 relay. Similarly, the 24Vac/40VA transformer on the Ultra-Aire should have no trouble supplying the current that will be used to energize the controls and damper.

Normal atmospheric CO2 levels and what you have might not necessarily be the same, there are a number of things that can affect it. I ran a data logger outdoors for 48 hours and the lowest I saw it go was around 350 PPM and I live in a rural area with lots of vegetation around. Don't set it to a level it can't achieve, you can never get it lower than outdoor conditions at your house. I'm setting mine for a 450 to 700 PPM range. This is easily adjustable on the sensor if you need to change. Remember you will have to condition the air you bring in.
Agreed. I was considering setting the range to 600-800. My thinking on the lower limit of 600ppm is that there is no need to try to get any closer to ambient outdoor CO2 if there are no adverse health effects below the 800ppm threshold. And, as you mentioned, any fresh air I bring in to dilute the CO2 levels will need to be cooled and dehumidified. Why did you choose a lower level of 450 in your application?

Running the air handler blower during dehu cycle only is optional, the Ultra Aire blower will be enough.
Mitsubishi recommends running the air handler blower continuously, however, the typical application is for a whole house rather than a single home theater complex, so I'm a little ambivalent about their recommendation. On the other hand, I haven't come across a convenient means of shutting off the blower when the room is unoccupied, other than purchasing some sort of centralized system controller that I'm sure is probably quite expensive.
Thank you again for all of your assistance on this design. I can't believe how fortunate I am to have someone with your knowledge and experience to be so giving of their time and expertise!

Mike
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I have been doing some more research on your pressure relief system. Dwyer makes a press differential switch ADPS-08-2-N that has has an adjustable range from 0.08" wc to 1.2" wc which is closer to the range you wanted. You would have to install a static pressure probe inside the room and another outside and run poly tubing from each probe to the switch. You could use this switch to control a powered damper, I'm thinking a 4" would be all you would need. I believe there would only be a puff of air exhausted before pressure was relieved and would likely happen before the damper even opened completely. You would have to pick up 24vac somewhere to operate the damper. The Ultra Aire has a 40va transformer which should be big enough and it would not be operating on a frequent basis. The switch is <$25 and the damper would be about $75. If you could use 4" duct the muffler is about $20 cheaper than a 6" and you won't need the backdraft damper, just a screened exhaust hood like a clothes dryer. That more than pays for the switch and a little thermostat wire. You might call Dwyer and talk to one of their application engineers about what you are trying to accomplish, their customer service is amazing. These folks have been working with very small pressures for a long time, they are truly experts in their field, and I'm sure could guide you much better than I can.

With the high end equipment and precision controls you are putting in, it just seems a little crude to use a barometric damper to accomplish the pressure relief. If you went the diff pressure switch route, you could pull the tubes off of the switch and connect to a manometer and measure what the actual difference is and adjust accordingly. As I've said many times, if you don't measure it, you're just guessing.

I installed a steam humidifier a few years ago in my home and used one of these switches to prove air flow before the humidifier would start. Not that you would ever need one, but steam humidifiers can add humidity even when there is no call for heat unlike the flow through models. You must have airflow to disperse the steam or it will condense and start rusting the ducts, this is my safety net for that system.
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You're very welcome for the assistance. I feel some ownership in this project. I hope you keep updating this thread as you work on this project and especially when it's complete. Once it is complete don't expect instant gratification especially in the humidity control and this is NOT an indication you bought the wrong size unit. That space will be very humid from being exposed to outdoor air as well as drywall mud, paint, and high moisture content building materials. It might take 48 to 72 hours to stabilize.

My Ultra Aire is installed in my basement and I did not use a secondary pan since it's not above a living space. I installed a flow through type switch on the drain line where it exits the unit. I had to use a small condensate pump to collect the water and pump it into the house drain system. The pump has a float switch that will break before it leaks out. I interlocked both switches into the 24vac circuit. You really don't have to use 2 but it's a $20 insurance policy. The emergency overflow pan should NEVER be wet so don't dump your condensate through it and you really want to know if it ever gets wet. That's like a 911 call.

If you do opt to use 2 float switches, just wire them in series common to the 24v or common wire before you tap the connection going to each device. It's all on the same power supply, you can't screw it up.

Yes, it's industry standard that all evaporator coils have 2 drain ports. If you look, one will be higher than the other, that's the secondary. Common practice is to just pipe the condensate away from the primary drain and install just a safety switch in the secondary. The condensate is more of a steady drip rather than gushing water. The same principle for the air handler as the dehumidifier, the emergency overflow pan should always be dry. You can pipe it into the primary drain system in the event it does ever contain water.

If you aren't experienced in plumbing drains, do some research. The condensate drains need to be trapped and vented downstream of the trap. In theory the line will be dry downstream of the trap, you need the trap in this case to keep the units from drawing outside air in through the drain line. Rectorseal makes a cool little switch that has the switch built into the trap and a removable cap to clean out the trap. They also include a little brush on a fiberglass rod to push through and clean the trap out. In any case, design your drains so you include a PVC pipe cap that you don't glue on to let you access the drain for cleaning. They do tend to clog up with mold and it's a good maintenance practice to clean them a couple of times per year and flush them out good with some bleach.

The short answer to why I chose the CO2 range is basically "because I can". I have been planning this project for years and it's become more and more complex over the years. I retired about a year ago and hopefully get to complete it later this year. I read the recommendations for years including the ASHRAE 62.whatever version they are up to now. They are all based on an average home leakage, climate, etc., they do some adjustments for sq footage and occupants. Basically it's just a guess. That's were I looked into the ultimate goal measuring the CO2 levels. My system will use a variable speed Fantech inline duct fan with an ECM motor. I'm going to use pressure diff transmitters to measure airflow into which ever of the 3 zones are calling and set the fan speed based on the CO2 transmitter and check and adjust flow based on the pressure diff transmitters. My target was set between 450-700 after measuring what my outdoor is, and setting flow rate based on a complete air exchange in a 4-5 hour period. I'll be using a small PLC with a lot of analog cards and if I need to make adjustments, it's just a program change. There will be outdoor conditions of high dew points or temps below 30 deg that will turn it off completely. By the way, I'll probably have north of $3500 in this thing and only my free labor so I really hope it works!

I'm not familiar with Mitsubishi thermostats, I have the Honeywell 8000 series with the IAQ interface module that is very versatile. My stats give me the fan choices of auto, on, and circ. Auto means it will only run the blower while there is a call for heat or A/C, on keeps the blower running all of the time, circ has an algorithm in the stat that runs the blower a few minutes every now and then between cycles. The experts recommend against running the blower all the time, but I personally like to have some air movement. My units are American Standard which are relabeled Trane products. It is built into the firmware that the variable speed blower will ramp down to about 20% speed when it is not in either a heating or cooling cycle, and this is not field adjustable. I suspect will be the case with the Mitsubishi. They modulate the compressor speed, condenser fan speed, blower speed, and metering valve orifice based on the load, that's where they get their efficiency. I don't believe that air handler is going to provide the cfm you desire unless it's in a cooling cycle. If you do hire a tech to do start up, you could ask him about blower speed between cycles but I doubt he could adjust it. A Mitsubishi field rep probably has capability to change it, but they likely wouldn't even respond to a home owner, nor adjust that speed. This is another good reason to use the Ultra Aire for fresh air intake, it's a constant speed fan.

If you do decide to contact Dwyer about possible solutions to the pressure relief, please post that. I'm really interested. They are located in Indiana, so it's same time zone as you.
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post #23 of 54 Old 05-13-2020, 08:11 PM - Thread Starter
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Originally Posted by Bourbon County View Post
I have been doing some more research on your pressure relief system. Dwyer makes a press differential switch ADPS-08-2-N that has has an adjustable range from 0.08" wc to 1.2" wc which is closer to the range you wanted. You would have to install a static pressure probe inside the room and another outside and run poly tubing from each probe to the switch. You could use this switch to control a powered damper, I'm thinking a 4" would be all you would need. I believe there would only be a puff of air exhausted before pressure was relieved and would likely happen before the damper even opened completely. You would have to pick up 24vac somewhere to operate the damper. The Ultra Aire has a 40va transformer which should be big enough and it would not be operating on a frequent basis. The switch is <$25 and the damper would be about $75. If you could use 4" duct the muffler is about $20 cheaper than a 6" and you won't need the backdraft damper, just a screened exhaust hood like a clothes dryer. That more than pays for the switch and a little thermostat wire. You might call Dwyer and talk to one of their application engineers about what you are trying to accomplish, their customer service is amazing. These folks have been working with very small pressures for a long time, they are truly experts in their field, and I'm sure could guide you much better than I can.
Bourbon, you are a bigger gearhead than I am! You have really opened my eyes to what is possible with these high-end systems and how they should be designed. That adjustable differential pressure switch sounds perfect for this application! I've had bad luck with just about every type of poly tubing holding up to the Texas environment. Just about any flexible tubing I have used outdoors has ultimately succumbed to the heat and UV radiation here so I will use either aluminum or copper tubing for the outdoors sample line. I will use the dehumidifier 24Vac to run the second damper for the Barometric Pressure Relief system. Combined, the two motorized dampers only draw 0.6 amps which is less than half the VA rating of the Ultra-Aire's transformer. I will probably need to build my own custom mufflers to control the bass I'm hoping to produce in this theater. Also, good to know about Dwyer's customer service and engineering!

With the high end equipment and precision controls you are putting in, it just seems a little crude to use a barometric damper to accomplish the pressure relief. If you went the diff pressure switch route, you could pull the tubes off of the switch and connect to a manometer and measure what the actual difference is and adjust accordingly. As I've said many times, if you don't measure it, you're just guessing.
Every time I try to devise a simple, passive system to accomplish a task with reasonable performance, you come back with this pinpoint sensor and motorized gizmo to exactly monitor and control the variable in question.
Keep up the good work!

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Quote:
Originally Posted by Bourbon County View Post
You're very welcome for the assistance. I feel some ownership in this project. I hope you keep updating this thread as you work on this project and especially when it's complete. Once it is complete don't expect instant gratification especially in the humidity control and this is NOT an indication you bought the wrong size unit. That space will be very humid from being exposed to outdoor air as well as drywall mud, paint, and high moisture content building materials. It might take 48 to 72 hours to stabilize.
I'll be happy if I can just bring the temperature down to 85° and the humidity down to 65% during the construction phase. I'll keep the delta-p switch and the CO2 sensor protected until the drywall is finished. I will do my best to keep this thread current as the project progresses. I think I mentioned it once before, but I plan to get the AC working just as soon as I have a dry shell to work in. I know having a comfortable work environment will go a long way toward enhancing my productivity.
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Yes, it's industry standard that all evaporator coils have 2 drain ports. If you look, one will be higher than the other, that's the secondary. Common practice is to just pipe the condensate away from the primary drain and install just a safety switch in the secondary. The condensate is more of a steady drip rather than gushing water. The same principle for the air handler as the dehumidifier, the emergency overflow pan should always be dry. You can pipe it into the primary drain system in the event it does ever contain water.

If you aren't experienced in plumbing drains, do some research. The condensate drains need to be trapped and vented downstream of the trap. In theory the line will be dry downstream of the trap, you need the trap in this case to keep the units from drawing outside air in through the drain line. Rectorseal makes a cool little switch that has the switch built into the trap and a removable cap to clean out the trap. They also include a little brush on a fiberglass rod to push through and clean the trap out. In any case, design your drains so you include a PVC pipe cap that you don't glue on to let you access the drain for cleaning. They do tend to clog up with mold and it's a good maintenance practice to clean them a couple of times per year and flush them out good with some bleach.
This is all great info!! I knew to add a standpipe, but all these other details are pure gold!
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I'm not familiar with Mitsubishi thermostats, I have the Honeywell 8000 series with the IAQ interface module that is very versatile. My stats give me the fan choices of auto, on, and circ. Auto means it will only run the blower while there is a call for heat or A/C, on keeps the blower running all of the time, circ has an algorithm in the stat that runs the blower a few minutes every now and then between cycles. The experts recommend against running the blower all the time, (Mitsubishi Application Note 1033: Indoor Fan Continuous Operation)but I personally like to have some air movement. My units are American Standard which are relabeled Trane products. It is built into the firmware that the variable speed blower will ramp down to about 20% speed when it is not in either a heating or cooling cycle, and this is not field adjustable. I suspect will be the case with the Mitsubishi. They modulate the compressor speed, condenser fan speed, blower speed, and metering valve orifice based on the load, that's where they get their efficiency. I don't believe that air handler is going to provide the cfm you desire unless it's in a cooling cycle. If you do hire a tech to do start up, you could ask him about blower speed between cycles but I doubt he could adjust it. A Mitsubishi field rep probably has capability to change it, but they likely wouldn't even respond to a home owner, nor adjust that speed. This is another good reason to use the Ultra Aire for fresh air intake, it's a constant speed fan.

If you do decide to contact Dwyer about possible solutions to the pressure relief, please post that. I'm really interested. They are located in Indiana, so it's same time zone as you.
Thanks again, Bourbon! I'll update the wiring schematic and system schematic tomorrow to reflect the changes we've discussed so far. I'm still not so keen about the Iris dampers in the Fresh Air system. I know it gives me a lot of flexibility, but for the money I feel this is something I can do at a later date, if needed. With the active CO2 control, I think my needs will be met with the Fresh Air inlet duct directly Tee'd into the return air duct of the dehumidifier, especialy if I use 8" duct for the Fresh Air inlet duct. Lastly, I still need to research attic cooling in Florida. I suspect this involves radiant heat barriers and rigid foam insulation on the exterior of the sheathing with additional interior rigid and flexible insulation, but my tank is empty for tonight...........

Mike

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There is some question in my mind about using the diff pressure switch. This switch does not have any span or range built in. If you set it to actuate at 0.04"wc then it will actuate when it goes to that and the turn back off once it drops below that setting. You don't have the option to open the damper at one set point and close it at another. It might not be a problem, but I'm thinking it will short cycle the damper motor. Remember it takes these things up to 30 seconds to operate. If the opposite turns out to be the case, the damper staying open too long, I do have a solution for that. Buy another of the same switches. The contacts are SPDT so you would wire to the NO contacts on the one set for your desired opening pressure, set the other switch for the pressure you desire to close the damper and wire the NC contacts on that switch in series with the NO contacts on the other switch. This might not be necessary and I would not do it in the initial install. If you see later that it's needed it's just another $20 switch and some tees for the poly tubing and a little wire.

There's no need to run the tubing out in the sun. you can install the outdoor probe in the soffit of your building. If possible, mount on either the east or north side of the building away from prevailing winds which will give a false indication of outdoor pressure. It's really critical the 1/4" ID tubing not get crimped or kinked. I used some just a little larger for the discharge of a small condensate pump and didn't like the looks of the tubing so I ran some 3/4" PVC conduit and fished the tubing in it. The tubing is kinda sticky an had to use some wire lube, but it looks much better and much less likely to get damaged. When you connect the tubing to the switch connect the outdoor tube to the negative or - port and the one from your theater to the positive or + port. It is possible to have higher pressure outdoors in cooler weather.

Being in the aviation field, I'm sure you know about turbulence and laminar air flow. These principles apply to duct work too. I know Ultra Aire shows a Tee fitting to connect the fresh air into it's return duct. A much better set up would be as the fresh air duct approaches the return install a 45 degree fitting turned toward the unit, leave enough room to install a straight piece of about 2-3 feet and connect to the dehu return with a Wye fitting. This will increase air flow and reduce turbulence in the duct. Supposedly a straight section of 2-3 feet will allow the air flow return to a more laminar flow.

Filtration:
I would highly recommend that instead of using filtered return grilles, buy a media filter box and install directly to the unit and attach the return to it. These have either a 4" or 5" thick pleated filter that has far more filter surface area that does a much better job of filtration, reduces static pressure on the system, the housings are much more airtight, and depending on room usage might only need to be changed once a year. There are several on the market made by Honeywell, Trion, Aprilaire, and others. I'll bet there is one designed to exactly fit the opening on your air handler. The filters come in a range of MERV ratings and cost about $20 or so based on size. I think the Trion models are made to accept more generic filters than the others. You are going to have to go into the attic to change the Ultra Aire filter and check condensate drains anyway. The fresh air does need some filtration as you have designed, but get the coarsest fiberglass replaceable or washable media you can find. You basically want a rock stopper but minimal restriction at that point, the Ultra Aire can be fitted with either a MERV 11 or 13 which will filter anything out before it goes into your room. In any case, NEVER use the 3M Filtreat 1" pleated filters. They load up too quickly and become extremely restrictive. HVAC contractors make a lot of money replacing blowers and systems failed because of low air flow, Filtreat is one of their best friends.

Ducting:
You mentioned building ducts out of OSB and/or drywall. DO NOT use any material with organic content exposed to the airflow, that's a recipe for mold. They will have darkness, humidity already and that will furnish a food source. There are types of paperless drywall on the market designed to help prevent mold. If you use duct liner, remember the duct needs to be sized for its net internal area. If you need say a 10" X 12" duct and install 1" thick liner, the net inside dimensions would be 8" X 10". I would also recommend that you locate your return grilles located high on the wall or even in the ceiling. You are in a climate that is primarily A/C, the warmer air in the room will naturally try to convect up as well as the heavier cool air will tend to push it upwards. This would be slightly less efficient during the rare times you need to heat the room, but more efficient during cooling.

When you get this system debugged and working like I believe it will, you might want to contact Mr. Gervais about writing an addendum to his book. Your system will provide more comfort and healthy air than a vast majority of houses in this country, it will be more like a lab environment.

I have earlier expressed my opinions of residential HVAC controls and I do realize that they are done that way to help keep equipment prices down and simplify things for the field techs. As you see you can integrate some commercial and industrial components to provide much more precise control and can be done without making it too complex.
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Forgot to mention, I was only recommending the iris dampers so you could possibly switch the fresh air from the Ultra Aire to the air handler. You don't need them the direction you have decided to go.

I bought my Ultra Aire from Sylvane a web sales site that is based in Atlanta i believe. I had some questions that I could not find answers in any of the documentation posted. I called their customer service and the guy had to dig pretty deep to get the answers, but he did. The point I'm really trying to make is that once he answered my questions he gave me a 10% discount code to enter when I placed my order. Their shipping is free and mine got here in 2 days. That phone call netted me over $120!
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Before you place your order with Dwyer you need to select static pressure pickups for the pressure relief system. Look at the RSM series pressure monitors which are made for clean rooms and operating rooms. No, I'm not suggesting you buy one of these $1100 devices! hit the accessories tab and they show several options for both indoor and outdoor static pressure pickups. They sell a really cool outdoor model that has a wind screen and is made to hold up against the elements. These are mostly in the $10-20 range. You will need one indoor and one outdoor.

If you think I'm obsessed with this company, you're probably right. They're like Mr. Haney on the old "Green Acres" TV show, he always had just what you needed just as Dwyer seems to always have just what I need.
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Originally Posted by Bourbon County View Post
There is some question in my mind about using the diff pressure switch. This switch does not have any span or range built in. If you set it to actuate at 0.04"wc then it will actuate when it goes to that and the turn back off once it drops below that setting. You don't have the option to open the damper at one set point and close it at another. It might not be a problem, but I'm thinking it will short cycle the damper motor. Remember it takes these things up to 30 seconds to operate. If the opposite turns out to be the case, the damper staying open too long, I do have a solution for that. Buy another of the same switches. The contacts are SPDT so you would wire to the NO contacts on the one set for your desired opening pressure, set the other switch for the pressure you desire to close the damper and wire the NC contacts on that switch in series with the NO contacts on the other switch. This might not be necessary and I would not do it in the initial install. If you see later that it's needed it's just another $20 switch and some tees for the poly tubing and a little wire.
Dwyer makes a slightly more expensive (~$50) switch, the Series 1900 Adjustable Differential Pressure Switch, that has listed deadbands that should work well in this application. In particular, the 1910-00 has an adjustment range between 0.07-0.15"wc with a 0.04"wc deadband. For example, if this switch is adjusted to actuate at 0.10"wc, it will not deactivate until the differential pressure has decreased to 0.06"wc. As an aside related to your comment a few posts above about the expected barometric pressure differential of this room vs. outdoors, one of Dwyer's info sheets related to COVID-19 mentions that negative pressure isolation rooms are only required to be 0.01"wc below the outer corridor pressure to satisfy CDC guidelines. That's 1/50 the static pressure developed by a typical residential ducted air handler!

There's no need to run the tubing out in the sun. you can install the outdoor probe in the soffit of your building. If possible, mount on either the east or north side of the building away from prevailing winds which will give a false indication of outdoor pressure. It's really critical the 1/4" ID tubing not get crimped or kinked. I used some just a little larger for the discharge of a small condensate pump and didn't like the looks of the tubing so I ran some 3/4" PVC conduit and fished the tubing in it. The tubing is kinda sticky an had to use some wire lube, but it looks much better and much less likely to get damaged. When you connect the tubing to the switch connect the outdoor tube to the negative or - port and the one from your theater to the positive or + port. It is possible to have higher pressure outdoors in cooler weather.
Great idea using the conduit!

Being in the aviation field, I'm sure you know about turbulence and laminar air flow. These principles apply to duct work too. I know Ultra Aire shows a Tee fitting to connect the fresh air into it's return duct. A much better set up would be as the fresh air duct approaches the return install a 45 degree fitting turned toward the unit, leave enough room to install a straight piece of about 2-3 feet and connect to the dehu return with a Wye fitting. This will increase air flow and reduce turbulence in the duct. Supposedly a straight section of 2-3 feet will allow the air flow return to a more laminar flow.
Great point.

Filtration:
I would highly recommend that instead of using filtered return grilles, buy a media filter box and install directly to the unit and attach the return to it. These have either a 4" or 5" thick pleated filter that has far more filter surface area that does a much better job of filtration, reduces static pressure on the system, the housings are much more airtight, and depending on room usage might only need to be changed once a year. There are several on the market made by Honeywell, Trion, Aprilaire, and others. I'll bet there is one designed to exactly fit the opening on your air handler. The filters come in a range of MERV ratings and cost about $20 or so based on size. I think the Trion models are made to accept more generic filters than the others. You are going to have to go into the attic to change the Ultra Aire filter and check condensate drains anyway. The fresh air does need some filtration as you have designed, but get the coarsest fiberglass replaceable or washable media you can find. You basically want a rock stopper but minimal restriction at that point, the Ultra Aire can be fitted with either a MERV 11 or 13 which will filter anything out before it goes into your room. In any case, NEVER use the 3M Filtreat 1" pleated filters. They load up too quickly and become extremely restrictive. HVAC contractors make a lot of money replacing blowers and systems failed because of low air flow, Filtreat is one of their best friends.
Awwhhh man! I just converted all my home filters over to the Filtrete 1900 1" pleated filters. Fortunately our HVAC system will warn us if the filters are restricting flow excessively. With regards to the filtered return grilles vs. the deep pleated filters in a dedicated filter box near the air handler, I will respectfully decline this feature. I know myself and I know I will rarely go up into the small attic space to clean or replace filters or clean condensate drains. It's a human nature thing and I just know how I work (or don't work) in these matters. With the filter grilles I know that with a simple step stool I will be able to reach up and replace the filter on a somewhat regular schedule. In the attic, not gonna happen....

Ducting:
You mentioned building ducts out of OSB and/or drywall. DO NOT use any material with organic content exposed to the airflow, that's a recipe for mold. They will have darkness, humidity already and that will furnish a food source. There are types of paperless drywall on the market designed to help prevent mold. If you use duct liner, remember the duct needs to be sized for its net internal area. If you need say a 10" X 12" duct and install 1" thick liner, the net inside dimensions would be 8" X 10". I would also recommend that you locate your return grilles located high on the wall or even in the ceiling. You are in a climate that is primarily A/C, the warmer air in the room will naturally try to convect up as well as the heavier cool air will tend to push it upwards. This would be slightly less efficient during the rare times you need to heat the room, but more efficient during cooling.
I had no idea about mold's desire for organic materials! I guess I could paint the interior of the duct with a mold resistant paint such as ZinsserPerma-White before I line the interior with duct-board.

When you get this system debugged and working like I believe it will, you might want to contact Mr. Gervais about writing an addendum to his book. Your system will provide more comfort and healthy air than a vast majority of houses in this country, it will be more like a lab environment.
I'm humbled by your expectations. I just hope the design survives my implementation! Also, I still need to run all this through my acoustics expert, Nyall, to make sure I don't defeat all the effort and expense I am undertaking to try to control all the bass I hope to generate. If my wife is still texting me to "Turn it down!", I will be one forlorn puppy.

I have earlier expressed my opinions of residential HVAC controls and I do realize that they are done that way to help keep equipment prices down and simplify things for the field techs. As you see you can integrate some commercial and industrial components to provide much more precise control and can be done without making it too complex.
I had to laugh when you said that it "...can be done without making it too complex." That's kind of the equivalent of me thinking that four refrigerator sized 21" horn-loaded Devastator subs in my theater with 8kw of amplification should be a good start for the LFE channel. When I started down this path my initial system concept was so simple, albeit potentially inefficient to the point of being marginally effective. It has evolved to what I consider to be a high-end commercial installation with significant automation just shy of a centralized, computer controlled building management system. But then again, I'm just an inexperienced noob.
Well, I know I promised updated schematics today, but I'm still recovering from my 24-hour shift yesterday with ZERO sleep, so maybe tomorrow. In a future post, I'll take a look at the expense these various controls and sensors have added to the equipment side of this system. My guess is that we are under 10% added cost for a significant increase in functionality and reliability. A number of your recommendations were to keep me out of trouble (can you say mold or secondary condensate pans!?!) while others have added closed loop control to a system whose performance otherwise was a poor guess (fresh air/CO2 and barometric pressure relief).

Mike
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Look at yourself! Researching deadband ranges in pressure differential switches, posting on Guphanti's thread about converting electrical loads to BTU/HR. If you really are a noob, you have learned so much in the past few days. A lot of people struggle to understand pressure differential at levels that low.

I'm really anxious to hear about how this system works when you do get it set up; get to work!

I don't know if you have ever looked at the Acoustic Fields website, it belongs to an acoustical engineer Dennis Foley that designs professional recording studios. He's an old gray haired guy with a pony tail and since he's like me in that sense, must have some credence. He says that anything <125 hz you can't absorb it, just try to manage it. He has designed an absorber filled with activated charcoal that is supposed to be the best thing for bass absorbtion. I remember seeing one of his Youtube videos showing a guy in Austin building one of these for his home recording studio. I know Austin is a big place, but you just might be able to locate him. I'll try to find it and send you the link. I have in my long range plans to buy his plans and build a couple of these. They are just MDF and some pegboard with some foam and activated charcoal. I have all of the woodworking tools needed to make it.
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Here's a couple of things to confuse you a little more, but one might put some $ in your pocket.

In a lot of areas there are rebates from utility companies, state and even local governments for installing high efficiency HVAC systems. when I had mine replaced my electric utility paid $100 per SEER point above the minimum required which is 14 here, and the natural gas utility paid some for any furnace above 95% efficient. I ended up with $1600 in rebates. If any of these rebates are available to you, you can run your own report. I'm sure they will require a copy before paying. Look at , they are the standard for efficiency rating. There are some tools you can punch in the model numbers of the condenser, air handler, and coil and it will generate a report. The manufacturers usually list the SEER rating for the condensers but AHRI considers all 3 components and generates an overall rating which is usually higher http://www.ahrinet.org/Certificationthan what the manufacturers list. It might get a little fuzzy being a dedicated home theater, but you could call it a home addition, it does represent an additional load on the power grid. If there are rebates, they reserve the right to do a site inspection. In the unlikely event they do an inspection, show him the ladder going to your attic and lend him your flashlight.

You mentioned getting a tech to help with the vacuum and charging; great idea. Most of the minis are charged by refrigerant weight, not temp and pressures or subcooling like conventional systems. If they show up and don't have a set of scales, send them on their way. This will cost you initially, but could be invaluable in the future. Have the tech do a full system commissioning. Research , they have a sample commissioning report that will consist of vacuum levels, static pressure measurements, measured air flow, refrigerant charge, outdoor temp, wet https://www.energystar.gov/sites/def...llable.pdfbulb, and dry bulb readings, etc. This will likely be costly, but get a copy of the report and if you should ever have issues with the system later down the road, you have baseline measurements and can pinpoint problems much quicker and efficiently. This would be a good time to dazzle him with your brilliance on how your dehumidifier, fresh air, and presssure relief system, and condensate management work, he should realize quickly that even though it's DIY you know what you are doing. You can also talk some smack with him if he starts talking about static pressures and so on.

Here's a link to the Youtube I talked about earlier:
The guy's name is Sam Small and he's building them from Dennis Foley's plans.
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post #30 of 54 Old 05-15-2020, 10:04 AM - Thread Starter
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Just a quick update - I called Dwyer and found out the deadband on the ADPS switch is the same as the 1910-00 I mentioned above, but for half the price. The functional difference is that the ADPS switch series has a repeatability of +/- 15% around the setpoint vs. the 1900 series which is +/- 3%. I think for the small amount of money involved, I would rather have the more accurate switch.

Also, I did a little back of the napkin calculation about how long it would take the room to vent down from the set point to the reset point (setpoint-deadband) in a 20'x20' room with an 8' ceiling for an internal room volume of 3200 cubic feet. Using the example above where the setpoint is 0.1"wc, the room pressure would need to vent down to a pressure of .06"wc before the switch would reset and close the Barometric Pressure Relief damper. Without getting too complicated, we need to vent ~1280 cubic feet of stale air before the room pressure was low enough to reset the switch. If we assume that a 4" duct would flow 50 cubic feet per minute ("cfm") and that we are not adding fresh air to the room, it would take a little over 25 minutes for the switch to reset. This sounds like a reasonable duty cycle to me. Even at 100 cfm, the damper would not be cycling all that often.
Ignore this paragraph, it's all wrong....

Mike

Last edited by mhutchins; 05-17-2020 at 09:08 PM. Reason: My calcs were wrong
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