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post #61 of 93
Dedicated....as in only for the theater room.

You will need a ducted mini system in order to add on the ERV or HRV option, you cannot do this with a ductless unit IIRC. Fresh air is important, but unless you are harmonically sealed into the room for hours on-end without opening the door even once, you'll get plenty of fresh air into the room just by opening the door every once in a while.

It would seem improbable (and expensive) that you could tap into the existing house HRV system, but probably worth the call to the originial installation contractor to ask the question.
Edited by TMcG - 8/20/13 at 1:38pm
post #62 of 93
Thread Starter 
So then, my original plan of heating/cooling with a dedicated 9,000-12,000 BTU Mr. Slim split and then providing air exchange via two dead-vents should work. I was banking on the 220 CFM number in order to get 6 ACH in the room. I suppose this is still correct, regardless of the split. Would be nice to use lower CFM fans in the dead-vents to reduce noise, but I don't want to sacrifice air quality. Thoughts?

Also, I'm going to have a fair bit of gear in the equipment room (all the theater gear, plus a pretty extensive setup for a distributed a/v system). My gut says simply exhausting the room into the basement should suffice. Should I consider a separate split (or head unit) for this room?
post #63 of 93
Thread Starter 
Quote:
Originally Posted by TMcG View Post

I
Regarding your picture above, there is no harm in "ovaling" an 8" duct by squeezing it into the entire joist bay as the total cubic inches of cross section is not changed (provided the duct is not crushed in any way)....but this is based on the premise that you are starting with a workable head-end system design. A ducted mini split seems like your most cost-effective option to get you what you are looking for. Running the supplies and return through a dead vent in / out of the room is an added soundproofing bonus if you go that route.

Getting back to one of my earlier questions. Yah, I think I could gently squeeze an 8" duct into the joist space. Would that be better than lining the joists themselves and using the entire cavity as a return? Probably about the same I guess?
post #64 of 93
Quote:
Originally Posted by memmo View Post

So then, my original plan of heating/cooling with a dedicated 9,000-12,000 BTU Mr. Slim split and then providing air exchange via two dead-vents should work.

Yes. Your first post in this thread was why I decided to chime in because it appeared your were on a track to go through a lot of effort to try and make an untested design work vs. just installing the Mr. Slim right from the start and eliminating almost all of your concerns about being comfortable in the theater for extended periods.

You could go with a dual dead-vent system running at equal CFM where one fan is pumping air into the room and another is pulling out....but that will mess around with the total conditioning load of the Mr. Slim if you are moving that much air from an outside source through the room. Does the DUCTLESS Mr. Slim have the ability to integrate fresh air as it runs or does it only recirculate? If it only recirculates, this is where a ducted mini system has a big advantage in that it is relatively easy to introduce fresh air into the system. And if the ductless does not introduce fresh air, this is where opening the door from time to time would assist with the fresh air you seek. Let me know your thoughts.
Quote:
Originally Posted by memmo View Post

I was banking on the 220 CFM number in order to get 6 ACH in the room. I suppose this is still correct, regardless of the split. Would be nice to use lower CFM fans in the dead-vents to reduce noise, but I don't want to sacrifice air quality. Thoughts?

I'm not sure exactly what you are saying here, but the Mr. Slim will give you a fixed amount of CFM output. As I don't know what specific model you are choosing out of the many available, I wouldn't be able to answer if there are higher CFM versions of units that have the same heating and cooling capacities. My suspicion is "No", but I'd call the company you are buying this unit from and ask first. Most important is selecting the appropriate cooling capacity...the rest is found in the specifications for your unit since it is a pre-packaged solution.
Quote:
Originally Posted by memmo View Post

Also, I'm going to have a fair bit of gear in the equipment room (all the theater gear, plus a pretty extensive setup for a distributed a/v system). My gut says simply exhausting the room into the basement should suffice. Should I consider a separate split (or head unit) for this room?

No. Not necessary. Even a simple Panasonic quiet bathroom fan exhausting through a 4" duct would be PLENTY.
Quote:
Originally Posted by memmo View Post

Getting back to one of my earlier questions. Yah, I think I could gently squeeze an 8" duct into the joist space. Would that be better than lining the joists themselves and using the entire cavity as a return? Probably about the same I guess?

I am never a fan of lining joist space unless you absolutely have to, especially if running cool air through the joists. The thermal loss is great and you have the potential for creating condensate, completing the mold trifecta of oxygen, water and a food source to start growth. I'd follow the advice of the Mr. Slim installation guidelines on duct sizing for your particular CFM unit. One other point....the larger the duct, the lower the air velocity in the duct. As a result, an oversized duct is not as efficient at mixing the air in the room to cool and dehumidify.
post #65 of 93
Thread Starter 
Thanks, I truly appreciate you taking the time to write such thorough responses.

Basically, the ductless split simply recirculates. It does not integrate fresh air. To go with the ducted version, I'd have to up the budget considerably and would still have to use a dead-vent for the return, so I'd rather not have to do that.

Are you suggesting that a split, plus opening the door occasionally is a viable option? That seems contrary to a lot I've read on here. Won't things get super stuffy if were in a seriously sealed room for 2 hours watching a movie?

Perhaps I could get smaller fans (say 120-150cfm) for air exchange - this would provide for approx 4 changes per hour. The added benefit is that velocity goes down in a 6 or 8" duct.
post #66 of 93
I don't see how it could get stuffy if the unit is removing heat and moisture from the theater's air and dumping it outside through the AC line set with condensation line. Perhaps a bit stale after a good long while (i.e. a lot longer than 2 hours), but certainly not warm and humid which I interpret to be "stuffy".

The simple fact is that adding a forced ventilation dual dead-vent system to introduce fresh air will significantly raise the amount of load put on your ductless unit which is trying to get all the air in the room at a certain comfort level. Introducing outside air through the vents is like moving the goal posts on the system.

Perhaps there is a way to get fresh air into the room without overtaxing your ductless system, such as a small quiet Panasonic bath fan located outside the room dumping 25- 40CFM of fresh air into the room through a small 4" duct. I don't think you'd have to include a passive ventilation system to balance the air pressure in the room because you could easily pick up the additional draw through your projector's hush box intake / output line. It's just a thought, but that would allow you to get a bit of fresh air in the room, save some $$ over ducted and utilize the projector's hush box to not only pull the heat from the projector out, but any additional CFM being dumped in by the bathroom fan so you don't end up with either a positive or negative pressure room. This seems the simplest way to me.
post #67 of 93
Thread Starter 
Sounds almost too good to be true smile.gif

Anyone else care to weigh in on this?
post #68 of 93
On a per-person basis, the recommended outdoor air is 15CFM. I have seen the ACH numbers you are talking about and I'm not in a position to say they are correct or incorrect.

I do think that the prospect of no air exchange is not something I personally would consider. I have my theater tied into the whole house CAC so I am getting cool air and exchanging air through that.

I can also say with the premier of my theater scheduled with 12 people, I am wondering if the stench of popcorn will be a problem. I also hope nobody had mexican for lunch. Lastly, I hope the cooling will keep up.

I figured my theater for typical use, not worst case. We're about to find out what happens in a worst case scenario smile.gif

I don't think you could go wrong running the biggest duct you can. At least you could change the fan later if you had to. Could you use the fantech you have in the equipment room and get the smaller Panasonic fans for the air exchange?

ERV does add load as they are not 100% efficient, but you probably have cooling to spare. A heat gain calc as suggested would be useful to figure that out.

Tim
post #69 of 93
Thread Starter 
I agree re: the no air exchange part.

I'm going to proceed and use the larger Fantech fan I already have for the equipment room and then purchase two of the smaller ones for the dead-vents. This will give me an opportunity to exchange air at a lower velocity and since I can then use Fantech fans instead of Panasonic fans, it means I can control their speed very easily. I'll still run 6 or 8" duct in where possible and I'll have the best of both worlds.

Thanks everyone for your input. Moving onwards smile.gif
post #70 of 93

Hey memmo,

 

I have a somewhat similiar problem to you regarding HVAC. My theater HVAC installation is happening tomorrow. My dimensions are similiar 19.5 x 13 x 10 and the end solution after months of back and forth will be a Mitsubishi Mini-Split (MSZ-GE18NA) 1.5 ton unit with about 18000 BTUs for heating and cooling and a Lennox HRV3-095 to introduce fresh air.

 

I also used some of the calculations mentioned here for 6 ACH and it came out to about 250 cfm for the HRV. Since the HRV my HVAC guy specced can only go up to about 70 cfm I asked him to check the numbers. He called one of the Lennox engineers and they said that amount of cfm for 6 exchanges per hour was unheard of for a space that size and would add a ton of humidity to the room. He send me an HRV sizing manual and one of the methods said that 1/3 ACH per hour was some kind of standard and that puts my new number at 13.5 cfm.

 

I am going to go with the above and hope the mini-split and HRV combo works out. Below is some of the sizing info for the method I chose. Good Luck with your HVAC:

 

 

Method #1

Size the HRV/ERV to provide 1/3 air change per hour - International Residential Code (IRC) 2006

This method requires determining the volume of the home and then providing enough air flow to have one complete air change every 3 hours.

Example: A home has 2000 square feet of conditioned floor space and 8 ft. ceilings.

The volume is 2000 x 8 = 16,000 cubic feet. To obtain required airflow in CFM, multiply by 1/3 and divide by 60 minutes/hour: Required airflow, cfm = 16,000 cu. ft. X 1/3 ACH / 60 minutes/hr = 88 cfm

post #71 of 93
Oh man.. start talking codes and I get all warm and fuzzy. biggrin.gif

That's sizing for an entire house. I don't think it correlates well to a dedicated theater room.

Take for example the IBC, "where the air infiltration rate in a dwelling unit is less than 5 air changes per hour when tested with a blower door at a pressure of 0.2-inch water column (50 Pa) in accordance with Section 402.4.1.2 of the International Energy Conservation Code, the dwelling unit shall be ventilated by mechanical means in accordance with Section 403. "

Skip to table 403.3 for living areas: "0.35 ACH but not less than 15 cfm/person". It also says 10cfm/person for stages/studios/media rooms

So I don't disagree that 6 ACH is a lot.. It seems like a lot to me. But as with many things I lack any experience in the field or empirical evidence to suggest anything to the contrary. Please do let us know how it works out. It seems like fresh air and hvac has just recently come to the forefront of theater design. I'd love to hear how yours turns out.

Tim
post #72 of 93
For the record, I agree that it would be ideal to have fresh air brought into the room...but considering that these units are directly marketed for bedrooms and other single room or small areas that have no introduction of fresh air, I see relatively little difference between having a closed off bedroom with one of these things on vs. a theater room with the exception of a higher level of insulation and to some extent - how much fresh air can get into the room. Nobody seems to have much concern about stale air with a couple of people being sealed in a bedroom for 8-10 hours per night and perhaps some of the "exercise" that may take place. smile.gif

But like I said, I agree that introducing fresh air is ideal, especially if your theater patrons partook in the aforementioned Mexican buffet lunch.... smile.gif

I couldn't find it now, but I have seen where Dennis posted the 15 CFM per person as per an ASTM specification. If I happen to find it, I'll post here.
post #73 of 93
Thread Starter 
Ok, I'm going to proceed.

I'm hovering over the buy button on a panasonic fan for the return due to its ability to sit up in my joist space, but I'd really rather the Fantech. I do have a spot I could mount a Fantech, but it would be at the end of the flex duct meaning it would be "pulling" instead of pushing the air out. It would mean about a 35 foot run however. I've been told this is not ideal yet that since I'm only going for 150 CFM or so, I might be ok, except for some static pressure issues I might have to overcome.

Thoughts?
post #74 of 93
Quote:
Originally Posted by TMcG View Post

I couldn't find it now, but I have seen where Dennis posted the 15 CFM per person as per an ASTM specification. If I happen to find it, I'll post here.

Well, I couldn't find where Dennis had posted, but Google didn't let me down....

Fresh air exchange as per ASHRAE Standard 62-2001.

Overview found HERE.

Full write-up with practical applications and examples HERE.
post #75 of 93
Thread Starter 
Ok, another thing I need advice on:

What is the best way to bring flex into the theater via the ceiling
What is the best way to connect it to a grill (or a linear diffuser)? I assume I need some sort of boot that is quite large so that I have more volume which in turn slows the air down? Is this needed on a return?

The fan will be pulling 150 CFM through either a 8" duct (crossing fingers it'll fit) or a 6" duct. The rear soffit dimensions are 14"w x 10"h.

post #76 of 93
150 CFM cannot be handled by either 6" flex or rigid. You'd need to be at 8" flex to handle 150CFM, but I would be concerned about noisy turbulence with that kind of CFM, especially if you start introducing twists and turns.

Refer to THIS DUCT SIZING CHART for recommended CFM based on duct size and type.

To enter the room you would terminate the flex to a piece of rigid pipe that is snug to a cutout in your soundproof shell. Ideally you would bring this penetration into a soffit or other protected area as a first line of soundproofing defense. Convert back to flex with at least one 90 (usually the bend to make the turn into the soffit) before terminating in your linear bar diffuser.

The return air duct typically gets a return air box, lined with duct liner. The size of the return duct needs to be sufficient to return as much air as all of your supplies are providing.

EDIT: If you make a 90, I would recommend go with rigid just for this one fitting as it will preserve laminar flow as well as can be expected.
Edited by TMcG - 8/22/13 at 7:01pm
post #77 of 93
+1. 8" is definitely the way to go. 6" will not cut it.
post #78 of 93
Yep, and take my word for this, you want gradual bends and smooth transitions. I've got an abrupt transition into a box in my theater's return, and it's causing my all sorts of grief.
post #79 of 93
Thread Starter 
I figured out a way tonight to get two 6" instead of one 8". Anyone see a problem using the one Fantech 150 CFM fan to pull through two return ducts via a "Y"?
post #80 of 93
Personally, I'd follow the KISS principle on this one....
post #81 of 93

Hey J_P_A,

 

What would be an example of an abrupt transition vs a smooth transition?

 

Thanks.

post #82 of 93
In my case, I have an 8" flex that terminates into a box that dumps into my soffit. Depending on how things turn out, I may have to replace that box with a register boot or something with a smooth 90 degree turn.

WIth air movement, anytime you have an abrupt change you create turbulence in the flow. Even letting the duct open up into a large enclosure will create localized turbulent regions at the edges of the duct. Using flex will help with this to some degree because it tends to want to make smoother bends. You just need to be careful when you transition from flex to whatever rigid ducts, boxes, etc.
post #83 of 93

So for this 8" insulated flex that runs down the middle of my ceiling above the joists I need to push it back to the far bay, then drop it thru between 2 of the 2x4 spacers and ultimately make its way to what will be a soffit on the right and then drop it into a box with a grate?

 

post #84 of 93
Thread Starter 
My plan is use a rigid 90 to penetrate the ceiling into the rear soffit where I can go another 1-2 feet with some flex before entering a boot.

I've come up with this design for a boot that will sit in the soffit and open to below. Are my calculations correct?

J_P_A - based on your experience - would you consider this a smooth or hard transition? Looks ok to me?


post #85 of 93
Thread Starter 
Its a curse that my HVAC guy isn't coming until next Tuesday. It gives me way too much time to dream up options and variations.

I wast just speaking with something who provided yet another possible solution - though super simple, seems to have its own set of issues

He suggested that I simply run a return under my riser and into the equipment room. The equipment room will have its own fan pulling air out and dumping into another part of the basement.

So, in theory - if I could stick the Fantech fan under the riser and have a very short and simple return. Possible issues:

  1. My riser will be two stage - the first being only 8". If I frame 16" o/c", could I get a grill(or two, or three) large enough to be sufficiently quiet?
  2. I'd have to build some sort of access panel for fan maintenace
  3. The riser is only 7' deep. So from the return grill in the theater to the exhuast grill on the other side of the wall would be short - is this a problem?
  4. Return down low - perhaps not ideal given the warmest air would be near the ceiling?

Thought i'd mention it. Seems like a reasonable solution that could perhaps be made quiet. The benefit of course is that I then would have no holes in the ceiling smile.gif
post #86 of 93
If you go this route, why wouldn't you just do the same, only through your soffit instead of through the riser. You could also add a bulkhead / dead vent in the equipment room on the flip side of the theater's back wall to provide further soundproofing and the ability to easily add an access panel for the in-line fan.
post #87 of 93
Regarding your return boot, that is essentially the design that's giving me issues just with different dimensions. The primary difference is you have a much lower velocity. Although I'm having resonant issues even when the velocity is slowed way down. That in mind, you might try adding a straight register boot to connect the duct to the box.

CREATOR: gd-jpeg v1.0 (using IJG JPEG v62), default quality

You should probably line the box with duct liner as well. Ideally you would have that transition as far away from the opening as possible to allow the duct liner to absorb any noise created by that transition before it gets to the opening.

Resonant phenomena is a system like this is going to be tough to predict. I can't say for sure one way or the other whether your particular design will have any issues or not, but I would go out of my way to try to limit the possibility on the front end if I could do it over.
post #88 of 93
Thread Starter 
I don't have enough room - the equipment room is already tight so a dead-vent is a no-go and the ceiling already has some existing duct work and plumbing that I can't move at this stage. Also, since I only want a 10" tall soffit in the theater, I'm limited in that area too.

I think I'll stay with my existing idea. Do you think it makes a difference if I dump the exhaust air into the hallway outside vs a bathroom, on the opposite side of the house? If I were able to dump it into the bathroom, I'd have straight runs of flex with no bends.
post #89 of 93
Thread Starter 
Quote:
Originally Posted by J_P_A View Post

Regarding your return boot, that is essentially the design that's giving me issues just with different dimensions. The primary difference is you have a much lower velocity. Although I'm having resonant issues even when the velocity is slowed way down. That in mind, you might try adding a straight register boot to connect the duct to the box.

CREATOR: gd-jpeg v1.0 (using IJG JPEG v62), default quality

You should probably line the box with duct liner as well. Ideally you would have that transition as far away from the opening as possible to allow the duct liner to absorb any noise created by that transition before it gets to the opening.

Resonant phenomena is a system like this is going to be tough to predict. I can't say for sure one way or the other whether your particular design will have any issues or not, but I would go out of my way to try to limit the possibility on the front end if I could do it over.

Not a bad idea. Perhaps I can just change the inlet to be 8" on the box and use a 6" to 8" transition to connect to the flex. Something like this:

post #90 of 93
Keep in mind this is all speculative, but ideally you would have an adapter that smoothly transitions from the shape of the duct (round) to the shape of the box (rectangular) with no sharp edges. Using a reducer leaves you with a round to square transition.
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