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Discussion Starter #1
i have read the dennis e. recommendation of locating the hvac returns and supplies high; returns over the seating area and the supplies in the front of the room. it seems to make perfect sense when cooling the theater, the returns exhaust the hot air from the people, cold air comes down in the front of the theater and moves towards the back cooling the occupants w/o a direct draft. my question is how this system will work with heating the space during the winter. several hvac contractors i spoke with think it may be a problem. their point being hot air rises, and with both the supplies and returns up high, the heated air will just circulate along the ceiling.


some background info that may make a difference...


i live in the chicago area

theater is approx 3300 cu ft. located in a full basement

seating for 9, but 90% of the time it will only be 2-4 people
 

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Quote:
Originally Posted by richh
i have read the dennis e. recommendation of locating the hvac returns and supplies high; returns over the seating area and the supplies in the front of the room. it seems to make perfect sense when cooling the theater, the returns exhaust the hot air from the people, cold air comes down in the front of the theater and moves towards the back cooling the occupants w/o a direct draft. my question is how this system will work with heating the space during the winter. several hvac contractors i spoke with think it may be a problem. their point being hot air rises, and with both the supplies and returns up high, the heated air will just circulate along the ceiling.


some background info that may make a difference...


i live in the chicago area

theater is approx 3300 cu ft. located in a full basement

seating for 9, but 90% of the time it will only be 2-4 people
That's a good thing. It gets quite toasty even in the winter months when you have multiple people in the room and the PJ on. It throws out a lot of heat. Having the return up high will pull more hot air out of the room, which is what you want.
 

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That's a good question. I'm just now getting to running my HVAC into my theater. I was going to put the supply lines along an exterior wall which would put one register in the front of the room and one in the back. I was going to put my return register in the back of the room on the opposite side of the supply vent. I'm also in the midwest and have the heat running more often then the A/C. I guess I'll wait to see what others have done or can suggest.


Brian
 

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I'd prefer to put the supply vents in the front of the room down low, and the return at the back of the room and up high... when cooling, the colder air will enter the room and start moving up, for two reasons: because it's warming up (and rising) and because the flow of air is up towards the return.



The difference here is that when cooling, cold air HAS to rise eventually. However, when heating the room, the heated air doesn't has to sink. If it comes from the floor, you're going to get better dispersion of the warmer air.



That solves both the cooling and heating problem. Just be sure and avoid placing the supply vents where airflow may move a screen (if applicable), or blow directly on people.
 

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Most commercial office spaces have the supplies and returns in the ceiling, so I don't think this will be a problem as long as the fan is on and circulating the air in the room. Just make sure you don't short circuit the airflow by having the supplies and returns too close, which shouldn't be a problem in that size of room (assuming you have less than a 10' ceiling). If you are installing a zoning system or separate HVAC system install the thermostat down low at the level that you are sitting and not at 5' off the ground. The only problem that might exist with your setup is cold feet due to the ground being cold and the best remedy would be thick underpad or radiant floor heat.
 

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I have a 5500 cubic FT DE designed theater that does not have the benefit of being in a cool basement. My vents are up high as are my returns (they are on opposite sides of the room). Heating the room is rarely needed (it is so well insulated and no windows). It sits on a slab and cold feet aren't a problem as I used 2 risers and the seating on the slab is covered with carpet and an exceptionally thick pad. I run run the AC in the middle of winter (if the outside temp is over 50 degrees).


That said, in my dedicated room, I have had zero issues with heating and cooling. In fact, following DE's plan, I have zero noise from the vents.


If your room is properly designed, AC will run the majority of the year. A well built theater is an air tight, densely built and insulated room with a very hot equipment and potentially many hot people sitting for an extended period of time. I have had up to 14 people in my room and at no time was ambient temp an issue. So, I'd trust your theater designer rather than Joe 6 pack HVAC guy..


Contractors always have opinions but the needs of a dedicated theater are out of their knowledge base. I simply told my HVAC companty to follow the theater design. Glad I did. Comfort in my room year round is excellent.
 

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Discussion Starter #7
uxbridge, from your title, i assume you're in the business? if so i was wondering if i can pick your brain a little bit. i had an hvac guy down to take a look at my current ductwork and my plans for the basement buildout. i currently have two furnace/ac units, one for the first floor/basement and one for the second floor. he said the trunkline for the first floor/basement was not big enough to tap off of for the basement supplies. he suggested adding a new trunkline dedicated for the basement supplies which could be zoned seperately from the first floor. cost for this was about 5K. that's for the new trunkline, the zone controls, and branch circuits for the supplies and returns for the basement buildout. i was looking at the smarthome web site and see that i could get motorized dampers for about $60 ea and a 2 zone controller for about $200. couldn't i save my self a lot of money and just use the current trunkline and add dampers for each supply. then the dampers for all the first floor supplies would close when the basement calls for heat and vice versa. there's 11 supplies for the first floor and i'll be adding about 7 or 8 supplies for the basement. am i missing something here?
 

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What size is the furnace/AC and what size is the main duct? Do you have a picture of the basement,and or the current duct layout. I would think that adding in a second main trunk for the basement that is acoustically lined (interior) would be a better choice than so many zone dampers, that will all need service/replacement access panels. Having two main dampers close to the furnace plenum would be better. You will also need a bypass damper to relieve the high static pressure when one zone damper closes (upstairs/downstairs). $5k US, why don't you just put in a separate AC system for the theater.


Bill
 

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Discussion Starter #9
Quote:
Originally Posted by thebland
I have a 5500 cubic FT DE designed theater that does not have the benefit of being in a cool basement. My vents are up high as are my returns (they are on opposite sides of the room). Heating the room is rarely needed (it is so well insulated and no windows). It sits on a slab and cold feet aren't a problem as I used 2 risers and the seating on the slab is covered with carpet and an exceptionally thick pad. I run run the AC in the middle of winter (if the outside temp is over 50 degrees).


That said, in my dedicated room, I have had zero issues with heating and cooling. In fact, following DE's plan, I have zero noise from the vents.


If your room is properly designed, AC will run the majority of the year. A well built theater is an air tight, densely built and insulated room with a very hot equipment and potentially many hot people sitting for an extended period of time. I have had up to 14 people in my room and at no time was ambient temp an issue. So, I'd trust your theater designer rather than Joe 6 pack HVAC guy..


Contractors always have opinions but the needs of a dedicated theater are out of their knowledge base. I simply told my HVAC companty to follow the theater design. Glad I did. Comfort in my room year round is excellent.


jeff,


for what's it's worth, my equipment will in a closet, outside the "envelope" of the theater so that might reduce the cooling needs somewhat. a couple of the hvac guys i talked to say that in my area, the ground outside the foundation stays pretty constant at around 50 degrees. i think that may make a big difference between the cooling needs of a room above ground vs one below ground. that and the fact that hot air rises and cool air sinks. during the summer months, the ac for the second floor of my house runs quite often while the ac unit for the first floor/basement rarely goes on.


uxbridge,


good points about the access panels, hadn't thought about that. i'll have to check on the size of the furnace/ac. is that info written on some sort of sticker on the inside? i do know that the supply trunk is 20 x 8 with a 16 x 8 return trunk (measured at the furnace, both taper down as they go). the furnace is one side of the house and the trunklines run down the length of the basement about 55 feet. with regards to a seperate ac just for the theater, isn't there a limit (40 or 50 degress) as to when you can or can't turn them on?
 

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richh,


What Jeff is saying is correct, once you insulate (to reduce the heat transfer) and seal the room (eliminates heat loss due to infiltration air), the amount of heat loss will be negligable.

BTUH=delta T x square feet/ R value of wall

therefore for a 20' wall 10' high with a 22 degree delta T(72-50) divide by an R-12 insulated wall = 367 btuh (a 100watt bulb produces 341 btuh of heat, One male occupant sitting in your theater will produce 450btuh)


Basement that are cold in the summer are caused by cold air droping through the stairwell but also do to the poor installation of the duct work; no insulation to reduce conduction through the metal, and holes in the main duct all over the place leaking air, none of the cleat is usually sealed or any of the take off connections. Also if the basement is not insulated it is still losing heat to the ground at a fast rate.



Can you provide the make an model of the furnace and A/C from there I can tell you the capacities. Are you sure about the supply and return usually the return is larger than the supply. In residential design usually the supply is sized for 1000 feet per minute and the return sized for 800FPM. From the duct size I would guess that you have a 2-ton A/C.


To get the A/C to run down below 40F we install a condenser fan cycling control. This maintains the systems head or high side pressure. Usually set for 230psig cutin and 180psig cut out. You will probably need to install one if you install a zoning system, if you don't install one then make sure you install a low ambient cut out that will turn off the condensing unit when it is below 40F outside.


Bill
 

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Quote:
Originally Posted by uxbridge
Most commercial office spaces have the supplies and returns in the ceiling...
Most commercial office spaces are also 50% occupied by employees who constantly moan about how hot/cold it is in the office that day. :)
 

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Discussion Starter #12
Quote:
Originally Posted by uxbridge
richh,


What Jeff is saying is correct, once you insulate (to reduce the heat transfer) and seal the room (eliminates heat loss due to infiltration air), the amount of heat loss will be negligable.

BTUH=delta T x square feet/ R value of wall

therefore for a 20' wall 10' high with a 22 degree delta T(72-50) divide by an R-12 insulated wall = 367 btuh (a 100watt bulb produces 341 btuh of heat, One male occupant sitting in your theater will produce 450btuh)


Basement that are cold in the summer are caused by cold air droping through the stairwell but also do to the poor installation of the duct work; no insulation to reduce conduction through the metal, and holes in the main duct all over the place leaking air, none of the cleat is usually sealed or any of the take off connections. Also if the basement is not insulated it is still losing heat to the ground at a fast rate.



Can you provide the make an model of the furnace and A/C from there I can tell you the capacities. Are you sure about the supply and return usually the return is larger than the supply. In residential design usually the supply is sized for 1000 feet per minute and the return sized for 800FPM. From the duct size I would guess that you have a 2-ton A/C.


To get the A/C to run down below 40F we install a condenser fan cycling control. This maintains the systems head or high side pressure. Usually set for 230psig cutin and 180psig cut out. You will probably need to install one if you install a zoning system, if you don't install one then make sure you install a low ambient cut out that will turn off the condensing unit when it is below 40F outside.


Bill
interesting formula... kinda make me think about not insulating the HT seeing as how heating the space would be easier than cooling the space :rolleyes: . i mean there is something ironic about well insulating a space and then figuring out how to cool that same space in the winter.


do you use that same formula to account for heatloss from the slab floor? just looking at heat loss due to the foundation walls, the perimeter of the area i'm finishing in my basement is about 160 feet. wall height is 8.75'. using a 22 deg temp delta and r12 i end up with about 7.5 100 watt lightbulbs being enough to heat the space! at last count i think i had about 30 can lights distributed thoughout the space. who needs supplies, just turn on the lights when it gets cold :) .


the furnace is a bryant 383KAV048111. sticker says input is 110,000 btu/hr, output is 89,000 btu/hr. i double checked the supply and return duct sizes and they are as i had in the previous post; 20x8 for the supply and 16x8 for the return.


for cooling the space when it cold out, rather that messing with the ac condensor, is there some sort of fresh air intake that can be tied into the ductwork? seems like that might be the easier solution (to the layman that is).
 

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"do you use that same formula to account for heatloss from the slab floor? "

Yes, but the R value will be much less.


"the furnace is a bryant 383KAV048111. sticker says input is 110,000 btu/hr, output is 89,000 btu/hr. i double checked the supply and return duct sizes and they are as i had in the previous post; 20x8 for the supply and 16x8 for the return."


From the model number the furnace is capable of 4 tons of cooling, the supply duct seems to be sized for 1500 feet per minute and probably delivers 1500cfm. I would think that it is quite loud.Is there more than one supply duct?


"for cooling the space when it cold out, rather that messing with the ac condensor, is there some sort of fresh air intake that can be tied into the ductwork? seems like that might be the easier solution (to the layman that is)."


I don't think a fresh air intake would be cheaper or easier.


Bill
 
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