Originally Posted by chirpie
Thank very much and it all makes sense except... most BTU calculators I've seen say 1 Ton for 400 square feet is a typical rule of thumb. Wouldn't that put a 1.5 ton unit right in the ball park for a 6,600 square cubic room?
Theaters are completely different from normal rooms. They are very tight and highly insulated, so standard heat loss calculations found on those sheets are not applicable. Theaters also hold more people than a standard residential room when all the seats are filled.
Originally Posted by JDontee
I wonder if being underground makes a difference for the btu requirement.
Everything makes a difference, including being underground.
Originally Posted by SierraMikeBravo
You have to calculate the number of bodies in there in addition to the volume. The average BTU's per hour of the human body while sleeping is 500. Calculate that times 8 and that's 4000 BTU's minimum. I usually error on the side on another 1000 BTU's. That would put it at 5000 BTU's for an eight man room. This is without any equipment in the room, and consider that everyone's metabolism is going to factor into the situation while awake. You could hedge on the error by as much as 2000 BTU's. Just depends. We use 2 ton units on average. We have never had an issue.
This number is not accurate. Nominal average for resting male is 356 BTU/hr. and 330 BTU/hr per resting female. Sleeping is a bit less, moving around slightly is a bit more. But for argument's sake, someone sitting in a chair is a nominal 350 BTU per person and there should not be a "hedge on the error by as much as 2000 BTUs (250 BTU per person per hour)". Technically speaking, the amount of skin surface area and muscle mass on that person are the two factors which determine their precise BTU output baseline at rest. And aside from BTUs of cooling, there is the minimum fresh air ventilation requirement of 5-7.5 CFM per person as per ASHRAE, of course.
The projector and lighting are your other two significant heating loads with the assumption your equipment will be located outside the room. Most well-priced projectors are in the 900-1200 BTU/hr. range, so let's call it 1000 BTU. LED bulbs are 3-7 BTUs per bulb per hour; incandescent averages 85 BTU per bulb per hour. If you have 8 males resting in the room with the projector on and lights off as would be typical, you are just under 4000 BTUs all-in. If it is just you and your wife most of the time....that's just 1680 BTUs.
I know this is a lot of information, but here is where the rubber meets the road....you have to be honest with yourself on the average number of people in the room on any given evening or weekend. If you're like most people, it's one or two....maybe three. What happens then if you have a 2+ ton oversized system? That's right...short cycling and a long time between cycles (because of the extreme air tightness and insulation)... which also means the room is not getting fresh air exchanges (assuming a dedicated system). I think you can start to see the problems having a 2+ ton HVAC system for such an incredibly small underground cooling load as the room will normally be used 95% or the time. Only an appropriately sized mini system or a standard system with 2 zones, motorized dampers and a variable speed fan have the capability of giving you sufficient run times with minimum cooling loads AND handle a full room of people. That's why I am suggesting you steer clear of an oversized single zone system.
One final thought - adding an ERV / HRV to your HVAC and running the system fan will go a long way to eliminating the stuffiness of a room between infrequent or too short cooling cycles. I would highly
recommend getting an ERV / HRV anyhow because it's the only device which introduces fresh air into the home in a controlled manner.
To offer one more perspective, my basement is just over 1800 square feet with 9' ceilings and uses a 1.5 ton system. I can't imagine how quickly that system would cycle if it only had to cool 1/3 of the area.