I would hire an engineer
I have a customer who owns a very old theater with 2 - 30 ton rooftops. Old units. Historic building.
Massive return air plenums - Air Handlers in the attic - one on each side of the stage. symmetrical.
The Air handlers have supply ducts that merge together (in a V shape pattern). So the air grills are in
the ceiling, above the auditorium and balcony. So the balcony stays cooler because it is closer to the ceiling.
The seating area on the ground floor gets hot is the summer. He pre-chills the auditorium to 65 deg and by
the time its full of occupants, the temp has risen to 75 deg. before the show starts. Each return plenum has
3 grates on the wall - one at ground level (next to the stage) one about 10 feet off the floor, and 3d about 20 feet high (which
is boarded off in an attempt to draw the cool air down below). The ceiling is probably 60 feet high. Seats 1500.
Oh, and there is no air on the stage. Very old building. Fire walls are solid brick. 3 feet thick behind the stage.
A very large attic with walk boards above the auditorium and stage. I think the building is over 100 years old.
We want to get some air in the lower seating and stage area. He is considering setting 2 - 5 ton AH's in each
return plenum (Either at ground level or on the second level which is 10 feet high) these plenums are 50 feet high.
I told him I would post a thread and hopefully get some feedback. We would set the condensers on the roof or a platform
in the alley on the side of the building. The idea (in his words) is to supercharge the existing units. I will be back later to
check for any posts and clarify if needed. What kind of problems might arise from this setup? Thank you.
td55
I would hire an engineer
Hiring an engineer sounds like a good idea.Without doing a load calc it seems like 60 tons is light for 1,500 people.
Take your time & do it right!
I'm confused as to why it is so hot on the main floor of the auditorium? I have a couple of theaters. One is a single screen that is about 80 years old. We have a problem there with the rear being too hot and the stage end being too cool (steep sloped floor). Returns are in the front wall, supplies in the ceiling. There is a very old 40 ton DX cooling system with one air handler. It handles the load pretty good for a sold out show (500 people) on a very warm day, but will get quickly get behind when it is over about 92 outside. Luckily, the busiest shows are always at night, so it is hardly ever an issue.
First, I think that you should unblock the highest returns. If you block anything, it should be the lowest one if you are having problems with it being too cool on the lower floor during the summer. Air will stratify badly in a room that large if you aren't moving it with enough velocity, but that is generally a problem more in the winter when all the heat rises to the ceiling.
Hopefully there is also some allowance for make-air in a room that holds that many people.
This theater has shows via a pull down screen. However it has a large stage - mostly live performances. No supply air on the stage. Maybe he (the owner) made a mistake by blocking off the high returns. I don't know how long they've been blocked. As stated, the building is 100+ years old with 60 ft ceilings in the auditorium. I have just started investigating this. I really posted prematurely without getting enough data. The rooftops have - I think 3" suction lines. Not wrapped very well. (They weren't wrapped at all till last summer. I think over the years the wrap deteriorated due to the exposure to the elements). The ducts may need insulation. I want to check air splits, get superheat reading, clean condenser coils. Could be pulling in attic air on the returns. The units have numerous leaks - not sure where they are leaking. I plan on spending some time there in the next few weeks -before it gets really hot. We are in south Mississippi. Thanks for the feedback. Another question, since we have so many leaks, should we convert to a replacement refrigerant and if so is one better than the other?
td55
I'm interested in the boarded off returns. I would like to know the sizes of all the returns.
I will have to measure return grates, they are appx. 2 1/2 to 3 ft. wide X 3 1/2 to 4 ft. tall. (not sure ???)
Could be 2' X 3' ??? I will let you know.
I don't think there is any make up air.
I doubt the rooftop condenser coils have been cleaned with cleaner in a long time.
I want to check air temps on the return grates, leaving the return, and at the registers.
I wandering if he has #1 air leaks on return, #2 poor insulation on supply ducts, not dumping the heat due
to dirty cond. coils, (Evap coils look pretty good), leaks in the supply ducts. Among other issues.
td55
Just so I make sure i understand, what is the problem you are trying to solve?
Let's say 500 BTUs a person watching a show. In a full theatre, that's 750,000 BTU just for people load. 60 tons of cooling is 720,000 BTU so that joint is shy just for the people. Add heat from outdoors, infiltration, lights (I spot at a community theatre, lighting is a huge load) and equipment and 60 tons is very light.
Last auditorium our theatre used had a 50 ton split for 500 people capacity. The group didn't have many shows in the summer anyway but even in cool weather, when we had a show the sucker was on. Really cold, no.
People are fanning themselves, because they are hot in the summer months.
Since there are many live performances, there is a heavy lighting load on the stage - Many lights. Some vendors
bring their own lights - They require 200 amps or so just for the lighting. There is no air on stage. The owner sets
fans in the balcony to push air down below.
Last edited by tonydykes55; 03-16-2014 at 09:39 PM.
td55