Air conditioners in a basement.

[wyoengr]

I've got a project where an owner wants to put (5) 10-ton air conditioners in an enclosed basement parking structure. The block load of the building is approx 32-tons, the elevation is 5500 ft. The parking structure is 6000 sf and approx 12 ft high. The condenser fans move approx 36,000 cfm (on high). I'm rejecting the 32-tons to the space every hour (plus compressor and fan heat), but what I don't know is the ability of the floor to absorb that heat (the walls are insulated). At what point will I lose control of the system? Is there any ability for the floor to coompletely re-charge in a single evening.

 

[mtngreen]

Couple questions:
Is the space ventilated?
Whats above the basement area?

First reaction is that this is a bad idea for a number of reasons.

 

[wyoengr]

The space does have a CO/NO2 ventilation system sized at 8700 cfm. The design outdoor condition is 95F.

I agree that this is a bad solution. My client (and his contractor) is convinvced that it's not and I'm trying to quantify it. I can predict the heat gain to the space from the air conditioners. What I can't predict is the rate at which the sub-grade floor will accept this gain, and what potentially will be my garage temperature by 4 pm.

 

[willard3]

Is the floor insulated? If it is, you know the thermal mass of the material and you know the heat flux.

If it's not insulated, the problem is probably not solvable.

Because the owner and contractor think it will work doesn't mean it will work. You are the Engineer.

 

[BM4BRANES]

What will be the opinion of the car owners, you know, the ones who continiouly have excessive dust deposits on the car they just washed.

 

[Waramanga]

You could just work out W/m2 that you are pumping into the space. You can assume an overall U value for the fabric and fiddle around a bit to see if what kind of U would result in an aceptable temp rise. If you get a ridiculously low u for the space you would be ok. If its line ball then err on the side of caution!

 

[DrRTU]

Don't walk away from the job - run. Based upon 11 EER, the THR is about 65 tons (130 btu/ft2). The condenser fans are 6 cfm/ft2. Even if you were able to achieve stable operation, the temperature, noise and air movement will bring complaints form the garage. I have placed aircooled units in warehouses and parking structures before but you have a sizable load going into a small space. Lets assume the units will only load to 75% = 585Mbtu and exhaust system removes 100Mbtu you have a net addition of over 485Mbtu to the structure. It will not take someone long to figure out why the other spaces are running over temp. Be very carful about installing aircooled units indoors. You may have a labeling issue. I had an inspector point out the units are listed for outdoor only installation (he gave us a pass). The coils will need constant maintenance due to no rain cleaning the coils. A floor drain and water supply helps. The noise echoes off all the hard surfaces. How will you get outside air for each system? You should not use the parking garage air as OA source and the codes require an economizer.