HW radiant floor heat in Commerical Garage.

[232gulfstream]

Guys,

I am laying out a radiant floor system for a fleet maintenance garage in a new building. The garage only has 1 exterior wall and roof and minor glass. It is 6200 sq. ft. The room is very well insulated and I am coming up with a calculated heat loss of about 25,000 BTU/HR. This number is purely sensible losses as my ventilation air is taken care of by roof top make-up air units and I will be delivering neutral air to the space. Im thinking I should probably bump this number up quiet a bit just to make sure I have ample heat (i.e. the old 25-40 btu/hr per sq. ft. so I know I enough heat. Once the slab gets warm there will be a lot of mass there but I am worried about the doors constantly opening and closing that could effect room comfort. Bear with me as I don't do a lot of radiant floor heat designs.

Thanks!

Gary

 

[EnergyProfessional]

You error has nothing to do with radiant floor. Regardless of system, you need to account for loads correctly, inc. infiltration losses and door operation.
Please don't claim the radiant floor makes it complicated, the faulty heat loss calculation is the problem.

 

[MintJulep]

The respose time of the radient heat will probably be much too slow to use to compensate for door opening.

The make-up air units would probably be a better choice. Depending on how big the space is, and how many make-up units you have, you could do this local to the door.

 

[Compositepro]

Radiant floors have a great deal of mass and are therefore very slow to heat-up. But this mass can also release a lot of heat when there is a door opened momentarily. But as EnergyProfessional says, that has little to do with sizing the heating system. If roll-up doors stay open for long periods you are basically heating the outdoors. Ventillation is a big issue in a garage and energy recovery would probably be advisable.

 

[EnergyProfessional]

Compositepro is right, heat recovery of a heated slab is actually superb. The heat transfer depends on dT between air and slab and the area. Once the cold air of the open door hits the slab you get multiples of the heat output instantly since dT increase immediately. the slab will stay warm for a long time (obviously it will need new heat from the tubes)

For sizing door infiltration I assume the air comes in at 50fpm. Then you use the area of the door and assign an average time it is open. that takes some guess work, could be 5 minutes every hour, or 30 minutes. Need to talk to operator of what is going on in that facility. Could be a door that opens once a year to remove a large device, or one that is open for a continuous hour every day for traffic.

Make sure you have a good design of how you install the tubes and and what height. If they lay at the bottom, you need more tubes. I also play with tube spacing. The perimeter and overhead door area may get 6" tube spacing, interior areas may get 18" spacing. Uponor et all have software for that.
I've seen projects where they designed the tubing to be int he top 3rd of the slab, but during construction they couldn't find a way to actually elevate the tubes while poring. This is a detail you need to hammer out before bidding.