Fabric Structure

GlenW.

We have been asked to re-engineer a "Summit Structure" 70,000 sq. ft. fabric/steel building for radiant heat. The building will be an indoor tennis court (asphalt). What concerns me about this particular structure is the two-layer fabric used for the ceiling: in order to prevent condensation in the ceiling, the company takes a percentage of indoor air from grade/midlevel/high level, and then injects it inbetween the two layers of fabric. Unique idea, yes, but...will the de-stratification of the air in this 30-40 ft. high structure render the in-floor ineffective? In other words, I am worried about the air-wash effect. Building loads are one thing, but this is another.

Mike T., Swampeast MO

Since large, low temperature emitters like floors do very little to encourage natural convection, temperature stratification is typically much lower than with other heating methods and virtually irregardless of ceiling height.

This sounds like a very large, very open and extremely lightweight structure with few and lightweight contents. Radiant panels work so comfortably because they in large part heat the air indirectly by first heating other objects which in turn warm the air.

In this case you may actually face a situation where you have a considerable deficit of mass in the ceiling and walls relative to the volume of air that must be heated which is artificially increased by active, room air ventilation of the air ceiling.

With such little mass, the ceiling--ordinarily the prime absorber of radiant energy from a floor panel--cannot store enough radiant energy in the form of heat to in turn increase the temperature of the air surrounding. I suspect that the generally regarded as highly safe 2 btu/hr/sq.ft (per degree of temp difference between panel and air surrounding) output estimate may not apply in this situation with the floor delivering significantly less energy than expected thus requiring increased panel temperature to maintain standard output.

The fabric ceiling is POTENTIALLY DEVASTATING!

You must determine if the ceiling has a radiant barrier!Many fabrics are quite transparent to infrared (heat) radiation. The IR transparency of fabrics can be manipulated. If an extremely effective IR barrier is not used, then an amount of infrared radiation from the floor proportionate to its opacity will literally be passing through the ceiling into the great outdoors heating nothing indoors in the process.

EDIT--ADDED

You cannot assume that any IR barrier short of a continuous metal sheet is reasonably perfect both looking in and looking out!

Again, IR barrier effectiveness can be manipulated in a multitude of ways and for intended affect. Contact the manufacturer of the roof to ensure that it is an effective radiant barrier between a warm floor and the nighttime sky. If they cannot supply engineering data, I would not consider using the floor to heat this structure.

If located in a cold climate, players could conceivably see their breath while they sweat and watch a piece of chewing gum spread on the floor.

GlenW.

Very well put. There are few times when I believe Radiant is not the answer...but unfortunately, this appears to be one of them.