Floor Condensation Control System

[brant2000]

We have a large space, approximately 6,000 sq. ft. total, which is supplied with 100% outside air. The space has very large, 12 ft diameter, pipes that run under the floor with cold water. We want to prevent the possibility of condensation forming on the surface of the concrete floor. An electric heat trace system has been proposed that would be installed in the floor, near the surface to ensure that the floor temperature remains above the dewpoint in the space. A feasible plan, however the manufacturer does not seem to have the ability to integrate a dewpoint sensor and floor temperature sensor in order to energize the system as these parameters approach each other. Does anybody have any alternatives or solutions?

 

[KenRad]

Are these pipes really 12 foot in diameter, or did you mean 12 inches?

Has anyone done the calculations to see if it is likely that the floor will sweat? You need to know slab thickness, water temperature, worst case room dewpoint and pipe material. It would be a shame to cut up the floor for heat trace only to find out that it wasn't needed.

I'm guessing that the floor slab is existing. If not, then you could put down a thin layer of rigid insulation prior to pouring concrete. This would give you enough R value to ensure that your floor never reached dewpoint temperature.

If you go the heat trace route, it would not be difficult to incorporate room dewpoint and floor temperature into a control loop that energizes a heat trace contactor. Find a controls company, because your heat trace company is obviously not qualified for this.

---KenRad

 

[brant2000]

Sorry, I neglected to mention some details. Nothing exists yet. Construction has not yet begun. Yes, the pipes are indeed 12' in diameter. Two pipes, centerline 8' below the concrete surface, leaving 24" to install heat the heat trace system. A monthly estimate of the surface temps and worst case dew points has been done. March will be the worst case and is the only month that our model may potentially "sweat". Nonetheless, since construction has not started, we are going to cover all bases now.

 

[KenRad]

How thick will your slab be? What are you going to do with the rest of the 24"? I strongly believe that you have no need for heat trace. You didn't mention water temperature and worst case room dewpoint, but I'd bet that 12" of dirt would give you enough thermal resistance to prevent that slab from ever sweating. If your still worried, then a 1" thick layer of polystyrene under the slab would definitely do it. Or you could put the insulation directly on the pipe. Anyway you look at it, heat trace would be serious overkill.

If I'm missing something here, someone please chime in!

---KenRad

 

[GMcD]

KISS: As per KenRad's note above - 2" (50mm) rigid insulation layer over top of the pipes, then your concrete slab, then de-humidify, if you still really need to, at the air handlers.