Controlling the Habitat house radiant wall

THE CONTROL LOGIC used in the Denver Habitat home is not your typical off-the-shelf control logic. The logic is one that is incorporated as a part of the Munchkin’s on-board control system. The controls use an outdoor reset control that also resets the set point of the boiler and modifies the logic, which causes the burner/ blower assembly to modulate as well.

In addition to this feature, the on-board controls control domestic hot water production and prioritization.

Because we were using non-electric thermostats in each room, we had no need for a conventional thermostat. The net effect of a non-electric valve is that its output and control are proportional to the actual demand. In other words, if the room needs just a little heat, the valve allows just a small amount of water to flow through the wall panels. Its flow is proportional to demand.

If there were a big demand for heat, for example, a window or door opened, the sensor would detect this and open the valve fully. It works wonderfully well and maintains a stable mean radiant temperature within the room being heated.

This is not to say that these radiant walls can’t be controlled with more conventional means, such as with individual low-voltage electric thermostats and motorized valves, but I fear that the bang-bang style of an on-off controller would have a tendency to create thermal expansion noises because of the difference in expansion between the tube and the heat transmission plate. All that much more reason to use the non-electric thermostatic valves.

In addition to the thermostatic valves, the mains include a non-electric pressure differ- ential bypass valve in case none of the thermostatic valves are calling. This avoids the deadheading of pumps in continuous circulation mode, and allows the pump to generate only the pressure required by demand to be moved through the distribution system.

By the time you read this column, the system will have been through roughly three of the winter months, I hope without a hitch. The homeowners and their children will have become accustomed to the comfort afforded by radiant heat, and that is a good thing.

This first article in this series (October 2002, pg. 34) was originally headlined “Radiant for everyone” for a reason. While it is true that the most comfortable radiant heating system in the world is a radiant floor, not everyone can afford radiant floors, especially the Joe and Jane Six Packs of the world. For that reason, I looked into the possibility of providing radiant comfort to ordinary people without the costs associated with radiant floors, using hydronic heating systems with radiant walls instead.

The bottom line is that when we increase the mean radiant temperature, we affect human comfort on a large-scale basis. As I have said before, radiant walls represent some of the greatest overlooked potential in the radiant heating business.

I believe in this strongly enough to have actually developed a prefabricated radiant wall panel using the same concepts that were proven during the installation of the radiant panels in the Habitat For Humanity home.

One major difference is the intentional lack of nail guards, which are not going to keep an errant homeowner from puncturing a tube mid-span between the studs. They also represents a resistance value to the thermal conductance path. We build the panels on a framed device that serves initially as a guide or template to the construction of the panel. When the panel is built, the frame acts as a carrier to transport the panel to the jobsite where it can be screwed into place by a trained professional and hooked up to the supply and return distribution system.

The use of this panel is not limited to the typical single-family dwelling. When properly applied, it can be used for multifamily dwellings, meeting places and virtually anywhere that thermal energy transfer is needed to satisfy the needs of mankind.

I hope that in the near future a recognized organization such as the Radiant Panel Association will adopt construction details for Sheetrock-based radiant wall panels that will give official recognition to the use and construction of these wonderful heat delivery devices.

That’s it for now from the snow-covered Hydronic Encampment located high in the Rocky Mountains of Colorado. Catch you next month, and until then, Happy New Year’s Hydronicing!

Mark Eatherton is a Denver-based hydronics contractor. He can be reached via e-mail at[email protected] or by phone at 303/778-7772.