Since radiant comfort can be delivered from any large surface area, I decided that the primary method of delivery in the existing portion of the structure at Hydronicahh would be radiant ceilings. The system of choice has a high tube density and incorporates high density insulation and a medium grade of aluminum thickness that works well with low operating temperatures.
The material of choice, which I purchased from Eric Anderson of Low Energy Systems in Denver, was the Roth Panel. Interestingly enough, there were no instructions in the installation manual for using the product as a radiant ceiling and no instruction precluding its use as a radiant ceiling, so I proceeded with caution.
I carefully laid out the whole system by first applying a ½-in. layer of plywood to the bottom of the ceilings rafters. This gave me a firm surface onto which I could attach the Roth panel without compromising the structural integrity of the roof truss system. This ceiling system is really no different than using the product for floor heating, except that this system will be covered with sheet rock, making layout, application and documentation more critical, which usually happens when you begin attaching the sheet rock to the structural framing members. And, obviously, screw placement is critical in order to properly affix the panels and avoid compromising the integrity of the tubing.
The sheet rock could have been doubled up to add additional thermal mass, assisting the flywheel mass effect, and to allow for the storage of more free energy from any of the numerous sources that will eventually be online, such as primarily solar thermal. However, I didn't want to overload the structure of the roof and wall framing system, so I opted to place just a single layer of sheet rock. One distinct advantage of a radiant ceiling over a radiant floor is that the occupants are not in direct contact with the heat emitter, so you are not limited to the 85°F surface temperatures as you would be with a radiant floor. There are limitations, but they are primarily dictated by the surface finish and the sheet rocks ability to resist thermal stress. A radiant floor is limited to an output of 35 Btus per square foot per hour, where as a ceiling can deliver up to 50 Btus per square foot per hour.
When I did the ceiling installation, I opted to do the whole ceiling instead of just the perimeter because it allows the ceiling to operate with lower fluid temperatures. This will allow me to utilize more of the free energy I will generate to maintain human comfort, and the ceiling will recover quicker when coming out of periods of no occupancy. It will also result in a higher average mean radiant temperature overall, which will enhance the comfort experience when properly controlled. Plus, my wife will be able to place large, thick throw rugs where ever she wants without affecting the heat emitter's ability to put heat out.
The supply water temperatures to the radiant ceiling will be controlled with an outdoor reset control, and non-electric and electric thermostatic operators controlled by advanced central computerized control logic, manufactured by Climate Automation Systems Inc. The product, which is named ENV, is fairly new to the American market, and I will look deeper into the control strategies in a future article.
The ceiling will also function as a radiant ceiling cooling system to provide base loading of the cooling system needs, requiring a close tab on the dew point in order to avoid the possible production of condensate on the cooled surface. Here in the Rockies, the dew point can change quickly, which may require the surface temperature to be raised in order to avoid condensate production. One minute, it is nice and sunny, and then a fast moving thunderstorm will roll through, significantly raising the dew point. The system must be capable of responding quickly to these constantly changing conditions.
In addition to this cooling system, a roof-top cooling system that will also act as my DHW pre-heat will be incorporated. The second system will consist of a large non-pressurized storage tank with an immersed coil. The coil will be the incoming cold well water service, serving the whole home.
The first stage of cooling will be to start a pump, which will be connected to a distribution header located near the peak of the roof. This will allow cool water to trickle across the roof, thereby lowering the roofs surface temperature, reducing conductive and radiant heat transfer through the roof and ceiling assembly. As the water picks up the heat from the roof, it will deposit it into the tank, thereby acting as a solar DHW preheat. The roof will essentially be a large, unglazed evaporative cooler/solar collector with the ability to perform night sky re-radiation cooling if the condition (peak summer cooling periods) warrants it.
This is some of the out-of-the-box thinking I am applying in an effort to prove that there are other ways of providing cooling comfort. Will it work? We won't know the net effect until it is up and running, but my gut tells me there is some benefit, as a DHW preheat if nothing else.
Tune in next month as we continue our journey through Hydronicahh. Until then, happy high-altitude hydroncing.
Mark Eatherton is a Denver-based hydronics contractor. He can be reached via e-mail at [email protected] or by phone at 720-479-9313.