MILWAUKEE — Hydronic heating systems are the enabler for all alternative energy technology, John Siegenthaler, P.E., told attendees at the Solar Thermal ’11 conference and show here in early December. Heat from solar collectors, geothermal heat pumps or pellet boilers can all be dumped into a buffer tank and efficiently distributed throughout a building via a hydronic system, said Siegenthaler of Appropriate Designs, Holland Patent, N.Y.
Hydronics is the optimal system to enhance the performance of a heat source, Siegenthaler said. It’s easier to move energy through a building using a smaller ECM pump and small tubing because of the physical qualities of water. The specific heat of water — its heat capacity — is 62.4 Btu/cu.ft./1°F, which means water can absorb 3,500 times more heat than air.
Caleffi Solar sponsored Siegenthaler’s seminar at Solar Thermal ’11, which was produced by the Midwest Renewable Energy Association. CONTRACTOR magazine was the media sponsor of the event.
To put the heat capacity of water into perspective, the same amount of energy can move through a ¾-in. tube as through a 14-in. x 8-in. duct. Buffer tanks provide easy thermal storage potential along with easy integration with conventional backup heat, Siegenthaler pointed out.
The small tubing of a hydronic distribution system makes for a minimally invasive retrofit. In a multi-family building, the heat used can be easily metered, a common practice today in Europe.
Modern hydronics in the ‘90s and ‘00s went into big houses, Siegenthaler said. Is the solution just to add a lot of solar collectors? That creates a problem with overheating solar “monuments.” It’s not economically sustainable and too expensive for the average customer.
Instead, the guiding design principle should be more insulation, fewer collectors and low-temperature distribution. Designers can also figure in passive gain from a tight building. A well-insulated building will also lower the electrical requirements to move heat around the building.
The trend today is for smaller houses, smaller loads, more passive solar and more interest from consumers about energy conservation. In such a house, the maximum supply water temperature at design conditions should be 120°F. That temperature, Siegenthaler noted, puts contractors right in the ballpark for all types of renewable energy technologies.
Is radiant floor always the answer? No, he said. If radiant is buried in a high-mass floor, the response time is too slow. Moreover, the load may be 10 Btuh/sq.ft., meaning the floor temperature only has to exceed the room temperature by 5°F. At 68°F, the floor temperature would be 73°F, which would feel cool to the touch.
Siegenthaler suggested other heat emitters such as tube and plate radiators, radiant ceilings, panel radiators and low-mass panel radiators. The traditional high-mass radiator, like that used with traditional high-temperature boilers, has more overshoot and undershoot than desirable, he said. Because a high-mass radiator is designed to operate at 160°F-180°F, it would produce only 30% of its rated capacity at 120°F.
Siegenthaler showed a variety of products in his PowerPoint. One was a British product called Heating Edge. The 8-in. tall radiator contains two ¾-in. copper tubes and the interior is filled with fins. It’s made by Smith's Environmental Products.
Panel radiators can go from setback to steady state temperatures in as little as four minutes, which Siegenthaler showed in a series of photos taken with an infrared camera. The bigger panels use lower water temperatures. They are also sized by the metal volume rather than water volume.
He showed a Jaga panel radiator that contains low-wattage fans, about the size of computer fans, which pull warm air through the fins.
He showed work-in-progress photos of site-built radiant ceilings and radiant walls. The panels are built from OSB, polyisocyanurate insulation board, and aluminum heat transfer plates with the PEX tubing snapped into it. The heat output of a radiant ceiling is Q = 0.71 x (T water – T room). The heat output of radiant wall can be calculated as Q = 0.8 x (T water – T room).
Siegenthaler also showed work-in-progress photos for slab-on-grade applications because it’s easy to do it incorrectly. The slab needs 2-in. of foam insulation on the underside. The tubing and mesh have to be raised to the middle of the slab so the heat doesn’t have to penetrate 6-in. of concrete to get into the room.
Thin-slab concrete is another option, but he pointed out that it loads 18-lbs./sq.ft. onto the structure. Poured gypsum underlayment is like poured-in-place drywall. It’s good for a low-resistance finish floor. Above floor tube-and-plate systems are a popular option but the typical residential application will require 130°F water to heat properly.