Radiant Heating Report: Renewable Radiant
Mike Tierney caters to a crowd that likes to get away from it all. If you want to travel to the award-winning Fitzgerald home after a heavy snowfall, then hop on a snowmobile. It's the only way.
Tierney's a Wet Head of a different sort. Sure, he knows all about boilers, but his main power source comes from sunshine.
In the early 1980s, he got a solar technology degree from a local community college. At the time, there were still solar energy credits on the books from the Carter administration. Tierney was a ski patroller in the winter and a white-water rafting guide in summer. The half-dozen solar jobs he began doing, mostly providing domestic hot water, supplemented his income.
But when the credits died in 1985, so did the solar energy market. Even still, while the credits created a false market for solar energy, a real market was slowly, but surely, building.
Take a look at the Fitzgerald home again. A snowmobile ride isn't the half of it. The Fitzgerald's front door is two miles from the nearest power pole. With the local utility charging up to $25,000 to provide extensions, solar power becomes the only practical way to provide heat and electricity for impractical home sites.
"More and more people are moving a long way away," Tierney says. "Solar radiant is the only way to go."
Which isn't to say a traditional boiler system doesn't go along, too. Tierney's radiant jobs primarily are solar powered with a boiler backup fired by gas, oil or even wood. The challenge is to find the most efficient way for the two systems to work together.
"We're always looking for a happy medium," Tierney explains. "If you rely too much on solar, you'll end up with a behemoth that won't even provide heat on cloudy days. If you rely too much on a traditional boiler, it's too expensive to heat the home."
The solar radiant system for the 2,200-sq. ft. Fitzgerald home, for example, was designed to provide 75 percent of the heating requirements and almost all of the domestic hot water needs. The rest of the demand is filled by a Buderus propane-powered boiler, situated in the best-looking "outhouse" we've seen. The building provided some comic relief one morning after a subcontractor bolted for it after drinking 20 cups of coffee during the drive to the construction site.
Tierney had to improvise for the boiler room since local building codes restrict propane systems from basements. In this case, the well-insulated outhouse uses the same weathered wood that gives the new home its rustic appearance. The propane tank and supply and return lines were insulated and buried underneath the outhouse.
The boiler is tapped only if the temperature drops below the setpoint. Renewable solar energy is always the first in line. Five 8 ft. by 4 ft. solar panel collectors channel the sun's rays to warm approximately 400 gallons of water stored in a custom-made stainless steel tank.
On most sunny days, the tank will store water in excess of 140 degrees F. At those temperatures, the water passes through a Danfoss thermostatic mixing valve.
The radiant floors are divided into seven zones, and are a combination of slab and staple down. Since you can't turn off the sun, Tierney also has to store excess solar heat when the home is unoccupied. (Keep in mind, this is a second home with the owners away frequently and for long intervals.) To do this, Tierney buried 250 feet of Kitec 1/2-inch tubing under the boiler room. Another setpoint controls this heat sink by switching on a pump, drawing heat from the tank when the temperature exceeds 195 degrees F.
The domestic hot water system uses a single pass and recirculation loop from the solar thermal system. A GL-30 controller circulates water between the main solar thermal tank and the heat sink. A 53-gallon Buderus indirect water heater also is used for storage. The recirc pump doubles as an instant hot water recirc pump.
Solar power is also the home's main source for electricity. A propane-powered generator does provide a backup but is not relied on nearly as much as the boiler for reserve heat. Also, the Fitzgerald home is completely off a utility grid, so its electrical load needs to be as low as possible. As a result, eliminating all "phantom loads" of electricity is a must. Phantom loads refer to the power demands of appliances sitting in standby mode but using electricity all the same. A television with a remote, for example, is always on, even if the tube is black.
"The culprit is the transformer," Tierney adds, "which dilutes the 120 volts of electricity entering a home down to 24 volts."
All these little power draws add up but are particularly critical for controlling the pumps and valves operating the heating system. "A standard system would quickly kill the solar electric system," he says. Tierney eliminates the transformer by using all line voltage thermostats and zone valves. In a nutshell, this setup acts as an on/off switch for the heating system.
"Absolutely no power is being used unless the thermostat is calling for heat," Tierney says.
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