Reprinted with permission from PME Supply House TimesPlumbing and Mechanical – Radiant Heating Report 2011 http://d27vj430nutdmd.cloudfront.net/8211/74536/74536.1.pdf
A Mountain of Green
This log cabin home in the Pocono Mountains features a radiant heating system that operates off solar energy.
Research is Lou Lifrieri’s forte. Lifrieri, who runs an engineering firm in New Jersey, did his due diligence when it came to finding a sustainable energy system for his family’s 2,800 square-foot log cabin vacation home in the Pocono Mountains in Roaring Brook Township, Pa. “I’m that kind of guy, I guess,” he laughs. “I could research forever, but what I needed was somebody to help make sense of what I’m looking at. I went through seven or eight different folks until I found someone who knew what I needed.”
That’s when Lifrieri met up with Patrick Spearing of Thermomax Industries in Victoria, B.C. Thermomax has been a manufacturer of U.K.- produced solar heating systems for more than 30 years (the company’s tubes are now manufactured by Kingspan Renewables). Thermomax’s domestic and commercial systems are used for solar hot water, radiant floor heating, space heating, pools and off-grid homes. Lifrieri’s log cabin can check off just about every function on the Thermomax list with the exception of heating a swimming pool and adding a photovoltaic system.
￼￼The solar thermal system powers radiant floor heating in the Pennsylvania log cabin. ￼“I had been researching renewable solar energy the last three years, including wind technology and solar thermal,” Lifrieri says. “This is a cabin on a piece of land in the middle of the Poconos, so I had to look at how to live completely off-grid.”
Spearing recommended the radiant floor system be designed with a 10-degree delta T instead of the usual 20 degrees. “This means water comes back only 10 degrees cooler,” Spearing explains. “We can run the tank reasonably cool and still do 100 percent of the radiant floor. The solar does not need to reach really high temperatures to make this system work. If you use radiators or radiant panels, it’s 130 degrees F or more. Baseboard heaters are 160 degrees F or more. The radiant fits in beautifully with the solar at 100 degrees F to 120 degrees F — close to the domestic hot water temperature.
“Radiant uses less energy no matter what the energy source is. But with solar you get a given amount of energy from the sky to put into the heating system, so it’s important it is dispensed efficiently.” Atlantic Solar Solutions’ Peter Tevendale, the designer and installer on the project, explains the basement radiant is in the slab on 2 inches of rigid insulation with a vapor barrier and almost 2,000 feet of Radiantec PEX tubing attached to a 6-by-6-inch metal mesh.
“The tubing is set in four loops terminating at a single manifold,” he says. The first-floor tubing is installed under the subfloor with aluminum sheets to spread the heat across the floor. An aluminum foil reflective barrier is placed under that to reflect heat upwards. The upper living area of the home required a different strategy. “The second floor is built with heavy exposed timbers with a 2-by-6 tongue and groove, which is the finished ceiling of the first floor,” Tevendale states. “We laid a black rubberized mat as a sound barrier and attached PEX tubing on top with wood sleepers. Again, we used aluminum sheets to spread the heat. We covered that with plywood and wood flooring. The manifold is up in the attic with the feed and return lines running back into the basement.”
Tank and wind: The heat generated by the solar collectors (up to 176 degrees F) is directed to the radiant floor by a stainless-steel SolarThermal off-grid water tank with R24 insulation. Spearing designed the tank 20 years ago when he found no versatile tanks to accommodate nonstandard situations. The tank used in Lifrieri’s home has two extra-large heat exchange coils instead of the usual single coil. The bottom coil receives heat from the solar collector. The top coil is the heat source for the radiant floor. The domestic hot water in the tank transfers the heat (see Figure 1). The tank has extra ports, including two for electric elements, so the top half of the tank can be backed up by any source of energy.
In this case, Lifrieri is using wind and a Bosch on-demand propane water heater (119,000 Btu). “When the solar energy starts heating the tank in the morning, the heat rises and passively prevents the backup from coming on — ideal for an off-grid system,” Spearing states. The property is a Class 4 wind area, which means a good electrical contribution can be expected from the wind generator.
“The house sits 15 degrees east of due south,” Lifrieri notes. “I’m capturing all of the sunlight I can up top and I’m getting a little extra sunlight being up on the mountain.
We should be generating quite a bit of energy, especially the complementary energy in the winter. This is designed for about 5,000 to 8,000 watts a day, depending on usage.” Two 24-volt elements in the tank connect to the wind generator, which heats the top half of the tank. That heat can go straight to the radiant floor so the tankless water heater works less, if at all.
“During the summer when the solar tubes are rocking, an inherent shutdown valve in each tube protects the system. But because there is less demand for heat, the hot water is run through a heat dump load,” Tevendale says. “The heat dump is a slab outside with another radiant loop. When the tank reaches the maximum temperature, the iSolar controller turns on a circulating pump to cool the water through the tubing, keeping the tank at a safe temperature.”
The first-floor tubing is installed under the subfloor with aluminum sheets to spread the heat across the floor. An aluminum-foil reflective barrier under that reflects heat upward.
A 13.5 kilowatt propane generator is tied into the hybrid solar wind system to provide automatic backup.
“Our construction techniques, including the insulating concrete forms for the foundation, took advantage of the latest insulation technology in an effort to reduce the heating and cooling envelope,” Lifrieri explains. “This resulted in lowering the overall energy demand to accomplish a ‘net zero’ result. We are producing all the electricity we need to maintain the cabin year- round through the use of renewable energy.”
The water tank used in Lifrieri’s home has two extra-large heat exchanger coils instead of the usual single coil. The bottom coil receives heat from the solar collector. The top coil is the heat source for the radiant floor.
The loop can be turned on manually to thaw ice off the patio in the winter. Lifrieri is researching another summer use — a hot tub. “He does not want to lose one ounce of energy his systems create,” Tevendale explains.
PV ArrayxMaximizing power: With 16 panels of roof-mounted solar PV coupled to two strings of 2VDC AGM batteries with dual 4 kilowatt charger inverters and 7.5 kilowatts of wind turbine, the cabin can be operated without the benefit of sunshine or wind for three days under normal use.
The log cabin is equipped with a fireplace, but Lifrieri points out it’s for ambience only. In fact, Lifrieri is so satisfied with the off-grid system that he’s looking at building more cabins on adjoining property. “It could be my retirement gig, so to speak,” he laughs.
Spearing is impressed with how Lifrieri has married together a variety of renewable energy sources to create his off-grid country home. “While return on investment is excellent, in an off-grid situation, performance and longevity are paramount,” Spearing says. “Most important is that feeling of security and satisfaction that arises when one has control over essential aspects of survival. Lou has put tremendous energy into realizing a dream many of us have.” ￼