Geo-to-Radiant Retrofit

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Three 300-foot-deep boreholes provide the thermal-coupling to the earth’s energy
Three 300-foot-deep boreholes provide the thermal-coupling to the earth’s stored energy. Geothermal heat pumps convert that thermal energy for use in space heating of the home, garage, and bunkhouse.
Fred Umble of Creative Energy (left) hot-fuses geothermal pipe connections
Fred Umble of Creative Energy (left) hot-fuses geothermal pipe connections at one of the three well-heads.
Scott Barnett works on the new ClimateMaster water-to-air heat pump
Scott Barnett works on the new ClimateMaster water-to-air heat pump, rated at 27-SEER. This unit provides all cooling and supplemental heat.
Dave Yates does final soldering on the buffer tank
Dave Yates does final soldering on the buffer tank that connects to the hydronic control panels in the background.
Merv Wenger, installs the Sea Tech “home-run” domestic water lines
Travis’s father, Merv Wenger, installs the Sea Tech “home-run” domestic water lines into the central manifold.
Dave Yates installs hydronic radiant tubes
Dave Yates installs hydronic radiant tubes to the underside of the garage subfloor.
Insulation directs radiant heat upward to the room above.
Insulation directs radiant heat upward to the room above.
Homeowner Rachel Wenger ties radiant tubing into place
Homeowner Rachel Wenger ties radiant tubing into place before the garage workshop’s concrete floor is poured.
Dave Yates installs backup Fujitsu minisplit heat pumps
Dave Yates installs backup Fujitsu minisplit heat pumps, which also provide airconditioning for interior garage spaces.
Three 300-foot-deep boreholes provide the thermal-coupling to the earth’s energy
Fred Umble of Creative Energy (left) hot-fuses geothermal pipe connections
Scott Barnett works on the new ClimateMaster water-to-air heat pump
Dave Yates does final soldering on the buffer tank
Merv Wenger, installs the Sea Tech “home-run” domestic water lines
Dave Yates installs hydronic radiant tubes
Insulation directs radiant heat upward to the room above.
Homeowner Rachel Wenger ties radiant tubing into place
Dave Yates installs backup Fujitsu minisplit heat pumps

Some outdoor enthusiasts go to great extremes to set up the perfect camp. An example of just how far the Wengers will go is the “regreening” of their rural lakeside log home in west-central Pennsylvania.

Travis and Rachel Wenger spent most of the autumn months of 2007 shopping for a family retreat and hunting lodge. During a second visit to one of the properties—a 2,400-square-foot, three-bedroom log home built in 1994—their decision was made much easier by the arrival of a 400-pound harbinger. While they were admiring views from the home’s deck, a black bear, ignoring them, had climbed up the other side of the deck to assault the gas grill.

Convinced it was “the sign we were looking for, we immediately agreed to buy the place,” says Travis.

From Idyllic to Ideal

Nestled on a mountainside, the 16-acre home site borders thousands of acres of state game lands where deer, turkey, and bear roam freely. Nearby are several state parks, the Juniata River, and miles of wildlife trails.

While the property was just what they’d looked for, the home itself was less than ideal. “Before the remodel, the place left a Sasquatch-sized carbon footprint,” says Dave Yates, the contractor hired to update the home’s mechanical systems. “The log home leaked like a sieve. Winters are brutal up there, so they were burning LP gas furiously and getting dizzy watching the electric meter spin.”

Yates visited the Wengers’ retreat that fall to calculate the home’s heating load and to take notes about the upcoming job, which included a geothermal-to-radiant space-heating system. “For the homeowners, improving energy efficiency was just as important as having year-round comfort,” adds Yates.

“The home had electric air-conditioning and a 140,000 Btu per hour propane furnace with supplemental heat from a fireplace and three old potbelly wood heaters,” says Yates. “They also used several portable electric heaters and an old electric water heater.”

The Wengers gave Yates a lot of flexibility in designing a “green” system, adding that if it made sense to keep some of the old equipment, fine; but where it made better sense to toss out the old to make room for the new…even better.

To prepare for the heating system overhaul, Travis and his father Merv, no strangers to remodeling jobs, added “truckloads of insulation,” upgrading many of the walls to R-16 or better and the ceiling to approximately R-48, with plans to add a radiant barrier to interior trusses this winter.

By the time the contractor’s crew began work at the home, 100 miles from their shop, the Wengers had already resealed all the logs in the home, began the basement remodel—including rigid-foam insulation—and set the foundation for the log garage, with a 150-foot, 4-foot deep trench from the house for an insulated loop to carry geo-to-radiant system heat between the two buildings.

The old 10-SEER (seasonal energy efficiency ratio) central air-conditioning system was disconnected and replaced with a 4-ton (48,000 Btu per hour) ClimateMaster Tranquility water-to-air system. Rated at 27-SEER—2.7 times the efficiency of the old air-conditioning system—this unit can also provide backup heat if needed.

For space heating, the Wengers settled on a unique mechanical system designed by Yates. For the heating season, the heart of this system is a high-temp, water-to-water ClimateMaster thermal hot water (THW) heat pump, two twin-coil Bradford White indirect water heaters that source heat from the heat pump system, and several preassembled HydroNex control panels by WattsRadiant—one of which is designed to accept solar heat for domestic water, then to share additional heat with the radiant system.

The heat pump system has a rated maximum output of 145°F with a peak coefficient of performance (COP) of 4.5, assuming sufficient geo-exchange, which required three 260-foot boreholes. The COP means that for every unit of (electrical) energy used to operate the system, 4.5 units of heating/cooling are available.

But the Wengers asked geothermal driller Dave Eriksen to drill down farther, lengthening each run by another 40 feet. “I knew from a friend’s geothermal system that their heating needs would occasionally max out the field’s capability,” says Travis, “so by adding 15% or so to the field size, I figured we’d have an underground insurance policy.”

Eriksen drilled three holes into which geothermal pipe was inserted. The holes were also thermally grouted, a process that injects a bentonite slurry to enhance temperature exchange between the pipe and earth.

“We believe this was the reason for one of the big surprises we had with the system’s startup in December 2008,” says Yates. “Though outside temperatures hovered between 10 and 12°F, the THW unit delivered system heat of 157°F—substantially higher than what it was rated for.”

Radiant Details

All of the home’s PVC plumbing—which, according to Yates, was a “snake pit of code violations”—was replaced with WaterPEX lines that connect to a central Sea Tech manifold in the new mechanical room.

While the basement remodeling was underway and the joists were accessible, the Wengers’ crew stapled 2,400 lineal feet of Onix radiant-heat tubing to the subfloor to heat the home’s main floor. The eight 300-foot loops were attached to manifolds with balancing valves and flow meters for precise control of heat distribution. “The Onix tubing flexes like rope, can be doubled-up and pushed through joist bay holes, and flattens slightly during staple-up, greatly improving heat transfer,” says Yates.

While the subfloor tubing was being attached, the crew mounted the control panels, which temper system water based on outdoor temperatures. “We designed the system so that the 36,000 Btu water-to-water geothermal unit sends heat directly into a 120-gallon, two-coil indirect water heater next to it,” says Yates. “This was the heat pump’s ‘thermal target,’ which efficiently exchanges heat that then moves to the control panels.”

Heat exchangers separate the geothermal system’s 50/50 methanol solution—a special antifreeze chosen for stability and heat exchange properties—from the water systems within the home. “We run the system all winter long,” says Travis, “so we didn’t need to circulate an antifreeze solution within the radiant tubing.” 

The home’s hydronic heating requires two water temperatures: a lower temperature for the floor loops (in three zones, each with a separate thermostat) and a higher temperature for several wall-hung radiant panels and the underground loop to the garage.

“The hydronic control panels—in the house and garage—came preassembled, with all the controls and components needed for low- and high-temp heat distribution,” says Yates, “saving weeks of labor.”

Rigging the Radiant System

“We could meet a lot of needs with the THW heating the 120 gallons of water in the main source tank between 145 and 155°F, but it couldn’t exceed 36,000 Btu,” says Yates. “So we had to choose carefully what and how to heat, and had to insulate real well in all directions. With house needs met, we still had plenty of Btu to heat the injection loop to the garage.”

Heated water is sent to the garage loop via R-flex, a polyethylene-insulated, tandem underground PEX pipe. The subterranean tubing thermally connects the house buffer tank’s 120-gallon volume with the garage’s slightly smaller, two-temperature radiant heat system.

In heating mode, high-temp water (145 to 155°F) from the buffer tank enters the garage’s control panel and then supplies two radiant zones. Water at about 125°F is sent through the 1,800 lineal feet of tubing that heats the guest quarters, and 90 to 110°F water is sent through the single, 300-foot loop of tubing embedded in the tool room’s 10-by-30 foot concrete slab.

The stapled-up tubing’s heat is directed upward by R-19 batting insulation below the tubing. By applying many layers of R-19 fiberglass batts, and 2-inch rigid insulation, the Wengers achieved R-90 in the ceiling and upper kneewalls of the garage.

“The massive dose of insulation started when we needed to thermally protect the long radiant supply and return tubing runs in one of the kneewalls,” says Merv. “We made a cocoon for the tubing that was as long as the garage and just kept adding layers. We had a good source for the material, so we decided to buy a good bit more than we’d need, knowing that it could only help to keep heat in the building.”

The only thing they didn’t ask of the geothermally heated water was to heat domestic water for the guest quarters’ sinks and shower, so an electric, 30-gallon tank-type water heater was placed in the radiantly heated tool room, directly below the shower.

Phase I Performance

Just before their first full heating season, the Wengers added more insulation in the ceiling of the home’s main floor and replaced the potbellied stoves with a more efficient, small, centrally located Vermont Castings wood heater.

“Last winter was amazing,” says Rachel. “Even though all the systems weren’t operational, we had plenty of heat for the house with the geo water-to-air heat pump, the new wood heater, and a little electric radiant heat that we used. This winter will be the first for the home’s main radiant system and the garage radiant, but we’ve prefired all parts of the system and everything went well. The thermostats are set, so all we need now is for the outdoor temperatures to drop.”

“Based on our preliminary calculations and the performance we’ve seen so far, the Wengers will probably see a 60 to 80% drop in their energy expenses,” says Yates. “The carbon footprint got a lot smaller, while they’ve added tremendously to the size of their comfort zone!”

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Manheim, Pennsylvania-based John Vastyan is a journalist and communications professional who focuses on the plumbing, mechanical, radiant heat, and geothermal industries. He can be reached at 717-664-0535.

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