Geothermal system provides comfort and savings for Oklahoma housing development.

A single 400-foot geothermal well was drilled on each property at Hope Crossing. A number of test homes have since been retrofitted with a single 230-foot well. Photo credit: ClimateMaster

G’Anne Derrickrecently went to visit her sister,Margaret, in Yukon, Okla. With the onset of summer, hot temperatures necessitated the use of air conditioning during the familial gathering.

“She has a traditional condensing unit and it never shut off,” Derrick says.

Upon arriving back to her home in the Hope Crossing subdivision in northeast Oklahoma City, it was a much different story.

“I set the thermostat down during the day,” Derrick states. “It had been flaming hot outside and my husband has a heart condition. I did not want him to come in and still have the house frying. Our unit wasn’t on and it was still 69 degrees. It stayed 69 until I changed it back to 72 degrees.”

The Derricks walked out of the blazing sun and into a comfortable home thanks to the installation of a geothermal heating and cooling system.

Their home is one of more than 200 in Central Oklahoma Habitat for Humanity’s Hope Crossing development that will eventually be outfitted with a ClimateMaster geothermal system. The 59-acre Hope Crossing features low-cost, single-story, three-bedroom, two-bath homes.

Oklahoma City-based ClimateMaster donated Tranquility 27 packaged water-to-air  geothermal systems to each home in the development. Another partner in the project is Oklahoma Gas and Electric, which provided funding for insulation systems, compact fluorescent lighting and high-efficiency windows. Upon completion, the homes in the development will be LEED-certified.

“The whole goal of this project is to bring the smallest utility bills to these people that we can,” statesChris Ellis, the owner of Oklahoma City-based geothermal heat pump specialist Comfortworks, which did the geothermal installations.“They need smaller electric bills more than anybody. To be able to provide that for them is amazing.”

With the geothermal system in place, homes in the Hope Crossing development are seeing electric bills as low as $35 a month, but never higher than $100 a month.

Taking a different path

A typical geothermal installation on a home might see two 200-foot wells drilled in the yard that connect the main return supply piping into the house. For the Hope Crossing project, each home contains one 400-foot geothermal well.

“The well has a two-ton capacity,” Ellis explains. “For these homes, we drilled right under the slab where the unit is. It’s a straight shot down. It reduces costs and it makes for an easy installation.”

Goldsby, Okla.-based B&H Construction drilled the wells at Hope Crossing. Each well boring in the development takes an average of one to four hours to complete.

“With the 400-foot well, you don’t have any header-line costs associated with the job,” notes B & H’sScott Munday. “With the 200-foot ones, you have to tie them together and take them to the building. With the 400, there is no welding or fusions. Everything stubs up at the unit for a simple tie-in.”

While using the single well creates savings with digging costs, the deeper well dig can pad the pocketbook even further.

“The secondary benefit is you are going deeper into the earth and getting a greater heat transfer, which results in a higher efficiency in the loop,” Ellis states. “When you get deeper into the earth, the temperature remains more constant. The more groundwater you have around that loop, the greater the heat transfer is going to be. That lowers the operating costs a little more.”

One-inch tubing in the geothermal well runs down 400 feet and comes back up 400 feet where the two pipes connect straight into the system, which is located directly beneath the floor slab. Six feet of piping sits above the slab to connect to the system. The homes have integrated ground-loop pumping and purging valves in the heat pump to save on space required, equipment cost and field labor content.

“ClimateMaster provided more of a turnkey package with built-in pumps and built-in flush ports,” Ellis says. “There is no need to pipe in anything. You come right out of the slab and into the unit. There is no need for ball valves. Everything is built into the system.”

A reversing valve controls the flow of hot and cool air - much like an air-source heat pump.

“The outdoor system is your ground loop,” Ellis says. “You’re either sending heat into the ground during the summer or taking heat from the ground in the winter.”

Drill away

Geothermal systems are more prevalent in Oklahoma due to favorable drilling conditions.

“Lower drilling costs make it fairly economical,” Ellis states. “In a place such as Colorado, you can hit major rock and drilling costs can be $15-$20 a foot, which is nearly quadruple what our costs are. Our soil here in Oklahoma is very easy to drill. We can drill through it fast.”

While hot weather is a given during the summer months in Oklahoma, winter months can produce temperatures that necessitate the heat being turned on in homes. The teeter-tottering climate fits nicely into a geothermal blueprint.

“There is a demand for both heating and cooling,” Ellis notes. “I’d put it at 50:50. You need as much heating as you do cooling here, which makes this state prime for installing a geothermal system.”

ClimateMaster donated its Tranquility 27 packaged water-to-air geothermal systems. Next to the system is a Bradford White water heater.

Going back for more

COHFH notes as of late June, 145 homes were completed in the development (a total of 217 will be built). Plans are already underway to implement enhancements designed to achieve even greater efficiencies. The Derrick home is one of eight in the development involved in a two-year study where a 230-foot single well has replaced the 400-foot one.

Each of the test homes now contains a similar ClimateMaster 27 series system with an updated control board and loop pump.

“These are experimental geothermal wells using different size holes and different types of piping,” statesAaron McRee, the construction manager at Central Oklahoma Habitat for Humanity. “At the end of two years, they will compile data and see which system works best. You tie the new line into the system and cap the old one. At the end of two years, you tie the new and old loops together to have twice the efficiency in the loop system. It’s a perk to the homeowner.”

Piping for each geothermal system is located directly beneath the floor slab. Six feet of piping sits above the slab to connect to the system. Photo credit: Aaron McRee/Central Oklahoma Habitat for Humanity

Sustainability equals savings

In addition to the geothermal aspect, the homes feature a variety of other green initiatives aimed at driving energy costs even lower. Insulated hot water lines sit under the slab, while the house wrap, insulation and windows all have green characteristics. Bradford White and A. O. Smith water heaters and Delta low-flow showerheads contribute to the green footprint as well. Habitat is touting the development - once completed - as the largest green-build Habitat community in the country.

That green footprint has allowed Hope Crossing homeowners to enjoy much-appreciated energy savings.

“If my water-heating bill was $2 a month, I would be completely floored,” Derrick states. “This system preheats the water. Two years ago here it was the summer from hell. There were days and days of temperatures over 100 degrees. Our bill never went over $85. Yes, the house is only 1,150 square feet, but even in the worst months that was the average bill.”

McRee has seen electric bills in the development as low as $35 a month, but never higher than $100.

“I would guess the average is about $85,” he states. “My house, which is slightly larger with a standard forced-air split system, is about $250-$300 a month in the summertime. I have a gas bill on top of that.”

ClimateMaster PresidentDan Ellis, Chris Ellis’ father, notes the geothermal homes at Hope Crossing will collectively save nearly 1,100 metric tons of CO2 per year, or 22,000 metric tons over a nominal 20-year lifespan, compared to the standard gas homes COHFH had been building. If all the homes had a 2.3 kW solar panel option, another 12,000 metric tons could be saved over 20 years.

“With all of those elements in place, as well as solar panels, the energy consumption of the homes is reduced by 75 percent,” Dan Ellis states. “They are going to save over $1,200 a year compared to a Habitat home built last year.”