DX Heat Pumps Deliver Savings and Efficiency for Canadian Homeowner

By Kelly Green

In the world’s seventh coldest capital city sits a 6000 square foot waterfront mansion equipped with the world’s number one heating and cooling system.  The direct expansion (DX) geothermal system provides the Ottawa home with 12 tons of heating or cooling energy.  Jean Daoust, the homeowner and a prominent commercial builder in Ottawa, said the economics were what sold him on the system.

“The primary motive for installing this system was the economics,” Daoust said.  “The engineering analysis for the cost of heating this home using both natural gas and electricity for running pumps and so on would bring the annual cost to just under $9000.  Going with geothermal that annual cost would be under $3000.”

The home’s DX heat pumps are an original design by Maritime Geothermal of New Brunswick, Canada.  DX heat pumps differ slightly from water-based geothermal heat pumps.  DX systems eliminate the need for a refrigerant coil inside the heat pump by using the buried ground loop as the only heat exchanger.  Instead of water or antifreeze solution, the DX systems circulate R410A refrigerant through copper piping buried underground.

According to John Lobb, of Earth Energy Solutions,  DX systems have been used in government buildings, businesses and residences throughout Canada since the early 1990s.  Earth Energy has positioned DX geothermal as a core product offering and is installing the systems in buildings throughout Ontario.

Glenn Kaye, president of Maritime Geothermal, said in the beginning, there were questions about the performance of a system using buried copper pipes.  Now, with DX systems in successful operation for more than 14 years, Kaye said many of these criticisms have fallen away.

“Many Canadian contractors have found DX systems easier to install,” Kaye said.  “There have been no issues related to use of copper pipe and the consumers are pleased with its reliable operation and the lack of service required for the system.”

According the Kaye, the popularity of DX systems in Canada is most likely related to the large percentage of Maritime distributors throughout the country.  Kaye said there was only one manufacturer of DX heat pumps in the United States.  Maritime also manufactures water-based heat pumps.       

Another factor contributing to the popularity of DX systems in Canada is the ability to install them in smaller city lots.  Kaye said the boreholes for a DX system are often smaller then those needed for a water-based system.  This translates into smaller drilling equipment and less space required for the installation.  For this reason, Lobb said the systems are also known as urban geothermal.

 Design and Control with DX Heat Pumps  

The Daoust home installation required 15 vertical boreholes, which were three inches in diameter, drilled to 100 feet.  The system has five fan coils that provide hot or cold air as required and the home is also outfitted with radiant floor heating.  According to Earth Energy Solutions, the system designer and installer, the system will heat the home for about half the cost of a natural gas system and about one-third the cost of a conventional air conditioning unit generating payback on installation costs in about seven years.  Daoust and his family have occupied the home since December 2005 but due to Ottawa’s unusually warm winter, he was unable to calculate his savings so far.

“We haven’t really had a benchmark year, but following next winter I will have better records and be able to benchmark it with respect to the initial study,” Daoust said. “The heat pumps are the prime source of energy right now so I have no doubt I am saving money.”

According to Daoust, it was necessary for his home to be designed with a pair of redundant heating systems.  The radiant flooring serves as the home’s primary heating system. The air system, which runs continually, circulates ambient air throughout the house and along the windows that cover more than 80 percent of the home.  Daoust said the moving air prevents those standing near the windows from feeling any cold coming off the glass.  The redundancy was also necessary to combat overnight changes in temperature, Daoust said. 

“We have here temperature changes overnight that can be drastic and the in-floor, radiant heating would not be able to react quickly enough to bring up the ambient temperature,” Daoust said.  “So in those cases, the hot water is fed to the fan coils, which then supplements the heat.”

The radiant flooring and air system are also independently controlled.  Daoust said they decided not to interlink the controls on the systems for a couple of reasons.  First, it would have been expensive and the contractors were unsure how it would be done. Secondly, Daoust said he has learned from experience that thermostats and controls often do not anticipate and react the way our bodies wish they would.

“So for cost and for comfort, we decided we would have independent controls,” Daoust said.

Other issues created the need for even more innovative design for the Daoust’s home.  Ontario building code required the home’s domestic hot water temperature to be 140 degrees Fahrenheit.  While the home’s heat pumps had the ability to keep the water at that temperature, their optimum efficiency was achieved with water at 120 degrees Fahrenheit, leaving Daoust and the system’s designers with a problem.  The end result was the decision to bring in a small gas-fired boiler to bring the domestic hot water up to code.

“Because there is a trade-off between having the heat pumps run a whole lot more to achieve the 140 degrees for our domestic hot water needs, we decided to have the heat pumps run at their 120 degrees optimum range and to boost the domestic hot water with the on-demand, gas-fired boiler,” Daoust said.

The Canadian domestic hot water code was established after an outbreak of a mysterious bacterial respiratory infection among American Legion convention attendees in Philadelphia, Penn. in 1976.  The bacterium, which is now known to cause Legionnaires’ disease, can survive in water temperatures up to 124 degrees Fahrenheit.

The Daousts also use natural gas for cooking and as a back-up system for the typically frigid winters in Canada.  Daoust said it was his understanding that on average there could be up to three weeks of extremely cold weather each winter where the DX heat pumps would have to work hard to keep the home at the family’s desired comfort level.  The natural gas will supplement in those instances should it be necessary.          

“These little adjustments to me are totally normal when you come in with something relatively new and innovative.  I mean, all of the components are tried and tested but each little application has its own quirks and so I’m not upset with these adjustments,” Daoust said.

Though heating is a primary focus of system installations in the Ontario area, the province is also known for hot, humid summers.  With average summer temperatures reaching 86 degrees Fahrenheit, the Daoust family is glad that the geothermal heat pumps will also provide cooling for their home during the summer season.  

Meeting Challenges with DX Heat Pumps 

 Economics were not the only reason Daoust said he decided to install a geothermal system.  For him, it was also about the environment.  This geothermal system paired with an upgrade to new energy-efficient appliances, helped Daoust meet the Canadian government’s “one-ton challenge.”  The challenge is a voluntary program encouraging Canadian citizens to reduce their greenhouse gas emissions by one ton, which equals about 20 percent.  According to the One-Ton Challenge Web site, the goal of the program is to generate awareness about climate change and provide information about ways citizens can reduce greenhouse gas emissions.  The Web site points out that space heating and cooling account for 29 percent of the average Canadian household’s greenhouse gas emissions.

Daoust’s concern for the environment and his belief in geothermal technology has also prompted him to promote geothermal heating and cooling for his construction projects.  He said he has worked on a few geothermal installations in the past and definitely plans to use it in the future.  Since the completion of his home, Daoust has also asked Earth Energy Solutions to make a presentation about geothermal technology to other local contractors.          

“I hope to really showcase this system and once I am able to benchmark it, I hope to be able to promote it to all our clients,” Daoust said.

Whether the system is DX or water-based, the benefits of geothermal technology are hard to deny.  Thanks to the design versatility of geothermal, the Daousts have the ability to heat one side of their home while cooling another.  The family can rest easy knowing they will never have to wake up to a chilly house after an overnight drop in temperature.  Equipped with this system, they can be proud of their home not only for its beauty but also for its efficiency and most importantly, the family can truly enjoy the home without cringing each time the utility bills come.  This home displays all the positives of geothermal and the ways energy efficiency can benefit a home, the environment and the community all at the same time.