Homes and businesses in the Greater Toronto Area are experiencing deep energy savings by harvesting ground heat with geothermal heat pumps, or “geoexchange” systems. With energy savings of 30-70% and 20-95% for space heating and cooling respectively, it is no wonder this emerging technology is experiencing increased interest across Canada. Geoexchange systems warm buildings in the winter by collecting and concentrating ground heat, and cool buildings in the summer by returning heat energy back into the ground.

Earlier this year the Toronto and Region Conservation Authority (TRCA) completed a major project to assess the energy performance of local urban geoexchange systems and document the experiences of stakeholders involved in developing and maintaining the projects. The geoexchange systems selected for analysis serviced buildings that ranged from small‐scale residential to large‐scale institutional/commercial. The research was funded by a TAF grant supporting the TRCA’s Sustainable Technologies Evaluation Program (STEP). The findings are outlined in several reports:

The survey found that the most prominent motivation for implementing geoexchange technology was to meet sustainability goals and/or position the building or organization as ‘green’, followed by reducing energy costs and improving comfort.  The most common concerns prior to implementation were technology risks (e.g. will the system perform as reliably and efficiently as expected?) and related financial risks (e.g. will expected energy savings be realized?).  However, in most cases geoexchange systems met or exceeded expectations. Overall satisfaction was high amongst system owners, operators, and building occupants. Respondents were cited as saying their geoexchange system (and related upgrades) provided improved air quality and thermal comfort, enhanced user control, energy cost savings, and reduced or equivalent maintenance and operations requirements compared to conventional HVAC alternatives. All of the surveyed building owners and operators indicated they would consider installing geoexchange systems in other buildings.

The survey results led to several recommendations, including:

  • Minimize system costs through careful planning and design, including reducing heating and cooling loads through building envelope upgrades, and carefully sizing the expensive ground-loop.
  • Get the right people on board by ensuring consultants and contractors are properly qualified and have experience with geoexchange projects.
  • Invest in commissioning and ongoing monitoring to ensure systems are working optimally.
  • Standardize processes for geoexchange system design, commissioning, and monitoring to improve outcomes in future projects.

The technical report involved in depth monitoring of 10 geoexchange systems around the GTA. Heat pump performance is measured in terms of Co-efficient of Performance (COP), a ratio of the heat energy provided (or subtracted in cooling mode) by the system to the electrical energy consumed by the system. Heating season COPs ranged from 2.4 to 3.5, while cooling season COPs ranged from 3.2 to 8.2. That’s pretty good considering a conventional natural gas-fired boiler or furnace system has a COP ranging from 0.5 to 0.9! The technical report is chalk full of other useful data for system designers and others, like capacity utilization, cycle times, and thermal balances. One of the monitored sites is using “free-exchange” cooling to dramatically improve efficiency, an approach which should be considered in future projects.  TRCA also found that many of the systems had room for further optimization based on the data collected, illustrating the value of monitoring system performance on an ongoing basis. For example, some sites were unnecessarily operating circulation pumps 24/7, even when no heating or cooling was required.

By evaluating the real-world performance of local systems, and documenting the experiences of system owners and developers, this research bring us one step closer to scaling up the use of geoexchange technology. And that’s important, because the potential GHG reductions are enormous: according to the Canadian Geoexchange Coalition, converting 16% of homes in Ontario to geoexchange could reduce emissions by almost 1,485,742 tonnes eCO2, similar to removing almost 500,000 cars off our roads.

Our thanks the TRCA STEP team for the great work, especially Erik Janssen, Tim Van Seters, Caitlin Meanwell, and Dahai Zhang.

Image credit: TRCA Restoration Services Centre

Posted with writing and research assistance from Devon Calder