Ground-source heat pumps are attractive in cold climates because the ground offers a more stable heat source than outdoor air. But stability is not the same as unlimited capacity. In a heating-dominated community, extracting more heat each winter than the ground receives back can gradually reduce ground temperature and system performance.

That long-term imbalance motivated a study I co-authored with Farzin M. Rad and Alan S. Fung, published in Renewable Energy under my academic publication name, Amir Hossein Eisapour. We modelled two hybrid systems for a Toronto community over a twenty-year period and compared their energy, environmental, and economic performance with a conventional natural-gas boiler and absorption-chiller system.

The two systems answered different questions

The first configuration combined ground-source heat pumps, borehole thermal energy storage, and photovoltaic modules. We called it HPPV. The second, ST-HPPV, added solar-thermal collectors to recharge the ground and reduce long-term thermal depletion.

The solar-thermal addition improved the seasonal coefficient of performance in heating mode by 15% after twenty years. Yet it did not improve cooling-mode performance for the community’s load profile. Our economic analysis found the simpler HPPV configuration more cost-effective and reliable because of lower operating and carbon costs. We recommended the solar-thermal configuration where annual heating load is at least 75% of cooling load.

Lesson 1: annual efficiency can hide a long-term problem

A first-year simulation may make two designs look similar. Borefield temperature changes gradually, so the better choice can emerge only over a longer horizon. For owners, this means design evaluation should match the expected life of the infrastructure. Ground temperature, peak loads, pumping energy, auxiliary heat, and seasonal performance all belong in the conversation.

Lesson 2: more technology is not automatically a better project

Solar thermal improved one important technical outcome, but added capital and system complexity. The preferred design depended on what was being optimized: long-term ground balance, lifecycle cost, emissions, or operational simplicity. This is why I resist technology-first decarbonization. Start with the load, constraints, and decision criteria; then select the system.

Lesson 3: heating-to-cooling balance is an actionable screening variable

The 75% threshold in our study is specific to its assumptions and should not be treated as a universal design rule. It is still useful as a screening insight. Load balance can indicate whether passive ground recovery may be sufficient, whether active recharge deserves study, or whether another hybrid strategy is more appropriate.

Lesson 4: electrification belongs within whole-building planning

Heat-pump performance depends on supply temperatures, distribution systems, envelope loads, controls, and electrical infrastructure. ASHRAE’s decarbonization guidance places thermal-system changes within a broader process of goal setting, planning, implementation, and tracking. That is the right frame for practice.

A recent NRC cold-climate retrofit case study reached a related conclusion from measured building data: after retrofit, heating and cooling accounted for more than 70% of total electricity use. Electrification can remove direct fossil-fuel use, but it also makes HVAC design, peak demand, controls, and measurement more consequential.

From research result to owner decision

The practical output of modelling should be a map of the conditions under which each option performs well. For a real project, I would test load balance, borefield constraints, utility rates, grid emissions, electrical capacity, carbon assumptions, maintenance capability, and sensitivity to future operating conditions.

That is the larger lesson I carry from research into decarbonization work: engineering performance, environmental benefit, and economic feasibility must be evaluated together. A solution becomes credible when its assumptions are visible and the decision can withstand a change in them.

About the author name

I use Amir Eisapour professionally. My academic publications, including this study, appear under Amir Hossein Eisapour.

References

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