Air to Water or Geothermal Heat Pump?
Introduction
Increasing Energy prices all over Canada and the US combined with more stringent energy efficiency requirements and generous grants (in some states and provinces) for more sustainable Heating and Cooling Equipment, are boosting the demand for non conventional Heating and Cooling devices such as Heat Pumps (both Air to Water Heat Pumps and Geothermal Heat Pumps), Evacuated Tubes Solar Collectors, PV Solar, Underground Seasonal Thermal Energy Storage and many other technologies.
In addition to the above design constraints, and especially post Covid-19 pandemic, homeowners are demanding more natural lights in their indoor spaces which translates into more glazed areas (higher Windows/Walls ratio) and higher energy demand. Many people nowadays are spending more time at home (working from home, etc...) and natural light is primordial especially in northern climates.
Thermal Comfort requirements are on the rise too: Infloor heating, radiant floor hydronic cooling, Condensation prevention of fully glazed facades in winter, etc.... add up another layer to design and energy efficiency challenges.
Air to Water and Geothermal Heat Pumps are able to satisfy the above energy efficiency and energy demand constraints, however each technology has its own pros and cons, which what this blog is about.
For the sake of this blog, we will be studying three different scenarios in two different locations: First Location will be where utlity rates are the lowest and the second one where utlity rates are the highest.
The three Scenarios: Conventional Air to Air Heat Pump (System 1), Air to Water Heat Pump (System2) and Geothermal Liquid to Water Heat Pump (System 3).
- Conventional Carrier Two Stages Air to Air Heat Pump - Summer COP=3.5 and Winter EER=12
- Hydrosolar Air to Water Heat Pump HSS060V2LS
- Nordic Liquid to Water W Series Geothermal Heat Pump
Energy Analysis Summary for States/Provinces with lower end utility rates provinces/states (Such as Quebec, Manitoba and British Colombia)
The above 3 systems or scenarios were energy simulated with electric back up heating system and with the weather data of the city of Montreal (QC), which is representative of most major Canadian cities. Domestic Hot Water Heating have not been included in the energy simulation since DHW heating depends not only on weather data but on many other demographic factors (Such as Qty of Occupants, Age, Living Habit, etc...).
For the utility rates, we have used Hydro Quebec (HQ) 2021 utility rates for the 3 scenarios. Despite the fact that HQ rates are among the lowest in North Americas, it does not affect the comparison between the three scenarios. Simulated Building is a Two Story residential Building (cottage) with 2100 ft2 of living space.
System 1: Conventional Air to Air Heat Pump
Total Space Heating and Space Cooling annual power consumption is 26,027.00 KWh and that includes fan power.
System 2: Air to Water Heat Pump
Total Space Heating and Space Cooling annual power consumption is 18,426.00 KWh and that includes fan & pumps power. This is a 29.2% reduction from base scenario System No 1
System 3: Liquid to Water Geothermal Heat Pump
Total Space Heating and Space Cooling annual power consumption is 14,606.00 KWh and that includes fan & pumps power. This is a 20.1% reduction from Air to Water Heat Pump scenario System No 2 and 43.88% reduction from Base Scenario System No 1.
SCENARIOS ANALYSIS: Initial Cost, Life Cycle Cost and Payback
As we can see in the above analysis that Base Scenario (System 1) has the cheapest project cost (Called First cost above), however it has the peak energy cost and maintenance cost (around 3,896.00 CAD$).
System No 2 (Air to Water Heat Pump Scenario) has a 14% higher first cost then System No 1, however it offers a 43% reduction in operating cost (energy and maintenance cost). The payback for System No 2 (assuming that System No 1 is the base scenario) is 4 years for a life span of 20 years (25% of equipment's life span).
Geothermal Heat Pump scenario (System No 3) has a first cost 65% higher than the one of system No 1 (due to the cost of Ground Heat Exchanger) , however it offers a 52% reduction in operating cost. The payback for System No 3 (assuming that System No 1 is the base scenario) is 15 years for a life span of 25 years (60% of equipment's lifespan).
The marginal benefit of Air to Water Heat Pump (43% Operating cost reduction) is triple the marginal cost (14% increase in project or first cost). When comparing Air to Water Heat Pump to Geothermal Heat Pump, the gap between marginal cost and marginal benefit is larger. Geothermal Heat Pump has a much higher marginal cost (65% additional cost Vs Base scenario and 44% Vs Air to Water Heat Pump Scenario) and a much relatively lower marginal benefit (52% Operating cost reduction Vs base scenario and 16% Operating Cost reduction Vs Air to Water Heat Pump Scenario).
When Taking into account the lower life cycle cost of Air to Water Heat Pump Scenario compared to the Geothermal Scenario, Air to Water Heat Pumps for small residential projects make more sense since it falls on the peak of the marginal benefit Vs marginal cost curve.
The three Scenarios: Conventional Air to Air Heat Pump (System 1), Air to Water Heat Pump (System2) and Geothermal Liquid to Water Heat Pump (System 3) in the higher end utility rates provinces/states
The above Energy Simulation was redone for the same residential home, in the Maritime (Sydney in Nova Scotia) where electricity rates are on the higher end (around 18 cents for every KWh) and homeowners in these provinces have no access to cheap natural gas (such as in Ontario or in Alberta). Results are a bit different since climatic design conditions are milder than central Canada, however percentages for savings and marginal benefits Vs marginal cost are very close to previous analysis.
In order not to make this blog very long for readers, we will only show in the below section analysis results. We will not show detailed results as in the above section (since trend and conclusions are very similar)
Energy Analysis Summary for States/Provinces with higher end utility rates (Such as the Maritimes)
As we can see in the above analysis that Base Scenario (System 1) has the cheapest project cost (Called First cost above), however it has the peak energy cost and maintenance cost (around 5,267.00 CAD$).
System No 2 (Air to Water Heat Pump Scenario) has a 14% higher first cost then System No 1, however it offers a 40% reduction in operating cost (energy and maintenance cost). The payback for System No 2 (assuming that System No 1 is the base scenario) is 3-4 years for a life span of 20 years (35% of equipment's life span).
Geothermal Heat Pump scenario (System No 3) has a first cost 65% higher than the one of system No 1 (due to the cost of Ground Heat Exchanger) , however it offers a 50% reduction in operating cost. The payback for System No 3 (assuming that System No 1 is the base scenario) is 14 years for a life span of 25 years (68% of equipment's lifespan). Payback for geothermal is longer in the maritime, since ground thermal conductivity in the eastern part of Canada is lower than the central part and extract the same amount of energy from the ground we require a larger ground heat exchanger.
The marginal benefit of Air to Water Heat Pump (40% Operating cost reduction) is close to the marginal cost (14% increase in project or first cost). When comparing Air to Water Heat Pump to Geothermal Heat Pump, the gap between marginal cost and marginal benefit is larger. Geothermal Heat Pump has a much higher marginal cost (65% additional cost Vs Base scenario and 35% Vs Air to Water Heat Pump Scenario) and a much relatively lower marginal benefit (52% Operating cost reduction Vs base scenario and 17.7% Operating Cost reduction Vs Air to Water Heat Pump Scenario).
When Taking into account the lower life cycle cost of Air to Water Heat Pump Scenario compared to the Geothermal Scenario, Air to Water Heat Pumps for small residential projects make more sense since it falls on the peak of the marginal benefit Vs marginal cost curve.
Hello Brad, a ground loop heat exchanger should have a 50 years lifespan when properly designed and installed. So in 25 Years, you’ll have to replace the Liquid Source Heat Pump not the ground loop heat exchanger. By combing solar thermal to geothermal, you could extend the lifespan of your ground loops even longer (ref: https://hydrosolar.ca/blogs/advanced-technical-zone/how-to-lengthen-geothermal-well-lifespan)
When the life of the ground unit is over, say 25 years, does this mean digging up the ground? Thanks
Thanks Roger, very useful information. What was the Design Temp and Heat/Cooling Load of the simulated residence? Which of the two Hydro Solar ATWHPs (the 50 or 60) is represented in the data as both were referred to in the description. What system components are included in the System 2 First Costs?
Thanks Roger, very useful information. What was the Design Temp and Heat/Cooling Load of the simulated residence? Which of the two Hydro Solar ATWHPs (the 50 or 60) is represented in the data as both were referred to in the description. What system components are included in the System 2 First Costs?
Roger Great info well done