Written By: Heike Schreiber
The AEE Canada East chapter was pleased to host a webinar titled ‘Cold Weather Heat Pumps: Technology and Application’ on March 26, 2022. We would like to thank Shawn Moore of Envari for the informative and encouraging webinar and for an engaging Q&A session afterwards.
While the presentation focused on data of residential installations from Envari’s pilot program with cold climate heat pumps, Shawn Moore also shared his experience with commercial applications in the Ottawa area. Some takeaways from the presentation and the following discussion are summarized below:
- Cold climate heat pumps, per definition, have a Heating Seasonal Performance Factor >10 and maintain at least 70% of their rated capacity with COP above 2 at -15°C. Manufacturers have developed reliable strategies to avoid damage at very low temperatures and offer cold weather kits, like snow baffles. When choosing the appropriate system for cold climate, cut off temperature and capacity at low temperatures remain the most important factors.
- First things to check when considering a heat pump are electric capacity limitations and the need for electric upgrades.
- Heat pumps are appropriate for retrofit applications for both residential and commercial, with various styles of indoor units, including 3rd party air handling unit (AHU) systems, also called DX kits by some manufacturers. For commercial applications this even enables the use of existing AHUs with VRF systems.
- In the residential pilot project, Envari retrofitted homes with heat pumps, mostly tied to ducted AHUs that had electric resistance heaters for backup. These installed systems achieved a seasonal COP of 3 on average.
- For equipment sizing, it was recommended to tune modeled building load profiles with utility data for gas consumption, to avoid oversizing of heating equipment. Compared to mostly oversized existing furnaces which would frequently turn on and off, the heat pumps ran more constantly at low loads. The usage of backup heaters is tied to heating control strategies, for example it was recommended to avoid nighttime setbacks for temperature control. The heat pumps operate best when it can provide heat at a constant low profile.
- The customers were reportedly very happy with the low noise level of their new heating systems.
- The installed systems realized large greenhouse gas emissions reductions at minimal cost savings. There are tax incentives that can be applied to help alleviate the investment costs.
- Old systems that need replacement are interesting candidates for retrofit with heat pumps.
After the webinar, a few questions lingered in our minds so we reached out to Shawn Moore to gather a little more insight.
Q1: There was one comment related to the marginal rates you cited in your analysis. I think your argument was that the account related charges were static and therefore not relevant in any sort of cost benefit analysis. But, if you are doing ROI work, despite those costs not factoring into any sort of incremental cost, aren’t they relevant to the buyer of the upgrade as costs they’d have to cover one way or the other? Would you want to elaborate on the decision and why you made it in your analysis?
A1: When discussing utility rates we feel the marginal utility rate makes the most sense for ROI since there will be no change in the flat monthly charges on a bill before or after a heat pump retrofit. The consumption of each utility changes and so the commodity costs are the only changing costs. One exemption from this would be if you are eliminating a gas account completely, then the flat monthly charges would also need to be factored into the cost savings. We have seen the elimination of natural gas accounts (commercial) make a big difference in cost savings when looking at heat pumps for small commercial applications.
Q2: In terms of the retrofit of existing and/or 3rd party coils from a central ODU. I think the question I asked didn’t really address the intent of the participants. In their experience I think they’ve had challenges feeding form a central ODU to 3rd party coils. In contrast, would feeding each coil to its own, paired ODU not make more sense/be more reliable? Thoughts on financials? Operability? Ease of installation/integration?
A2: When we have used the 3rd party coils we have kept them on a dedicated ODU. We did this since we were keeping our systems into multiple smaller refrigerant loops (10-16 tons) at each school. Given the size of the coils and the remote location of the gymnasiums it made sense for our application to have a dedicated ODU. I haven’t had experience integrating 3rd party coils and typical indoor units on the same ODU so can’t make much of a comment on that aspect.
Q3: In your work did you select units based on the cold climate performance, the typical/average performance or something in between? What challenges may present themselves if we choose the wrong selection criteria?
A3: We selected based on the cold climate performance. The systems were designed to operate the majority of the season and only need the backup heat source (electric resistance) under low temperatures. We had estimated we would rely on more backup heat then the data has shown. That said, the homeowners are pleased since the backup heat is hardly needed which keeps operating costs low. Sizing a heat pump is critical and I would recommend NRCan’s air source heat pump selection and sizing guide as a starting block. The wrong size heat pump will mean you may rely on backup heat quite heavily if it is undersized. An oversized heat pump may struggle to perform due to the required higher airflows. A qualified designer and installer are crucial in having a well sized and installed heat pump.
Q4: In your analysis of COP comparison one participant suggested that perhaps including the fan energy was not appropriate or require. Thoughts?
A4: Dan and I will be meeting to discuss after the Easter break. I think for most homeowners they want to know the energy in versus the energy out. More importantly the dollars in. To eliminate fan energy from the equation is removing a key component since the heat needs to be distributed. That said, I suspect the thought may be to exclude it since the base case (natural gas furnace) also has fan energy. I’ll chat with him more about this but I think fan energy should be accounted for.
Q5: Is there a report or other public summary of this work available (or will it be when complete)? I think there are some out there who would love to see a little more detail from your analysis.
A5: At this point we don’t have intentions on publishing any major reports since it can be quite time consuming to prepare and finalize that type of document. I wouldn’t be surprised if something smaller like a quick white paper or case study gets prepared. We will let you know if anything more formal comes of our pilot.
Q6: Have you learned enough to generate a Cold Climate Heat Pump playbook? A series of key decisions/questions that would drive one to evaluate their own situation? I imagine electrical service would be one…others?
A6: I think we have a few steps that we can share. The steps are likely a bit much for the typical homeowner to handle on their own. Contractors also vary on their understanding and ability to size heat pumps. Proper comparison between heat pumps is critical and typically needs review of manufacturers engineering specifications for complete tables of performance at various outdoor air temperatures.
- Review electrical capacity
- Decide on backup heat source (electric or gas)
- Heat load calculation for house
- Select ideal heat pump capacity and heat pump make/model
- Check duct sizing is adequate for heat pump
If you weren’t able to attend the webinar live, please visit our events page for links to watch the recording and download the slide presentation.
Heike Schreiber is a research officer in the Integrated Building Performance Group of the Construction Research Center at National Research Council Canada. In her spare time, she sits on the AEE Canada East board and is an active champion for our Council on Women in Energy and Environmental Leadership (CWEEL) initiative.