Choosing a Heat Pump
Hi all,
Our home currently has an oil boiler, and we’re trying to figure out a way to get away from fossil fuels altogether while still staying warm. We live on the south shore of Prince Edward Island, just on the edge of a 6A planting zone, and we’re sheltered by trees that break the north wind. All this to say that it’s among the warmer places in Atlantic Canada to live: a typical winter day is between -5’C and -11’C, with some proper winter storms and just a few colder snaps mixed in.
While our home is about 17 years old, we had an energy audit, and it did fairly well. We’re making some improvements to the attic insulation, as recommended, but the bigger question is which heat pump to install. When I asked a local company about getting off oil, they mentioned Daikin’s VRV Life system, but I haven’t been able to find much information about it, other than what Daikin provides, perhaps because it’s relatively new. Obviously, because we don’t have ducts, installing a central heat pump would come at a considerable cost, but one we’d be willing venture, if it got us away from fossil fuels for good.
The other option is an Aurora multi-split with four heads, paired with a wood stove in a supporting role. I should say that our home is a raised rancher, about 2000 sq feet, with a cathedral ceiling over the living room at the centre of the home. We’re south facing and benefit from passive solar heat, and we also plan to add solar panels to offset the electricity we use.
We know that while the multi-split will continue to work at cold temperatures, the COP is 1 on a coldest days, so it’s not all that different from electric heat. The VRV apparently works better at lower temperatures, but it’s actual COP in such conditions is a bit of a mystery—or it is to me at least, as I can’t find specific figures listed anywhere.
Any thoughts here? As I said, if we went with the multi split, we’d burn wood as a back up, whereas the VRV would be installed with a heating coil, if that’s what it’s called, in the handler. It’d be fantastic to have a central heat pump and solar, but making a considerable investment in a system with no readily available test cases or customer testimony (from Canada, at least) feels like a leap of faith.
Thanks everyone in advance for your thoughts,
Dave.
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Replies
Hi Dave,
I'm bumping your question to the top in hopes that someone can speak about the specific products you are considering. More generally, you may find this article, High-Performance HVAC, by the editors of Fine Homebuilding helpful.
Thank you!
If you have fill up data, you can do a quick calculation to find out how much heat your house needs:
https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new
Once you have the data, you can go to here https://ashp.neep.org/#!/product_list/ and find which heat pump will work for you.
Most hyper heat units will have a COP of around 2 in your climate on cold day, much better than resistance heat and will probably average around 3 to 3.5 for the whole year.
Your bigger problem is heating water with heat pumps. Generally it is significantly cheaper to convert to forced air, air to water cold climate units are pricey and very few options. Even then, the mostly provide low temperature water (120F) which can sometimes be made to work with older systems by either improving the insulation of the house or adding in additional radiators.
An in between option is to keep the exisiting rads, install a resistance boiler plus a central hyper heat mini split. The mini split would do the bulk of heating and the rads would only be used to even out temperature around the house.
Thanks for the thoughtful reply. Lots to think about here. Since we just moved in last spring, we don’t have all the figures needed to do a reliable calculation, but from what I read in the link, the estimate we received seems plausible and well sized to our home.
As for keeping the rads and pairing them with a centrally located mini split: friends of ours did just that, after they installed their solar panels, so that’s a possibility, too.
Doesn’t seem to be a lot of love out there for multi-splits. I understand they involve some level of compromise, but I’d be curious to hear from people who are reasonably happy with them.
The big issue with multi splits is the marketing. They are pitched with the head in every room type of setup. This just does not work (I have this at home). The heat/cooling load is 3x to 5x less than the smallest head you can install, which creates issue with humidity removal, efficiency and comfort.
You can make a multi split work, but it has to be done right. Since the units have much lower modulation range and the indoor heads don't modulate, you have to size them to closely match your actual loads.
The one setup that does work is to install a wall/floor/ceiling unit in the main living space and a ducted unit to feed the rest of the rooms. I've done a couple of these and it does work well.
In a place that needs a lot of heating and only a bit of cooling, this might still cause issues as the unit will be over sized for the cooling load but it can be made to work.
Since getting all the details sorted out is not simple and there are many ways of messing it up, I would stick to one to one instead of multi split. These have much better modulation range, better efficiency and are about the same cost as a multi split.