Seems like all you need is a detailed energy model of a real case scenario. The issues you're outlining are all valid; what varies is the degree to which they are valid. This is something that needs to be discussed between a design engineer, manufacturer, and energy modeler. Moreover, there are 2 electric resistance elements to speak of: the heating backup as you mentioned and the defrost one (which I assume you meant by "equipment protection").
In my practice, I've seen the defrost being both electric resistance and "reverse cycle" which is a heat pump running the other way around. Though I'm not a design engineer, all the project's I've modeled had a "reverse cycle" defrost. Having the electric resistance one would hurt the energy performance a little.
But the big one, as you mentioned, is the heating backup. And I don't think you can get away with a heat pump without resistance as backup, certainly not in a cold climate. That backup can be designed to kick in at 40°F outdoor air temperature or at, say, 20°F. This, as you can imagine, will have a huge impact on the energy performance of the system as a whole. Brookline might have ~500 hours annually where temperatures dip below 40°F but only ~30 hours where it dips below 20°F. Again, a discussion would be needed to sort this out, and better technologies and improvements are always introduce in the marketplace.
In general, I wouldn't trust a manufacturer's "marketing" literature, as it could use vague language that is technically correct in a very narrow sense. But I would trust the detailed technical information they provide. For example, a high efficiency condensing boiler will advertise that it is 96% efficient in it's marketing literature, however, the conditions for it to achieve 96% efficiency are almost never achieved (at least I've never seen them achieved). But digging deeper, you'll find a chart that shows the full spectrum of efficiencies, and you'll notice that most engineers design systems that achieve an efficiency of 88-90%, which is not bad, but it's not what's actually "advertised".
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Waleed AlGhamdi AIA
Sustainability Enabler
Eskew+Dumez+Ripple
New Orleans LA
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Original Message:
Sent: 01-14-2020 15:22
From: James Carr
Subject: Looking for real-world evidence for/against cold climate air-source-heat-pumps
Hello, friends -
I am looking for well-researched papers or (detailed and technically sound first-hand experience) about the effectiveness or lack thereof of Cold Climate Air Source Heat Pumps. This technology sounds great in manufacturer literature and even some academic studies that I have seen. In principle it would allow buildings in cold climates to be heated (and provided with domestic hot water) with electricity that is significantly more efficient than traditional electric resistance heat (baseboards.)
However, I have been learning about the technology in real-world applications and it seems that (as with many new things) the hype might be more exciting than the reality. It appears that most (all?) of these cold-climate systems (as well as the regular ASHPs) rely on electric resistance heating coils as backup, and the controls usually favor the use of that backup as a safety measure even in less-than severe weather to prevent damage to the equipment. Of course, this isn't an advertised "feature" because while it protects the machinery from freeze-ups it is not any more efficient (and maybe less efficient given fans and heat distribution dynamics) than traditional (and inexpensive to install) electric baseboard heating.
My concern is that as clients jump on the cold-climate ASHP wave that the unintended consequences may well outweigh the benefit for a considerable time. Not only in winter energy use, but in the additional use of AC in the summer by people who might not otherwise have installed AC. And also that people who are installing these systems at considerable cost may be unaware that the nice, reliable-seeming and even quiet operation of these units in winter is really just an electric resistance coil inside the wall unit, while the ASHP sits outside in a shut-down mode and no one is the wiser.
Maybe I am being over-cautious and skeptical here. But so far I have yet to find any good, real-world, non-biased and detailed information to show that these things are really working as advertised. Help would be appreciated!!
Background: here is Brookline, Massachusetts, Town Meeting has recently passed an ordinance (yet to be approved by the Attorney General) that prohibits installation of new fossil fuel infrastructure in new buildings and major renovations of most existing buildings in town. Proponents have argued that Air Source Heat Pumps (ASHP) are now viable in cold climates, and that makes it not only feasible but effective to go all-electric as a step towards the town's carbon reduction goals.
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James Carr AIA
Brookline MA
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