Interesting step forward
Technology is a wonderful thing. Producing heat at 20 below is pretty incredible for heat pump.
I know some inspectors have a conversation or even narratives referencing auxiliary or emergency heat. The narrative often includes high energy costs associated with heat strips. Additionally, here in the south, heat kits are not always installed in which some inspectors will mention this in the report to help manage expectations.
IMO, inspectors who use these types of narratives should stay up to date and look for ways to identify these advanced systems.
I don’t see a lot of heat pumps, so I will ask a stupid question. Is the supply air coming out of the registers the same temperature when the outside temp is 32F as it is at -20F?
Air source Heat pumps are improving, but when it is super cold outside the heat pump has difficulty drawing warm air from the cold air outside. It loses efficiency and often can’t keep the home comfortable. Hence the need for auxiliary heat kit (typically electric heat strips but sometimes a gas furnace is used).
The output temperature is the same, the BTU capacity and efficiency drop, eventually, at brutal low temperatures.
That curve is from a CO2 refrigerant split system heat pump from https://www.eco2waterheater.com/
As the outside temperature goes down, the efficiency drops (down to about 2x as efficient as electric).
At -5F the capacity drops: it can’t make as much hot water.
At -27F it can still make 145F water, just not that much of it (the blue curve ought to show this, but the chart goes not go that far)
Note that this model is common in Japan, and has been for years.
The US is not the world leader in heat pumps by a longshot.
Good article Brian, thanks. 'Course it won’t matter when the electric grid fails. Just like the left coast AC dilemma. Heat or charge your car? Can’t do both.