As temperatures drop, air source heat pumps lose efficiency and their COP (coefficient of performance/coefficient of power) decreases. In situations where the temperature drops below freezing overnight, the COP rapidly decreases from as high as 4 (meaning you get 4x the heat out of the power you put into it) to 1 (effectively equivalent to a resistance heater).
This means that for traditional wintertime HVAC scheduling, where your thermostat set temperature drops overnight during sleep and jumps back up in the morning, you are putting the greatest load on your heat pump when its efficiency is at the lowest of the day. The COP differential can swing from mildly less efficient in lows around 40Ā°F to significantly less efficient with lows well under freezing.
My initial thought process here is that it may make sense to create automations that factor in the forecast low, which usually occurs pre-sunrise. If the low is, for example, 40Ā°F or above, my HVAC would act similarly to a gas fired furnace - turn on an hour before we wake and the house will be plenty warm. However, if the temperature is forecast to be lower, I may have some changes. One might be to leave the heat set point much higher all night long, which would intuitively use more energy, but when plotted against the COP curve, might actually use less energy despite the homeās heat loss. It also would mean waking up to a warm house instead of a home that is struggling to reach the set point.
All of this preface just to ask: has anyone else considered this? One thing I find myself doing a lot is creating something only to find out someone has already done it, and done it better than me. I recognize there are a lot of other factors to consider, like energy TOU prices, occupancy, etc., but Iām just thinking about the base concept for now.
Thanks for reading.