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Heat pump electrical usage does not go up as the temperature drops. In fact the actual heat pump itself uses less electricity because the compressor needs to sl
by jakedata 4y ago
Heat pump electrical usage does not go up as the temperature drops. In fact the actual heat pump itself uses less electricity because the compressor needs to slow down in order to scavenge the outdoor heat needed to vaporize the refrigerant.
What causes a spike in electrical usage is the backup resistive heat source that kicks in when the compressor cannot satisfy the demand for heat.
Installing a heat pump that is engineered and properly sized for extreme cold will prevent this issue. My heat pump does not have a backup resistive heater and I can watch the compressor cycle in realtime on my Sense Home Energy Monitor. The pattern is quite obvious once you understand what you are looking at.
-edit- power consumption tracks the heat load in normal temp ranges, I am referring to the backup heat source turning on during extreme cold.
- thehappypm 4y agoIncorrect, efficiency drops as the temperature differential grows. This is a basic law of thermodynamics, since you can extract energy from a temperature difference, it must require energy to create one.
- jakedata 4y agoAbsolutely true - efficiency drops. Electrical consumption also drops if your heat exchanger can't scavenge enough heat from the air to vaporize your refrigerant. The compressor must slow down. Or as I pointed out - you can activate a backup heat source which causes a huge spike in electrical usage. Probably better than freezing however.
- thehappypm 4y agoMost heat pumps don’t have a backup built in anymore, though. I have 2 (LG and Mitsubishi) and neither has a resistive backup built in.
- timbit42 4y agoMy heat pump is 11 years old and doesn't have a resistive heater. I thought resistive heaters were a new thing. Many people in the Northern US and Canada need some kind of backup and a resistive heater in the heat pump would be a selling point for many.
- tootie 4y agoI know all the excitement is around air source pumps, but I'd love to see ground source get cheaper to install. It's nearly impervious to weather conditions. If you live some place that actually gets cold enough to stymie an air pump, then maybe investing in ground source is worth it.
- thehappypm 4y agoGround source is losing the war. Too expensive to install, and if something goes wrong, start digging. Air source is getting better and better all the time.
- timbit42 4y agoIn parts of Canada, such as Alberta, where it goes to -40C, anyone buying an air source heat pump is nuts. Ground source is the only viable heat pump option, in spite of its much higher cost. I guess they'll be stuck on natural gas until the climate rises some more.
- thehappypm 4y agoAir source + natural gas for when it’s that cold is still cheaper than ground source.
- timbit42 4y agoOver how many years? An air source heat pump that you only use 8 or 9 months of the year will take longer to pay for itself.
- thehappypm 4y agoModern heat pumps are rated to about -15F. In Fort McMurray, a large-ish city in northern Alberta, the average low temperature in the coldest month (January) is -7F. The average low temperature is below -15F about 15 days a year on average. That means you’re really using your heat pump for a huge percent of the time.
- jakedata 4y agoI am forced to reply to myself again before my parent comment gets downvoted to oblivion. YES - Heat pump efficiency drops with external temperature. HOWEVER - A typical heat pump will be unable to operate at full power when it approaches it's lower temperature limit. It is unable to move more heat at any efficiency. The compressor will slow down or stop completely while waiting for the liquified refrigerant to vaporize in the evaporator coils. THEREFORE - Regardless of efficiency the compressor will be using less power because it is either not running or running slowly. WITH THE EXCEPTION OF - certain heat pumps with auxiliary electrical heaters that cause energy use to spike at extreme low temperatures.