Woodsrider wrote: You neglect to take into account the huge energy offset by not running the compressor in the winter, which drastically reduces net CO2 production. Compression is far more energy intensive than heating.
The compressor does not reject heat the condenser does. Plus locating the condenser inside would make warm months unbearable. The Freeaire system provides significant energy savings from the controls alone.
Yes the condenser does transfer more heat than the compressor. They are often co-located so I didn't bother distinguishing.
Now stop and think about your first and second statement. You are looking at electricity consumed, I'm looking at total energy.
What happens to the energy used by the compressor? Heat from resistive losses, heat from friction, from compression, and heat from the work done in running the refrigerant around the circuit, which comes out the condenser. The final stop of all energy use is heat. (Sure, you can do work and store energy either chemically or gravitationally, but when you use that stored energy the final stop, again, is heat.)
In the winter heat is good. Killington is a winter resort that closes many lodges in the summer, and whose peak walk in cooler demand is in the winter.
If all this heat is directed into the building, the HVAC plant needs to provide less heat, and less fuel is consumed. If you exhaust any of that heat outside, as the Freeaire system does, you lose that heat outdoors. All the warmed air in the walk-in cooler that gets exchanged with cold outside air is wasted. This heat from the warmed air from the walk-in is coming from the heated building. That's the loss in efficiency I'm talking about.
Now envision a system that has the compressor and the condenser located inside the building, with no air exchange for the walk-in. In the winter, all the heat produced is used to warm the building. In the summer, you could easily direct the unwanted extra heat from the condenser outdoors through the same type of duct work.
So in the cool months, the Freeaire system will use less electricity,
but lose more net energy. The heat lost with Freeaire is vented outside. Without the Freeaire the heat is retained indoors. The greater use of electricity indoors without the Freeaire is transferred to heat. This heat (from the compressor as you point out) means less fuel is burned by the HVAC plant. It is not wasted.
So to sum up, without Freeaire: More electricity used by the compressor but less composite energy of the HVAC/walk-in total.
With Freeaire less electricity (which requires more HVAC fuel burned to replace the loss in heat produced by using that extra electricity) but greater total energy/fuel consumed as you are venting heat from the building outside. That vented heat must be replaced by burning more propane or fuel oil.
And of course in the summer the Freeaire system has no advantage.