Air Conditioners don’t necessarily just cool your building. An air conditioner essentially moves heat from one place to another. In the case of your typical AC set up, we absorb the heat in your office and we put it outside with a gigantic condenser coil. What if we did the opposite?
Air Conditioning the Outside
Speaking in terms of pure-physics, there’s pretty much always heat outside. To us living, breathing creatures, 0 degrees may seem like there is no-heat, but to a physicist, that’s orders of magnitude above the coldest cold possible “absolute zero.” That means we can put that ‘heat’ to use.
In a configuration like this, the outdoor coil will become incredibly cold. This will allow it to absorb heat from the outside air and bring it indoors. Inside, the refrigerant is condensed and we basically get heat. We’re literally switching the roles of a traditional air conditioner.
Systems such as this are often called Heat Pumps. Technically speaking, anything that moves warmth is a heat-pump, even an air conditioner or a fridge, but the term in particular is related to using air conditioning hardware for heating purposes.
The Extra Hardware
Achieving this requires some special tweaks. If we’re going to have an air-conditioning-heater, we need some extra valves, control logic, and tweaking the design of your coils. Your coils will now both be able to function as evaporator and condenser coils. There’ll be two expansion valves, extra piping, and a reversing valve.
During regular AC operation, the reversing valve and extra expansion valve aren’t used. The coolant flows in a normal loop between the compressor, evaporator coil, and condenser coil. When it’s used as a heater, the reversing valve is used to redirect the flow so that the coils change roles in the system.
With systems like this it is also necessary to implement defrost controls on both coils. It is possible for either coil to become iced over and damaged, depending on which mode its operating in. This can be especially likely for the outdoor coil during the winter. With temperatures already below freezing and plenty of moisture present from ice and snow, it won’t take much for a system to ice over.
The colder your environment gets, the harder it’ll be for a heat pump to actually work. There’s still energy in the air, but you’re going to be fighting the ice and trying to squeeze more from less as it gets colder. Generally speaking, almost no heat-pump will operate below -20C (-4F). About this point, it takes significant effort, which makes the system too inefficient to be useful over installing dedicated combustion or electric heat.
This hardware can also be used in a strictly heating configuration. If you’ve heard of things like GeoThermal heating, you’ve seen an application of a heat-pump. The principal here is that we absorb heat from the ground. The Earth itself is massive, the ground is very, very dense, there is a lot of ground, and consequently, deep underground the temperature is just about constant.
There is just so much dirt and material that the ground doesn’t manage to change temperature on any ‘fast’ time scale. It absorbs massive amounts of heat and it would take years of continuous winter to actually remove all that thermal energy. At the same time, it would take a massive amount of heat to increase the temperature underground by any significant margin.
We essentially have a thermal-battery. We can stick a specially designed coil underground and it will behave predictably year-round. Our system can draw heat from underground essentially anywhere. Geo-thermal heating doesn’t require volcanic activity to actually function.
Always Something New
Our modern ideas of heating and cooling are based on design and clever thinking. If we can find a way to exploit physics to make something better, it’ll happen. Things that seem counter-intuitive, like air conditioners that are also heaters are the norm. Maybe some day we’ll have a heater the burns so cold it’s an air conditioner?