This is the weird stuff I wake up thinking about. Last week I woke thinking (dreaming maybe) of a system that would recycle some of the energy wasted in compressing refrigerant in an air conditioning system.
If you recall how the refrigeration cycle works, you basically run a compressor that smashes a gas to a high pressure, which causes it to get hot. Since it is now hotter than ambient air, blow ambient air over the hot gas to cool it off, while staying at the high pressure. Then move this high pressure, slightly cooled gas back to where you want to be cool (inside your house), and let it rapidly expand thus causing it to cool off a bunch. Use this coldness to cool your house (blow house air over it to cool it), and then repeat this process with the gas which now contains the heat taken from your house.
I had read recently about a generator being used in the oilfield to generate electricity by replacing the choke in the gas well with a generator. A choke is just a smaller opening through which the gas has to slow as it flows out the well, since many gas wells would flow to quickly without one. So this generator replaced this simple choke with a turbine that would provide the same flow slowing effect, but with the benefit of using this pressure drop to spin a turbine and produce electricity– energy that would otherwise just be lost.
So, do you see the applicability to the AC system? The compressor in this system is pressurizing gas to a high pressure, but then this energy stored as pressure is “lost” as the gas simply expands across an orifice, just like the gas well choke. Why couldn’t the compressor benefit from some form of turbine attached to the outlet which would recover at least a portion of the energy used in compression? It should still provide the refrigeration benefits as the gas is still expanding and thus cooling.
So, I did a quick search and sure enough it looks like the Japanese have a colleciton of patents on this technology. This one is pretty much it exactly: http://www.google.com/patents?id=2qAMAAAAEBAJ&dq=6543238
Strangely, it seems a US patent was issued in 2007, quite a bit newer than the japanese ones: http://www.google.com/patents?id=IGCEAAAAEBAJ&dq=7272932 (although it does seem more broadly defined).
So now I’m only curious if A. this is being used at all and B. I’m pretty sure it isn’t, so I wonder why not? I know with many ideas like this, the benefit just doesn’t justify the addional cost, so I’ll have to assume this is the case. Let me know if you have any comments on this one.
This whole discussion got me thinking about resonant refrigeration and what the current state of the art is in this arena, but I’ll save that for another day. Some quick searching didnt turn up much, but I’m sure there has to be more info out there on this topic.