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In Vapor-compression refrigeration, a refrigerant is compressed releasing heat (typically outside a building) and then decompressed in another location, absorbing heat.

A residential air conditioner works on this principle with a compressor outside the home and a blower over the decompression coils to circulate cold air.

Would it be feasible to compress ahead of cooling demand, storing the compressed refrigerant in a high pressure container for use at a later time of the day, thus shifting the power consumption to times of the day where there is less electrical demand?

By feasibility, I'm thinking of questions like:

  • How much storage volume would one need for a typical household usage over an afternoon of running air conditioning given a container type that would be available cheaply, ex: propane canisters?
  • What would be the sources of efficiency loss added by something like this?
  • etc.
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  • $\begingroup$ Storage of the liquid refrigerant would take a fairly large tank. The much bigger problem is how to store the decompressed gas afterwards. sCO2 might work though! $\endgroup$
    – Neil Belt
    Commented Sep 27, 2022 at 8:59

2 Answers 2

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I happen to have a bottle of refrigerant in my house and another in my car (besides the stuff already being stored in my AC units).

While this is definitely more of a physics question, or perhaps a question for the HVAC guys on the Home Improvement SE... to generally answer your question, there are many factors for cooling a home, like size and location, for example. But let's say your average 2-ton window-unit AC pumps 24,000 BTU's per hour... and 4000 BTUs requires 1 gallon of refrigerant per minute.... you need 6 gallons per minute (being released through an evaporator coil) to match a window unit AC.

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  • $\begingroup$ So 6 gal/min * lets say 2hrs of cooling = 720 gallons. Could that be reduced further by additional compression? For example, a quick search reveals that a typical A/C compressor is about 200-400 PSI, whereas, for example, the hydrogen tanks in a toyota mirai can store hydrogen at 10,000 PSI. Does pressure/volume work linearly like this such that going from 720 gallons at 400PSI would give you 28.8 gallons at 10,000 PSI? $\endgroup$
    – Gregable
    Commented Jul 26, 2016 at 18:19
  • $\begingroup$ That's liquid refridgerant... which is just run around in circles. Liquids are not really compressible. At 10,000 psi you might get 1% or 2% compression. So at 10,000 psi you need ~712 gallons. Or at 100 psi you would need 720 gallons of liquid refrigerant (for 2 hours use). $\endgroup$ Commented Jul 26, 2016 at 18:41
  • $\begingroup$ Ah, bummer. Just curious, but this doesn't sound very feasible. Thanks! $\endgroup$
    – Gregable
    Commented Jul 26, 2016 at 19:08
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A BTU is a unit of heat, just like joules or calories. An air conditioner's capabilities are measured in cooling/time and $\pu{24,000 BTU}$ is colloquial used to mean $\pu{24,000 BTU/hour}$. The circulation requirements would be defined by

X gallons of refrigerant circulating per hour would yield Y BTU/h of cooling capacity

Apparently (I'm not an AC guy) that translates to ~$\pu{66,7 BTU/minute/gallon}$, or $\pu{4,000 BTU/hour/gallon}$.

If the main AC unit's cooling capacity is $\pu{24,000 BTU/hour}$, which comes down to about $\pu{7 kW}$ or $\pu{25 MJ/h}$ (that's astounding for a home appliance!), you need a certain amount of refrigerant in constant cycle.

If the assumption is $\pu{4,000 BTU/hour}$ per gallon of circulating refrigerant per minute, you would then need at least $6$ gallons of refrigerant to reach the 24,000 BTU/h. More is always a possibility, though.

P.S. I speak metric, so I rounded off enthusiastically in conversions.

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