[VAC] Re: '48 Wee Wind renovation/modernization... a bundle of

[Dr. Gerald N. Johnson, electrical engineer]

I'm wondering if the absorption refrigeration cycle is the most energy
efficient. Even at the scale of the under the counter refrigerators for
a Bambi or Caravel. Things that make me wonder include the fact that The
only uses of absorption refrigeration tend to be RVs or extreme back
woods where only propane is available. I don't know of absorption being
used for any power line only refrigerators. If the absorption cycle was
energy efficient, it surely would be commonly used for gas power
refrigeration and air conditioning, at all scales including homes,
industries, and refrigerated semi trailers. Instead the tendency is to
use some sort of internal combustion engine, either running on natural
gas, propane or a diesel (on the semi) to turn a conventional
compressor. This says to me that the absorption cycle is less efficient
than the internal combustion engine which rarely exceeds 30%. Getting
heat to the absorption cycle should be very high, at least 70% from
flame, or higher from an electric heating element.

I'm wondering if maybe the "dorm" room sized refrigerator running on AC
may be more energy efficient than the standard RV absorption
refrigerator. Likely its marginal because of poor power factor leading
to more volt amps than a DC equivalent, such as sold by SunFrost.

The AC compressor running from an inverter won't work well as shipped
because the power factor of the standard induction motor is poor which
makes for extra load on the inverter. If the power factor was improved
by adding shunt capacitors to the motor circuit the inverter may prove
to be rather practical. One would use paper type motor run capacitors,
and adjust the value to minimize the line current. For best efficiency,
the inverter rating should closely match the load, but a motor will take
about 5 times running current for starting so the inverter has to be
oversized, or at least have enough surge rating for that motor start.

I suspect that the AC operated small hermitic compressor with proper
power factor correction can be made to run on maybe half the power of an
absorption refrigerator. Either can be improved by better insulation and
door gaskets to keep the cold in and the outside heat out.

Gerald J.



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