Quote:
Originally Posted by Hersbird
They can't be shut off and on over short periods of time and they are slow to cool. So it might work on a semi truck that just stays running with the AC left on, but you can't get in the car, turn on the AC, get it cool within a few miles, then 5 mins later shut it off, go into the store for 15 minutes and repeat on the way home. Even the article the OP posted talks about how it protects itself in a power failure. That happens 10 times a day in a car by design.
They are for a slow constant cooling.
I was surprised how little power the AC system used in my PHEV Pacifica. That's a huge volume van and that AC could freeze you out without running the ICE. It used 1/3 the watts of the heater 1500-2000 and that obviously also includes the circulation fan which you would have with either system.
That's under 3 horsepower. So while the van made over 250 using 3 more at idle or even normal driving if anything probably puts it in a better thermal efficiency spot as you are just wasting power with throttle losses and no load. Plus with modern start stop, they can shut it off at a light and there is still enough cold refrigerant in the system to keep it cool until the light changes and the ICE starts again.
The absorption systems can't be too bad as I have had them on a small fridge camper. They would run for a long time on a 20 pound propane bottle or use about 15 amps on a 12 volt circuit. That was a tiny space andbon really hot days it struggled to keep a well insulated 1.3 ft3 box cold.
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That depends on the climate and area. Slow steady cooling would not work well here. For one the air needs to fall below the dew point to condense the humidity and actually make the vehicle feel comfortable. Here in North Texas in stop and go the temperature above the black top road reaches 120-130F in summer. With that much heat radiating into the vehicle along with power train heat, the cold refrigerant might give you 5 seconds of cool air. Even on recirculate at highway speeds the air becomes warm very quickly when the compressor cycles to prevent evaporator freeze up. Then throw in days that are close to 100F and 80-90% humidity. Those days are the biggest challenge and the hybrid and electric vehicle ac units I have been around, you might as well roll the windows down. They do not have an electric compressor that comes close to rivaling a decent belt driven compressor.
The Sanden SD7H15 that pulls the dual evaporator system in my 97 Express van is 9.5 cid yet only uses 1.25 kw @ 1,000 rpm and 4.25kw @ 3,000 rpm compressor speed. That is 10,000-25,000 BTUs of cooling or the equivalent of a large window unit at idle and 2.5 large window units at cruising speed. The resulting ac output is 3 kw @ 1,000 rpm and 7.5 kw @ 3,000 rpm. Due to pulley ratios on the drive belt, it operates at 1.36 times the crankshaft RPM. At 750 rpm idle it is a shade over 1,000 rpm compressor speed. Cruising 80 mph down the highway the engine is at 2,350 rpm and the compressor around 3,200 rpm. The compressor cycles regularly at cruising speeds even on a 105*F day. Given the engine makes over 400 ft/lbs down at 2,000 rpm the compressor drag is not even noticeable.
Even with that much ac output, lots of added insulation in the walls, roof and floor because it is a conversion van, the dual ac still struggles to bring down the interior temperature until the van has been driven a few miles at sustained speed. Once it has driven a few miles, the dash vent temps will drop into the upper 30s and it will freeze you out, resulting in the blower speeds being reduced. Lower evaporation demand, less compressor run-time and less blower amperage all adding up to saved fuel.