High Efficiency Air Conditioning Units for non-generator powered campers

[luthj]

The marine units are rated differently than residential or even RV units. RV units are often tested under very mild conditions. the Marine units assume lower water temps. Ask them for power consumption data with 90 degree water! Many will use 2x the power.

kingtek (spelling?) is a decent asian made brand. They have a 12-24V roof (or split type) unit in the 10k BTU range. It is very efficient with coefficient of performance around 3. They are not cheap, at around 4-6k$ per unit. You would need to find a dealer, as they don't sell direct to consumers in the USA.

 

[LeishaShannon]

The Mitsubishi 2kW SRK20ZSXA-W is still -miles- ahead of any 12/24/48v DC unit in efficiency.
Its coefficient of performance is 7 and it costs less than $500USD.
Add a quality Victron 800VA 240v inverter to run it and you're still under $750USD
Nothing else comes close in terms of efficiency or price.

 

[john61ct]

2 kW is 6,800 BTU/hr, correct?

 

[luthj]

2 kW is 6,800 BTU/hr, correct?

Yes. My Russian thermodynamics teacher thanks your for using the correct form BTU/Hr

 

[john61ct]

So the marine Frigomar unit specs I quoted - from actual usage in tropical waters

is in the same ballpark as that Mitsubishi.

Not saying they are comparable units otherwise, certainly leadt of all on price.

But that "Ah per btu" seems to be as good as can be expected with today's technology.

Now being able to feed a bank fast enough to keep one going, that's a different story, IMO requires ICE level power.

 

[luthj]

Correct, high efficiency scroll compressors have a known limit. From there efficiency of the cycle is simply a matter of evap and condenser temps compared to total heat flow needed (watts, BTU/HR). The biggest gains recently have been with inverter type variable speed units. Much better performance in varying (read real life) environments.

The SRK20ZSXA-W lists is COP of 5.56. That is quite good, but remember they are probably providing that at modest exterior temps, and interior humidity; and it may not be at full load. COP is equal to heat removed from the evap divided by input power. So 2kw extraction consumes 2,000/5.56= 360W.

 

[cobratom]

What sort of interest would there be for a source of reliable 7500~ BTU 12VDC Compressors?
These would be three speed brushless units that use standard automotive refrigerant and have their controller built in?
COP around 2.0

Can be used with standard off the shelf evaporators and condensers, or plumbed into your existing cab A/C system

 

[luthj]

A datasheet with proposed specs would be useful. I think Danfoss/Secop had a unit in that range/COP, but it was prohibitively expensive.

If the price and specs are good, such a unit could be used to convert some of the more common AC units for DC only service. The control unit would need to support some type of variable speed input, either via voltage signal, PWM, etc.

There are already common 12V automotive cond/evap units on the market for engine driven compressors, so it would be a matter of speed control (possibly via head pressure), and getting all the fittings sorted out.

 

[cobratom]

These units are specifically 3 speed only. (Ground Wire - Speed 1 1500RPM Speed 2 2200 RPM Speed 3 4000 RPM)
They are identical to the units Roadtrek has been putting into their Ecotrek vans with Rear Battery Powered A/C. The results have been very good with Roadtrek and it appears the new owner will continue this trend.

 

[luthj]

I would personally be interested in a unit depending on price. Obviously I am sure order quantity on your part has a significant impact.

Based on 7500btu and a COP of 2.0, you would expect full load watts to be around 1,100W?

 

[cobratom]

I would personally be interested in a unit depending on price. Obviously I am sure order quantity on your part has a significant impact.

Based on 7500btu and a COP of 2.0, you would expect full load watts to be around 1,100W?

Full load, full wattage is 1152W @ 12V (OR 96A). Most Lithium setup at 80% SOC are above 13V, so at 13V 88.6A Draw.
No hard start either, because it is brushless it tapers its start with a lower initial starting amperage.

 

[java]

Interested if the costs work out.

 

[cobratom]

The compressors are not cheap by any means, a Australian reseller is selling the compressors under the Renvu name for the equivalent of $1400usd. How many are sold, I am not sure. But I may have a line on them around the $700 mark.

 

[jmnielsen]

The Mitsubishi 2kW SRK20ZSXA-W is still -miles- ahead of any 12/24/48v DC unit in efficiency.
Its coefficient of performance is 7 and it costs less than $500USD.
Add a quality Victron 800VA 240v inverter to run it and you're still under $750USD
Nothing else comes close in terms of efficiency or price.

Where are you finding the Mitsubishi unit for that price?

 

[Buffalobwana]

I wondered the same.

I suspect that price was just the air handler/evaporator and the compressor/condenser wasn’t included. Bc I see the package at $1000 or so.

I hate to waste $, but I hate being hot more.

Also, my favorite saying, “I never regretted the money spent on quality, and almost always regretted the money wasted on an inferior product”.