Something doesn't add up with that 12V A/C. It says 19A in eco mode, but 12A x 12V = 228W, and the unit claims to be a 2000W model. I have to wonder how much cooling is actually taking place in eco mode?
I am certainly not trying to promote this particular unit. It’s just the first one to pop up as an example when I did a google search.
But just for fun, let’s take a closer look at the numbers Dometic provides. I think a few folks here are confusing cooling output with power consumption. This units max cooling output is 2000w or 6800btu/hr (1 watt = 3.41 BTU/hr) because air conditioners/heat pumps, in simple terms, are just moving heat from inside to outside, or outside to inside. Rather than converting electrical energy into heat, an efficiency of greater than 100% is possible (and any half decent ac/heat pump does achieve better than 100% when the outside temp and inside temp are within 10 degrees Celsius of each other. For example, I have attached a screen shot for the dometic penguin II showing that, in the right conditions, it can extract more than twice as much heat energy as it consumes, and this isn’t a particularity efficient unit.
EER ratings also show this, as they are a ratio between power consumption in watts, and BTU/hr output. An EER of 3.41 would indicate a “100% efficiency”. As Richm pointed out above, EERs in the teens are possible indicating 5+ times the electrical input can be achieved.
Determining a defendable EER for a DC powered Air conditioner, I would imagine, is somewhat difficult, as depending on battery type, cable run, wire size, battery state of charge etc. The unit is likely to see anywhere between 10.5 and 14v. Also, I have no idea if the numbers posted on the dometic website are for the same conditions as required for an official EER. But as a quick and dirty exercise, using domestics numbers, (max BTU/hr = 6824, max current = 58 amps, and a nominal voltage of 12.5) we get an EER OF 9.41.
Assuming a linear efficiency (unlikely, but hey, this is a theoretical exercise) if 58 amps produces 6824 BTU/hr, then 19 amps would result in 2200BTU/hr. I figure my 19 has about 450 sq feet of surface area, and if we assume an r value of 2 (this is just a guess, I have the extra insulation) then the eco mode would achieve a 5 degree Celsius temperature reduction inside the trailer (running non stop), and reduce humidity some. Not earth shattering, but enough to make it comfortable a lot of the time. If you had say 300 amp-hours of lithium, 8 hours of run time in eco mode would be ~50% of your battery capacity.
Certainly it would seem that the mini split options are more efficient. But I like the idea of skipping the big inverter and mounting it in the same spot as the existing AC. That being said, I will admit the 4awg cable run would be a bit challenging to conceal nicely. Hmmm…..
