Thoughts on solar powered air conditioning for the Dolphin

I have been pondering the ac and solar system in the Toyota motorhome. Mental exercise at this point. I first thought about a window unit ala Pleasure Ways  and Roadtreks.  The idea is to have the batteries be able to power the rear ac going down the road. The problem is that air conditioners are energy pigs.

The small size of the dolphin has an advantage over the bigger motorhomes. I do plan to gut the entire box and rebuild from scratch. Giving this project another advantage. We can tighten up the envelope. We can insulate properly.  Get rid of large windows. Great for views but horrible insulation properties. R1 at best.  Most heat is lost through windows and doors. Then the ceilings. If you are going to need to park it in full sun. Better have a well insulated roof.

After looking at specs for 9000 watt units. Muddling through  ratings, Can’t  manufacture use the same formulas for all units? Anyway, I quickly came to the conclusion that window units used too much power even for the low cost. I did not consider downgrading to a 5000 btu unit. It was not going to cool us down except for a 80 deg night and I want this unit to keep us cool traveling down the interstate without a generator .

I am familiar with mini split systems. The run the spectrum from piece of shit to this might work. The important part here is SEER Rating. The higher the number the less amps or watts it pulls. I am not going to factor in inverter loses. Simply the SEER Rating is a ratio between the watts per hour and the BTU rating. I have found units from 13 seer to 27 seer in 9000 btu models.

lets do the math on the 13 SEER model first. 9000/13 equals 692 watts. Divide the 692 by 12 volts ( our battery working voltage) we get roughly 58 amps out of our batteries. Actually more amps are used because of inverter inefficiency. Working with 220 usable amp hours of  batteries,  3 hours will drain batteries without a charge.

When we check out the 27 SEER unit. 9000/22 equals 333 watts and by 12 we get 28 amps an hour out of our bank. Twice as efficient as the 13 SEER.  6 hours easy . That means on a sunny day 400 watts of panels can keep up with this load. The panel manufactures fib a bit on output .  Add 15 percent to your calculations to cover them. 9000/12 equals 33 amps .In the real world figure 26 -28 amps. Pretty sure a heavy duty alternator is capable of keeping up with that going down the road. May need to upgrade some extra components in the charging system. Relays etc.

The down side is this arrangement is two times the cost of the 13 SEER. You get what you pay for!

Another great feature is the ability to run them on smaller inverters. The larger inverters have higher standby losses. We don’t plan on a microwave so the ac would be the heaviest load on the system. A decent pure sine brand in the 1500 watt range , Samlex or equal.

I was going to upgrade the alternator to a heavy duty high output model. Still researching the charge controller from the alternator and the panels. I need a smart charger that can monitor the batteries and handle the ac load as well as a heavy charge rate from the alternator.

 

The added bonus is we get a heat pump with this package. I was looking at a diesel cab heater for the heat . Open flame heaters really don’t belong in a RV anyway. Another rant another evening.

i would love to hear feedback on this.

 

 

 

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