Do you run house AC while on the road
I am contemplating the purchase of a motor home... class A or Super C. I currently pull a 31’ trailer and am looking to consolidate the living and driving into 1 vehicle, adding conveniences like auto...
Forum Discussion
way2roll wrote:
Doesn't the dash AC compressor put drag on the engine thus decreasing MPG? I would think adding a second compressor would rob a good bit of power. The genset is far more efficient at producing power. I am not sure I believe the dash AC is more powerful but even if it were it's far less efficient at cooling a large space compared to the rooftop air.
The genset is actually not more efficient at producing power if you have to run the main engine anyway, at least not in the vast majority of cases. The main engine almost certainly has a better specific fuel consumption than the generator's engine (especially if the generator is an air-cooled unit). It might be true that running the generator is more fuel efficient in producing electricity than idling the main engine solely for that purpose, but if so that's primarily because the main engine has a lot more moving parts and thus requires more fuel to idle (and producing only a few horsepower for a generator is effectively idling for it). It definitely is often true that idling the main engine for a long period of time is undesirable for various other reasons.
An Onan QG3000 has a brake specific fuel consumption of somewhere in the vicinity of 0.9 lb/(hp*hr), based on its published specifications, which is twice (or more) that of modern automotive powerplants. To put it another way, the engine in my motorhome's generator is half as efficient at turning gasoline into usable mechanical energy as a modern car or truck engine.
Of course, when talking specifically about air conditioning, one has to also compare the efficiency of the engine driven AC compressor vs. the electrically-driven one in a roof air conditioner, the efficiency of the electrical generator and motor (for the roof air), any energy loss in the belt and clutch for an engine-driven unit, and many other such factors. And indeed, when driving down the road, in either case the fuel used for air conditioning is very much dwarfed by that used for simply moving an RV along the highway.
