Running Generator for Cooling Coach while on the Road

[keithhk]

Hi,  I have a question on is it better to run the Generator for the Coach  Air conditioners  on the road to cool the coach when it is Hot,  or just run the Engine Air conditioner to cool the coach as I have heard suggestions for both ways. Thanks  Keith

 

[Tom]

Keith

It's really a function of comfort level and the outside temperature. In our prior coach I ran the gen and roof air quite a bit driving down the road in the summertime, but haven't had the need to do that in our current coach. I've found the dash air to be adequate in the latter case.

 

[Bob Maxwell]

>>It's really a function of comfort level and the outside temperature.<<

Wizop Tom nails it with that sentence!

There have been times running from New Mexico to the Carolinas and back that both Ac's and refrigerator were operating off the 120 volt put out by the generator, my fantastic fan was going on a temperature set switch and the auto airand front window fans were going full blast for days!

Then there's the high country from northern NM to the Arctic where the heat strip might be nice in the morning. In winter, I've run the generator in the San Louis valley of southern CO as my furnaces were running 24x7 and with the TV's etc, that a lot of power being used. I don't has as much coach battery reserve as others, so I'm not at all concerned about hitting the gen start switch.

And our poptop tent campers here in the southwest almost all have an AC on their roof as well! ;D

Generators were made for running and need weekly running all year long. The time of usage with the manual will tell you when to do the oil changes and other maintenance, something that many if not most of us do ourselves.

 

[Ron]

Tom is correct by his statement >>It's really a function of comfort level and the outside temperature.<<.  We sometimes run the roof air conditions and Generator just to excersize the Generator. 

 

[blueblood]

Hi,  I have a question on is it better to run the Generator for the Coach  Air conditioners  on the road to cool the coach when it is Hot,  or just run the Engine Air conditioner to cool the coach as I have heard suggestions for both ways. Thanks  Keith

It is more fuel efficient to run genset ac then dash ac.  I not only don't use dash air, I took belt off engine so I'm not losing any parasitics. A second benefit is that it removes a source of heat from engine compartment that by being in rear is a cooling challenged location.

 

[Bob Zambenini]

Keith, its also a matter of economics. My first RV was a 34 ft gasser and it was far more economical to run the roof airs as dash air would knock my mpg way down and the roof air would do a better job at far less cost.  My belt to the dash air broke and for the last 5 years I had the coach, I did not bother to replace as we got completely away from the dash air. Circulation was a problem in this rig so I set up a box fan to push the cool air  around the drivers area.

In my diesel now we find the dash air is very adequate but  sometimes run the roof air to exercise the generator and also we run the roof airs to cool the entire coach  for the last 30 minutes or so before arrival at a hot place, like over 100 degrees in Las Vegas or Palm Desert.

 

[NC DaveD]

Our dash air hasn't worked for 5 years (can't find anybody within 100 miles to fix it :), and have always run the genny and roof airs on those hot, humid days while on the road. Great exercise for the genset and keeps our temperment on the cool side when we need it the most?

David Derway
'96 Windsor

 

[Smoky]

I agree with Tom and those supporting his view.

"It is more fuel efficient to run genset ac then dash ac."

I really find that hard to believe.  I burn an extra half gallon of diesel an hour running the genset, even more with air running, and cannot see any difference with the dash air.

I will try to watch this more closely.  I have daily logs and will adjust my log to tell me when the dash air is on (which is most of the time this tiume of year).  My log already shows genset usage.

 

[thenosyone]

Hi everyone,

I do agree with Smoky.
I can't find why an AC driven by an gen. set  would work more economic.

Gen set to  roof AC                                                  motor - alternator - electric motor - AC pump / roof AC
Main motor to dash AC                                              Main motor - AC pump / dash AC

With the dash AC you skip a few losses        So Smoky check your log and give us some results.

Well thats how I see it, explain me if you think I am wrong

The people who took the belt off from their AC dash pump, for years, are likely to have problems if they ever want to start their dash AC again.

thenosyone

 

[Ian H]

Our Landrover Discovery in the UK had the belt removed (no Need for ac ) and within 2 years all the seals dried ,now with the weather extremes over here i thought the problem would be magnified.I am inclined to agree with Smoky on this one and no doubt we will get a complete analysis

 

[blueblood]

I did a detailed analysis of this several years ago. It is clearly more efficient. However, at today's fuel prices I suspect it is not nearly as cost effective as when I did the analysis. I can't get to my work since I'm on a four month trip. 

 

[John From Detroit]

Leo, you might be surprised, I don't know how much of the cost is fuel but it may well be it results in greater savings

I have just gotten home from a 4 day trip..  Turns out the campground was a bit short on power so if I wished to run BOTH rooftop units it worked better if I generated my own... So I did, for a few hours yesterday

Today, as we were taking down the generator suddenly quit working... Could not find a reason way (It's supposed to get chatty when it fails and blink me a code)

Turns out it was easily fixed... At the first gas station I did not pass  (Thankfully the generator runs outta gas before the chassis engine does, about 50 miles before the chassis engine does)

Next time I go there I make 2 stops at the flying J, one each way

Oh gas prices... At the first place I got gas 2.499  Flying J 2.319  North of 8 minle (I live just s of 7) 2.359  South of 8 mile 2.319 (same as the J) I have a J-discount card

 

[Gary RV_Wizard]

My rig (a large gasser) is definitely more fuel efficient when using the genset/roof air than dash air.  My mpg is almost unaffected by the genset consumption - rarely more than 0.1 mpg difference, whereas dash air costs about 0.3 mpg on a hot day.  I've compared the two  several times and the results have been quite consistent.

Another factor for me is the heat load on the engine cooling system (radiator).  Since mine is a front engine rig, I can hear the radiator cooling fan(s) run when they switch on and on 90+ days they run a lot with the dash air on.  Using the roof air, none of that extra heat  gets dumped into the engine radiator and the fans stay off or run far less often.

 

[John From Detroit]

That is one thing,,, The generator in my righ (ONAN 5500) At full load draws only about 1 gallon per hour

At 60 MPG if I"m lucky I'm getting 6mpg on the engine (10 gph) so the additional gallon is 1/10th difference

If I'm not luckey I"m running 12gph on the main engine so the additional contribution of the genset is now 1/12th

 

[BernieD]

I did a detailed analysis of this several years ago. It is clearly more efficient. However, at today's fuel prices I suspect it is not nearly as cost effective as when I did the analysis. I can't get to my work since I'm on a four month trip. 

Leo
I don't know why it wouldn't be even more cost effective ??? The price of fuel has no impact on the amount used, so if the generator saves fuel compared to dash air, the $ amount saved would be even higher.

 

[thenosyone]

Hi

So far nobody has explained me, why power taken of a small engine (gen.set) would be more efficient, than power taken from the main (big) engine.
As I was for 27 years a ships engineer, hope someone can explain me here what I am missing. Always want to learn something new.

For as far as I known, I can only talk for/from this side of the Atlantic, small engines still consume more fuel for every KW/hour.

So please explain why the  AC driven by the gen.set would be more efficient, if both are using the same fuel... gas-gas or diesel-diesel. The only way to make a profit on the gen.set AC,  is,  if you would use a different fuel.  propane/butane, or gas / diesel where no road taxes are paid for. Well thats how it would work overhere.
   
Greetings from Antwerp

 

[thenosyone]

Another factor for me is the heat load on the engine cooling system (radiator).? Since mine is a front engine rig, I can hear the radiator cooling fan(s) run when they switch on and on 90+ days they run a lot with the dash air on.? Using the roof air, none of that extra heat? gets dumped into the engine radiator and the fans stay off or run far less often.

Hi Gary, here how I see it

Your  large gasser is normally equipped with  a main engine in exes of 300 HP, your gen.set is probably 10 HP. Running the gen.set on the road, will only take the amount of  heat, generated by the extra 10HP (dash AC), from your radiator. this amount in just  1/30 or 3.3% of his cooling capacity.  Normally, with dash AC the fan would work 3.3% more.  Is your cooling system in good condition Gary?

The heat generated from the AC, has nothing to do with the main radiator, well, I think in US just like on the old continent, dash AC  has his own. radiator.
Greetings from Antwerp

 

[Tom]

Thenosyne

I can't speak for the efficiency or relative fuel consumption, but reality is that the dash air conditionning on our prior gas propelled motorhome wasn't adequate when driving on hot days, whereas the dash a/c on our current diesel propelled coach is just fine. I suspect that there are many factors involved, such as poor insulation in the walls and roof of our old motorhome, and our current dash a/c has a much higher cooling capacity.

Sometimes we (I) misuse the term "efficiency" by stating that roof a/c powered by the generator is more "efficient" at cooling than the dash a/c powered by the main engine. What I (we) mean by such a statement is that the roof a/c does a much better job of cooling the coach in a short period of time. This is probably due to the fact that the two roof a/c units on my coach have a much higher combined cooling capacity than the dash a/c.

Realize that it's 100oF (38oC) here today and many cars would overheat if the a/c was left on when climbing mountain passes, but having the generator running to power the a/c has no effect on the main engine cooling. I haven't tried running the dash a/c on my coach while climbing those mountain passes, so I can't comment on that.

Hopefully you don't misconstrue this response as an attempt to increase the "number of posts after my name"  ;D

[edit]Specify temperature in oF and oC[/edit]

 

[John From Detroit]

Hi Gary, here how I see it

Your  large gasser is normally equipped with  a main engine in exes of 300 HP, your gen.set is probably 10 HP. Running the gen.set on the road, will only take the amount of  heat, generated by the extra 10HP (dash AC), from your radiator. this amount in just  1/30 or 3.3% of his cooling capacity.  Normally, with dash AC the fan would work 3.3% more.  Is your cooling system in good condition Gary?

The heat generated from the AC, has nothing to do with the main radiator, well, I think in US just like on the old continent, dash AC  has his own. radiator.
Greetings from Antwerp

In a car the AC condenser coil (it's radiator) is located in front of the engine's radiator, thus if you are running the AC the air reaching the engine's radiator is hotter and thus not as able to cool the engine

In an RV,,, I'm very simply not sure,  I would have to crawl around under and over mine with a flashlight and take a closer look, I do know I have a pair of fans that are supposed to be for additional cooling for the AC per something I read but I"m not sure of the air path for engine cooling.  Does it make a difference? I don't know.  I've had no overheat issues using dash air

But on my rig, sometimes the rooftops are just not enough and you need dash air as well

 

[Smoky]

Tom:

I think we would all agree that the genset cools the entire coach more efficiently than the dash air.

My interest, however, is which is more economical when going down the road.  Since I travel alone or with one other human, I don';t need the entire coach cooled when in transit.  I just want to be comfortable at the helm, and the dash air does that.  So, in that scenario, is the dash air more economical?  Hard for me to believe it isn't, but I am open to more data on this interesting subject.