Best way to cool coach while driving

[JimC]

Gas mileage ways, is it more efficient to use the dash air or the roof air w/generator? If there were a strong headwind, would it make a difference in the drag by the AC vs the gas used by the generator?

JimC

[16ACE27]

Generally, the dash A/C has a much higher cooling capacity than the roof A/C and is more gas efficient than running the generator if it is working correctly.

But it still may not cool the coach sufficiently while driving so a lot of people don't see it as an either/or choice, they see it as a "both" choice.

Some things we have done to avoid running the roof A/C when possible are:
Pre-cool the coach before you leave. Get it into the 60s if you can for at least an hour to cool down not just the air, but all the material in the RV. If you start out with all the material in the coach at 80 to 90 (or higher) temperatures you will never cool it down
Rig a curtain behind the cab so you can separate the living area of the RV from the driving area. This puts less of a cooling load on the dash A/C while traveling and the roof A/C while parked.
Rig a curtain behind the seating area of the RV. That way if you have more than two people traveling you are only cooling the area where people are. It can also serve as a privacy curtain between the living area of the RV and the bedroom/bathroom area.

[JimC]

Thanks for your reply. Most of the time, I will have 5-6 occupants and two [large] Bernese Mountain Dogs in the coach.

When traveling South in Okla, we offen encounter 25+ mph headwinds. Would that make a difference in the answer? Would the reduction in engine drag help enough to offset the gas use by the generator?

I have a Class C, Chevy 6.0 l , 4500 Express chassis.

[Chance]

Originally Posted by JimC

Thanks for your reply. Most of the time, I will have 5-6 occupants and two [large] Bernese Mountain Dogs in the coach.

When traveling South in Okla, we offen encounter 25+ mph headwinds. Would that make a difference in the answer? Would the reduction in engine drag help enough to offset the gas use by the generator?

I have a Class C, Chevy 6.0 l , 4500 Express chassis.

Normally, no. We can always think of theoretical exceptions, but under normal driving conditions the headwind will make the engine work harder, which “often” (but not always) makes it burn more gas but while at higher efficiency. It’s not worth considering either way. The amount of extra power a motorhome needs to fight a 25 MPH headwind is huge compared to powering an air conditioner.

If everyone is comfortable enough with dash A/C I’d drive that way. If you need more cooling, then what other option is there but starting the generator to power rooftop A/C.

[Bob Denman]

With that many occupants in your RV: you're pretty much going to have to use the roof-mounted A/C units as well...
Not everybody will be able to sit up close to where the dash A/C can do it's best work.

[be happy]

I have never experienced driving a class C so what I think may not make much difference. I would think the front air would be great to keep the up front passengers cool, but nothing else.

In both of my class A's I have always used the on board ac units to keep the coach cool. Heres my thoughts on the use of a generator while traveling. With it running not only do I keep the whole coach cool by using the ac, I also keep the refrigerator cold by using elect. instead of propane. When traveling 6hr plus days we also like to have something cooking in the slow cooker so when we are done for the day supper is ready.

Lets talk my idea of mileage, yes its nice to know what mileage you are getting but when it comes down to it are you going to stop rving if your mileage drops down. I would say no. The running of the generator uses so little fuel to me its not worth not running it.

You have an RV so go out and use it have fun and at the end of the day you will feel great.

[Chance]

For what it’s worth, a generator burning 1/2 gallon per hour of gasoline will have the equivalent effect of reducing MPG from say 8 to 7.5 while on highway at around 65 MPH. It’s unlikely running dash A/C will lower MPG by that much, so vehicle dash A/C is the more efficient option as long as it’s enough cooling.




P.S. — I hope soon a single motorhome rooftop A/C can be powered indirectly by engine through use of alternators and inverter, making it unnecessary to run generator. This is already possible on some van campers (although smaller camper size normally makes it unnecessary to run the rooftop A/C). When this option is available, fuel economy should be no worse than running a generator.

[ducksface]

Your generator should get about 90mpg at 60mph.
At $3per gallon that's how many cents per mile?
How many dollars per hour?

Comfort is worth it.
Run both together.

[lwmcguire]

Most of us have to run the generator as well as the dash in very hot weather

[Bob Denman]

Since it's just the two of us (and one tiny dog...): We put a curtain behind the seats, and it keeps us comfy in ALL conditions.
https://www.thorforums.com/forums/at...1&d=1588872874

[dkoldman]

Originally Posted by JimC

Thanks for your reply. Most of the time, I will have 5-6 occupants and two [large] Bernese Mountain Dogs in the coach.

When traveling South in Okla, we offen encounter 25+ mph headwinds. Would that make a difference in the answer? Would the reduction in engine drag help enough to offset the gas use by the generator?

I have a Class C, Chevy 6.0 l , 4500 Express chassis.

Could you or someone explain your angle with 25+ headwinds?

I can clearly how it may impact gas mileage for engine, but don't follow the connection with it's impact on Dash AC? How do you compare rooftop AC with engine gas usage? Rooftops will burn X gallons per hour when at full load on a generator and Dash AC will burn Y gallons per hour when at full load. We know X > Y ; but I don't see how 25+ headwind will effect X or Y?

[dkoldman]

Originally Posted by ducksface

Your generator should get about 90mpg at 60mph.
At $3per gallon that's how many cents per mile?
How many dollars per hour?

Comfort is worth it.
Run both together.

Let me see what it is worth to me. 1st I will assume your data is 100% correct, after all you are the Duck 2nd I will assume I have a 500 mile trip in the hottest weather possible 3rdly I will assume my RV gets 9 mpg.

I am going to need 55.5 gallons just to run the Engine. @ $3/ gallon that is $166.66

To run the Generator on the same trip I will need 5.5 gallons to run both ACs. @ $3/gallons that is $16.66

So total cost is $183.32

Do I care to save $16.66 and be hot in a 8 hour and 20 minute trip? That is $16 I would love to spend and just enjoy the RV. Most folks don't run their generators enough anyways; then they complain they have issues with carburetor etc. The way I figure, I cannot get enough hours on my boat or generators, I will gladly run them whenever I think I have any kind of excuse, need or opportunity.

[Chance]

Originally Posted by dkoldman

Could you or someone explain your angle with 25+ headwinds?

I can clearly how it may impact gas mileage for engine, but don't follow the connection with it's impact on Dash AC? How do you compare rooftop AC with engine gas usage? Rooftops will burn X gallons per hour when at full load on a generator and Dash AC will burn Y gallons per hour when at full load. We know X > Y ; but I don't see how 25+ headwind will effect X or Y?

As I said previously, no, it won’t make much difference. It’s very possible/likely that motorhome engine operates more efficiently due to headwind (obviously using more gas at same time), which makes running dash A/C even less costly.

But that wasn’t the question asked in OP.

The question as I read it was using dash A/C “OR” the rooftop RV A/C powered by generator. One or the other, not both.

If choosing between them, the dash A/C should “practically” consume less gas all the time. However, in “THEORY” it may be possible that his 25 MPH headwind “PLUS” the added load of the dash A/C on engine “COULD” cause the motorhome to drop down a gear (shift down), which could cause more fuel consumption than running generator to power rooftop A/C.

In “THEORY” it’s possible, but odds of it happening is like winning the lottery.

[Bob Denman]

Regardless of your power usage: a 25 mph headwind is going to make anybody's day a whole lot longer...

[dkoldman]

Originally Posted by Chance

As I said previously, no, it won’t make much difference. It’s very possible/likely that motorhome engine operates more efficiently due to headwind (obviously using more gas at same time), which makes running dash A/C even less costly.

But that wasn’t the question asked in OP.

The question as I read it was using dash A/C “OR” the rooftop RV A/C powered by generator. One or the other, not both.

If choosing between them, the dash A/C should “practically” consume less gas all the time. However, in “THEORY” it may be possible that his 25 MPH headwind “PLUS” the added load of the dash A/C on engine “COULD” cause the motorhome to drop down a gear (shift down), which could cause more fuel consumption than running generator to power rooftop A/C.

In “THEORY” it’s possible, but odds of it happening is like winning the lottery.

Wow... no wonder I missed the intent of OP's angle. You explained it nicely.

Put me down for 6-32-17-41-29

Thus far we have never needed the generator to run and we have 30ft coach with 2 AC's. The dash actually blows too cold and my wife complains. In our SUVs sher has her own thermostat control. She doesn't say it but if we are driving and it is really hot outside and dash blowing cold inside she will close her vents or get up and move to main living area and work on something as it is a tad warmer. I do close the bedroom door if it is hot outside so it is on 20ft or so that is being cool. That is not too much longer than a SUV.

However when we have folks riding with us we always run the generator. We normally direct most if not all Air to the front unless we need both ACs.

With all that said, if there are 25+ winds in any direction, I am going to strongly consider pulling up somewhere to lay low for awhile. A sudden big wind gust is one of my greatest concerns. I look for 15 mph winds or lower.

[Bob Denman]

Perhaps RVs should come equipped with anemometers that show the speed and direction the the wind...

[Travelin' Texans]

Originally Posted by dkoldman

Wow... no wonder I missed the intent of OP's angle. You explained it nicely.

Put me down for 6-32-17-41-29

Thus far we have never needed the generator to run and we have 30ft coach with 2 AC's. The dash actually blows too cold and my wife complains. In our SUVs sher has her own thermostat control. She doesn't say it but if we are driving and it is really hot outside and dash blowing cold inside she will close her vents or get up and move to main living area and work on something as it is a tad warmer. I do close the bedroom door if it is hot outside so it is on 20ft or so that is being cool. That is not too much longer than a SUV.

However when we have folks riding with us we always run the generator. We normally direct most if not all Air to the front unless we need both ACs.

With all that said, if there are 25+ winds in any direction, I am going to strongly consider pulling up somewhere to lay low for awhile. A sudden big wind gust is one of my greatest concerns. I look for 15 mph winds or lower.

You must be from from East Texas if 25mph winds stop you.
West Texas or the panhandle of Texas along with most of the plains states 25mph is a light breeze, especially spring time.
Back to the fuel mileage, if that's of big concern as to getting 6 mpg or 8 mpg then you should probably not get into rving, whether driving or towing a RV fuel is going to be the biggest expense. So cool it down by whatever means it keeps you comfortable & go enjoy.

[Bob Denman]

Wyoming has their own issues with the wind...

https://www.thorforums.com/forums/at...1&d=1588958448

[lwmcguire]

We travel I70 and I80 several times per year getting to the Rockies and usually during mid summer so a dark coach gets warm. Generator on and at least two of the Heat Pumps cranking out cold air while the dash air is always full on and in recirc mode to maximize cooling.

As far as wind probably one out of 10 trips we don't have at least 30 mph winds along the route. Best way to handle it is shorter segments and longer rest times to help minimize the extra effort. The Tuscany handles the wind fine but the increased noise and steering effort is tiring and will be no matter what you are driving.

There are few coaches out there that approach 40 feet that don't require AC help on hot days.

Back to the OP, the dash air set to recirc is always used at max before supplemental AC is added.

[ducksface]

Originally Posted by Travelin' Texans

Back to the fuel mileage, if that's of big concern as to getting 6 mpg or 8 mpg then you should probably not get into rving, whether driving or towing a RV fuel is going to be the biggest expense. So cool it down by whatever means it keeps you comfortable & go enjoy.

Forget all that other crap I said, this is what I meant all along.

Bob... Dammit....
I'm going to have to build that damn sign now.
I hate welding.

They'll make great Christmas gifts.