7500 Onan creates too much heat in the RV

[GoWestMan]

Just wondering if there's a way to mitigate the heat production from the genny. We've been running it all day to power the AC units and currently have put up a curtain just behind the front seats to try and trap the heat, otherwise the AC units are working even harder just to counteract the genny's heat.

The curtain makes a huge difference in temp already, when its a nice 22C (72F) in the RV its 26c (79F) in front of the curtain which makes it uncomfortably hot when I have to drive. You can feel the heat rising up under the dash. Is there a way to dissipate more of the heat from the genny when the RV is parked?

I have a small 2.2kW gas genny along and I can run that away from the RV, but it only powers one AC unit which isnt enough to keep us comfortable.

[jacwjames]

Where is the generator and how is it mounted.

My generator is on a slide in the front.  Never had a big problem with heat but if I did I might try sliding the generator out a little and see if that would help.  Could also put a small fan there and help blow the hot air out.

When they build my coach the used a bunch of the foam spray on the underside of the front and the stairwell, you might check if yours is the same. 

[Tom Cherry]

24 minutes ago, GoWestMan said:

Just wondering if there's a way to mitigate the heat production from the genny. We've been running it all day to power the AC units and currently have put up a curtain just behind the front seats to try and trap the heat, otherwise the AC units are working even harder just to counteract the genny's heat.

The curtain makes a huge difference in temp already, when its a nice 22C (72F) in the RV its 26c (79F) in front of the curtain which makes it uncomfortably hot when I have to drive. You can feel the heat rising up under the dash. Is there a way to dissipate more of the heat from the genny when the RV is parked?

I have a small 2.2kW gas genny along and I can run that away from the RV, but it only powers one AC unit which isnt enough to keep us comfortable.

Since your MH is a bit older, we have little experience on the HEAT factor of the Onan. We all have the 7.5/8 or 10 or 12.5KW units.

GENERALLY speaking....the Front firewall is a FARCE.  The insulation is nil.  BUT, one really sharp member started checking for AIR LEAKS between the back of his dash and the genny area. He found holes that he could put his fingers through. He has the MH in a building and turned on the ceiling fans and used them to push out air.  Some of the RV shops use this technique...as putting a BIG floor fan in the center of the living area...slides closed, if there and then opening a rear bedroom window...with the AC's on HIGH and seeing if they can "FEEL" cool air coming out on the genny side of the firewall.  He used spray expanding foam and filled all the gaps. He said it was amazing when you drove on really HOT or COLD days.  

That would be my first test...  NOW, my experience is that the GLASS is really the Culprit...so if you put up a curtain, you are blocking the thermal heat through the glass or cold air. I had a Winnie Gasser and with the engine off and the Genny was in the rear, it was like an oven. I used the BIG fold up RV silver reflectors and strung 3 across the windshield that was like NIGHT and day during the hot days.

SO...Maybe the Genny is the culprit...but I'd work on air leaks.  THEN run a test.  On a warm day...say 80 dF.  Measure the temperature (hang a remote thermometer) right behind your curtain.  THEN keep the AC set so it cycles and NOT super cools.  Run that for a few hours and watch or record the temps.  THEN start up the Genny.

MEASURE the Delta T or the increase.  It might be substantial...if so, then maybe you need a fan on TOP of the genny, while parked and blowing OUT or dissipating it.  If not much difference, then it is the GLASS HOUSE or GREEN HOUSE effect of the cockpit and the reflectors will keep it much cooler.

Just general comments....

[GoWestMan]

24 minutes ago, jacwjames said:

Good points, sir.

Unfortunately, mine's solidly bolted to the chassis, no slide. Which seems odd to me because you have to lie under it to service it and it has to be dropped to do anything more than an oil or air filter change.

I could try the fan thing, and mount one to blow air forward and out the front grille. Cant make it worse.

Never thought about spray foam. Defintely dont have any under my floor, just plywood covered with tin. But thats not a bad idea... a little tricky to put on now but doable.

 

10 minutes ago, Tom Cherry said:

I will definitely check for holes in the firewall and floor area. Ive done some modifying so its possible I forgot about something in that area.

>NOW, my experience is that the GLASS is really the Culprit...so if you put up a curtain, you are blocking the thermal heat through the glass or cold air. I had a Winnie Gasser and with the engine off and the Genny was in the rear, it was like an oven. I used the BIG fold up RV silver reflectors and strung 3 across the windshield that was like NIGHT and day during the hot days.

Pretty sure its the genny, not thermal heat from the glass. The heat is high even when the RV is facing away from the sun or parked under shade trees. Its definitely coming up from below. When I open the fuse block access door on the passenger side I can feel the heat pouring out.

 

 

[Tom Cherry]

4 minutes ago, GoWestMan said:

 

The foam was just to FILL the holes or the cracks or the poor job the Monaco did in assembly....on the firewall...those air leaks create issues when parked and are monumental when driving.  There was NO added insulation or any type of shielding....just to clarify.

My point was that having spent a career in manufacturing and facilities maintenance and also reading projects where some fast talking "Energy Consultant" (reminded me of Professor Harold Hill from the Music Man) had told the plant engineer or manufacturing services manager that THEY and their CRACK team could slice their heating and cooling with a simple wave of their magic wand.

SO...call me a skeptic on such...BUT, the logic that I always asked the project writer to do...  TEST and THEN figure out what is going on.

SO, my point....  If you have NOT got an hard data on whether the Onan is the culprit....or just the glass house of the cockpit...I'd spend some time experimenting and then if it was a factor....one that can be measured...then start to use the simple fixes 

Air circulation is critical to heat dissipation.  SO, a 14" Oscillating fan on top of the Genny might be a good test.

We only have 2 Roof Tops on our 40 and MOST folks have 3 on their Tags or 43 Ft.  It doesn't take a NASA scientist to do the math.  My TWO units are 15K each or 30.  The 43 footer are two 15 and a 13.  Total of 43. Divide y 30 by 40 Ft.  That is 3.4 or 0.75 K BTUS) per foot.  The 3 AC rigs are at or closer to a FULL K or 1000 BTU per foot.

SO, I can't compensate... Therefore I use fans and such.  BUT, there is NO practical way to eliminate the GLASS...without building walls...

My THOUGHTS.  Hope this is food for thought.

[Benjamin]

Like Tom says, air leakage is the biggest issue to address.  In houses, they do a blower door test to identify and measure air leakage, you can do a DIY version with a used furnace blower, the "squirrel cage" centrifugal blower which will blow a steady volume across a higher pressure than a typical household fan. Put a centrifugal blower in a window or other vent to pressurize the whole interior, then check for air leaks around the generator, and the A/C's while you're at it. They make smoke pencils for identifying small air leaks, you could use those, but you're really looking for large air leaks. Both the generator and the air conditioners are moving a lot of air, that can be working against you if the A/C is blowing cool air outside, and the generator is blowing hot air inside.  After the first round of air sealing, you could measure the air pressure inside with the A/C's running to see if they're exhausting measurable air.  A u tube manometer is a simple DIY device to measure such pressure, or just crack one small window open and feel the air flow.  The generator air flow may be able to be channeled to suck fresh air over the RV surface, and blow the hot air out and away.

The next step after air sealing, and air flow improvements, would be improving the insulation between the generator and the interior. 

Edited July 26 by Benjamin