High Ambient Temp Operation

So I finally found a place to load test the roof AC units. We have been traveling down I-10 from Houston to I-8 and on to San Diego.

Out of Houston on Sunday evening, we ran the dash air and two ACs on inverter and it was plenty cool.

Started with that Monday morning and ended up with the generator on around Fort Stockton with the OAT around 97.

Started this morning in Las Cruces with the generator and 4 ACs and hit Tucson at about 104 and still cool.

Now we are between Gila Bend and Yuma with the OAT at 112. Dash AC is on high as are the 4 roof air units. The roof airs are running a 14 to 12 degree delta between inlet and outlet and holding the front of the coach around 77. The galley / rear is 73. The sun is shining in the front quite a bit.

The roof on this coach is not coated which I think makes a big difference.

I never had our OTR air coach out in this kind of heat but so far we have made it thru the heat of the day pretty comfortable.

Jerry,I had my coach in Florida this past weekend and traveled quite a lot and the temps were in the mid 90s to high 90s and the bus air would keep the coach 63 degrees,I was floored.I have a question,there was a customer from Memphis picking up a 2008 Marathon at Millennium and he stated that he could only run 3 AC units on shore cord but all 4 on generator,is he correct?

Must depend on what else is running. I have had all 4 running on shore power with no problem. If you turn the dryer on it may shed some load for you. Wonder if he has the right shore cord amperage plugged into the inverter?

Also, I didn't have any trouble keeping it cold when the temps were in the 90's but up above 110 and headed into the sun, it's tough sledding.

I didn't think that made sense,all 4 would be necessary sometimes.We are a greenhouse heading into the sun with our huge windshields,I have never seen temps over 102 so I really can't compare.

Rant On: I know I am in the minority but I still cannot understand why anyone willing to spend the dollars necessary to own a Prevost conversion will not get OTR. First, the current rating of the OTR is 109,000 BTU. My guess is the Prevost engineers realize it takes that much performance to keep the interior of a coach comfortable. But supposedly intelligent people drink the KoolAid that converters are handing out telling them 3 or 4 15,000 BTU AC units are all that is necessary. That's bullshit.

You folks with 3 AC units in a 45 foot coach with slides have my sympathy.

Rant Continued: Worse, Prevost owners somehow think driver's air and two (or one) inverter powered AC is adequate while driving. Our coaches have a generator. It is there for a reason. When the temps soar into triple digits, crank up the generator and run every AC unit possible. If the coach gets warm it takes a lot of AC power to cool down all the mass of a coach interior, espcially with that big cast iron engine block sitting under the bed. Folks, if you are not lucky enough to have OTR, and you are driving into the sun in the desert with 100 plus temps get ahead of the curve and run everything you have, even if you need to put on a sweat shirt to stay warm, because as the day wears on, your AC units may not be able to keep up with the heat, and eventually it will warm up inside your mega buck conversion.

We are all different, so what might be comfortable temps for some, are going to be too cold or too warm for others. But it sure is nice having an excess of heating and cooling so whatever temp I desire can be achieved. If I had a 77 degree coach interior I would be sweating like a hog. I want it so cold the windows sweat on the outside.

Rant Off.

Yesterday coming to Houston in the 106 F temps, nothing really worked. My CC OTR air started blowing fuses so I fire up the generator and turn on all 3 roof airs at full throttle. Dash air wide open and blowing 80 F air. I know it is good cause I just had the Dash AC and the OTR Air checked last week in prep for trip to cooler climate next week. Almost comfortable. My roof airs, like everyones is a ducted system which is really not very efficient at best. I am with Jon, if I had 109,000 BTU's I would be in heaven.

Jack I have 4 Roof Airs, and have only experienced a couple of parks that could handle the power load thru the 50amp shore cord to power all 4 units. It usually pops the breaker at the pole, if I try and run 4 units.

The power draw thru the cord just won't handle the power needed to run 4 roof airs like the generator will. I don't even try any longer to run more than 3 units when plugged in to shore power, however, we are usually just as cold as we want it to be with just the three running.

We were in Mesa, AZ. two weeks ago with 115 degree heat. The bus took one day to get down to temp inside, but remained nice and cool the next two days we were there. However, when you stepped outside the bus it took your breath away and felt like a convection oven.

Glad to be back home to 100 degree temps and moisture.

Gary S.

Quote:

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Originally Posted by Jerry Winchester

So I finally found a place to load test the roof AC units. We have been traveling down I-10 from Houston to I-8 and on to San Diego.

Out of Houston on Sunday evening, we ran the dash air and two ACs on inverter and it was plenty cool.

Started with that Monday morning and ended up with the generator on around Fort Stockton with the OAT around 97.

Started this morning in Las Cruces with the generator and 4 ACs and hit Tucson at about 104 and still cool.

Now we are between Gila Bend and Yuma with the OAT at 112. Dash AC is on high as are the 4 roof air units. The roof airs are running a 14 to 12 degree delta between inlet and outlet and holding the front of the coach around 77. The galley / rear is 73. The sun is shining in the front quite a bit.

The roof on this coach is not coated which I think makes a big difference.

I never had our OTR air coach out in this kind of heat but so far we have made it thru the heat of the day pretty comfortable.

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Sounds like a good "real world" test. Glad that you're keeping your cool :cool:

Speaking of roof coatings, I'm considering having our bus done as the clear coat needs attention anyway. Our roof is nearly black in keeping with the factory color scheme. I can't believe that there is any benefit to maintaining a dark colored roof.

Any experience with white or light colored roof coatings that enhance cooling? Any special materials that provide a layer of insulation/heat rejection?

Many, many years ago at an FMCA rally Newell had two coaches. One with a base color of white and one with a black base color.

They were lined up nose to tail so they both got the sun equally. When we were about to enter one of them the people before us commented to pay attention to the interior temps. The two Newells had all ACs running, but the difference between the black one and the white one had to be at least 10 degrees, with the white one that much cooler.

That made a believer out of me.

Gary,

You should be able to run all four CAs or roof airs on 50 amp shore power.

The biggest current draw for 15,000 BTU roof airs is about 15 amps. Starting load is much greater but that is temporary. You have to manage your power usage however. You must set the inverters to the lowest charge rate, or even turn them off until you can operate on less than 4 ACs. Obviously you cannot use any high consumption devices like a clothes dryer, or a microwave, or even a big coffee maker. We reserve the time to run the dryer or make coffee for in the morning when two or three ACs will keep the coach cool, and then after we are done drying the towels or having coffee we put the other AC units on.

What is especially important to consider are those things that cycle on and off without any input from you such as a HW tank. You don't think about it, but if it cycles on when two ACs are running it can trip a breaker at the shore power box.

Having said that, if you can keep your current draw to less than 40 amps per leg, lower if possible you should not be tripping shore power breakers. If they do trip it is likely a breaker that has outlived its usefullness or is something as simple as a loose connection.

My cruise airs draw 11-12 amps which means 24 amps per leg with all 4 running,I usually see 35-40 amps per leg with battery chargers,water heater,water pump,etc. running on each leg total.

That sounds logical to me, Jon.

And, I wouldn't trade my genuine Prevost OTR air conditioning for a roof load of air conditioners.....

I kinda like the way my sun glasses immediately fog up the moment I step outside the bus on a nice hot day :cool:

Quote:

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Originally Posted by jack14r

My cruise airs draw 11-12 amps which means 24 amps per leg with all 4 running,I usually see 35-40 amps per leg with battery chargers,water heater,water pump,etc. running on each leg total.

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I'm running all 4 right now and drawing 36.7 amps on one leg and 34.4 on the other. It only becomes an issue if both the hot water heater and pump kick on at the same time.

Paul, if you search "tapecoat" you will find a thread about their product. It is an elastomeric and I applied it to my roof about 16 months ago. I think it definitely improves the heat rejection characteristics of the roof. Product still looks great and does not show any adverse weathering or soiling.

On the other hand, the white color is very visible on the roof if you are standing back from the coach. Doesn't bother me, but it may bother some.

My original color was metallic gray or silver, so if you go over your black with the tapecoat product, I suspect you will really notice a difference in temps.

Gordon,

Thanks for the info. I'll definitely check into this product.

My paint scheme is essentially a black outline, probably a foot or so wide, around the perimeter of the roof with a dark gold color center. I wouldn't mind a white roof color at all.

Quote:

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Originally Posted by Jerry Winchester

So I finally found a place to load test the roof AC units. We have been traveling down I-10 from Houston to I-8 and on to San Diego.

Out of Houston on Sunday evening, we ran the dash air and two ACs on inverter and it was plenty cool.

Started with that Monday morning and ended up with the generator on around Fort Stockton with the OAT around 97.

Started this morning in Las Cruces with the generator and 4 ACs and hit Tucson at about 104 and still cool.

Now we are between Gila Bend and Yuma with the OAT at 112. Dash AC is on high as are the 4 roof air units. The roof airs are running a 14 to 12 degree delta between inlet and outlet and holding the front of the coach around 77. The galley / rear is 73. The sun is shining in the front quite a bit.

The roof on this coach is not coated which I think makes a big difference.

I never had our OTR air coach out in this kind of heat but so far we have made it thru the heat of the day pretty comfortable.

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Jerry,

Your post mimics how my systems work in extreme heat. However, I have found that if I lower all my salon window shades, I notice a significant decrease in the heat load from the outside. During a run through Forth Worth with 105 temps, I lowered my shades and the roof airs started cycling.

Such a simple thing as lowering the shades reduces the heat load inside the salon area significantly.

Also, I have installed an insulation product on my roof. I can not remember the name of the product. I am currently on the road, when I get home I will look up the name from one of the leftover cans.

I can't tell if the coating or the lowering of the salon shades enabled the roof airs to cycle during the high heat.

Hector

I would think that not only would your shades keep the heat from in, but the cold from going out as fast. Rick

JDUB,
Wally Melia at Freightliner in Houston is using a"Cool Coat" application on our roof after he removes the old clearcoat. On mine, the removal is a 30 hour job because he is removing the sealant around all roof attachments, a/c's etc. The application he is using is the same product recommended for school bus roofs. I do not know if this is a good recommendation or not but trust his judgement and experience with the product. If you want the specific name, I will obtain it for you. It is white and I believe more of a soft finish which I assume is of a rubber type base... good or bad?? Thoughts?
Pres