Are 5 rooftop a/c's really necessary?

daddyoften · June 17, 2015, 10:55:57 AM

So, on the interstate yesterday I passed a couple of Prevost's and both of them had roof top a/c's lining the roof. Both had 5 a/c's up there! I'm building my GM and a/c's are one of the things I'm trying to figure out and I've been reading the recent posts about mini splits and how may roof a/c's and all that. Some say 1 is enough, most say 2, and a large group say 3. But I have never read on any of these boards needing 4 let alone 5! Is there something I'm missing?

Thanks,
Eric

moosemanusa · June 17, 2015, 11:04:00 AM

funny you ask that - was asked the same yesturday, hope you don't mind hijacking the thread..

If a high enough BTU unit and lowest am-page unit is used surely this eliminates the need for extra units?

Any recommendations?

eagle19952 · June 17, 2015, 11:07:13 AM

Many/most of those units are entertainers with 20kw gens and promoters money to burn...
They are dressing rooms for as many as 8 people sweating and putting on Alice Cooper make-up

Scott & Heather · June 17, 2015, 12:18:29 PM

Moh peeps moh heats. If you have 6 or 12 people riding in those things, it's gonna get hot going down the road on a hot sunny day. Most of us don't need such cooling power.

HB of CJ · June 17, 2015, 04:06:07 PM

I have seen some crew buses retro fitted with roof top A/C units run off an appropriate gen set. One had six (6) units on top. It all depends where and how the coach is used. Sitting in the sun going nowhere in 120F heat with 25 guys inside would place a very high demand upon cooling indeed. HB

robertglines1 · June 17, 2015, 04:14:57 PM

FWIW, over the road air is usually around 96,000 btu.

sledhead · June 17, 2015, 04:17:21 PM

I posted this on another site

this is my next set up ... 18k unit above drivers window with a 6 k or a 9 k cassette unit over the rear bed were the roof shaker is now . 240 volt single condenser in the same spot as the one I have now . higher seer for better use of power with 240 volt . I just got my 4024 hybrid inverter to day and already have a outback 120 volt to 240 volt transformer .as I have had no problems with the old system and I think the 2 unit 240 volt system should work fine but as Bob has said if something craps out no a/c . the problem I have is I am running out of space to put stuff . not sure when I will change it over as with my 3 k inverter gene and with the help of the new 24 volt hybrid inverter I will be able to run both a/c units I have now when driving . when parked my 9 k will cool the coach fine other then trying to get the cool air into the bed room so when I have to I turn on the roof shaker . man is it load ! why can't someone make a r/v roof shaker that is efficient and quiet . with the split units you can hardly hear them

dave

Lin · June 17, 2015, 05:26:10 PM

Our 35 ft MC5a has two 13500 units and it's more than adequate for us in the SoCal desert. Most times we just close the door to the back (bed and bath) and run with one unit on. Of course, we are both comfortable at 80 degrees. If changing anything though, I would go with a 15000 BTU unit up front. It also should be as far forward as possible.

Darkspeed · June 17, 2015, 06:47:35 PM

I guess this depends on

1. what color your bus is
2. how well insulated
3. how air tight
4. are your windows insulated
5. what is the solar heat gain

For the last four years I lived in full sun, Florida in a 31' vintage Airstream that is very well insulated shell, non insulated windows, white roof, and I can keep it cool with a 120vac 8000BTU window unit so does a well insulated bus really take that much more cooling?

I know when I was gutting my 4106 there was almost no insulation and no thermal isolation.

eagle19952 · June 17, 2015, 07:43:27 PM

Quote from: Darkspeed on June 17, 2015, 06:47:35 PM
I guess this depends on

1. what color your bus is
2. how well insulated
3. how air tight
4. are your windows insulated
5. what is the solar heat gain
6. how many kids open the door how many times

belfert · June 17, 2015, 07:47:21 PM

I have three roof units which is barely enough on a hot day. On a 107 degree day in the desert, even with a white roof, the units would start shutting down because they couldn't reject heat fast enough. I don't think more units would have helped. If I ever went to the desert in that heat again I would probably build covers over the A/C units with Reflectix with an air space kinda like the Saudi MC5 double roofs.

Scott & Heather · June 17, 2015, 08:05:24 PM

I've run our roof airs in 107 degree heat and they never shut down on us. I'm wondering why they shut down in certain cases and not in others. Another thing we did once in Wisconsin when it was over 100 degrees and we only had 13,500 roof air, was during the hottest part of the day, I took a garden hose and watered the roof of the coach and set the hose nozzle in such a way as to mist the roof top a/c cooling fins. Made a difference and got us through the week of over 100 degrees in a bus with just one tough little Coleman 13,500

Sent from my iPhone using Tapatalk

DKO · June 17, 2015, 09:20:50 PM

We have four in 45' and I am very glad I have each one of them. I usually run two but on very hot days in direct sun we will sometime run three. They are not ducted so with an AC unit in four positions I can decide which two or three to run. There are only three of us in the bus. With 12 people in there it is very easy to see why five are necessary. I have bus air while moving down the road and hate to do without it even for a day.

Davy

scanzel · June 18, 2015, 03:22:48 AM

They also do 5 so that if one fails there is some backup.

RickB · June 18, 2015, 06:52:28 AM

Another reason for all those roof airs on touring band coaches is the crew all have different schedules. Between unloading the trucks, rigging and trussing, flying and line checking the PA, hanging and aiming lighting there are people coming and going out of those buses all day. It's kinda like opening your fridge a couple hundred times a day outside in the heat.

RB