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Author Topic: I can't make up my mind, rooftop A/C vs basement A/C  (Read 2123 times)
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« on: April 05, 2009, 12:42:40 PM »

Folks, I have purchased 3 DuoTherm Penguin low profile ducted rooftop heatpumps.   I thought this would suit my needs..   However....

Right now I have 2 3 ton split system commercial A/C units.   The "outdoor" units are in the basement and take up alot of space.  The indoor coil unit and fan/heat strips take up space mid cabin.   Bottom line is I want to remove them.   In order to run them OTR I have to keep my 17KW genset running.   I want to get rid of this MO.   

I have seen 3 Marathon coaches that have 4 and 5 low profile unit recently and even with the awning system the units are visable.   The height of these buses are clearly over 13 feet.   I am 12' 9" right now without roof air.

Nick and Gumpy have basement A/C and that is what I thnk would really be the best suited system.   The question that I have is>>  Can one basement A/C system be run off a large engine alternator thru my Trace SW4024 (2 each)      Duotherm makes a large single unit basment unit but I am thinking that it would be wise to install 2 vs 1 large unit.

With this said, I have one major design issue,  I have 6 bunks midship.   I want to cool to 70 degrees, with the fan running thru the entire night.   I know that I can run the heat pumps off my battery bank.   But I don't know if the basement units will be able to run 6 to 7 hours.  This criteria might push me to the rooftop units.

I realize that this is a personal choice with "us"..   There are pro's and cons.   I don't want to be ripping off my roof airs..   As it was this past summer, low tree branches raked my roofline already..   Drivers error at dusk..
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« Reply #1 on: April 05, 2009, 06:33:54 PM »

Looks like nobody is going to make your mind for you.>>>Dan
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« Reply #2 on: April 05, 2009, 06:50:57 PM »

The basement units are still going to take up a lot of bay space and require large amounts of fresh air to properly cool.  They also require room inside for ducting.

Rooftops might look ugly to some, but they are easy to service and are relatively cheap and easy to replace if they do fail.
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« Reply #3 on: April 05, 2009, 06:55:56 PM »

Zero,

I am not the HVAC heavy on here.....Nick is.  I think you should PM him personally as your situation is different than most.  With 6 bunks I would take a wild guess and say you have 8 people on board usually or often.  That is a BIG load for AC.  The next major consideration is what kind of insulation do you have?  What kind of windows and how many?  Where will you be traveling?  SW and Maine are different requirement zones for picking tonnage.  Nick can compute this stuff while he is doing something else.

Did you find that the 2 three ton units were adequate, marginal or weak for your needs?

I and many others on here agree with you on the backup/redundancy issue.  Every chance you get.

I wonder what others feel but I would absolutely have air driven from the engine for OTR.  Many run gennys but for my money that would be something to avoid.  If you were out "anywhere" with your full population and you lost that genny you would almost certainly have top fly home.  You couldn't stay in the bus in the sun....couldn't.  With OTR and maybe two compressors you would have that to fall back on and it would get you home.  With 8 people you are going to have a fresh air consideration and that will impact you tonnage.  ya need Nick and have answers ready for him.  One evaporator in the front for the driver, one amidships and one in the rear.  You might want to consider the OTR upgrade before you do the conversion/replacement of the 3 ton units.....then again, maybe not.

HTH,

John


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« Reply #4 on: April 05, 2009, 07:03:04 PM »

Hi Zc,

A basement unit will draw the same amount of current as a roof air. The duel basement unit is 27,000 btu's while you

will get a true 2 1/2 tons {30,000 btu's] with 2- 15,000 btu single units stacked. Plus you will get double the fan cfm's

using the 2- 15's together. The duel unit's compressors can only be cycled by the thormostat, while you can cycle a whole

compressor/system off the loop using the 2- 15 set up by curcuit breakers or a seprate t-stat.

If you choose to go with 2 basement units, I will be glad to help you through it.

Good Luck
Nick-
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« Reply #5 on: April 05, 2009, 07:16:05 PM »

Zero,

I am not the HVAC heavy on here.....Nick is.  I think you should PM him personally as your situation is different than most.  With 6 bunks I would take a wild guess and say you have 8 people on board usually or often.  That is a BIG load for AC.  The next major consideration is what kind of insulation do you have?  What kind of windows and how many?  Where will you be traveling?  SW and Maine are different requirement zones for picking tonnage.  Nick can compute this stuff while he is doing something else.

Did you find that the 2 three ton units were adequate, marginal or weak for your needs?

I and many others on here agree with you on the backup/redundancy issue.  Every chance you get.

I wonder what others feel but I would absolutely have air driven from the engine for OTR.  Many run gennys but for my money that would be something to avoid.  If you were out "anywhere" with your full population and you lost that genny you would almost certainly have top fly home.  You couldn't stay in the bus in the sun....couldn't.  With OTR and maybe two compressors you would have that to fall back on and it would get you home.  With 8 people you are going to have a fresh air consideration and that will impact you tonnage.  ya need Nick and have answers ready for him.  One evaporator in the front for the driver, one amidships and one in the rear.  You might want to consider the OTR upgrade before you do the conversion/replacement of the 3 ton units.....then again, maybe not.

HTH,

John





John brings up some good points in this post.

If you plan on using basements while driving, you won't be happy with cooling capacities! Even 3 roof airs/basement units

together will not be enough if you are used to the two 3 ton systems...

Many entertainer coaches have your set-up and most are 2-3ton systems. It is mostly for rapid cooling of the coach. If the

coach sits in the sun for a few hours, the inside temps could rise very high. So, just as an average car's A/C system is around

5 tons, so should be your bus to bring down the temps in a reasonable amount of time.

Personally, I would use the OTR A/C engine system while traveling. Entertainer coaches sit at venues for many hours at a time

so, it is more cost effective to run a generator vs the main engine.

Good Luck
Nick-
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« Reply #6 on: April 05, 2009, 07:35:52 PM »

Thanks guys for the replies...

I do NOT have OTR A/C for the entire bus.   Just the standard Prevost issue drivers compartment.   

The coach is Charcoal in color with 5 double insulated windows.   As Nick said it is a entertainer H3..

I have been in the Texas in June and the 6 Tons will freeze you out.   It takes around 20 minutes to bring the temps down from 100 to 70 degrees.   The drivers air really is efficient and does work well keeping the front 10 feet of the coach liveable while driving. 

The coach is divided into 3 compartments.   Nick how much BTU's basement air do you have?   2 27K units might be required?
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« Reply #7 on: April 05, 2009, 08:56:36 PM »

Height is an issue.  But....stay out of the trees. 
Rooftops are the way to fly with band and entertainer buses with divided bunk compartments.  That's why million plus dollar band buses have rooftop ACs....albeit, sometimes 5 or 6 of the things. 
You can easily (and cheaply) replace a rooftop if one quits.  Still, rooftops are very dependable.
Rooftop fan noise is desirable for bunk compartment applications. 
Rooftops will cool down a compartment quickly...they move a lot of air. 
The various compartments don't need complicated ducting... 
Rooftops resolve the loss of bay storage issues too. 

JR
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« Reply #8 on: April 06, 2009, 03:35:03 AM »

Thanks guys for the replies...

I do NOT have OTR A/C for the entire bus.   Just the standard Prevost issue drivers compartment.  

The coach is Charcoal in color with 5 double insulated windows.   As Nick said it is a entertainer H3..

I have been in the Texas in June and the 6 Tons will freeze you out.   It takes around 20 minutes to bring the temps down from 100 to 70 degrees.   The drivers air really is efficient and does work well keeping the front 10 feet of the coach liveable while driving. 

The coach is divided into 3 compartments.   Nick how much BTU's basement air do you have?   2 27K units might be required?

Hi Zc,
I have 2- 15k btu Heat Pumps, Stacked. There was only 1 occasion that I needed them OTR when my condencer fan motor quit on the otr system.
Yes, you can easly stack 2- 27k 's in the same manor. I used 2" flexable duct to each outlet from my main trunk which may work for you too.
Nick-
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« Reply #9 on: April 06, 2009, 09:48:33 AM »

ZC,

As Nick pointed out, the compressors associated with OTR, such as yours, are most often very large capacity.  Nick mentioned 5 ton.  I have been told that you can hook TWO evap units to one compressor.  I was always concerned about oil circ but there must be a way to deal with that.  I have seen pics of buses with that enormous three cylinder compressor removed and TWO auto type clutches compressors added.  The custom Pres have a evap unit in the front and one in the bedroom and only one compressor.  Two compressors would give you redundancy and let the system run at half load when it could or when you desired....two thermostats.  Just spit ball'n here.

John
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« Reply #10 on: April 06, 2009, 10:42:30 AM »

Thanks John and Nick..   I'll get the tag off the compressor to let us know that specs for BTU output for the OTR compressor.

So what I am following is..  Nick you only have 30K BTU worth of cooling when parked.  You didn't raise your roof did you on your 102?

I have another question?   Has anyone installed makeup air into there basement air.   Many moons ago when I was in high school I worked as a tin bender and if you installed a mod motor/damper you would bring in outside air into the return air system.   This fresh air would pressurize the enclosure.   I would think that bringing in fresh air at 5% would be a good thing.   Nick did you do that?
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« Reply #11 on: April 06, 2009, 10:43:47 AM »

Hi John,

The bus compressors are usually 11 tons capacity. I was referring to automotive/car types which are about 5 tons.

Nick-
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« Reply #12 on: April 06, 2009, 10:55:44 AM »

Hi ZC,

Yes, I have 2 1/2 tons when parked and it is plenty for keeping the inside at 70.  And by the way, it only takes 1 HP in the winter weather to maintain 70 deg.

until the temps drop below 30 deg outside ambient. At that point, my proheat with a hydronic coil in the air return kicks in.

I didn't raise my roof but I lowered my ceiling and over insulated in the area.

I didn't install make-up air because most busses have too many air infiltration leaks allready...  doors, windows, compartments, ect..

Nick-

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« Reply #13 on: April 06, 2009, 12:58:13 PM »

I have 3-13,500btu/hr Colemans with a 40ft transit that has 2.25" of blown in insulation.  I have yet to have a situation (I've been in up to 107 degree weather) where the roof airs weren't enough.  Driving down the road, I usually only use the front and back, and use the middle one when parked.  Roof tops are the cheapest and easiest to use.  Although, I'm going to use the Duo-Therm basement airs of 15,000btu/hr each that I've found at $970.00 ea including thermostat at WWW.ADVRV.com.  Good Luck, TomC
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