Low voltage Air Conditioning [RE-wrenches]

Tue Apr 22 17:19:40 PDT 2008

Thank you all for the responses. 

APU's are very costly. RV, camper rooftop AC units are 13,000 BTU, 120 VAC and very noisy. The DC compressor based systems I have found are over priced. Peter, evaporative cooling would be great here in Yuma with our 6% humidity. However, the trucker spends many days in Texas and the central states; very high humidity so water removal is key to comfort.

It looks like I will have to install an inverter. I can use a mini split AC that draws 700 watts. It provides 9000BTU of cooling, too much for the sleeper space but it's the smallest I can find and it's very quiet. 

 8 hours of continuous operation is 5.6 kWhr. 80% on time is 4.5 kWhr. Four 8D's are about 12 kWhr. A 1500 watt (Invertek) inverter efficiency is 88% at 50% load. So, the batteries will average about 50% DOD in 8 hours. The truck will be started and run for 11 to 14 hours The batteries will fit easily and the mini split bolts to the back wall of the sleeper. If he buys, I'll let you all know how it works out.

Larry Crutcher
  ----- Original Message ----- 
  From: Travis Creswell 
  To: RE-wrenches at topica.com 
  Sent: Monday, April 21, 2008 10:18 AM
  Subject: RE: Low voltage Air Conditioning [RE-wrenches]

  Hello Larry,

  You mention a "small diesel generator".  Are you talking about an Auxiliary
  Power Unit or a generator?  APU's are becoming really popular on trucks from
  what I've seen.  They are generators and air conditioners so they take care
  of two birds with one stone.  Here is an example of one.
  http://www.rigapu.com/index.php  I have no affiliation with them, it's just
  the first hit on Google (who I also have no affiliation with).  They "comply
  with strict idling laws" so I would assume they are allowed.  I'm sure it's
  pricey but so are all those batteries.  By the way, where are you planning
  to put 18kWh worth of batteries?  That's ~8 L-16's or ~14 T105's by my math.
  Plus that weight results in that much less freight he can carry which might
  be a deal breaker all by itself.

  According the specs; 20,000 BTU of cooling capacity, 6kW generator and 60
  amps of DC output, .3 gallons per hour at full load.   Hmnn...these could be
  a solution for off gridders that wanted/had to have air conditioning. (No
  comments needed from the efficiency peanut gallery, please)

  Best,
  Travis Creswell
  Ozark Energy Services

  -----Original Message-----
  From: Larry Crutcher, Starlight Solar [mailto:larry at starlightsolar.com] 
  Sent: Monday, April 21, 2008 11:27 AM
  To: RE-wrenches at topica.com
  Subject: Re: Low voltage Air Conditioning [RE-wrenches]

  Wrenches,

  I did not get a response to my post from last week. I know most of you do
  not work with battery based systems but is there anyone here that can offer
  some experiential advice about low voltage air conditioning? 

  Thanks again,
  Larry Crutcher
    ----- Original Message ----- 
    From: Larry Crutcher, Starlight Solar 
    To: RE-wrenches at topica.com 
    Sent: Thursday, April 17, 2008 11:30 AM
    Subject: Low voltage Air Conditioning [RE-wrenches]

    Does anyone have experience with DC air conditioning equipment? I have a 
    customer with a semi truck and wants a roof air for the sleeper.  Many 
    truck stops now forbid engine idling for more than 5 minutes so they can 
    not use the cab air. 

    A small diesel generator is one solution but the trucker is not sure if 
    some truck stops may forbid that as well. Since the truck engine is only 
    off for 10 hours or so, it looks like 18kWhr of battery @ 50% DOD  will 
    operate the A/C load until the engine starts again. 

    Some customers in Mexico are running mini-splits successfully but I 
    don't want to add the complexity of an inverter if there is a low 
    voltage DC solution.

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