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Author Topic: Very efficient air conditioner  (Read 4785 times)
Jerry Liebler
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« on: May 26, 2006, 04:00:07 PM »

Since I really need more cooling in the front of my bus, I've been shopping for efficient ductless mini split air conditioners.
I think I've found a winner but it's not cheap at about $1500 delivered and I'll need to put a transformer in front of it because they only come in 240 volt.  But for a 12000 BTU/h heat pump with a SEER of 17 I'll end up only drawing 5.9 Amps oif 120  (705 watts).  I just checked Ebay for suitable transformers and there are a couple with buy it now prices of $40 or less.  Has anyone else considered the Mitsubishi MSZ A12 NA ?
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Jerry 4107 1120
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belfert
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« Reply #1 on: May 26, 2006, 05:19:13 PM »

What reason for needing the low amp draw?  There are a number of 12,000 BTU mini-splits that are 110 volt and cost about 1/3 as much.

Brian Elfert
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Jerry Liebler
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« Reply #2 on: May 26, 2006, 05:35:43 PM »

Belfert,
     I have a couple of reasons for high efficiency.  One is that I can only count on  about 1800 watts from my inverter while driving, Another is to run as much AC on limited shore cord sizes.  It's real easy to find a 15 amp hook up when I'm visiting a relatiive or friend. 
Regards
Jerry 4107 1120
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Nick Badame Refrig/ACC
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« Reply #3 on: May 26, 2006, 05:46:50 PM »

Jerry,

If I'm not mistaking, doesn't the 230v model draw 5.9 amps on each leg?  that would add up to 11.8 draw from your transformer!

than you would be better off with the 115v A/C

Nick-
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Jerry Liebler
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« Reply #4 on: May 26, 2006, 06:15:07 PM »

Nick,
     I never found an actual current draw.  What I did was Divide the BTU/h by the SEER to get watts 12000/17 = 705. Then divide watts by 120 volts  or 705/120= 5.88 amps from the 120 source.  The 240 volt current would be 705/240=2.94 amps.  These of course are the averages under the conditions for the SEER rating. and don't allow for the 3 or 4 watts or so that the transformer would need.
Regards
Jerry 4107 1120
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Nick Badame Refrig/ACC
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« Reply #5 on: May 26, 2006, 07:05:42 PM »

Jerry,

Here is a conversion table I found,

watts
To convert from watts to:

Btu/hr, multiply by 3.4129.
Btu/min, multiply by .05688.
erg/sec, multiply by 107.
foot-lbs/min, multiply by 44.27.
foot-lbs/sec, multiply by .7378.
horsepower, multiply by 1.341E-03.
horsepower (metric), multiply by 1.36E-03.
kg-calories/min, multiply by .01433.
kilowatts, multiply by .001
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belfert
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« Reply #6 on: May 27, 2006, 04:08:20 AM »

You also need to include some amps for the evaporator and condenser blowers.  This unit could easily run on 110 volt like most 12,000 BTU mini-splits.  Make sure this unit isn't 230 volt 50Hz for Europe.

Brian Elfert
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« Reply #7 on: May 27, 2006, 06:48:40 AM »

Belfert,
     I have a couple of reasons for high efficiency.  One is that I can only count on  about 1800 watts from my inverter while driving, Another is to run as much AC on limited shore cord sizes.  It's real easy to find a 15 amp hook up when I'm visiting a relatiive or friend. 
Regards
Jerry 4107 1120

Is your inverter output pure sine wave or modified square wave (like most cheaper inverters)?
A typical step-up transformer, or your high efficiency AC may or may not function correctly with a modified square wave type.
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TomC
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« Reply #8 on: May 27, 2006, 08:16:33 AM »

Although buses ride very smoothly, the unit you are looking at is probably a land based unit.  Meaning no consideration has been made for vibration and twisting naturally occuring while going down the road.  Highly recommend you look into units made to go over the road, rather than so much emphasis on high efficiency.  What good is having a high efficiency unit if your spending money on the unit to keep it running?  Not to mention the fact that when it goes you'll be exhausting the freon from the unit. All freons are bad for the environment-just some are less than others.  Highly recommend you go to www.tundra.cc and look at the split units made for the trucking industry.  These units have been designed for severe vibration and alot of miles to be able to live in the trucking industry.  I know that if these units were out 12 years ago when I was designing my bus, I would have used it instead of the roof models.  I'm still contemplating using one for quiet nightime use since my Colemans aren't exactly what I would call having a quiet low speed fan-although they work great and haven't had any problems with the three roof tops since I intalled them 11 years ago.  Good Luck, TomC
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« Reply #9 on: May 29, 2006, 06:51:51 PM »

I am wondering how you would run a 220 unit on a 15amp 110 hook up

I have been looking into a split system as well (Thanks TomC for the info) for dash cool going down the road and the bedroom when you are trying live on the FAMOUS relatives extension cord.

Let us know what you find out.

Melbo
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« Reply #10 on: May 30, 2006, 06:00:39 AM »

For anybody who likes to experiment

Walmart has a little "Window Shaker' 6000btu @ 5 amps for 96.00 that you could split and have a little science project without to big an investment.

Cliff
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DrivingMissLazy
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« Reply #11 on: May 30, 2006, 06:09:24 AM »

I am wondering how you would run a 220 unit on a 15amp 110 hook up
Melbo
You would need a 120 volt to 240 volt step upl/down transformer. The amps at 120 volts would be double that of the 240 volt rating.
FYI, auto transformers are less expensive but are not really designed for this application.
Richard
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« Reply #12 on: May 30, 2006, 07:27:20 AM »

I too go for “split-air-condition” system….higher efficiency to avoid cooling long-duct system.

First of all…..all electric motor equips appliance or whatever need “starting” amperage which usually 1/3 to 2/3 higher than “running” amperage.

So if it require 5.9 amp running mean it need at least 11.8 of available current at air condition’ compressor unit before it will accelerate fast enough to be in run mode……otherwise automatic circuit-breaker will pop until cool-off.

Now to use “step-up” transformer….primary need to handle double of “240 volt” current draw…which is 23.6 amperage at 120 volts. Suggest going for 30 amps to allow heat-resistant or already warm-up winding from previous shut-off cycle to be on the safe side.

However transformer produce heat….it need to be cool via fan or very good stand-still venting system.

Transformer will break-down due vibration and higher than design incoming “spike-voltage”. Not counting possible “buzzing” noise due to lamination problem.

Talking about “efficiency”…this back-ward way to begin with. All out side source come from very high voltage line to be reduce via oil-cooling transformer to single phase 240 (2 – 120v lines)…go thorough extra heavy wiring to handle current to MAINTAIN require wattage to run whatever to meet your satisfaction.

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Jerry Liebler
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« Reply #13 on: May 31, 2006, 06:41:58 PM »

SEER ratings are very misleading as they do not reflect actual operating conditions. Good old EER or actual amp ratings are desireable.  I found another candidate.  I haven't found a price yet but it looks quite interesting, it is the Fujitsu 12RLQ.  This is another 240 volt unit but it's rated curent while delivering 12,000BTU is 4.5amp at an EER of 13.5 or 889 watts and it's maximum curent (while delivering 14,500BTU) is 7 amps.  I'd use a 1 kva+ 120 volt isolation transformer to supply the other half of the 120/240.  Fujitsu has another interesting candidate in the 12RQ it is 120 volt but doesn't have the 'overload' capability to do 14500 BTU, it's 12,000 BTU, draws 9.9 amps and 1070 watts.
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Jerry 4107 1120
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Buffalo SpaceShip
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« Reply #14 on: May 31, 2006, 11:43:27 PM »

Not to hijack this thread, but since I already have a genset in the old coach A/C condensor compt., where would I put the compressor part of a mini-split system... cut a hole in the side of a bay door or floor?

Just curious... in case I decide to add one to my rig.

Thanks,
Brian Brown
4108-216 w/ V730
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Brian Brown
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