| [GMCnet] Attwod air conditioner [message #274372] |
Thu, 26 March 2015 07:36  |
Advanced Concept Ener
Messages: 112
Registered: December 2014
Karma: 0
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Senior Member |
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I hate to pontificate ( maybe not) but proper sizing for one AC unit does not exist unless you have a variable speed compressor and fans. Air conditioning is for comfort. Comfort is a function of temperature and humidity as defined by Dr Carrier when he defined the psychometrics of comfort. Coils only remove humidity when they they have refrigerant is running through them. When the compressor cycles off the humidity jumps up and it takes time for the humidity to be pulled down after the compressor restarts. When relative humidity cycles your body can't respond quick enough to feel comfortable. Trying to hold the temperature lower requires much more humidity removal to maintain RH. The lower the humidity in the coach the faster moisture from outside comes into the coach from every nook and cranny. The size of the AC unit requirement goes up exponentially as the temperature inside the coach gets lower. If you really need it lower than 80 deg and 50 % RH in the coach than run a
second AC or even a dehumidifier. Cycling AC units will result in lower comfort levels. Been doing this for 45 years and am considered an expert on a national level and have numerous patents based on humidity temperature control. This is not hearsay it is physics and thermodynamics combined with 45 years hands on experience. My house has an AC system 20% undersized and a window shaker that I start that 5% of the time that we get full load conditions.
Jon Darcy ACES
North Jersey 76 stretch, flares, 4 bag, Alcoa's, bunkhouse,MAC Dash
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| Re: [GMCnet] Attwod air conditioner [message #274401 is a reply to message #274372] |
Thu, 26 March 2015 15:38  |
Chr$
Messages: 2690
Registered: January 2004
Location: Scottsdale, AZ
Karma: 1
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Well Put, Jon.
I switched from a marginal 5 Ton to two 3.5 Ton units on my 2600 SQ Ft house in AZ. The smaller units run longer when it is 110* outside and I get much more comfort. The 5 ton ran 24/7 from the end of may to the middle of sept, but it also didn't keep the comfort level very high. Ductwork was the major issue.
We also alternate which one runs (bedrooms at night, living space during the day) which makes a difference on the electric bill, about 20% lower. When these Lennox Package units die, I'm going with Mini Splits.
Undersizing a bit increases the run time and makes a huge improvement in comfort level.
My GMC had two 15K units. I now have moved one of those to my similarly sized travel trailer, and the one does fine. The GMC needed two even with all the insulation I added... Regardless of outside temps, I have never been comfortable in a GMC with one roof air. The solar gain is tremendous.
-Chr$: Perpetual SmartAss
Scottsdale, AZ
77 Ex-Kingsley 455 SOLD!
2010 Nomad 24 Ft TT 390W PV W/MPPT, EV4010 and custom cargo door.
Photosite: Chrisc GMC:"It has Begun" TT: "The Other Woman"
[Updated on: Thu, 26 March 2015 15:38] Report message to a moderator |
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| Re: [GMCnet] Attwod air conditioner [message #274407 is a reply to message #274372] |
Thu, 26 March 2015 18:26 |
Joe Weir
Messages: 769
Registered: February 2013
Location: Columbia, SC
Karma: 7
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Senior Member |
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Advanced Concept Ener wrote on Thu, 26 March 2015 07:36I hate to pontificate ( maybe not)...
Go for it, man
Quote: My house has an AC system 20% undersized and a window shaker that I start that 5% of the time that we get full load conditions...
LOL. The window shaker in our bedroom is the only reason that last ac guy is still alive...and it is not me he needed to fear... 
We have summer like you have winter. So the full load conditions here are from May to September. When it is not over 100 it feels like it. You really gotta hate snow to live here.
In my experience, I think your average AC guy does not understand that finer nuance of comfort as you so eloquently detailed it. Instead we get the Father Guido Sarducci 5 minute university version. "Bigger is not better" "20 degrees below outside is all it will do". While both those statements may be true, they are not the whole truth.
I know full well if the ac guy goes home to an 80 degree humid house in the heat of a South Carolina summer he is either single, is going to be single soon, or is married to a masochist.
Just saying.
76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator, brakes, Sully airbags, fuel lines, seats, adult beverage center... those Coachmen guys were really thinking about us second hand owners by including that beverage center...
Columbia, SC.
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| Re: [GMCnet] Attwod air conditioner [message #274409 is a reply to message #274401] |
Thu, 26 March 2015 18:43 |
Joe Weir
Messages: 769
Registered: February 2013
Location: Columbia, SC
Karma: 7
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Senior Member |
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Chr$ wrote on Thu, 26 March 2015 15:38Well Put, Jon.
I switched from a marginal 5 Ton to two 3.5 Ton units on my 2600 SQ Ft house in AZ. The smaller units run longer when it is 110* outside and I get much more comfort. The 5 ton ran 24/7 from the end of may to the middle of sept, but it also didn't keep the comfort level very high. Ductwork was the major issue...
...Undersizing a bit increases the run time and makes a huge improvement in comfort level
Ah, but you didn't downsize. You went from 5 tons to 7 tons (3.5 x 2) of capacity. The smaller units run longer, but not 24/7, which in my novice mind is a sign the unit has maxed out.
76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator, brakes, Sully airbags, fuel lines, seats, adult beverage center... those Coachmen guys were really thinking about us second hand owners by including that beverage center...
Columbia, SC.
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