Article 1168 of sci.engr.heat-vent-ac:
From: ghg@cidmac.ecn.purdue.edu (George Goble)
Message-ID: <3ue99k$8el@mozo.cc.purdue.edu>
Newsgroups: sci.engr.heat-vent-ac
Subject: Re: AC doesn't work when it's _HOT_ outside!
Date: 17 Jul 1995 18:14:12 GMT

In article <3ue0d8$772@vu-vlsi.ee.vill.edu> reynolds@vu-vlsi.ee.vill.edu writes:
 >I'm a person who likes COLD things-- cold weather, cold beer, and COLD 
 >air-conditioning.
 >
 >I'm curious to know why my 12x12 room "isn't air-conditionable" (told to 
 >me by customer service "professional"), at least not to my standards.
 >
 >My idea of AC isn't something that reduces outside temperature by 20 
 >degrees(F)-- coming into an 85deg. room after a day in 105+deg. sun isn't 
 >exactly my idea of comfort. My idea of AC isn't something that works 
 >worse as the temperature goes up-- it should be most effective on very 
 >hot days, when I want the cold air most. My idea of a "temperature" dial 
 >is not a thermostat(shuts the unit off at a certain temp)-- when I turn 
 >the dial down, that means I want COLDER air coming out. My idea of AC 
 >isn't something that blows out 65deg. air for hours and hours trying 
 >unsuccesfully to cool a 120+deg. room.
 >
 >Imagine if freezers worked the same way as window air-conditioners? 
 >"Sorry, Mrs Jones... you can't expect your ice cream to be kept solid 
 >when it's so hot outside. Buy a bigger freezer, maybe that will work." 

During the 120F Heat-index heatwave, many Lafayette, IN restaurents
had hot "cold" food, melted cottage cheese and icecream..
Kitchen temps were around 130F.


 >That's essentially the line I'm getting from the service people. They 
 >just don't seem to understand that I want my room kept coldest on these 
 >hot days. They say that's not how a/c's work-- they don't necessarily 
 >make a room cool, they only make it coolER than it is outside. Blah!
 >
 >So, anyway... I have this new Carrier 6100 BTU window unit. I'd like it to 
 >cool a 12x12 room TO MY LIKING. They say this unit will never do the job, 
 >and no "fix" can be made to make it do so. Is this right? Can't they pump 
 >it up with a different (colder) freon? And do something to the fan so it 
 >shoots out more air?
 >
 >Why is it that I can sit in the blazing sun with my car a/c on and have 
 >it pump out 25deg. air, yet my window a/c that's in the shade dispenses air 
 >that's nearly 3x as hot?
 >
 >What do BTU's have to do with the price of apples? This new 6100 BTU a/c is 
 >replacing a smaller 5000 BTU unit. Those 5000 BTU's would freeze people 
 >out of the room, but now 6100 BTU's can't even keep the room comfortable. 
 >What gives? Do BTU's refer to temperature, or just some air displacement? 
>
>Enough griping... Does anyone have any suggestions on what kind of a/c I 
>should buy? Commercial a/c's in stores freeze people out, why can't I get 
>the same perfromance from a smaller window unit?
>
>Jim. (about to move to Alaska)

There are two kinds of heat load, called "sensible" heat
(the temperature), and "latent" heat, which is generated by
the removal of humidity.  High humidities make people feel
"clammy" even if the temp is ok.. High humidities also reduce
the sensible (real temp) cooling capacities of units.

To make matters worse, newer is not always better..There have been
a steady stream of "efficiency" gov't regulations which are forced
on new A/C mfgrs.  They must achieve higher and higher "SEER's"
(measure of energy efficieny) as time goes on...

One common way to comply with these regs is to raise the
evaporator temp (the inside cooling coils) to be 55F or higher.
This results in moving the SAME BTUs of heat with less electricity
or a few more BTUS of heat with the same electricity., So the 6100
BTU unit is probably just the 5000 BTU unit redesigned for higher
inside coil temps.

Here is the rub.  By raising the cooling coil temps, good cooling
efficiency is achieved, but humidity removal goes to zip.
To get good humidity removal, one needs a "lower" efficiency
(older unit), which runs the cooling coils near 32F, not 55-60F
to get the humidity out. Usually, an older unit (properly cleaned
and serviced), will cost only a few bucks more per month, but
will do one hell of a job on the humidity as well.

In some cases a new "high efficiency" unit may actually cost more
to operate than an older unit under humid conditions, since
humidity removal is poor, and thermostat has to be set lower to
achieve comfort..

Good humidity removal also depends on sizing the unit correctly,
so it cools enough and still runs most of the time.  A too large
unit will only run 1/2 time or less and not do a good job on
the humidity.

If I were you (and assuming you live in a humid area), I would get
rid of your 6100 BTU unit

Get a used 12,000 BTU (cleaned and in good shape) unit and an
older 5000 BTU unit.  When you come home to a hot room, turn 'em
both on (17,000 BTUs), and then shut one of them off, so that
the one which is on runs most of the time to keep the humidity 
down.

Car A/C's are rated 3 or 4 "Tons" in capacity, 1 ton = 12000 BTU/hr.
So you have roughly 50,000 BTUs/hr in a car..

Window units use R-22 refrigerant, which does only 1/20 of the
ozone damage as R-12 (in cars), and R-12 is on it's way out.

Using refrigerant "blends" it is possible to increase cooling
capacity and efficiency, and greatly reduce the "pull down"
time (time to do initial cool down when hot).
I invented two such blends (replacements for R-12).
One is R-406A and it will be legal for cars starting Sept 18,1995.
It is EPA SNAP approved for stationary uses now.
A 2nd (no R-number assigned) blend has also been tested for a
time "called GHG HP" for now.

My car, a 1990 Pontiac transport, at 100F outside, R-12 puts
out 56F air.  R-406A does 42F air, and "GHG HP" does 28F air
(on the highway), and 35-38F air in the city. But the latter 
blend pushes the system harder, higher pressures, etc.
90F outside, raining (100% humidity), GHG-HP achieved 30%
cabin humidity in 4 mins during a 1991 test.  Some cars
require a "defrost" timer (under design now) to off the 
compressor for 10 sec every 4-5 mins to keep it from
freezing up. Like you, I hate hot humid air and am trying
to do something about it.

--ghg (Inventor R-406A and GHG-HP refrigerants)
http://ghg.ecn.purdue.edu
http://worldserver.com/R-406A