absorption air conditioning [RE-wrenches]

[Jeffrey Wolfe, Global Resources]

Maybe it's just my big building background, but I hate window AC units. 
Inefficient (even SEER 11, which is excellent for a window unit, looks 
pretty shoddy next to SEER 18), noisy, and full of maintenance. I also 
would be careful with the 1000 SF number for area cooled. That's 750 SF per 
Ton of air conditioning (1 Ton = 12,000 BTU, it's a common term in AC). 
Offices (Yes, standard inefficient ones) are usually 300 to 400 SF per ton. 
Houses are less, but it highly depends upon the amount of ventilation air 
(either leaking in or purposefully introduced). And if the ventilation air 
is humid, the numbers go up fast. So the 1000 SF may be possible in a shop 
that is much less loaded than an office, but expect some compromises (which 
may be perfectly acceptable.)

You are right that on a per energy input basis, vapor compression systems 
are much more efficient than absorption units. the only time absorption 
really makes sense is when some "waste" heat source is available at a 
decent temperature (above 190 deg F for typical purposes). Off-grid though 
it is much less expensive (until propane costs equal the cost of PV power, 
maybe next week). You window shaker unit would use about 5 - 8 kWh per day, 
depending unpon how much space it's cooling, etc. This is more than *most* 
of the off grid house we do use for everything. Certainly there may be 
extra energy in the summer, but on most of the systems we see around here, 
this means the generator runs less, not that they have excess power to 
burn.

Anyone who's looking to do larger system AC, definitely look into 
geothermal standing water column systems. SEER's of up to 30 are truly 
available. The other side of the AC is the fan operation. Radiant cooling 
can greatly reduce the need for this. I'll stop now before I get anymore 
boring....

Jeff


I am shopping around for a window unit for my new shop.  Without any
difficulty I found a 16,000 BTU,11 SEER unit at, you guessed it, Home 
Depot.
11 SEER is excellent for a window unit.  Most are somewhere in the range of
8 to 9 SEER.  I'm thinking it stated 12 amps @ 120 vac but I would need to
confirm that.  Assuming the 12 amps is accurate then its going to use
something under that during normal operation.  I'd say 10 amps or 1200 
watts
would be a very safe number.  16,000 BTU would cool down a well insulated,
somewhat open 1000 ft2 with no problem.  You can also step down to window
units as small as 5000 BTU.

Also, I have seen a outdoor unit with a SEER of 18.  I'll email the
manufacturer and see what kind of load it pulls in a 2 and 3 ton unit.


Travis Creswell
Ozark Solar

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