Anthony Matonak said:
...
I can't help with you actual question. I can suggest that you can
find window air conditioners much cheaper than $300. A quick web
search found me a number of 10,000BTU units for around $220 which
is claimed to be enough for 400+ square feet.
They are power hogs but they will work regardless of the humidity.
The $298 Mastercool Mobile MMB10 (Grainger 5MU36) has a garden hose
connection and draws 3.5 amps at 120 V. Adobe Air says it can cool
2000 cfm of 110 F 10% RH air 32 F, about 69K Btu/h (6 tons), like 14
5K Btu/h window air conditioners
An airtight 20'x20' room with no internal heat gains and 1040 ft^2 of
R11 walls and ceiling and 1040ft^2/R11 = 95 Btu/h-F of conductance at
80 F on a 100 F day would only need (100-80)95 = 1900 Btu/h of net
cooling. Air at 100 F and 10% RH has humidity ratio wo = 0.004 pounds
of water per pound of dry air, vs wi = 0.012 for 80 F indoor air at
60% RH. If we evaporate P pounds of water per hour and ventilate with
C cfm of outdoor air at 0.075 lb/ft^3 and P = 60C0.075(0.012-0.004),
C = 27.8P. If 1000P = 1900+(100-80)C = 1900+556P, P = 4.3 and C = 119,
so an MMB10 might run about 100x4.3/69 = 6% of the time and a $55 Lasko
2155A 16" 90 W 2470 cfm window fan would only run 100x119/2470 = 5%
of the time, just coasting
Exhaust air might leave the room via
the attic, to keep the room cooler.
For more cooling capacity with dry outdoor air, we might put an MMB10
(or its MMB8 younger brother) in a box near a window inside a house
with a Lasko intake fan in the window and use the fan thermostat
to turn on the cooler when the room temp rises to 80 F and a humidistat
to turn on the fan when the indoor RH rises to 60%, with 1-way plastic
film dampers in a box between the cooler and the window to force
outdoor fan air to flow through the cooler pad when the fan is running
and make indoor air flow through the cooler when the window fan is not
running, like this, viewed in a fixed font like Courier:
left | |
| |
---------
| |llld| |
|c| d| | outdoors
|o| d|f|
<==|o| d|a| <== With the window fan off, indoor air
|l| d|n| would flow in through left and right
|e| d| | dampers lll and rrr. With the fan on,
|r| d| | damper ddd would open and the fan air
| |rrrd| | would force lll and rrr closed.
---------
| |
right
We might have 4 modes:
80 F >60%| window fan cooler fan cooler water
--------------|-----------------------------------------------
1. no no | off off off
2. no yes | on off off
3. yes no | off on on
4. yes yes | on off on
Case 3 would maintain indoor comfort with less water than an external
swamp cooler, for a house with significant natural air leakage, ie
for almost all houses.
Nick
