re: evaporative cooler question
15 jan 2005
>> moving lots of air wastes water and electricity.
>why do you say that? they use relatively little water - only that which is
>evaporated and a bit more if some is bled off.
"evaporative cooler water use" by martin karpiscak and mary h. marion at
http://ag.arizona.eduj/pubs/consumer/az9145.pdf cites a survey showing
an average water usage of 7.6 gph, which seems like a lot compared to the
7.6 gpd below. and these things have 1/2 to 1 hp motors.
>>a las vegas homeowner might do better with sam's portable 797895 arctic
>>breeze cooler mounted inside a house near an open low window and
>>an exhaust fan in a higher window with a one-way plastic film damper.
>you can't recycle the air in the house. you have to get rid of the moist
>air as it will not cool.
that's what the exhaust fan does, controlling the indoor rh precisely with
a humidistat, vs a swamp cooler without a humidistat.
>>turn on the cooler when the house temp reaches 80 f and turn on the
>>exhaust fan when the rh reaches 60% to keep the house air at the upper
>>right corner (80 f and w = 0.012) of the ashrae 55-2004 comfort zone.
the 80 f comes from a room temp thermostat.
>your house would be like a steam bath.
i disagree, as do 21,000 ashrae comfort survey participants.
>the maximum cooling is when the humidity is very low. once it gets to
>30% cooling becomes marginal.
you are thinking about the air outside vs inside the house.
>> keeping that house 80 f while evaporating p lb/h of water into c cfm of
>> outdoor air means 1000p = (91.1-80)(128+c). p = 60c(0.075)(0.012-0.0066)
>> = 0.0243c makes c = 108 cfm and p = 2.62 lb/h, ie 7.6 gallons per day.
>> if the house has significant thermal mass (eg a floorslab), we can save
>> more water and energy by only running the cooler at night.
>> why do we need 5000 cfm???
air-leaky houses with no insulation, poor controls, ignorant owners and
hvac criminals? :-)
it's a snap to save energy in this country. as soon as more people
become involved in the basic math of heat transfer and get a gut-level,
as well as intellectual, grasp on how a house works, solution after
solution will appear.
tom smith, 1980