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re: swamp cooler to refrigeration a/c
9 apr 2006
abby normal  wrote:

>>> >>we tried out your split-cycle swamp cooler idea a couple of nights ago
>>> >>using a jerry-rigged humidistat using a sht11 and a computer to control
>>> >>the exhaust fan, and the brains of a commercial refrigerative split-cycle
>>> >>system for the swamp cooler.  we closed all the windows (against standard
>>> >>practice with swamp coolers) and ran the swamp cooler to a fixed temp
>>> >>(22c) and the humidistat to a fixed humidity (65% at your suggestion).
>>> >>that night it was 28c and 35% outside.
>>> >
>>> >>it was very effective.  it would shut off for maybe 10 minutes, then run
>>> >>for 2.  the fan didn't always come on, making me suspect that the vapour
>>> >>was leaking out other ways.
>>> >
>>> >>i discussed it in the tearoom the next day (we have our own little frugal
>>> >>living research group who meet in the tearoom in csse.monash.edu.au) and
>>> >>people were surprised it worked, but i did the maths on the whiteboard
>>> >>and they were sold...
>>>
>>> >... it sounds like the ozzies were just pressurizing the house then and
>>> >letting it 'efiltrate out' where ever it could and exhaust fans turned
>>> >on when humidity hit 65%.
>>>
>>> there was no pressurization.
>>>
>>> >does not sound like your 'humidify the indoor air scheme' and turn on
>>> >the exhaust fan at all...
>>>
>>> no. it was exactly the scheme i suggested.
>>
>>i just don't see the part where the ozzies mentioned recirculating air.

an indirect clarification from the ozzie:

  ok, i've read the posts on this newsgroup, and i do have to wonder about 
  the sort of people who have time to pointlessly argue and flame each other 
  but not enough time to learn the basic physics about their topic of 
  interest.  i'm certainly not interested in posting directly to the group.

> just to be sure, the swamp cooler was entirely inside the house, adding
> water to indoor vs outdoor air, right?

  that's correct...

  we have a 'closed room' with an evaporative cooler in the room.  a duct 
  taped box fan sits in the window and is run whenever the humidity rises 
  above 60%.  conceptually it is the same as forcing the air into the house, 
  except that it is demand driven, which seems to make it more efficient. 
  the room also seems to cool down faster, as we use the existing somewhat 
  cooler air for cooling first, and perhaps we heat exchange the air with 
  the walls and doors as fresh air leaks in.

two potential improvements: 1) exhaust house air to an attic ("upducts")
or some other cavity bordering an exterior surface, eg a garage or sunspace
or storage space, and thereby reduce the usual conductive heatflow from
the warmer outdoor air into the living space, or 2) use a humidistat and
a reversible fan like lasko's $55 2155a 16" window fan (90 watts at 2470 cfm
on high speed) and grainger's 2a179 $88.15 programmable cycle timer and
its $4.37 5x852 octal socket to periodically reverse the fan direction when
it needs to run, making a "shurcliff lung" that turns all the cracks and
crevices in the house envelope into bidirectional air-air heat exchangers.

we need to get rid of moisture vapor, but it's more efficient to do that
using cooled vs uncooled outdoor air. for optimal ventilation, run the fan
long enough to actually move some outdoor air in through the wall cavities
(vs moving a smaller amount of cavity air back and forth), but not so long
that the wall thermal mass heats all the way to the outdoor air temp on
the intake cycle. 

>> this works in melbourne australia...

> few use swamp coolers there.

  what complete crap (do you normally spout unsubstantiated rubbish?). 
  evap coolers outsell heat pumps about 3 to 1 i'd be guessing.  every new 
  house seems to come with a roof mount evap cooler.

> not in melbourne they dont.

  i wonder whether people are thinking of melbourne, fl.
  (perhaps these illiterates don't actually read before posting.)

> double check the facts because the comment about closing windows
> against standard practise really makes it sound like they were
> pressurizing.

  any time you move air around you are creating a pressure difference.
  i'm not sure what you are claiming here.

i believe abby was thinking the swamp cooler was trying to push outdoor air
into the living space vs recirculating indoor air, ie "pressurizing" the
living space. but the exhaust fan would depressurize the living space... 

  the reason the windows are closed is because extra air coming in through
  an open window would simply add more heat, which we would have to remove.
  once we are cooling enough to overcome infiltration extra air has no
  long term benefit.  commercial systems attempt to overcome this with
  a very big blower.  blowers are inefficient and noisy.

nick




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