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Posted by Ecnerwal on April 21, 2006, 12:03 pm
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> Are you saying that the act of drawing the moisture out of the air uses more
> energy?
It does. Condensing water vapor (gas->liquid) causes it to give up the
latent heat of vaporization.
> If I understand what you are saying, a room at 90 deg will be cooled quicker
> and easier by an AC unit if the humidity in that room is low than it would
> if the humidity was high?
Correct.
--
Cats, coffee, chocolate...vices to live by
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Posted by RoyJ on April 21, 2006, 2:04 pm
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Dave Lyon wrote:
>>In your case, your current AC units are spending a fair amount of time
>>and energy ($$) pulling water OUT of the air.
>
>
> Are you saying that the act of drawing the moisture out of the air uses more
> energy? I was under the assumption that dehumidifying the air was just a
> nice byproduct of running your AC unit.
Taking the water out of the air costs cost 540 BTU's per pound, same as
the heat needed to change water to vapor. So, it takes energy to squeeze
the water out. The reason the AC unit pulls the water out is that once
the coil temp gets down to the dewpoint temp, all the "cold" below that
temp goes into dropping the dewpoint. So if the coil temp could be as
low as 38 degrees and the dewpoint is say 60 degrees, your ouput air
will never get below 60 degrees until you pull some moisture out.
>
> If I understand what you are saying, a room at 90 deg will be cooled quicker
> and easier by an AC unit if the humidity in that room is low than it would
> if the humidity was high?
Exactly right. A 1 ton (12kbtu/h) AC that puts out a gallon of water per
hour is spending 4320 (ie (8*540 )or 1/3 of the cooling capaity to pull
water out. Only 2/3rds left to cool.
Another factoid for your luncheon enjoyment: Your comfort level is much
more a factor of the dewpoint than the relative humidity. It really
comes down to how effective your sweat function is working. At 10F or
20f dewpoint (desert air), any sweat is immediatly evaporated. At 70F
dewpoint, the whole sweat thing doesn't work well (difference between
98F body temp and the dewpoint). Most people feel dewpoint in the 60's
to be "fairly humid" and starting to get uncomfortable. 50's is "nice",
40's is "dry"
What all that says is that pulling the dewpoint down WITHOUT changing
the temp will FEEL cooler. So keep the door closed!!!
Cheers.
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Posted by Dave Lyon on April 21, 2006, 2:10 pm
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>
> Exactly right. A 1 ton (12kbtu/h) AC that puts out a gallon of water per
> hour is spending 4320 (ie (8*540 )or 1/3 of the cooling capaity to pull
> water out. Only 2/3rds left to cool.
>
Thank you. My mind works better with numbers. I have a much better
understanding of the energy needed to cool a room now.
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Posted by Larry Jaques on April 21, 2006, 11:56 am
Please log in for more thread options On Fri, 21 Apr 2006 14:40:06 GMT, with neither quill nor qualm, "Dave
>
>While we're on the subject...
>
>
>My shop is a 4000 square foot metal building with just a little insulation.
That's downright stupid, Dave. It costs -much more- to cool a poorly
insulated shop (year after year) than it does to insulate it properly,
a one-time cost. I'd almost guarantee that you pay more in electric
fees annually for that shop than you would for sheets of insulation.
>I've got 2 residential air conditioning units that keeps it bearable, but
>not comfortable in our Missouri summers. I've heard that our humidity is too
>high to use an evaporitve cooler in this area effectively, but I've always
>wondered how one of those would do in a shop that has two central air units
>running non stop. Would it actually add any cooling? Would it cause my
>equipment to rust? It would sure be cheaper to operate than a 3rd AC unit.
That would be self-defeating. You'd be introducing hot air and
moisture into the air which would then have to be removed by the A/C
units, causing them more work. And yes, it might increase the humidity
enough to cause more tool rust. Don't even think of it.
.-.
Better Living Through Denial
---
http://www.diversify.com Wondrous Website Design
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Posted by Ignoramus12493 on April 21, 2006, 11:59 am
Please log in for more thread options >>My shop is a 4000 square foot metal building with just a little insulation.
>
> That's downright stupid, Dave. It costs -much more- to cool a poorly
> insulated shop (year after year) than it does to insulate it properly,
> a one-time cost. I'd almost guarantee that you pay more in electric
> fees annually for that shop than you would for sheets of insulation.
>
I am tending to say that the most sensible solution with this metal
building would be to have this shed wide open and install some
powerful fans, 1/2 HP or so, and just blow air around to keep the body
cool.
i
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