[Tfug] *Way* OT: Swamp coolers, ACbrrs, etc.

[Bexley Hall]

--- Jeremy D Rogers <jdrogers at optics.arizona.edu>
wrote:

> > if (outdoor_temp > indoor_temp + 25)
> >    dont_use_cooler;
> 
> You need to factor in humidity. I would say
> something more like:
>  if (outdoor_temp > indoor_temp + 25 | humidity >
> 50%)
>     dont_use_cooler

Yes, sorry -- I was just giving a 0-th order
assessment to show an example.

 
> Or better yet something like:
> if (outdoor_temp < 80)
>    break
> elseif ((outdoor_temp - 80) / (1 -
> percent_humitidy/100)^2 > 30)
>    use_cooler
> else
>    use_ac

You can actually measure dewpoint directly (typically
using a chilled mirror sensor -- or, compute it from
RH and temperature).  From that, you can do the thermo
to figure out how efficiently you can move heat into
water vapor, etc.

But, it *still* sucks as it only looks at a snapshot
(i.e. does it make sense *now* to turn the cooler on)
and not a practical assessment that takes into
consideration what is likely to happen in the
"near future" (i.e. will the outdoor temp rise
so much that the cooler should eventually be turned
*off*?  Then, further cooling would have to come
at the expense of using the ACbrr -- which now has to
remove all of that moisture from the air, etc.

> That keeps you on cooler up to about 105 if the
> humidity stays under
> 10%, but quickly drops the bar as humidity rises.
> I'm sure there would
> be a better way based on equations that describe
> evaporation rates,
> conservation of energy, pv=nrt, etc, but I'm way to
> lazy to think that
> hard about it right now. Also, your cooler may need
> tweaking of the
> cutoff temp and humidity exponent, but mine was
> great well into the
> hundreds as long as the humidity was low. It was

Exactly.  But, even during "summer" (vs. "monsoon")
the humidity can vary substantially.  And, the cooler
must run *continuously* to maintain a comfortable
temperature once it gets 105+ outside -- OTOH, the
ACbrrr can cycle to maintain that temperature since
it recirculates air instead of reintroducing outdoor
air, etc.

> monsoon season that killed it.



       
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