[Equest-users] evaporation from cooling towers

David Eldridge dse at grummanbutkus.com
Wed Jun 2 10:10:32 PDT 2010


Cooling tower evaporation is going to be directly related to the cooling
load.  Btu's of load in the building will be approximately equal to the
Btu's of evaporation.  There is some sensible cooling at times, especially
if the tower will be operated at lower ambient temperatures.  Chiller kW
is probably not the best report to use, go straight to the coil loads.

The variable that you aren't modeling in the software is the blowdown
which will depend on the cycles of concentration that you operate
at...you'll have to check with the client on what they intend to use, or
verify with existing clients what the levels are.  Three or four cycles
are probably reasonable defaults unless the client can confirm something
higher.

ASHRAE Handbook of HVAC Systems and Equipment has some equations you can
use for evaporation, and once you know evaporation calculate the blowdown.

The handbook also has some suggestions for drift calculations, which is
related to condenser flow as was mentioned, as well as some other factors
that you probably aren't modeling.

David


David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, HBDP
Grumman/Butkus Associates



> -----Original Message-----
> From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-
> bounces at lists.onebuilding.org] On Behalf Of B. Fountain
> Sent: Wednesday, June 02, 2010 11:23 AM
> To: Dahlstrom, Aaron
> Cc: equest-users at lists.onebuilding.org
> Subject: Re: [Equest-users] evaporation from cooling towers
>
> Not that I know of - I believe it is something like 3% of condenser flow
> for an open tower between evapouration and drift.
>
> You could perhaps determine how much water the heat rejected by the
tower
> from the PS-H report could evapourate.
>
> Would love to hear a better solution.
>
> >
> > Does anyone know if eQUEST reports the annual amount of water
evaporated
> > from cooling towers?
> >
> > I could estimate based on the chiller power consumption and some
> > efficiency factors... but I'm looking for a more elegant solution.
> >
> > Thanks,
> >
> > Aaron Dahlstrom , PE, LEED(r) AP
> > In Posse - A subsidiary of AKF| 1500 Walnut Street, Suite 1414,
> > Philadelphia, PA 19102
> > d: 215-282-6753| m: 267-507-5470| In Posse: 215-282-6800| AKF:
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> > e: ADahlstrom at in-posse.com | in posse web:
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