[Equest-users] Direct evaporative cooling

Nick Caton ncaton at smithboucher.com
Wed May 9 08:48:46 PDT 2012

Hi there Sachin,

I've taken a look and first notice the brunt of your energies are fan energy, which is to be expected for evaporative systems.  I take it you feel your lighting/misc consumptions are in check.

The math adds up:  You have fans that (A) aren't terribly efficient,  (B) running 24/7, and (C) pushing a lot of air (your 1.5 system sizing factor is in play here).  The systems are going to draw a lot of fan energy as long as all those features are true.  For illustration, pulling that sizing factor back to 1.0 (reverting to your specified CFM) and allowing the fans to operate intermittently vs. continuous brings your consumptions down pretty drastically - this is without touching your fan efficiency inputs:

[cid:image001.png at 01CD2DCC.0C10AC50]

Specifying effectively 0% outside air for your systems gives me pause - I assume this is a conscious decision on your part, but carefully consider where ventilation air is coming from and (if at all).

Following the above edits (perhaps not required - use your judgment) I observe an hourly min/max of 77.7F and 104.95F for one zone using the report variable "Current hour zone temp (deg F)."   No -999 entries (perhaps you were returning a schedule value?  I can only speculate.)...

104.95 itself is probably cause for concern - this is largely the result of your decision to stick with an OA drybulb cap of 90F to limit system operation.  Raising that cap to 120 brings your spaces much closer to "comfort" (about 85F max during the hottest hours).  Consumptions move upward nominally but not drastically from the above chart.  Again, these numbers/observations follow edits above.

Hope that helps guide you and others struggling with evaporative modeling.  I suggest you review/revise your inputs using your judgment in the order I presented, as applicable.  If you or anyone else is branching into systems that use evaporative cooling jointly with refrigeration, I advise reviewing the help files and searching for related posts within the mailing list archives for further guidance.


[cid:489575314 at 22072009-0ABB]


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From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of sachin sharma
Sent: Monday, May 07, 2012 7:35 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Direct evaporative cooling

Hi all,

I have modelled a direct evaporative cooling system for a building. But the results which I am getting are unacceptable. The space cooling load in the month April, June is of the order of 3000 kWh (24 hour building). Also when I check the hourly reports the zone temperature is -999°F. Is there something wrong with the model. Please suggest changes. I am attaching the pd2, inp and weather file of the project.

with regards,
Sachin Sharma
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