[Equest-users] Free cooling for air-cooled chillers

[Neil Patel]

Thanks for the help Joe!

We set the cooling tower design output temp to 44F, which is the output of the regular chillers.  Our 'free cooling' also utilizes fans and we've modeled this in the cooling tower fan power.

Thanks again,
Neil

From: Joe Fleming [mailto:joe at thespinnakergroupinc.com]
Sent: Thursday, April 07, 2011 8:46 PM
To: Neil Patel; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Free cooling for air-cooled chillers

I have modeled it as follows, (I don't think I dropped the ball);  Set up a water cooled chiller and set the chiller type to "water-side" economizer.  This will essentially model a cooling tower that pumps chilled water into the building when the outdoor conditions permit (low wet bulb for the tower).  Make sure to set the "approach" of the tower to something that matches your air cooled chiller performance and do the same for the tower range and fan power.
Run a couple of iterations to see if the chilled water pumps are used.  If they are then set the pumping power to a very small number, since you want your condenser water pumps in the model to be your chilled water pumps in the design.
Attach this chiller and cooling tower to the chilled water loop with the other large chillers, with the proper design capacities.
It should cycle on in the order that it was created, not sure if the free cooling chiller will take precedence in the cycling (it's been a while), maybe someone else can help here.  If you want to change the sequencing to match the design that is another subject and it can be handled in the loop controls under "Equipment Controls".

Let us know how it turns out.


Joe Fleming, E.I., LEED AP BD+C, BEMP
Commissioning Agent
561-602-3132

The Spinnaker Group
www.thespinnakergroupinc.com

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Neil Patel
Sent: Thursday, April 07, 2011 6:12 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Free cooling for air-cooled chillers

I'm modeling a building that wants to use modular air-cooled chillers.  So in addition to several modular chillers, they want to install a few 'Free Cooling' units.  These units will be tied in with the regular chillers and will be able to provide free cooling during the winter whenever the outdoor temperature drops below the mid 30s.  To my understanding, this works when the ambient temperature is low enough, the return glycol is sent through economizer coils before it enters the evaporator.  With colder temps, the refrigeration compressors unload until they are no longer required, and the full cooling capacity is provided by the condenser-fan alone.

I was wondering if anyone has had any experience with these types of chillers and what are some of the ways to model this 'free cooling.'

Thanks in advanced for all the help,




Neil Patel, EIT, LEED AP BD+C

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