[BLDG-SIM] Condenser Water Reset in eQuest

Mike Tillou miket at etcgrp.com
Thu Aug 17 10:58:05 PDT 2006

> Hi all..I thought I would share a couple of tips on using Condenser
> Water Reset Strategies in eQuest . Hopefully some of you will find
> this useful.
> We just finished modeling a chiller plant where we looked at using low
> condenser water temperatures ( below 60F ) as an energy efficiency
> measure.  The project is in a climate with very low wetbulb
> temperatures .  There are a couple of quirks I thought I would share
> about trying to model a strategy like this.  
> The Condenser Loop Control tab has several options for resetting the
> loop temperature.  If you notice MIN-RESET-T always defaults to 70F. 
> Issue  #1:  If you reset the Condenser loop MIN-RESET-T lower than 70F
> (say 65F) and then run an hourly report to check the loop temperature
> everything looks like it's working fine.  BUT..if you also check the
> chiller entering condenser temperature you will find it never goes
> below 70F even though the condenser loop says it should be lower.
> This is because the chiller has a keyword MIN-COND-T that defualts to
> 70F and cannot be changed from within eQuest.  You have to change the
> keyword manually in the input file by adding the line, MIN-COND-T = 65
> underneath the definition of your chiller.
> The most likely reason this defaults to 70F is because the default
> chiller performance curves were not designed for condenser
> temperatures below 70F  ( someone should correct me if this is wrong)
> If you want to try and model condenser water temperatures below 70F I
> highly recommend you create custom performance curves that include
> data points that describe the operation of your chiller at the
> appropriate condenser water conditions.
> That brings me to Issue #2.
> The MIN-COND-T keyword has a lower limit of 60F.  In other words even
> if you create the appropriate performance curves  and then try to set
> MIN-COND-T lower than 60F you will get a simulation error.  
> You can work around this by using the DIAGNOSTIC keyword "NO-LIMITS".
> In effect this turns off both the Max and Min keyword limits.  You can
> then simulate chiller operation with very low condesner water
> temperatures.  
> If you use the "NO-LIMITS" keyword do so very carefully.  This is a
> very important error checking function of DOE2.2 eQuest.

Michael Tillou, PE
etc Group, Inc.
PO Box 7, Williamstown, MA 01267
ph. (413) 458-9870 fx. (413) 458-9875


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