[Bldg-sim] eQuest evaporative pre-cooling

[Jim Dirkes]

Dear Nidhi,
I am not familiar with eQuest, so I cannot help much with the specifics of that program.
About one year ago I modeled an indirect evaporative system (Maisotsenko cycle specifically) in EnergyPlus and had some difficulties which I have noted below.  They may help focus your efforts!

1.            Energy Plus version 6 cannot place the condenser coil in the exhaust of an indirect evaporative cooler.  It can be defined with an evaporatively cooled condenser.  We assume that good results can be obtained by choosing the same evap effectiveness as for the M-cycle and making them both available for the same months.
2.            Energy Plus cannot currently model a VSD secondary / exhaust fan for an indirect evap cooler.  Energy reduction for both a cycling and VSD-equipped secondary / exhaust fan was assumed similar to that experienced by the supply fan.  This is modeled by reducing the secondary fan delta P  to xx%  (varies by climate) of actual.
3.            Secondary / exhaust air  can come only from the outdoors in EnergyPlus.  Thus no mixed air can be used.
4.            Economizer controls in EnergyPlus always look at the outdoor air temperature. We'd rather control based on the temp leaving the M cycle heat exchangers.  This requires a special, climate-specific schedule in EnergyPlus.  Not difficult, but takes more time.


From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Nidhi Vyas
Sent: Friday, July 13, 2012 10:26 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] eQuest evaporative pre-cooling

Hi everyone,

I am working on a California project pursuing Title-24 2008 and using eQuest for the analysis. The project includes VAV with chilled water cooling and hot water reheat system . Additionally the system is 100% OA system and also includes indirect evaporative pre-cooling in the design. My model indicates that the evaporative pre-cooling is helping on the cooling energy savings ( as expected) but I am getting heating penalty because of it.

After digging into the simulation output reports it seems that the reheat energy has increased significantly and the space temperature for the zones have more hours in the cooling temperature band. I believe that the evaporative pre-cooling is overcooling the spaces. Further, I think that the evaporative pre-cooling is treating OA with dry bulb as low as 55F.

Can somebody please suggest how to control the evaporative pre-cooling so that it comes on for OA above 70F temperature only. eQuest has a high limit set point for evaporative pre coolers but no low limit one.  Also, any thoughts on how to control the increase in reheat energy.

Thank you

Nidhi
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