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
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.
Dear Jim,
Thank you for your input.
In eQuest there is an option to use the return air as secondary air so that
is helpful.
I tried to control the evaporative pre-cooling entering air temperature
through economizer controls and schedules too but unfortunately nothing is
working out. If I look over the hourly reports i still see that evaporative
pre-cooling is treating the OA below 70F.
Again thank you for your help.
Nidhi