Hi All,
I am modeling a VAV system using water cooled DX air handlers on four of
five floors. 24/7 load spaces use CHW fan coil units and the entire fourth
floor uses chilled water VAV air handler. Each DX VAV has an economizer
coil so hours in the winter when the CW temp is low enough the internal zone
receives free cooling. The entire chilled water loop also has a water-side
economizer so all the chilled water equipment can recieve free cooling.
As seen by the elec consumption graphs I'm having a problem with the CW loop
control strategy. Either the loop operates at the commanded setpoint of 85
deg. Which means there is no free cooling. Or when I try to use OA-Reset
the cooling loads during the winter are met via free-cooling but during the
summer the chiller barely runs and the cooling tower tries to meet the load
of the CHW loop.
I was able to find the way to disable the error caused by condenser water
below 65 deg thanks to post from board veterans like Mike TIllou, Steve
Gates, John Albach, and others). I do not know what else to try.
Thanks,
MH
Something interesting that I noticed with your model (that is sort of
besides the point): most of your PIU systems have ~ 2600+ hrs when the
zones are undercooled, yet your BEPS report only shows 7.5% hours unmet
load hours....interesting.
To the actual problem at hand: it would appear your chilled water and
condenser water loops use the SAME reset schedule...this can't be right,
can it? You're basically forcing your heat rejection loop to be at 63
degrees during the summer, which is why you have such high heat
rejection power consumption #s.
Maybe fix that first?
James Hansen, PE, LEED AP
Better yet, I'll tell you how...place the commands below just before the
equipment you want to disable the limits.
" DIAGNOSTIC NO-LIMITS
.."
MH