VAV in eQuest

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I am working on modeling the HVAC system of large office building. The
building has a central air handler per floor with chilled water coils, VAV
for core areas and PIUs with electric heat for the perimeter areas. In the
wizard, I have specified the system as "Parallel VAV with electric reheat"
as well as specified the heating capacity of the system. Once in the detail
mode, I have gone through the zone terminal and specified the terminal type
for core areas as STD VAV instead of Parallel PIU. (coincidently, eQuest did
not like it when I specified system as "Standard VAV with electric reheat"
and tried to modify all the perimeter zones to Parallel PIU) Once
simulated, the detailed reports indicate that my core areas (VAV) do not
have enough heating capacity. Furthermore, eQuest reports a large amount of
unmet heating load hours. Can someone explain to me why eQuest wants a
heating capacity for the core zones, when in reality, the VAV for the core
has no heating, just modulation of cool air into the space? Has anybody
else dealt with this issue and might be able to lead me to a better
solution. I have attached the .pd2 and .inp files for reference. Thanks
for all your help.

Marcus Eliason, LEED AP

Marcus Eliason's picture
Joined: 2011-09-30
Reputation: 0

This is a common problem I deal with also. I'm pretty sure it's because
the shutoff boxes have a minimum supply airflow rate (30% for example),
and if your AHU is supplying 55 degree air, it wants to reheat it to
maintain space setpoint (particularly if the room is unoccupied, or
there is a diversity in the lighting / power, or it is the heating
season). I usually fix this by having a low primary air minimum
percentage (5%) and supply air reset on the AHU, both of which can be
accomplished with current BMS systems.

James Hansen, PE, LEED AP

James Hansen's picture
Joined: 2011-09-30
Reputation: 200