[Equest-users] Packaged VVT System Modeling Help

[Routh Consulting Engineers]

I am trying to model HVAC systems using the Carrier 3V VVT zone and bypass
dampers with packaged gas/electric units and can't seem to find a good match
or dummy in enough other things to make up. Here's what I've tried and, so
far, failed with:

 

1)      I've tried the PVVT system model, but the control zone doesn't have
a VVT damper so the equipment cycles off with no demand in that zone. If
other zones are still needing the same mode of operation as the control
zone, or worse, they need the opposite mode, demands go unsatisfied and I
end up with a large number of hours with loads not met. I've tried using
different zones on the same system as the control zone, but I still end up
with too many unmet hours. The actual system has zone dampers for all zones
and controls figure out which mode to put the unit into and dampers throttle
accordingly. It also can change into the other mode of operation if enough
zone thermostats call for it.

2)      I've also tried the RESVVT system. It's zone dampers and ability to
switch modes within the same hour is closer to how the actual system really
works, but the RESVVT system has no outside air capability. The DOE-2.2
manuals note this and say to use a separate air handling unit serving a
dummy zone with essentially nothing but the outside air equivalent to the
necessary outside air of the RESVVT system, which works OK for minimum
outside, but doesn't tie to the actual zone load to operate an economizer
properly.

3)      I've tried the CBVAV system, which bypasses extra air as zone
dampers throttle, similar to the actual system, but the leaving air
temperature control is essentially zone of greatest cooling demand dominated
and then relies on reheat for spaces needing a little heating with zone
dampers a minimum position, which I've allowed to go essentially closed. The
actual system has no reheat at the zone dampers.

4)      Last, I've tried the PVAVS system, but this system is also
controlled to zone of greatest cooling demand and relies on reheat, and it
slows down the fan as zone dampers throttle instead of bypassing air and
keeping the fan at essentially constant volume.

 

If anyone has modeled similar actual systems and equipment or knows a way
around these limitations, I'd appreciate hearing from you.

 

Rick Routh

 

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