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<p class=MsoNormal>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:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>1)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>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.<o:p></o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>2)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>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.<o:p></o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>3)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>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.<o:p></o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>4)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>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.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>If anyone has modeled similar actual systems and equipment
or knows a way around these limitations, I’d appreciate hearing from you.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Rick Routh<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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