[Equest-users] Which system is best to use?
Chris Jones
cj at enersave.ca
Thu Mar 22 08:21:46 PDT 2012
It's a frustrating issue. In a typcal "real"
building, the VAV central coil resets based on
the zone with the highest cooling demand. On
cold mornings, the reset can be as high as 70°
F. According to the documentation in
DOE22Vol2-Dictionary, the keywords COOL-CONTROL,
HEAT-CONTROL, HEAT-SET-T, COOL-MAX-RESET-T and
HEAT-MIN-RESET-T and some others should allow you
to simulate a VAV system that has a heating coil
that can reset the supply air temperature. I
have never been able to find that magic
combination that results in the hourly reports
the heating coil providing heating when I would expect it to.
The issue with the preheat coil is that you have
to set the exiting temperature a few degrees
lower than the cooling MIN-SUPPLY-T to account
for fan heat so you don't increase heating
significantly. This still results in too much reheat required at the zones.
sa
At 04:04 PM 15/02/2012, Rob Hudson wrote:
>When using the VAV or PVAV system types the
>heating coil can be sized by using the leaving
>air temperature conditions, but never turns
>on. The true way to use a heating coil for a
>VAV is to call it a preheat coil, and specify a
>leaving air temperature close to what you have
>in reality. Occasionally, the reality is higher
>than what eQuest allows (something like 70
>degree F) and then you need to "fake" it by
>making up the rest of the heating load in the reheat coils.
>
>Hope this helps!
>
>Rob H.
>
>
>
>
>
>
>On Wed, Feb 15, 2012 at 2:31 PM, R B
><<mailto:slv3sat at gmail.com>slv3sat at gmail.com> wrote:
>I have a system with VFD on the fan, central
>heating and cooling coils (no reheat), and
>chilled water for cooling. Curious to see how
>others would model this, or if I am missing something very obvious.
>
>If I use VAV, even though there is central coil,
>it does not come on. The heating seems to be
>only through the reheat coil. I could do the
>warmest zone control, but I think this uses only
>return air, not heating coil for the
>
>If I use single zone reheat, cannot get the fan to be variable speed.
>
>PVVVT might work (never tried it) but it does not use chilled water.
>
>I could use a dual duct single fan and the min flows be zero fo both ducts?
>
>
>Thanks
>-Rohini
>
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>
>
>--
>Rob Hudson
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Christopher Jones, P.Eng.
Suite 1801, 1 Yonge Street
Toronto, ON M5E1W7
Tel. 416-203-7465
Fax. 416-946-1005
email cj at enersave.ca
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