[Equest-users] Which system is best to use?

Robby Oylear robbyoylear at gmail.com
Thu Mar 22 08:59:47 PDT 2012


To account for your last comment you can enter a user-defined expression
into the PREHEAT-T (Preheat Leaving Temp) entry.  Something like:
#L("MIN-SUPPLY-T")-#L("SUPPLY-DELTA-T")

On Thu, Mar 22, 2012 at 8:21 AM, Chris Jones <cj at enersave.ca> wrote:

>  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 <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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