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The VAVS and PVAVS systems do not correctly implement the central heating
coil as documented. <br>
Ideally one would like the VAV system to control the supply air
temperature to meet the cooling load of the "warmest" zone with
its box open. The supply air reset temperature is controlled by
<br>
COOL-MAX-RESET-T.<br><br>
One would expect the heating coil to kick on during heating season so the
supply air temperature is reset up to somewhere between MIN-SUPPLY-T and
COOL-MAX-RESET-T. From the documentation under
HEAT-CONTROL:<br><br>
"In SYSTEM TYPEs VAVS, RHFS, PVAVS, and PIU the HEAT-CONTROL keyword
is activated when COOL-CONTROL<br>
is set equal to WARMEST and a central heating coil has been specified by
giving HEAT-SET-T a<br>
value greater than MIN-SUPPLY-T; in this case the only non-ignored value
for HEAT-CONTROL is COLDEST.<br>
When coldest/warmest control is specified the controller first looks to
see if any ZONE has a cooling demand; if<br>
there is a ZONE cooling demand the AHU discharge temperature is reset to
attempt to just satisfy the ZONE with<br>
the largest cooling demand. If no ZONE has a cooling demand the
controller looks to satisfy the ZONE with the<br>
greatest heating demand but without forcing any ZONE into creating a
cooling demand. If neither a heating or<br>
cooling demand is found for any ZONE mixed air is passed."<br><br>
That does not happen. If you do the hourly report runs and check
the supply air temperature, the OA T, the mixed air temperature, and some
of the zone loads, you will find that the supply air temperature doesn't
get reset as expected. <br><br>
Note that you do need to set a wide throttling range - 4° - 6°F.
<br><br>
You can also try changing the RESET-PRIORITY keyword to see if that
helps.<br><br>
<br>
I have found the only way to avoid over use of the electric baseboards is
to add a pre-heat coil and set the temperature to the MIN-SUPPLY-T less
the fan delta-t. At least you will a supply air temperature that is
the minimum. You will still get some over use of the electric
baseboards.<br><br>
You can try a COOL-CONTROL = RESET and play with the temperature
schedules and BASEBOARD-CTRL = RESET, and adjust the schedules.
<br><br>
<br>
0At 06:56 PM 22/06/2012, David Reddy wrote:<br>
<blockquote type=cite class=cite cite="">Ramana-<br><br>
It appears you have not defined at Hot Deck Max Leaving temp
(HEAT-SET-T), which needs to be specified for the central Furnace coil to
be energized in the simulation. Also, for PIU (and I believe all
the other multizone systems), the central coil LATs will track the Cool
Control properties, which in your case, is an OA Reset Schedule. I
suggest setting up an hourly report for the air handler coil leaving air
temperatures, and observing what is happening are to understand how the
control set points are being implemented.<br><br>
Hope this helps, <br>
David<br><br>
On 6/22/2012 1:25 PM, Ramana Koti wrote:<br>
<blockquote type=cite class=cite cite="">Dear all,<br>
<br>
My question relates to distributing space heating between the central VAV
RTU (natural gas furnace) and PIU terminal units (electric resistanct
heating). My elecriticy consumption for space heating end use seems very
high from November to April which makes me suspect that the system is not
set up accurately - majority of space heating is wrongly being picked up
by electric resistance in terminal units as opposed to being picked up by
the natural gas furnace in the RTU. <br>
<br>
From the BEPS report, of the total annual energy consumption of 372.7
MBTU, 148.7 MBTU is electricity space heating and 7.6 MBTU is natural gas
space heating.<br>
<br>
I have attached eQUEST screenshots of my heating and cooling cap/control
settings for this system. Any input on how this situation can be
rectified will be highly appreciated. <br>
<br>
Thank you,<br>
Ramana Koti.<br><br>
<br><br>
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Christopher Jones, P.Eng.<br>
Suite 1801, 1 Yonge Street<br>
Toronto, ON M5E1W7<br>
Tel. 416-203-7465<br>
Fax. 416-946-1005<br>
email cj@enersave.ca<br>
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