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RE: [EnergyPlus_Support] Fixed Minimum outside air rate
Mike,
Thank you for the reply.
Shortly after uploading the model last week, I changed the value of the
"Minimum Limit" field to "FIXED MINIMUM" in "CONTROLLER:OUTSIDE AIR" and
run the simulation. The change did not affect zones where the supply
flow rate is calculated to be less than the "FIXED MINIMUM" outside air
flow rate. In this case, the program simply reset the input "FIXED
MINIMUM" outside air rate to match the calculated design supply flow
rate. I am still not clear why that is occurring, but according to your
reply, it appears that I have bigger issues to resolve.
The system I am trying to model consists of (3) AHUs independently
serving (3) separate zones which have thermal interaction with one
another. Cooling and heating air is provided from each AHU to the zone
it serves, using a single-duct system. An air-cooled chiller and a
boiler supply cooling and heating coils within each AHU with 45oF CW and
130 oF HW, respectively. The zone thermostat control is Dual Setpoint
with Deadband, which is a direct result of defining temperature
setpoints using the COMPACT:HVAC:THERMOSTAT object. Chiller Plant
Operating Scheme and Hot Water Plant Operating Scheme are both set to
the default type in their respective COMPACT:HVAC:PLANT objects.
Is there a COMPACT:HVAC object that I can define differently, such that
the expanded model will have coil controls that will be sensitive to
zone loads? Or, must the coil control scheme be defined in the Expanded
model? In any case, are there any sections of the User Guide or example
files you suggest I go over?
Thank you for your valuable time.
Regards,
Merid
________________________________
From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Michael J.
Witte
Sent: Monday, October 15, 2007 11:55 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Fixed Minimum outside air rate
On 10 Oct 2007 at 18:28, aboyemeplus wrote:
> I am running sizing simulations using winter and summer design-day
> weather data. The minimum ventilation rate is set to a fixed value.
> All other plant/system/zone level flow rates are auto sized.
> While the results show the correct O/A rate for the summer design
> day, winter O/A flow rates are much lower than the minimum fixed
> rates entered in Zone/System sizing objects.
In CONTROLLER:OUTSIDE AIR, the MinimumLimit field is set to
"PROPORTIONAL
MINIMUM". This means the outside air amount will vary in proportion to
the
total system air flow in this VAV system. If you want the OA quantity to
remain constant as the system flow varies, set this field to "FIXED
MINIMUM".
> The results also show that peak system heating and cooling capacities
> are comparable to values generated using a simpler model, one with
> "PURCHASED AIR" objects. However, the subject model depicts
> simultaneous heating and cooling during both design days, resulting in
> zone temperatures not meeting setpoint. Can anyone help me figure out
> 1)Why the minimum fixed outside rate is not applied to winter design
> calculations, and 2)Why there is simultaneous heating and cooling
> during design day calculations.
There is simultaneous heating a cooling because the chilled water coil
leaving
air setpoint temperature is 12.78C and the heating coil air setpoint
temperature is 37.8C. The coil controls on this system use SET POINT
MANAGER:SCHEDULED, so they have no sensitivity to zone loads.
Also, the VAV terminal units "SINGLE DUCT:VAV:NOREHEAT" will not vary
air flow
rate when there is a heating load in the zone, they will stay at minimum
flow.
What type of system are you trying to model? How is it controlled?
Mike
>
> I have uploaded the Input file in the Problem Submittals\MAB3 folder.
>
> Thank you for your support.
>
> Merid
>
>
>
>
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>
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>
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>
>
>
>
>
========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support
EnergyPlus-Support@xxxxxxxx <mailto:EnergyPlus-Support%40gard.com>
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