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RE: [EnergyPlus_Support] Fixed Minimum outside air rate
For this sytem type, in zone sizing, if the Min OA is greater than the cooling
supply flow rate, then the Min OA requirement will override. But it will not
check the min frac of a VAV terminal unit to make sure this is >= the Min OA
requirment for the zone. The only way to control this is to manually compute
the required min frac setting for the VAV terminal unit.
For the heating controls, I am still not completely sure what to recommend.
Will the heating mode supply air temperature be controlled to a fixed
temperature with all control made by varying the VAV damper? Or will the VAV
flow and supply temperature both vary?
The only option that will work directly from Compact HVAC is to delete the
central heating coil and add a hot water reheat coil with REVERSE ACTION
damper. This will give you the appropriate amount of heating energy, but it
might not give the correct amount of fan power, depending on the answer to my
question above.
Mike
On 15 Oct 2007 at 16:19, Aboye, Merid (US SSA) wrote:
> 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
> >
> >
> >
> >
> > The primary EnergyPlus web site is found at:
> > http://www.energyplus.gov <http://www.energyplus.gov>
> >
> > The group web site is:
> > http://groups.yahoo.com/group/EnergyPlus_Support/
> <http://groups.yahoo.com/group/EnergyPlus_Support/>
> >
> > Attachments are not allowed -- please post any files to the
> appropriate folder
> > in the Files area of the Support Web Site.
> >
> > EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under
> the
> > Documentation link and press the "search" button.
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
>
> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support
> EnergyPlus-Support@xxxxxxxx <mailto:EnergyPlus-Support%40gard.com>
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
>
>
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov
>
> The group web site is:
> http://groups.yahoo.com/group/EnergyPlus_Support/
>
> Attachments are not allowed -- please post any files to the appropriate folder
> in the Files area of the Support Web Site.
>
> EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the
> Documentation link and press the "search" button.
>
> Yahoo! Groups Links
>
>
>
>
>
========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support
EnergyPlus-Support@xxxxxxxx
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are not allowed -- please post any files to the appropriate folder in the Files area of the Support Web Site.
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