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RE: [EnergyPlus_Support] Fixed Minimum outside air rate

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] Fixed Minimum outside air rate
From: "Michael J. Witte" <mjwitte@xxxxxxxx>
Date: Mon, 22 Oct 2007 14:12:54 -0500
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If I understand your system correctly, COMPACT HVAC:ZONE:FAN COIL would be 
equivalent - supply fan runs continously with fixed amount of outside air, hot 
water and chilled water coils modulate to meet the zone heating/cooling load.

If you prefer to keep what you have, change the SET POINT MANAGER:SCHEDULED 
objects for the heating and cooling coil to be SET POINT MANAGER:SINGLE ZONE 
HEATING and SET POINT MANAGER:SINGLE ZONE COOLING.  These will control the 
central coils based on the thermostat demand for a single zone.

Mike


On 22 Oct 2007 at 15:02, Aboye, Merid (US SSA) wrote:

> Mike,
> 
> 
> 
> In the actual system, heating and cooling supply temperatures are
> controlled, while flow rates are held constant. I used the COMPACT
> HVAC:SYSTEM:VAV object because the Compact HVAC feature does not offer
> the option to model constant-air flow rate systems with central boilers
> and air-cooled chillers.  What can I do to simulate a constant flow
> system without throwing out the expanded model? Thank you kindly for
> your support.
> 
> 
> 
> Merid 
> 
> 
> 
> ________________________________
> 
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Michael J.
> Witte
> Sent: Monday, October 22, 2007 2:36 PM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: 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%40yahoogroups.com> 
> > [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com> ] On Behalf Of Michael J.
> > Witte
> > Sent: Monday, October 15, 2007 11:55 AM
> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com> 
> > 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>
> <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/> 
> > <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>
> <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 <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





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References:
- RE: [EnergyPlus_Support] Fixed Minimum outside air rate
  - From: Michael J. Witte
- RE: [EnergyPlus_Support] Fixed Minimum outside air rate
  - From: Aboye, Merid (US SSA)

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