Another issue to consider is the tolerance for what constitutes not meeting setpoint. One can use the OutputControl:ReportingTolerances object to control how far from setpoint counts as being unmet. If you don’t use that object then the default is only 0.2C. 90.1 isn’t too clear on this point, but it seems one can use a value appropriate for the real building’s thermostat throttling range which likely higher than 0.2C. I believe a tolerance value of 0.55C matches DOE-2’s definition of an unmet hour and so is probably consistent with the original intent behind the 300 hour criterion.
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of luke_dorna
Sent: Friday, January 25, 2013 1:59 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: Unmet load hours due to increased fan pressure rise
If your thermostats are set up the way you like, and you are still not meeting your load hours even with autosized equipment there are other steps you can take.
If unmet load hour appear to be happening equally across your model use the Sizing:parameters object to oversize your entire hvac system to meet the peak loads.
Sizing:Parameters,
1.25, !- Heating Sizing Factor
1.15, !- Cooling Sizing Factor
4; !- Timesteps in Averaging Window
If the problem appears to be isolated to a single thermal zone you can use the section highlighted below in the sizing:zone object to increase the capacity for just the zone in question.
Sizing:Zone,
f1:airlineops216, !- Zone or ZoneList Name
SupplyAirTemperature, !- Zone Cooling Design Supply Air Temperature Input Method
12.8, !- Zone Cooling Design Supply Air Temperature {C}
, !- Zone Cooling Design Supply Air Temperature Difference {deltaC}
SupplyAirTemperature, !- Zone Heating Design Supply Air Temperature Input Method
32.0, !- Zone Heating Design Supply Air Temperature {C}
, !- Zone Heating Design Supply Air Temperature Difference {deltaC}
0.0085, !- Zone Cooling Design Supply Air Humidity Ratio {kgWater/kgDryAir}
0.0080, !- Zone Heating Design Supply Air Humidity Ratio {kgWater/kgDryAir}
SZ DSOA F1:AIRLINEOPS216,!- Design Specification Outdoor Air Object Name
, !- Zone Heating Sizing Factor
, !- Zone Cooling Sizing Factor
DesignDay, !- Cooling Design Air Flow Method
, !- Cooling Design Air Flow Rate {m3/s}
, !- Cooling Minimum Air Flow per Zone Floor Area {m3/s-m2}
, !- Cooling Minimum Air Flow {m3/s}
, !- Cooling Minimum Air Flow Fraction
DesignDay; !- Heating Design Air Flow Method
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Nino Letti wrote:
>
> I´m having the same problem.
>
> 2013/1/25 JFCS
>
> > **
> >
> >
> > Still can't figure this out, how do you properly manage your setpoint?
> >
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, jeannieboef wrote:
> > >
> > > Fan Pressure should have zero bearing on unmet loads. Its only
> > > function is to calculate electricity consumption. even though the
> > > motor heat will enter the airstream if it is designated as being in
> > > the airstream, I doubt this is your problem.
> > >
> > > That being said, your method for baseline fan power sizing by
> > > adjustment of the pressure rise looks right.
> > >
> > > You are allowed 300 hours unmet load, as long as the design case also
> > > has 250 or more but less than 300 (deviation of 50), though proper
> > > setpoint management should keep you under 50 for a good model.
> > >
> > > Sent from my iPhone
> > >
> > > On 17.01.2013, at 10:15, "JFCS" wrote:
> > >
> > > > My model gains unmet load hours or time set point not met during
> > > > cooling operations, when even i increased fan pressure rise of my
> > > > fans.
> > > >
> > > > First I autosized a working model with complete hvac system for my
> > > > Baseline case as per "G3.1.2.8 Design Airflow Rates". Then I need to
> > > > adjust my VAV's fan power as "G3.1.2.9 System Fan Power" therefore I
> > > > need to increase the pressure rise of my fans. Thought i got the
> > > > correct fan power but the unmet load hours is below 300hours...
> > > >
> > > > Any suggestions?
> > > >
> > > >
> > >
> >
> >
> >
>
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