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[EnergyPlus_Support] Re: How to reduce "not met hours"

Thank you! Jim.  We will follow your advice to figure out the problem.  The thing puzzles me is that we increased the sizing factor but it appeared to have very little effect on the unmet hours.  In fact, we also tried to change the sizing factor in the VAV PFP template provided in the example files.  Surprisingly, it did not significantly change the unmet hours either.

Are we missing something here?  

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Jim Dirkes" <jim@...> wrote:
>
> Dear Xing Shi,
> 
>  
> 
> I recommend that you add numerous Output:Variables to help you understand
> what is happening within your air and water system.  I normally report:
> 
> .         The outdoor air, return air and mixed air flows in each air loop
> 
> .         The primary and secondary airflow for the zone terminal units
> 
> .         Temperature at each Air Loop node
> 
> .         Energy use for each energy-consuming device
> 
> .         Flow and temperature at each System node for water loops
> 
> .         Flow in each branch for water loops
> 
> .         Unmet load hours for each zone (heating and cooling)
> 
>  
> 
> When you look at detailed information, you are normally able to understand
> which portion of a particular zone or loop that is causing the unmet loads .
> and then determine the proper corrective action.
> 
>  
> 
> This practice is also helpful to discover hidden errors.  Just this week, I
> ran a model which had very few warnings and very low unmet load hours. Then,
> as I reviewed the detailed information from  Output:Variables, I noticed
> that one system which was supposed to be using 100% outdoor air, was
> actually using 0% outdoor air.  The model looked "perfect", but was really
> perfectly wrong.
> 
>  
> 
> In that case, I had 20,000 lines of Energy Plus input which were all correct
> except for one line!  The Output:Variables helped me discover the error and
> correct it (with the assistance of the Help Desk).
> 
>  
> 
> The Building Performance Team
> James V. Dirkes II, P.E., BEMP , LEED AP
> 1631 Acacia Drive NW
> Grand Rapids, MI 49504
> 616 450 8653
> 
>  
> 
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Xing Shi
> Sent: Saturday, September 17, 2011 4:27 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: [EnergyPlus_Support] How to reduce "not met hours"
> 
>  
> 
>   
> 
> Dear All,
> 
>  
> 
> We have an ASHRAE 90 system 8 baseline building.  The E+ model appears to be
> correct but the "unmet hours" is a little too high.  Cooling and heating
> unmet both exceed 200.  According to ASHRAE 90, we should increase the
> system capacity incrementally until unmet (cooling + heating) is below 300.
> We changed the sizing factor in Sizing:Parameters but surprisingly found
> that it had very little effect on the unmet hours.
> 
>  
> 
> Attached is the IDF file.  Why is that?  What should we do to reduce the
> unmet hours.  Thank you!
> 
>  
> 
> XS
>




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