[Equest-users] Excessive Unmet Heating Load Hours with an Auto-Sized HVAC System

[Bruce Easterbrook]

In your air side HVAC section go into the zone level and check that your 
sizing option is set to "adjust loads".  If it is from loads go to the 
summary tab and change all your zones.  Also beside that is throttling 
range, you can try adjusting that upwards say to 4 deg.  You can also 
change your control zone to see it this helps.  If your AHU is off at 
night you can also adjust it to come on before the occupancy.  You SS-O 
report will show this if the hours are lumped near the start up time.  
Then add more heat as Pasha said.
Bruce Easterbrook P.Eng.
Abode Engineering

On 10/06/2010 10:55 PM, Pasha Korber-Gonzalez wrote:
> I have found with my own projects that even sometimes when the HVAC 
> designer has specified a specific capacity for htg water equipment 
> that sometime in my model file I still have unmet loads for htg.  I 
> suggest at this point specify additional htg capacity by either 
> increasing the reheat delta-T from say 30F to 50F and/or adding zone 
> level baseboards.  By adding the baseboards you are adding a component 
> of the system that will supplement the skin losses being experienced 
> by the simulation model.
> by adding baseboards for the additional requrired heat then you should 
> be able to meet your heating loads.
> hope this helps,
> pasha
>
> On Thu, Jun 10, 2010 at 7:38 PM, Robert Des Rosiers 
> <desrosiers at studioma.com <mailto:desrosiers at studioma.com>> wrote:
>
>     All:
>
>     I have completed an energy model for a baseline scenario from
>     which to compare my proposed design.  The baseline HVAC system is
>     a constant volume single zone AHU w/ no reheat; the AHU is served
>     by HW and CHW loop from a central plant.  I have set this up in
>     eQuest as a "Variable Air Volume" system type with the AHU fan
>     control set to "Constant Volume"; my thought here is that each
>     zone fed by the AHU will control temperature using a VAV box w/ no
>     local reheat or cooling.  Flow and temperature from the AHU will
>     be delivered based on the coolest or warmest zone it serves.
>
>     All seems fine with the design flows, ventilation flows and
>     cooling capacities.  My problem is with the heating capacity as I
>     have excessive unmet heating hours (50,000).  I have allowed
>     eQuest to size the heating capacity of the preheat and heating
>     coil as well as the minimum flow ratios. _Does anyone have any
>     thoughts as to what is causing these unmet heating load hours?  Is
>     the way I have set-up the desired baseline HVAC system incorrect?_
>
>     Any guidance is greatly appreciated.  Thanks -
>
>     Robert Des Rosiers, LEED-AP
>
>     *STUDIO MA*
>
>     130 N Central Avenue, No.300 Phoenix, Arizona 85004
>
>     Telephone 602 251 3800
>
>     Fax 602 251 3100
>
>
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