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

[Bruce Easterbrook]

Do the baseboards, once you click yes it is all automatic.  If you have 
a lot of zones use the summary tab and go down the list.  The baseboard 
heat will be broken out in your sim so you know what the contribution is 
in each zone.  I had a zone this week with 13000 hrs, the adjust loads 
adjustment was missed, this brought the problem down to 1000 hrs, 
changing the zone command got me to 300 hrs.  Even with baseboards that 
was the best I could do with a constant volume system on that zone.  I 
was running 4 deg throttling range.
Bruce

On 11/06/2010 12:39 PM, Dakota Kelley wrote:
>
> Robert,
>
> 50,000 hours is much more than I would anticipate for a capacity 
> issue.  You are essentially describing a hydronic VAVT system, which 
> is begging for unmet heating hours if there is a lot of diversity in 
> the zones’ demands and no reheat capabilities.  My experience has been 
> that eQUEST over-sizes hot water systems, and this is exacerbated if 
> the “simple” method is used to define the windows.  It can be as much 
> as 250%-300%.   That many hours sounds like the system is not 
> functioning as intended – almost as if the heating loop is not 
> assigned to the zones/system, or something similar.  Or, not having 
> reheat could be inappropriate for the building use or climate.  
> Regardless, adding zone reheat as Bruce and Pasha indicated should 
> make a huge difference.
>
> Thanks,
>
> *DAKOTA KELLEY ***
>
> Project Designer | Energy Analyst
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> Office: 214.744.6199
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> *From:* Bruce Easterbrook [mailto:bruce5 at bellnet.ca]
> *Sent:* Friday, June 11, 2010 6:33 AM
> *Cc:* equest-users at lists.onebuilding.org
> *Subject:* Re: [Equest-users] Excessive Unmet Heating Load Hours 
> withan Auto-Sized HVAC System
>
> 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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>
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