[Equest-users] Tip for unmet heating hours in VAV systems

[R B]

I have found the same thing as Maria, increasing the flow increases unmet
heating. Another place to check is the min flow - reducing min flow also
reduces unmet heating.

On Fri, Sep 16, 2011 at 2:59 PM, Maria Karpman <
maria.karpman at karpmanconsulting.net> wrote:

> Pasha and Bill,****
>
> ** **
>
> I also often use this keyword, but usually increase the fraction
> incrementally by 0.1 instead of just setting it to 1, to avoid
> out-of-control behavior described in DOE2 help. Here is the related quote:
> ****
>
> Some reverse-acting VAV systems may go out of control if the maximum
> heating airflow is not restricted . As the zone temperature drops, the box
> progressively opens to deliver more air. However, since the supply air is
> usually lower than the zone temperature, more coil energy is required to
> offset the non-useful reheat (difference between zone temperature and supply
> air temperature), potentially leaving less coil/boiler capacity available
> for useful heating. As a result, a terminal at full flow may deliver less
> useful heating than at lower flow, resulting in an out-of-control situation;
> the box may go to full flow even though a reduced flow would heat more
> effectively. The solution is to restrict the maximum flow during reheatng
> coil and/or boiler is not sized sufficiently large, ****
>
> I did see this scenario happen in some projects, when adjusting the value
> of the keyword up beyond certain point increased heating, cooling, and fan
> power, but did not help much with under-heating.  ****
>
> Thanks,****
>
> Maria ****
>
> ** **
>
> *From:* equest-users-bounces at lists.onebuilding.org [mailto:
> equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Pasha
> Korber-Gonzalez
> *Sent:* Friday, September 16, 2011 3:23 PM
> *To:* Bishop, Bill
> *Cc:* equest-users at lists.onebuilding.org
> *Subject:* Re: [Equest-users] Tip for unmet heating hours in VAV systems**
> **
>
> ** **
>
> Thanks Bill--I think this will be helpful.  I currently have a baseline
> model with whacked underheated hours and with upsizing ratios and autosized
> calcs nothing is changing for me.  I will try this input adjustment and see
> if it works.****
>
>  ****
>
> Thanks for sharing!****
>
> Pasha****
>
> On Fri, Sep 16, 2011 at 8:33 AM, Bishop, Bill <wbishop at pathfinder-ea.com>
> wrote:****
>
> Thought I’d share a tip for addressing unmet heating hours in VAV systems
> using eQUEST 3.64.****
>
>  ****
>
> eQUEST 3.64 adds the HMAX-FLOW-RATIO keyword in System -> Fans -> Flow
> Parameters. The default value is the greater of the fan MIN-FLOW-RATIO and
> 0.5, but this value is determined by the program and you don’t see it when
> you look at the Flow Parameters tab. Entering a value of 1.0 corrected an
> unmet heating hours problem for me that appeared when I opened a model in
> 3.64 that I originally created in 3.63. This works for both VAVS and PVAVS
> system types.****
>
>  ****
>
> Regards,****
>
> Bill****
>
>  ****
>
> [image: Senior Energy Engineer]****
>
>  ****
>
>
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