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

[Pasha Korber-Gonzalez]

Thanks Bill and Maria for your experience and advice.   My terms of
'whacked' is not the same--here's my 'typical' scenario:

Finished LEED equivalent model with 100% DD drawings;
Receive Value Engineering changes before I received the 100% CD drawings;
Low-and-behold the value engineering had changed the HVAC systems by approx
60% of what the original design was;
My proposed models are fine, BUT my 'new' baseline model (which is inline
with the new proposed changes due to VE efforts) is now seeing
underconditioned hours in the magnitude of 550 as opposed to 63 hours in my
previous baseline model.....

this is why it is whacked (by my own description):  I had the baseline
calibrated to an acceptable range, the VE changes really didn't make a big
impact in the overall energy use (small impact), but for some reason I now
have a new basline model where I am further behind the finish line than
before these VE adjustments....I stared at this for 6 hours two nights ago
with no progress or further insight what-so-ever.  Ugh!

I will try the suggestions by you and Maria and RB---thanks all for your
tips.  I hope I can get this fixed ASAP as I am working on multiple model
projects that all need to be finished ASAP--as always.   "Simulation
Frustration" is the name of this game.  ;)

Cheers,
Pasha

On Fri, Sep 16, 2011 at 1:59 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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