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

[Maria Karpman]

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

 

Senior Energy Engineer

 


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