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

Fri Sep 23 13:18:47 PDT 2011

Following up on this issue (HMAX-FLOW-RATIO), I have determined that the
original cause of the unmet heating hours was the fact that I had my
PVAV system COOL-CONTROL set to "Constant". Changing this to "Warmest"
with the default reset settings and letting HMAX-FLOW-RATIO default
resulted in a huge reduction in heating energy and cooling energy (by
reducing simultaneous heating & cooling I presume), with only minimal
unmet heating hours.

Bill

From: Pasha Korber-Gonzalez [mailto:pasha.pkconsulting at gmail.com] 
Sent: Saturday, September 17, 2011 3:51 AM
To: Maria Karpman
Cc: Bishop, Bill; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Tip for unmet heating hours in VAV systems

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

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