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<font size="+1">A single system can be a lot of problem. There is
just so much variation between the zones most times and there are
not enough T-stats. I don't know the number of zones and the
space size but if you are down to the 100 hour unmet range I think
you are as close as you are going to get it. One other thing to
look at is the timing of the unmet hours. Many times I have
found, more so with higher mass buildings is a one hour warm up is
not enough and you will get a lot of unmet hours right at the
start of the day. Sometimes bringing the AHU off night set back 2
hours before is enough to get rid of these shoulder hours. There
can be a big difference in the heat and cooling capacity required
from maintaining a set point verses trying to recover the space
from a 4 degree set back. Equipment these days is sized closer to
the line and it takes a little more time for the system to get the
space under control.<br>
Bruce Easterbrook P.Eng.<br>
Abode Engineering<br>
<br>
</font>
<div class="moz-cite-prefix">On 11/09/2012 12:40 PM, John Shen
wrote:<br>
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<div dir="ltr">
Thank you very much for the response, they were extremely
helpful. I was able to reduce my unmet hours to ~100 hours but
not without a whole lot of effort. It appears that my zones had
a large load discrepancies between one another, the central
zones had minimal load while certain outer zones had large heat
loss due to window frames, zone area etc. This seemed to result
in a system being very sensitive to air flow and I was
previously making too large of an increment with my min air
flow. Increasing the reheat-delta-T did make the system much
easier to deal with as eQUEST seemed to distribute air flow when
auto-sizing. In the end there were still zones where ~100 unmet
hours was as low as I could get it no matter how I changed the
air flows, as the system did appear to be fighting itself to a
degree. The only fix was to auto-size baseboards in these
trouble zones. I suppose these issues aren't uncommon when you
have a single system serving large a number of zones.<br>
<br>
<div>
<hr id="stopSpelling">Date: Mon, 10 Sep 2012 12:42:45 -0400<br>
From: <a class="moz-txt-link-abbreviated" href="mailto:bruce5@bellnet.ca">bruce5@bellnet.ca</a><br>
To: <a class="moz-txt-link-abbreviated" href="mailto:johnshen1@hotmail.com">johnshen1@hotmail.com</a><br>
CC: <a class="moz-txt-link-abbreviated" href="mailto:equest-users@lists.onebuilding.org">equest-users@lists.onebuilding.org</a><br>
Subject: Re: [Equest-users] Power induction unit/ reheat delta
T<br>
<br>
<font size="+1">It seems to me you have gone overboard on your
zone air flows which will generate unmet hours and also
waste energy. This is all a balancing act between several
conflicting items, air flow just being one. I don't think
your delta T is the problem. Terminal units can heat and
cool and it sounds like yours are not cooling. I would also
suspect your system is fighting itself. You are going to
have to troubleshoot what is going on and figure out a
solution. Your sim reports will tell you how much heating
and cooling each zone requires. From there you can figure
out how much air you need to to accomplish this. Compare
that to how much air you are putting in. I don't do a lot
of these types of systems to give you a quick answer with
the information I have. Most of the time there is no quick
answer anyway. All HVAC systems follow a logical pattern.
You need to find where and why you have deviated. As you
can see eQuest will take you way out into left field if you
let it.<br>
Bruce Easterbrook P.Eng.<br>
Abode Engineering<br>
<br>
</font>
<div class="ecxmoz-cite-prefix">On 07/09/2012 06:05 PM, John
Shen wrote:<br>
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<div dir="ltr"> <br>
I am working on a building with air handling units on each
floor. Interior zones are served by the AHU while exterior
zones are served by the AHU as well as FC unit which
provides furthur heating and cooling. I modeled the system
as a Power Induction Unit with series PIU to represent the
FC units. I used a reheat delta T determined from AHU and
FC's spec'd heating capacity and air flow rates and
allowed eQUEST to autosize and distribute airflow. Thanks
to the advice given from members on this list I was able
to reduce my unmet hours to a reasonable range.
<div><br>
</div>
<div>I am working on the baseline model and am again
having issues with unmet hours. As mentioned the heat
capacity of VAV systems are determined by the design
flow rate and the reheat delta T. In order to reduce
unmet hours I would increase flow rates to particular
zones by manually increasing Min design flow rates with
my reheat delta T set at 20F which is what is required
by ASHRAE. I've been at this for a while and my building
is basically a wind tunnel, I have floors with supply
cfm upwards of 100,000 CFM and I still have thousands of
unmet hours. (my throttling range are at 6)</div>
<div><br>
</div>
<div>Am I allowed to change reheat_delta_T to a larger
value? </div>
<div><br>
</div>
<div>For a power induction unit with series PIU boxes, is
there any way for the boxes to provide zone cooling?
Looking at hourly reports for "zone coil cooling" I have
0's.</div>
<div><br>
</div>
<div>Much of this might be brought about by the fact that
my building heating and cooling load has doubled in the
baseline model.</div>
<div><br>
</div>
<div>Any advice would be much appreciated.<br>
<div>
<hr id="ecxstopSpelling">Date: Mon, 27 Aug 2012
09:40:41 -0400<br>
From: <a moz-do-not-send="true"
class="ecxmoz-txt-link-abbreviated"
href="mailto:bruce5@bellnet.ca">bruce5@bellnet.ca</a><br>
To: <a moz-do-not-send="true"
class="ecxmoz-txt-link-abbreviated"
href="mailto:johnshen1@hotmail.com">johnshen1@hotmail.com</a><br>
CC: <a moz-do-not-send="true"
class="ecxmoz-txt-link-abbreviated"
href="mailto:equest-users@lists.onebuilding.org">equest-users@lists.onebuilding.org</a><br>
Subject: Re: [Equest-users] Power induction unit/
reheat delta T<br>
<br>
<font face="Times New Roman, Times, serif" size="+1">For
reference on the sim reports go to help/Tutorials
and Reference/Detailed Simulation Reports Summary.
It will explain all the reports. I don't use the
SS-G report much. I also don't do much chilled
water cooling. I looked at a DX design I had done
and the SS-G shows no cooling.<br>
Cooling is the most difficult to get right because
the delta-T is almost always lower than the heating
side and on the heating side you can always cheat a
little with baseboards to do a final trim even if
you don't have them in your system. You can get a
quick idea of the magnitude you are short. Cooling
has no final trim and the eQuest focus is on
cooling. You have also bumped into another limit on
cooling capacity. You are correct that the cooling
capacity is dependent on the delta-T and the air
flow. There are 2 delta-T's, the one on your water
and the one on your air. You can play with the
water one all day but if you don't have enough air
you won't get anywhere. Equest has a default on the
airflow to a zone that is 0.6 cfm/SF. Your main AHU
maximum flow will be based on this value for the sum
of all the zones it is supplying. Most of the time
this value is too small for a sun side perimeter
zone.<br>
I would start with the zone with the worst unmet
hours. You want to use zone reports, start with
LS-A which will give you your peak heating and
cooling loads for all your zones. LS-B will give
you the components of that load except OA. SS-R is
handy. Keep an eye on SV-A, it will list the zones
and their airflow's as sub-components of the main
AHU.<br>
You want to go to the air-side HVAC tab and select
the zone you want to work on. Right click and
select "Properties". In the "Basic Specifications"
tab you will see on the right side half way down
"Zone Design Flow Rates", the first value is "Min
Design Flow" and is probably set at 0.6 cfm/SF,
start increasing this value. You may need to be in
the 1.2 cfm/SF range, it depends on the zone and the
cooling load. You can calculate what you need
too. As you bring the number up you will see the
AHU airflow increase and also the cooling/heating
capacity of the AHU increase in SV-A. Remember that
you just want enough air. Excess air moving wastes
energy. Your unmet hours should be decreasing for
that zone. Some of the other zones will begin to
decrease as well but your main problem zones should
still have unmet hours. Deal with each one the same
way.<br>
Remember this, it is probably THE most important
setting in eQuest on the air side.<br>
Bruce Easterbrook P.Eng.<br>
Abode Engineering<br>
<br>
</font>
<div class="ecxmoz-cite-prefix">On 24/08/2012 05:16
PM, John Shen wrote:<br>
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<div dir="ltr"> Thank you for the response, couldn't
have asked for a better explanation.
<div><br>
</div>
<div> I was able to get the heat unmet hours down
to a reasonable range. However, I am having
difficulties with the Cool unmet hours. It
appears I am unable to acquire any cooling
capacity which is resulting in a few unmet hours
(~150). As mentioned the heating capacity is
dependent on the reheat delta t and airflow. I
can't seem to find a place to enter delta T for
cooling, I have coil delta T set along with an
appropriate CHW loop. Yet I don't get any
cooling in any of my zones in the SS-G section
of the report. Any further help would be
appreciated.</div>
<div><br>
</div>
<div>John<br>
<br>
<div>
<hr id="ecxstopSpelling">Date: Fri, 24 Aug
2012 09:57:49 -0400<br>
From: <a moz-do-not-send="true"
class="ecxmoz-txt-link-abbreviated"
href="mailto:bruce5@bellnet.ca">bruce5@bellnet.ca</a><br>
To: <a moz-do-not-send="true"
class="ecxmoz-txt-link-abbreviated"
href="mailto:johnshen1@hotmail.com">johnshen1@hotmail.com</a><br>
CC: <a moz-do-not-send="true"
class="ecxmoz-txt-link-abbreviated"
href="mailto:equest-users@lists.onebuilding.org">equest-users@lists.onebuilding.org</a><br>
Subject: Re: [Equest-users] Power induction
unit/ reheat delta T<br>
<br>
<font size="+1"><font face="Times New Roman,
Times, serif">You can try changing your
interior control zone as this will effect
the base capacity that the AHU will supply
to the floor. As for the exterior zones
your heat/cool capacity is based on the
delta-T and the airflow. You said you
specified the air flow. Let eQuest
auto-size the flow. By specifying the air
flow you have removed most of eQuest's
ability to adjust capacity. One other
thing to remember is eQuest is working on
the maximum flow as well as all the
intermediate conditions as well. It is
these intermediate loads which will
trigger most of your unmet hours. As the
sun moves across your exterior zones
through the day the peak load will be
shifting through the exterior zones as
well. So a zone which was the peak at 10
am won't be the peak at 3 pm. eQuest will
count an unmet hour if you are high or low
on a zones temperature. By specifying the
cfm to the zone I would guess you may be
over cooling some of the zones and
triggering unmet hours. eQuest, if
allowed, would reduce the airflow to the
10 am zone later in the day and shift the
CFM to the 3 pm zone. This is mostly
under the hood stuff and you have to drill
pretty deep into your reports to have an
idea of what is going on and you won't
find the direct answer as to the lower cfm
to the zone. You can get an idea of the
heat/cool capacity eQuest is dealing with
in each and follow it across the building.<br>
Bruce Easterbrook P.Eng.<br>
Abode Engineering.<br>
<br>
</font></font>
<div class="ecxmoz-cite-prefix">On 23/08/2012
01:56 PM, John Shen wrote:<br>
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<p class="ecxMsoNormal">Working on a
building with an air handling unit which
serves the entire floor. In the exterior
rooms there are Fan coils to supply
further heating and cooling to the
floor. I have split the floor up into
interior zones and exterior zones (each
containing a fan coil unit). The AHU I
have modeled as a power induction unit
which serves all the zones on the floor,
the interior zones have terminal type
std VAV and the exterior zones have
series PIU. With in the exterior zones I
have specified flow rates, heat/cool
capacity reflecting the FC. However I am
getting lots of unmet hours from these
exterior zones (~500 hrs each). I
inputted a REHEAT-DELTA-T in of 57F
(based on fan flow rates and heat
capacity) into each of the exterior
zones. This greatly reduced the unmet
hours; however I find it strange because
the unmet hours are completely dependent
on REHEAT-DELTA-T and completely
independent of the zone heat capacity. I
appear to have a poor understanding of
how the PIU system works, if anyone
could provide further insight it would
be much appreciated.</p>
<p class="ecxMsoNormal"><br>
</p>
<p class="ecxMsoNormal">John</p>
</div>
<br>
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