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I have a hard time believing that eQUEST /DOE-2 has been missing
this important cooling load component (latent load from outside air)
all these decades.<br>
How are you modeling this outside air flow? In LOADS as
infiltration or in SYSTEMS as mechanical ventilation? If it's the
latter, do you have the FAN-SCHEDULE<br>
set to always on? If you're simply trying to see the change in
loads from a constant change in outdoor air flow, why don't you
model it as INFILTRATION, and that<br>
way you can see the impact on sensible and latent loads due to
INFILTRATION as well as circumvent any of the interactions between
this outside air<br>
flow and the system operations. I would be quite surprised if indeed
DOE-2 has been missing this latent component, and that you're not
seeing some other<br>
unexpected or unaccounted for effect.<br>
<br>
Joe<br>
<pre class="moz-signature" cols="90">Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
<a class="moz-txt-link-abbreviated" href="mailto:yjhuang@whiteboxtechnologies.com">yjhuang@whiteboxtechnologies.com</a>
<a class="moz-txt-link-abbreviated" href="http://www.whiteboxtechnologies.com">www.whiteboxtechnologies.com</a>
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"
</pre>
<br>
On 3/13/2013 3:16 PM, Z Smith wrote:
<blockquote
cite="mid:66FE4ED8A3A23C4FBFFD51226EE1A4CF2D85B1E7@BL2PRD0611MB409.namprd06.prod.outlook.com"
type="cite">
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<div>
<p><span>Thanks to both David and Bruce, whom I’ll answer
together: </span></p>
<p><span> </span></p>
<p><span>The beauty of the VLI metric is that it doesn’t depend
on how a particular HVAC system will get the ventilation air
to the comfortable condition (75°F / 50%RH)—it just
quantifies the enthalpy difference between the outdoor
condition and the desired endpoint inside the building. It
could be that an Outdoor Air unit is cooling warm moist
outside air from to 55°F and then doing re-heat, or it could
be that the re-heat is being provided from internal gains or
solar gain—but the VLI doesn’t care. </span></p>
<p><span> </span></p>
<p><span>In our first message, we turned off heat for clarity.
When we have also run cases where we use DX cooling + heat
pump, and also DX cooling and electric resistance heat—but
we always find that eQuest predicts that New Orleans and
Tucson (which have similar HDD and CDD but very different
VLI) should have very similar EUI, and the very high Outdoor
Air rates (at which we would expect New Orleans to show off
a much higher EUI) do not show a different predicted EUI for
the two cities. They should have different EUI vs ACH, but
they don’t—they match in slope and value. </span></p>
<p><span> </span></p>
<p><span>To David’s point about ACH and fan power: The ACH in
our discussions are not recirculating air rates but the rate
of Outdoor Air. We plot up EUI vs OA ACH; you would expect
fan energy for handling skin loads to fall away as an effect
once we get to high ACH. Our results are very similar
whether we introduce this outdoor air as deliberate
ventilation or as infiltration—so the fan energy associated
with actually introducing the outdoor air is not a big
effect compared to the energy to condition this air. </span></p>
<p><span> </span></p>
<p><span>To the question of what we’re really trying to do here:
When we work in hot-humid climates, we are concerned that
eQuest will show the correct benefit for either decreased
infiltration or improved energy recapture from systems like
Enthalpy Recovery Ventilators. We have set up the Tucson /
New Orleans comparison as a thought-experiment where common
sense tells us that we should see a big difference but
eQuest shows none. </span></p>
<p><span> </span></p>
<div>
<p><b><span>Z Smith, AIA, LEED AP BD+C </span></b><span>| Director
of Sustainability & Building Performance |<b> </b></span><b><span>Eskew+Dumez+Ripple</span></b><span>
| 365 Canal Street, Suite 3150 | New Orleans, LA 70130 |
504.561.8686 |<b> </b></span><span><a
moz-do-not-send="true"
href="http://www.eskewdumezripple.com/"><span>eskewdumezripple.com</span></a>
</span></p>
<p><span> </span></p>
</div>
<p><span> </span></p>
<div>
<div>
<p><b><span>From:</span></b><span> David Eldridge
[<a class="moz-txt-link-freetext" href="mailto:DEldridge@grummanbutkus.com">mailto:DEldridge@grummanbutkus.com</a>]
<br>
<b>Sent:</b> Wednesday, March 13, 2013 4:51 PM<br>
<b>To:</b> 'Hall, Brendan'; Z Smith;
<a class="moz-txt-link-abbreviated" href="mailto:equest-users@lists.onebuilding.org">equest-users@lists.onebuilding.org</a><br>
<b>Cc:</b> Corey Squire<br>
<b>Subject:</b> RE: [Equest-users] Does eQuest properly
account for latent loads in infiltration &
ventilation? </span></p>
</div>
</div>
<p> </p>
<p><span>The VLI is meant as a method of comparing different
climates and informing the designer about suitable
technologies when looking at design loads, as opposed to
being used as a direct predictor of energy usage. </span></p>
<p><span> </span></p>
<p><span>The VLI approach used for energy calculations is also a
little bit of an oversimplification to only supply room
neutral air – the system in eQUEST (or any other software)
would typically be supplying cooler air at the cooling coil,
and then some combination of the load in the space and
reheat brings the total quantity of air back to the room
conditions – obviously not the same calculation as the VLI
method. </span></p>
<p><span> </span></p>
<div>
<p><span>If the goal is to recreate the VLI calculation, then
you probably want to have a room that doesn’t have ANY
exterior walls, as well as removing internal gains from
occupants and lights, etc. You may also want to zero out
the fan power, which may be included in the SEER rating.
For instance in your 1 ACH case the room may not be in
control if the thermal load requires more than 1 ACH at
the peak times. Another issue is the VLI is operating in
terms of load, while the modeled building is using
equipment efficiencies which are going to vary over the
range of annual conditions. The SEER approach tries to
account for that, but the modeled buildings would have
varying tempeature and humidity ranges which affect the
system efficiencies in different proportions – but mainly
to say that using the same SEER in the hand calc won’t
necessarily give the same results as an energy model,
unless you had also replaced all of the equipment
efficiency curves. </span></p>
<p><span> </span></p>
<p><span>Anyway, not knowing what the purpose of the effort
is, to recreate the VLI you’ll need to strip the model of
many other factors, and there is likely to be a
combination of environmental conditions and system
efficiency causing the Arizona / Louisiana results not to
behave as you expected. Start with verifying the AHU
configuration and setpoints, and whether the modeled
spaces are maintained at the same temperature and humidity
between the two cases, secondly verify if the conditions
were the temp/humity that were desired. From your
description of no heating system I’d expect some variation
from the constant conditions used in the VLI calculation.
</span></p>
<p><span><br>
David </span></p>
<p> <span> <span> </span> </span> </p>
<p> <span>
</span> <span> </span></p>
<p><span> </span><span> </span></p>
<p><span>David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP,
BEAP, HBDP </span></p>
<p><b><span>Grumman/Butkus Associates</span></b><span> </span></p>
<p> <span>
</span> <span> </span></p>
<p><span> </span><b><span>From:</span></b><span> Bruce
Easterbrook [<a class="moz-txt-link-freetext" href="mailto:bruce5@bellnet.ca">mailto:bruce5@bellnet.ca</a>] <br>
<b>Sent:</b> Wednesday, March 13, 2013 4:22 PM<br>
<b>To:</b> Z Smith<br>
<b>Cc:</b> Hall, Brendan;
<a class="moz-txt-link-abbreviated" href="mailto:equest-users@lists.onebuilding.org">equest-users@lists.onebuilding.org</a>; Corey Squire<br>
<b>Subject:</b> Re: [Equest-users] Does eQuest properly
account for latent loads in infiltration &
ventilation? </span></p>
<p> </p>
<p><span>I would think without the ability to heat or reheat
you aren't controlling your humidity to 50% RH in the New
Orleans building.<br>
Bruce Easterbrook P.Eng<br>
Abode Engineering</span> </p>
<p><span> </span></p>
</div>
<p><span> </span></p>
<div>
<div>
<p><b><span>From:</span></b><span>
<a moz-do-not-send="true"
href="mailto:equest-users-bounces@lists.onebuilding.org">equest-users-bounces@lists.onebuilding.org</a>
[<a moz-do-not-send="true"
href="mailto:equest-users-bounces@lists.onebuilding.org">mailto:equest-users-bounces@lists.onebuilding.org</a>]
<b>On Behalf Of </b>Hall, Brendan<br>
<b>Sent:</b> Wednesday, March 13, 2013 3:40 PM<br>
<b>To:</b> Z Smith; <a moz-do-not-send="true"
href="mailto:equest-users@lists.onebuilding.org">equest-users@lists.onebuilding.org</a><br>
<b>Cc:</b> Corey Squire<br>
<b>Subject:</b> Re: [Equest-users] Does eQuest properly
account for latent loads in infiltration &
ventilation? </span></p>
</div>
</div>
<p> </p>
<p><span>One note about using heating and cooling degree days
for that purpose is that ventilation air is usually locked
out during unoccupied times so the annual total would be
much lower. From a quick read of the paper you cited it
seems that they used all 8760 hours. You would need to
isolate the occupied hours when the economizer is not likely
to be in use to get a more accurate number. </span></p>
<p><span> </span></p>
<p><span> </span></p>
<p><span>Brendan Hall </span></p>
<p><span> </span></p>
<div>
<div>
<p><b><span>From:</span></b><span>
<a moz-do-not-send="true"
href="mailto:equest-users-bounces@lists.onebuilding.org">equest-users-bounces@lists.onebuilding.org</a>
[<a moz-do-not-send="true"
href="mailto:equest-users-bounces@lists.onebuilding.org">mailto:equest-users-bounces@lists.onebuilding.org</a>]
<b>On Behalf Of </b>Z Smith<br>
<b>Sent:</b> Wednesday, March 13, 2013 3:26 PM<br>
<b>To:</b> <a moz-do-not-send="true"
href="mailto:equest-users@lists.onebuilding.org">equest-users@lists.onebuilding.org</a><br>
<b>Cc:</b> Corey Squire<br>
<b>Subject:</b> [Equest-users] Does eQuest properly
account for latent loads in infiltration &
ventilation? </span></p>
</div>
</div>
<p> </p>
<div>
<p><span>We are interested in using eQuest to evaluate the
impact of improved air-sealing or changed outdoor air
ventilation rates. Even with very simple test case
buildings and run-of-the-mill HVAC systems, we get results
that make it seem as if eQuest is not accounting for the
latent component of outdoor air brought into a building. </span></p>
</div>
<div>
<p><span> </span></p>
</div>
<div>
<p><span>We are using Lew Harriman et al.’s 1997 ASHRAE
Journal paper on the “Ventilation Load Index” as a reality
check. </span></p>
</div>
<div>
<p><span><a moz-do-not-send="true"
href="http://masongrant.com/pdf_2008/Ventilation_Loads.pdf">http://masongrant.com/pdf_2008/Ventilation_Loads.pdf</a>
</span></p>
</div>
<div>
<p><span>The authors characterize the total load (latent and
sensible) for bringing 1 cfm continuously into the
building for a number of cities. It’s interesting to
consider two cities with comparable CDD but very different
latent loads for ventilation air: </span></p>
</div>
<div>
<p><span> </span></p>
</div>
<div>
<p><span>New Orleans CDD=2776 VLI=12.3 [latent] + 1.8
[sensible] =14.1 ton-hrs/yr </span></p>
</div>
<div>
<p><span>Tucson CDD=3017 VLI= 1.5 [latent] + 3.0
[sensible] = 4.5 ton-hrs/yr </span></p>
</div>
<div>
<p><span> </span></p>
</div>
<div>
<p><span>The VLI is the cumulative load to bring 1cfm from
whatever the hourly condition is in the TMY2 file to 75°F,
50% RH (65gr/lb). Its units are ton-hr/yr for
convenience, converted to annual kBtu by multiplying VLI
by12 kBtu/ton-h. </span></p>
</div>
<div>
<p><span> </span></p>
</div>
<div>
<p><span>So, for example, if we have a building with 2,000ft2
of floor area and a volume of 20,000ft3 with a ventilation
rate of 1ACH, outdoor air is being introduced to the
building at 20,000/60 = 333cfm. The annual cooling &
dehumidification load associated with this airflow is 333
x 14.1 = 4,695 ton-hrs/yr in New Orleans and 1,383
ton-hrs/yr in Tucson. If, for simplicity, we assume the
air system brings this air to 75°F, 50% RH with a SEER of
13 kBtu/kWh in both cities, then the energy consumption
associated with 1ACH for this 2000ft2 building is 4,334
kWh in New Orleans and 1,383 kWh in Tucson. The impact on
building site EUI will be 7.4 kBtu/sf/yr in New Orleans
and 2.4 kBtu/sf/yr in Tucson – a difference of about
5kBtu/sf/yr. If one were to consider ventilating at
10ACH, then the impact would be 10x as large—74kBtu/sf/yr
in New Orleans vs 24 kBtu/sf/yr in Tucson—a difference of
~50 kBtu/sf/yr. </span></p>
</div>
<div>
<p><span> </span></p>
</div>
<div>
<p><span>When we run an eQuest model of a hypothetical 2000ft2
building with no windows (to rule out solar gain
differences) and no heating system, only cooling, we find
that the EUI does increase with ACH at the two
locations—but there is almost no difference in how the
predicted EUI rises with ACH for the two cities with
wildly different VLI. The EUI rises by the same ~35
kBtu/sf/yr when going from 1ACH to 10ACH at both
locations. </span></p>
</div>
<div>
<p><span> </span><span> </span></p>
</div>
<div>
<p><span>Results summarized below for total building EUI
(kBtu/sf/yr): </span></p>
</div>
<div>
<p><span> </span><span> </span></p>
</div>
<div>
<p><span> eQuest Simple model
using VLI </span></p>
</div>
<div>
<p><span> ACH New Orleans Tucson New
Orleans Tucson </span></p>
</div>
<div>
<p><span> 1 42 40
36 30 </span></p>
</div>
<div>
<p><span> 10 76 74
126 74 </span></p>
</div>
<div>
<p><span>------ -----------------------
----------------------- </span></p>
</div>
<div>
<p><span> 1->10 34 34
90 44 </span></p>
</div>
<div>
<p><span> </span><span> </span></p>
</div>
<div>
<p><span>(This windowless test building had R10 walls, R20
roof, R5 floor – but all we are interested in is the *<b>difference</b>*
in total EUI associated with the increased ACH, which
shouldn’t depend on these choices). </span></p>
</div>
<div>
<p><span> </span><span> </span></p>
</div>
<div>
<p><span>Z Smith, AIA, LEED AP BD+C | Director of
Sustainability & Building Performance |
Eskew+Dumez+Ripple | 365 Canal Street, Suite 3150 | New
Orleans, LA 70130 | 504.561.8686 | eskewdumezripple.com </span></p>
</div>
<div>
<p><span> </span><span> </span></p>
</div>
<div>
<p><span> </span><span> </span></p>
</div>
</div>
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