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I agree that heat recovery makes a huge difference on the heating
load and have seen that in many models. Try changing your cooling
setpoint in the VAV model from "warmest" or "fixed" to "OA-Reset".
<br>
<br>
Regarding separating out outdoor air heating loads -- the quick,
imprecise method is to look at the difference between the LS-C and
the SS-D peak heating loads -- which you are already doing. The
primary difference between these two is ventilation. (but peaks
could occur at different times etc.)<br>
<br>
The more precise method is to run your model with and without
outdoor air (which is a pain).<br>
<br>
Note that EE4 only does the reduction of OA for zonal system types
-- for other systems it is using heat recovery routines in DOE-2.1e.<br>
<br>
(Still haven't had a peek at your model -- hopefully tonight.)<br>
<br>
On 12/9/2010 4:26 PM, Daniel Knapp wrote:
<blockquote
cite="mid:A20AE930-E980-42BA-88BD-0618C2262C95@arborus.ca"
type="cite">Hi Brian,
<div><br>
</div>
<div>Your point about OA fraction and supply air setpoint is well
taken, but I have also tried modelling this with 50% OA (25,000
cfm) in a single zone system at higher supply air setpoints of
95ºF without seeing much of a return. Maybe my expectations
have been set unreasonably high by EE4's crude method of cutting
OA volumes to model ERV, but I still tend to think of OA heating
as a fairly high fraction of the peak heating load in winter.
(ERV peak heating is nearly double the building peak loads (LS-C
report), but is still a fraction of the HVAC peak load (SS-D
report, which is partly so high because it's at building
warmup)). </div>
<div><br>
</div>
<div>Is there a clear way to separate out the outdoor air heating
load in the SIM file? </div>
<div><br>
</div>
<div>Thank you everyone for your thoughtful and helpful replies!</div>
<div><br>
</div>
<div>Cheers,</div>
<div>Dan</div>
<div><br>
</div>
<div>—</div>
<div>
<div><span class="Apple-style-span" style="border-collapse:
separate; color: rgb(0, 0, 0); font-family: Verdana;
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white-space: normal; widows: 2; word-spacing: 0px;
font-size: medium;">Daniel Knapp, PhD, LEED® AP O+M<br>
<a moz-do-not-send="true" href="mailto:danielk@arborus.ca">danielk@arborus.ca</a><br>
<br>
Arborus Consulting<br>
Energy Strategies for the Built Environment<br>
<a class="moz-txt-link-abbreviated" href="http://www.arborus.ca">www.arborus.ca</a><br>
76 Chamberlain Avenue <br>
Ottawa, ON, K1S 1V9 <br>
Phone: (613) 234-7178 ext. 113<br>
Fax: (613) 234-0740<br>
<span></span><br>
<br>
</span>
</div>
<br>
<div>
<div>On 2010-12-09, at 1:30 PM, Brian Fountain wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">
<div bgcolor="#ffffff" text="#000000"> Hi Daniel,<br>
<br>
I haven't looked at your model yet -- will try and take a
look this afternoon. <br>
<br>
One thing to consider is the outdoor air fraction and the
supply air temperature setpoint. If you have a low OA
fraction, say 15% and a low supply air temperature, say
55F -- then often you will be mixing to satisfy that SAT
and the heat recovery will only come into play for very
cold temperatures. Meanwhile, you will be adding static
pressure on your system and seeing notable increased fan
energy.<br>
<br>
On the other hand, if you have a dedicated outdoor air
system then you will see dramatic savings with an ERV. <br>
<br>
I saw that you were playing with the ERV control -- FLOAT
is the default and maximizes heat recovery always -- this
would be typical of a heat pipe where you can't modulate
the heat recovery. Trim economizer is non-typical --
bringing in more OA to compensate for excess heat
recovery. I usually use MA reset. Have a look at the ERV
report in the .sim report to see actual heat recovered
(plus the added fan energy which is NOT reported on the
SV-A report and defaults at 1" for both supply and
return).<br>
<br>
Brian<br>
<br>
<br>
<br>
On 12/9/2010 12:55 PM, Daniel Knapp wrote:
<blockquote
cite="mid:7005472E-008C-480E-83E3-4D401A1EF4C6@arborus.ca"
type="cite">
<pre wrap="">Hello,
I've been trying to understand how ERV works because I am finding the energy savings to be somewhat less than I had expected. Ottawa has a very cold climate in the winter and a warm, humid climate in the summer and I would expect enthalpy wheels to be a very good energy saving strategy. Instead, I am finding that in many cases the building uses more energy and in the best case scenario (OA exhaust DH, mixed air reset, modulate HX) on a VAV system saves only 0.15%. I have built a simple box model with one system in a two-storey office building and tried a number of different control strategies (see attached tables for results). I have tried a VAV and a SZ system. The ERV is able to save marginally more energy in the SZ system, but in neither case are the results what I was expecting.
My question is this: are these results to be taken at face value and believed or is there a better way to model ERVs in a Canadian climate? It seems very unlikely to me that ERVs cannot be controlled in such a way as to save significant energy in a climate of extremes. (.inp file attached as well).
With thanks and best wishes,
Dan
—
Daniel Knapp, PhD, LEED® AP O+M
<a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="mailto:danielk@arborus.ca">danielk@arborus.ca</a>
Arborus Consulting
Energy Strategies for the Built Environment
<a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="http://www.arborus.ca/">www.arborus.ca</a>
76 Chamberlain Avenue
Ottawa, ON, K1S 1V9
Phone: (613) 234-7178 ext. 113
Fax: (613) 234-0740
</pre>
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