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<p class=MsoNormal><span style='font-size:11.0pt;color:black'>Derek, <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:black'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:black'>I’m not
sure if this is exactly what you’re running in to, but I thought I’d
share what I learned over the weekend re: modeling CRAC units using PSZ systems,
with humidity control.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:black'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:black'>I have set up my
CRAC unit as a PSZ with DX cooling and electric heat + humidification. Required
space conditions are 70 degF +/-5 degF and 50% RH +/- 5% RH; supply air is 55
degF. Initially, in an hourly report, I saw that space temperature and high
humidity level were being met. However, the low humidity limit was not being
met. In fact, the unit’s return air humidity ratio was tracking the OA humidity
ratio (as low as 15% RH at 70 degF), until it reached the high limit (dehum
worked fine). This tracking was particularly strange as the unit is 100%
recirculation (0 CFM outside air). Further checking showed that no heat was
being used by the humidification coil, even though it was installed and set
properly. <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:black'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:black'>After some back
and forth, I tried setting the outside air quantity at 0.0001% (~1 CFM OA, for
this particular unit). A re-run and re-check of the hourly data showed that all
required conditions (including the low humidity level) were being met. Strange,
no? In my case, I don’t think it would impact the energy consumption at
all. Theoretically, I shouldn’t need any humidification if I don’t
have any outside air coming in (I haven’t modeled any moisture losses,
and my 55 degF off-coil condition (55 degF DP) won’t remove moisture from
the 70 degF, 50% RH (50.5degF DP) room air). <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:black'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:black'>If you’re
seeing something similar, some questions to think about are: what are the
conditions that you’re trying to achieve? What is your supply air
condition? How much outside air are you bringing in? Do you have any moisture
losses (infiltration)? I hope that’s of some help. If not to you, than to
someone else! <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:black'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:black'>Regards,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:black'>Pete<o:p></o:p></span></p>
<div>
<p class=MsoNormal><span style='font-size:10.0pt;color:black'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:black'><o:p> </o:p></span></p>
<p class=MsoNormal><b><span style='font-size:11.0pt;color:black'>Peter Worley</span></b><b><span
style='font-size:11.0pt;color:black'><o:p></o:p></span></b></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:#595959'>Mechanical
Engineer<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:#595959'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:#595959'>155 Avenue of
the Americas New York NY 10013 USA<o:p></o:p></span></p>
<p class=MsoNormal><b><span style='font-size:10.0pt;color:#595959'>t</span></b><span
style='font-size:10.0pt;color:#595959'> +1 212 229 2669 <b>d</b> +1 212
897 1339 <o:p></o:p></span></p>
<p class=MsoNormal><b><span style='font-size:10.0pt;color:#595959'>f</span></b><span
style='font-size:10.0pt;color:#595959'> +1 212 229 1056<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:#595959'>www.arup.com<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:#595959'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:#595959'><img width=78
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Derek Huang
[mailto:Derek.Huang@atce.com] <br>
<b>Sent:</b> Saturday, July 10, 2010 9:10 PM<br>
<b>To:</b> equest-users@lists.onebuilding.org<br>
<b>Subject:</b> [Equest-users] Humidity control in PSZ Heat Pump system in Base
design<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Hi
all,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Per
ASHRAE 90.1, I have to specify PSZ heat pump for each zone. Each unit serves
one zone of a data center. From the DD Wizard, I have modified to add humidity
controls in Detailed Data Edit mode but it seems the Base model didn’t
take this into account (can tell from the energy summary). Any ideas ?<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Thanks<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'><o:p> </o:p></span></p>
<p class=MsoNormal><strong><span style='font-family:"Gill Sans MT","sans-serif";
color:#181B53'>Derek Huang, LEED AP,
CPD
<o:p></o:p></span></strong></p>
<p class=MsoNormal><strong><span style='font-family:"Gill Sans MT","sans-serif";
color:#181B53;font-weight:normal'>Mechanical Engineer</span></strong><strong><span
style='font-size:10.0pt;font-family:"Gill Sans MT","sans-serif";color:#181B53;
font-weight:normal'><o:p></o:p></span></strong></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><img width=181 height=36 id="_x0000_i1025"
src="cid:image003.jpg@01CB21AA.F64E3AB0"><o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Gill Sans MT","sans-serif";
color:#67917D'>97 E. Brokaw Road, No 300<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Gill Sans MT","sans-serif";
color:#67917D'>San Jose, CA 95112<o:p></o:p></span></p>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Gill Sans MT","sans-serif";
color:#67917D'>Direct</span></b><span style='font-size:10.0pt;font-family:"Gill Sans MT","sans-serif";
color:#67917D'>: 408 487-1305<o:p></o:p></span></p>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Gill Sans MT","sans-serif";
color:#67917D'>Fax:</span></b><span style='font-size:10.0pt;font-family:"Gill Sans MT","sans-serif";
color:#67917D'> 408 436-1511<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Gill Sans MT","sans-serif";
color:#221B53'><a href="http://www.atce.com/">www.atce.com</a><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Gill Sans MT","sans-serif";
color:#221B53'>derek.huang@atce.com<o:p></o:p></span></p>
<p class=MsoNormal> <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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