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<DIV>All;</DIV>
<DIV>I'm not sure this is a huge deal. Somehow folks manage to use the PRM and simulate air-cooled DX equipment (rated/baseline condensing drybulb T 95F) in Las Vegas and Phoenix (design drybulb condensing T 110F). </DIV>
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<DIV>The program will decrease the baseline/rated chiller or compressor efficiency and capacity at the higher hourly condensing temps, be those water or air, during the simulated year compared to the baseline/rated temperatures. I don't think any rating authority would argue with increasing the rated chiller capacity in the baseline to offset the loss of capacity at actual/simulated conditions. (And there is a 15% safety factor built in somewhere, for baselines modeled to the PRM.) One might want to chart the COP and capacity vs. ECWT curves for centrifugal chillers to make sure they extrapolate reasonably to the high ECWT temps. This would be an issue even if the baseline conditions were adjusted, and whatever program is used. </DIV>
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<DIV>Fred Porter</DIV>
<DIV>AEC<BR><BR>>>> "Matutinovic, Luka" <LMatutinovic@halsall.com> 06/05/09 2:06 PM >>><BR></DIV>
<DIV><SPAN class=591544819-05062009><FONT face=Univers color=#0000ff size=2>David,</FONT></SPAN></DIV>
<DIV><SPAN class=591544819-05062009><FONT face=Univers color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=591544819-05062009><FONT face=Univers color=#0000ff size=2>Thanks for your suggestions. We are planning to submit a CIR and also raise this issue with the 90.1 committee as Bill suggested. I thought about using the same COP / same conditions in both models to demonstrate a more realistic comparison. One approach would be to adjust my own chiller COP to match the operating conditions of App G. However, there may be potential hiccups in eQuest if the software is smart enough to realize it cannot generate the ECWT specified by App G using the actual weather data. So the other approach is to use the actual operating conditions in both models, but to adjust the reference building COP.</FONT></SPAN></DIV>
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<DIV><SPAN class=591544819-05062009><FONT face=Univers color=#0000ff size=2>Luka</FONT></SPAN></DIV><BR>
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<FONT face=Tahoma size=2><B>From:</B> bldg-sim-bounces@lists.onebuilding.org [mailto:bldg-sim-bounces@lists.onebuilding.org] <B>On Behalf Of </B>David S Eldridge<BR><B>Sent:</B> Friday, June 05, 2009 3:48 PM<BR><B>To:</B> bldg-sim@lists.onebuilding.org; bldg-rate@lists.onebuilding.org<BR><B>Subject:</B> Re: [Bldg-sim] Modeling chillers at non-standard operating conditions as per Appendix G<BR></FONT><BR></DIV>
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<P class=MsoNormal><SPAN style="COLOR: black">I think your (pretty strong) argument is that your Appendix G cooling tower will have difficulty producing 85F ECWT if the wetbulb is 86F. Your design is 9F difference, there must be some acceptable value between -1F and 10F for the baseline building approach.<o:p></o:p></SPAN></P>
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<P class=MsoNormal><SPAN style="COLOR: black">I speculate that the wording of G3.1.3.11 was to make the baseline use a colder ECWT below 85F as standard where available, not to penalize hot-humid projects.<o:p></o:p></SPAN></P>
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<P class=MsoNormal><SPAN style="COLOR: black">You may want to submit a CIR to establish a reasonable ECWT schedule, and/or review the 90.1 addenda so that you can move forward.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: black"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: black">Given that we can establish that both proposed and baseline chillers operate outside of non-standard conditions in Table 6.8.1J regarding the efficiency of the chiller, in most cases where something is excluded from the standard the approach is to use the same value in both models so not penalizing you, but not a place for efficiency gains either. This may be the approach rather than your extrapolated efficiency it is either covered by the standard, or not covered, so the same performance curves could be used in both models.<o:p></o:p></SPAN></P>
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<P class=MsoNormal><SPAN style="COLOR: black">Unfortunate that this would be such a potentially large energy end-use. Still there might be opportunities since that would only apply to the mandatory efficiency of the chiller at the non-standard conditions. The number of chillers, heat exchanger pressure drop/pumping power, water temperatures and temperature reset schedules could all vary focus in these areas for efficiency opportunities in your proposed design.<o:p></o:p></SPAN></P>
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<P class=MsoNormal><SPAN style="COLOR: black">I hope this helps, and please others chime in if you agree or disagree with this approach.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: black"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: black">David<o:p></o:p></SPAN></P>
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<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; COLOR: gray; FONT-FAMILY: 'Tahoma','sans-serif'">David Eldridge, PE<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; COLOR: gray; FONT-FAMILY: 'Tahoma','sans-serif'">LEED® AP, HBDP<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: 'Tahoma','sans-serif'"><BR></SPAN><B><SPAN style="FONT-SIZE: 10pt; COLOR: #365f91; FONT-FAMILY: 'Tahoma','sans-serif'">Grumman/Butkus Associates</SPAN></B><SPAN style="FONT-SIZE: 10pt; COLOR: gray; FONT-FAMILY: 'Tahoma','sans-serif'"> | </SPAN><SPAN style="FONT-SIZE: 10pt; COLOR: #8db3e2; FONT-FAMILY: 'Tahoma','sans-serif'">820 Davis Street, STE 300 | Evanston, IL 60201 | Ph: (847) 328-3555, ext 224 | Fax: (847) 328-4550</SPAN><SPAN style="FONT-SIZE: 10pt; COLOR: gray; FONT-FAMILY: 'Tahoma','sans-serif'"><o:p></o:p></SPAN></P>
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<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; COLOR: gray; FONT-FAMILY: 'Tahoma','sans-serif'">Energy Consultants and Design Engineers</SPAN><SPAN style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: 'Calibri','sans-serif'"><BR></SPAN><SPAN style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: 'Tahoma','sans-serif'">____________________________________________________________________________________________________________________<o:p></o:p></SPAN></P>
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<P class=MsoNormal><B><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Tahoma','sans-serif'">From:</SPAN></B><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Tahoma','sans-serif'"> bldg-sim-bounces@lists.onebuilding.org [mailto:bldg-sim-bounces@lists.onebuilding.org] <B>On Behalf Of </B>Matutinovic, Luka<BR><B>Sent:</B> Thursday, June 04, 2009 12:52 PM<BR><B>To:</B> bldg-sim@lists.onebuilding.org; bldg-rate@lists.onebuilding.org<BR><B>Subject:</B> Re: [Bldg-sim] Modelling chillers at non-standard operating conditions as per Appendix G<o:p></o:p></SPAN></P></DIV></DIV>
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<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Univers">Thanks to Linda and Bill for helping me out with this issue. As far as App G is concerned, there is a specific set of condenser and chiller temperatures and condenser flows that must be used in the reference building that represent ARI standard conditions for which the COP is 6.1 (for centrifugal chillers > 300 tons). Therefore the reference building always operates at standard conditions, while the proposed building's performance varies depending on specific operating conditions.</SPAN><o:p></o:p></P></DIV>
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<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Univers">While this is tantamount to asking someone to model the proposed building with a Chicago weather file, compare it to a reference building with a Miami weather file and require you to reduce cooling use, the rules are at present clear. Unreasonable, but clear.</SPAN><o:p></o:p></P></DIV>
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<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Univers">So, my question to the design/simulation community is this: </SPAN><o:p></o:p></P></DIV>
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<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Univers">Has anyone been able to spec a large centrifugal chiller (900-1500 tons) with a full load COP matching or at least approaching 6.1, for a Zone 1 climate? (Specifically my design conditions are 122F db, 86F wb, 42/57F CHW, 95/105 CW) If so, if you could please post the spec sheet that would be fantastic. Unfortunately the manufacturers don't post this kind of performance data so a call to the local rep is needed to produce project specific data.</SPAN><o:p></o:p></P></DIV>
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<P class=MsoNormal style="MARGIN-BOTTOM: 12pt"><B><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Tahoma','sans-serif'">From:</SPAN></B><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Tahoma','sans-serif'"> Matutinovic, Luka <BR><B>Sent:</B> Tuesday, June 02, 2009 7:28 PM<BR><B>To:</B> bldg-sim@lists.onebuilding.org; 'bldg-rate@lists.onebuilding.org'<BR><B>Subject:</B> Modelling chillers at non-standard operating conditions as per Appendix G</SPAN><o:p></o:p></P>
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<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Univers">Hello All,</SPAN><o:p></o:p></P></DIV>
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<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Univers">I have a question regarding the minimum centrifugal chiller efficiencies for conditions not covered by ASHRAE 90.1-2004 section 6.4.1.2. Specifically, I'm trying to model a chiller for a building in a hot humid climate. The specified operating conditions for the condenser EWT are 95ºF (35ºC), which is beyond the range of conditions covered by ASHRAE.</SPAN><o:p></o:p></P></DIV>
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<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Univers">In this case, what should I use for the minimum chiller efficiency in my reference building? Do I still have to follow Appendix G section G3.1.3.11 which states that my condenser supply temp shall be the lower of 84ºF (29ºC) or 10ºF (5.6ºC) approach to design wet-bulb. The wet-bulb in this climate is 86ºF (30ºC), so the 10ºF approach is therefore 96ºF, which means my condenser supply temp (EWT) shall be 84ºF (29ºC), the lower of the two. At this condenser EWT, the minimum ASHRAE efficiencies from Table 6.8.1J vary depending on condenser flow. Since condenser flow is not specified by Appendix G, should I simply used the Kadj equations at the bottom of that table? If that's the case, the condenser DT is 15ºF (8ºC) and the Lift is 41ºF (22.7ºC) and I arrive at an adjustment factor Kadj of 0.88. Applied to my standard COP of 6.1, I get a COP of 5.4. </SPAN><o:p></o:p></P></DIV>
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<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Univers">My issue with this approach is that this COP is very difficult to achieve at our operating conditions. In my opinion, this is an unfair comparison for chillers in very hot humid climates since Appendix G is prescribing operating conditions which are considerably more "temperate" than the extreme conditions under which our chillers will operate. We can realistically achieve a COP of 5.1. In this climate, cooling is a dominant load, yet due to Appendix G "rules", it will be very difficult to meet the LEED energy prerequisite, since our chiller are worse than reference.</SPAN><o:p></o:p></P></DIV>
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<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Univers">Finally, I'm assuming that since ASHRAE does not cover this operating range, I don't have to worry about meeting the mandatory provisions for efficiency listed in Tables 6.8.1H, I and J in my proposed building, ie there is no minimum chiller efficiency for this range.</SPAN><o:p></o:p></P></DIV>
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<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Univers">Any help in this matter would be much appreciated. If I've missed something in my calculations or wasn't clear enough, please let me know because this issue is a big concern to our project.</SPAN><o:p></o:p></P></DIV>
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