HI all, thanks for the excellent feedback, just wanted to report back for the archive;<br><br>Yes, since hotel is considered residential, I am applying PTHP. <br><br>In ASHRAE 90.1-2007 SI, table 6.8.1D, the COP equation is 3.60 - (.213 x Cap/1000) where Capacity is in units of [kW]. This must be an error? Cap units should be [W] or equation should be 3.60 - (.213 x Cap). Using this equation, this limits the COP of a PTHP to between 3.15 for 2.1 kW units and below and 2.66 for 4.4 kW and above (with COP inclusive of fan energy). Thanks for drawing my attention back to this equation, this significantly increases the Baseline cooling. <br>
<br>I agree, my pump and fan energy also needs to be correctly sized according to pressure drop, I just used the defaults as a place-holder until detailed design. <br><br>Generally the point of chilled water vs. Dx having no clear advantage is a good one, chilled water introduces greater heat transfer approach as pointed out and requires pump energy. However, we have learned that the client is actually only using VAV in certain zones, the guest rooms will be served by zone terminal variable flow chilled water coils (fancoils) and AHU's with enthalpy recovery. Unfortunately modeling this system is proving quite challenging in EnergyPlus so I don't have any updated results yet. <br>
<br>Sincere thanks again for the comments! <br><br>Cheers,<br><br>Marcus<br>-- <br>Marcus Jones, LEED AP, M.Sc. <br><i>Freelance energy consultant</i><br><i>Vienna, Austria</i><br><br><br><br><div class="gmail_quote">On Tue, May 24, 2011 at 5:40 PM, Paul Riemer <span dir="ltr"><<a href="mailto:Paul.Riemer@dunhameng.com">Paul.Riemer@dunhameng.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div link="blue" vlink="purple" lang="EN-US"><div><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D">Marcus,</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D">Compared to packaged DX equipment, an air cooled chiller has two fundamental efficiency disadvantages: extra heat transfer approach and the pumping energy of the water.</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D">Load reductions always help, but to hone in a comparison of the efficiencies of these mechanical systems, I also suggest you look closely at:</span></p>
<p><span style="font-size:11.0pt;color:#1F497D"><span>-<span style="font:7.0pt "Times New Roman""> </span></span></span><span style="font-size:11.0pt;color:#1F497D">the COP values and their corresponding rated ambient temperatures in the referenced standards and on your equipment literature</span></p>
<p><span style="font-size:11.0pt;color:#1F497D"><span>-<span style="font:7.0pt "Times New Roman""> </span></span></span><span style="font-size:11.0pt;color:#1F497D">compressor types, sizing, and curves</span></p>
<p><span style="font-size:11.0pt;color:#1F497D"><span>-<span style="font:7.0pt "Times New Roman""> </span></span></span><span style="font-size:11.0pt;color:#1F497D">maybe, thermal storage</span></p><p class="MsoNormal">
<span style="font-size:11.0pt;color:#1F497D"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D">Good luck,</span></p><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D"> </span></p>
<div><p class="MsoNormal" style="text-autospace:none"><b><span style="font-size:10.0pt;color:#5F574F">Paul Riemer, PE, LEED AP</span></b><span style="font-size:11.0pt;color:#1F497D"> </span></p><p class="MsoNormal" style="text-autospace:none">
<span style="font-size:10.0pt;color:#5F574F">Associate / Mechanical</span><span style="font-size:11.0pt;color:#1F497D"></span></p><p class="MsoNormal"><b><span style="color:#C4262E">DUNHAM</span></b><span style="font-size:11.0pt;color:#5F574F"></span></p>
</div><p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D"> </span></p><div><div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in"><p class="MsoNormal"><b><span style="font-size:10.0pt">From:</span></b><span style="font-size:10.0pt"> <a href="mailto:bldg-sim-bounces@lists.onebuilding.org" target="_blank">bldg-sim-bounces@lists.onebuilding.org</a> [mailto:<a href="mailto:bldg-sim-bounces@lists.onebuilding.org" target="_blank">bldg-sim-bounces@lists.onebuilding.org</a>] <b>On Behalf Of </b>Bishop, Bill<br>
<b>Sent:</b> Tuesday, May 24, 2011 9:57 AM<br><b>To:</b> Marcus</span></p><div><div></div><div class="h5"><br><b>Cc:</b> <a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a><br>
<b>Subject:</b> Re: [Bldg-sim] PTHP Baseline outperforming VAV</div></div><p></p></div></div><div><div></div><div class="h5"><p class="MsoNormal"> </p><div><p class="MsoNormal">Hi Marcus,</p><p class="MsoNormal"> </p><p class="MsoNormal">
I agree with your selection of PTHP for the baseline, since your project is a hotel, which is specifically listed in the notes to Table G3.1.1A as being a residential building type.</p><p class="MsoNormal">I am not surprised that you are showing an energy penalty versus an ASHRAE 90.1 PTHP – the cooling and fan energy is relatively low for those units.</p>
<p class="MsoNormal"> </p><p class="MsoNormal">As James said, make sure you are accurately modeling your fan and pumping energy in the proposed system. Unfortunately, there are no pressure drop adjustment allowances for Systems 1 & 2.</p>
<p class="MsoNormal">The maximum allowable SHGC (0.25) is already pretty low for Abu Dhabi, so your “better windows” might not have a lower SHGC than the value required for the baseline, and you will not get a solar load reduction in the proposed model.</p>
<p class="MsoNormal"> </p><p class="MsoNormal">Since your baseline cooling efficiency is dependent on the system capacities, make sure you are not using too large of a baseline cooling COP. (It should actually be calculated separately for each baseline system.) Using the efficiency equation from Table 6.8.1D, assuming 400 cfm/ton air flow rate and removing the fan power energy from the efficiency, I calculate COP = 2.94 for a 15,000 Btu/hr unit (for example). There is a separate heating COP but your heating load is negligible per your report below.</p>
<p class="MsoNormal"> </p><p class="MsoNormal">Regards,</p><p class="MsoNormal">Bill</p><p class="MsoNormal"> </p><p class="MsoNormal"><img src="" alt="Signature in jpg form" height="123" width="496"></p><p class="MsoNormal">
</p><div><p class="MsoNormal"><b>From:</b> <a href="mailto:bldg-sim-bounces@lists.onebuilding.org" target="_blank">bldg-sim-bounces@lists.onebuilding.org</a> [mailto:<a href="mailto:bldg-sim-bounces@lists.onebuilding.org" target="_blank">bldg-sim-bounces@lists.onebuilding.org</a>] <b>On Behalf Of </b>Cheney<br>
<b>Sent:</b> Monday, May 23, 2011 9:55 PM<br><b>To:</b> James V Dirkes II, PE<br><b>Cc:</b> <a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a><br><b>Subject:</b> Re: [Bldg-sim] PTHP Baseline outperforming VAV</p>
</div><p class="MsoNormal"> </p><p class="MsoNormal">Hi Marcus, </p><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">Also pay attention to better glass in the proposed design. In a cooling-dominated building, better window means the heat can not easily escape from the building. You will not easily get credit from improving your window here. </p>
</div><div><p class="MsoNormal"> <br clear="all"></p><div><p class="MsoNormal">Regards, </p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">Cheney</p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">
LinkedIN @ <a href="http://ca.linkedin.com/pub/yu-cheney-chen/27/637/72b" target="_blank">http://ca.linkedin.com/pub/yu-cheney-chen/27/637/72b</a> </p></div><p class="MsoNormal" style="margin-bottom:12.0pt"> </p><div><p class="MsoNormal">
On Mon, May 23, 2011 at 3:18 PM, James V Dirkes II, PE <<a href="mailto:jim@buildingperformanceteam.com" target="_blank">jim@buildingperformanceteam.com</a>> wrote:</p><div><div><p class="MsoNormal">Dear Marcus,</p>
<p>· It seems that your Baseline system, at >5 floors, should be VAV with a chiller instead of a heat pump (using LEED 2009).</p><p>· As modeled, your baseline DOES have a notably higher COP, so it may well use less energy. <u>Part load performance</u> will have a significant effect, so you may want to check and compare those curves.</p>
<p>· Also check pump delta T and total pressure drop. If you continue with a non-chiller system, pump energy is a significant factor. If your Baseline becomes a chiller system, pump energy will probably become similar.</p>
<p>· Check fan total pressure drop for each system since your fan power is significantly larger in the Proposed system.</p><p>· In the US, it is common to apply occupancy sensors on a LEED project and ASHRAE 90.1 allows a 10% power reduction when these are used. You are not taking advantage of that and may want to do so.</p>
<p class="MsoNormal"> </p><p class="MsoNormal" style="text-align:center" align="center"><b>The Building Performance Team<br>James V. Dirkes II, P.E., BEMP , LEED AP<br></b>1631 Acacia Drive NW<br>Grand Rapids, MI 49504<br>
<a href="tel:616%20450%208653" target="_blank">616 450 8653</a></p><p class="MsoNormal"> </p><div><p class="MsoNormal"><b>From:</b> <a href="mailto:bldg-sim-bounces@lists.onebuilding.org" target="_blank">bldg-sim-bounces@lists.onebuilding.org</a> [mailto:<a href="mailto:bldg-sim-bounces@lists.onebuilding.org" target="_blank">bldg-sim-bounces@lists.onebuilding.org</a>] <b>On Behalf Of </b>Marcus<br>
<b>Sent:</b> Monday, May 23, 2011 4:24 PM<br><b>To:</b> <a href="mailto:bldg-sim@lists.onebuilding.org" target="_blank">bldg-sim@lists.onebuilding.org</a><br><b>Subject:</b> [Bldg-sim] PTHP Baseline outperforming VAV</p></div>
<div><div><p class="MsoNormal"> </p><p class="MsoNormal">Hi all, <br><br>Having some difficulty in an App. G model for a 6-floor 14,000 m2 GFA Hotel in zone 1B (Abu Dhabi). Assuming standard design for each, should a proposed VAV system out-perform window AC units (the baseline)? <br>
<br>Proposed: <br>VAV with 2 Air-cooled centrifugal chillers, chiller COP = 3.1 (2.8 if condenser fan energy included)<br>Envelope - Better windows decrease heating demand by 8% rest of envelope is minimum required for compliance<br>
<br>Baseline: <br>System Packaged terminal heat pump, COP = 3.52<br><br>Using Energyplus v6.0 the results are;<br><br>Site Energy in End Uses BL Proposed COP5<br> MWh MWh MWh<br>
Space Cooling 747.5 1052.0 715.6 <br> Heat Rejection 0.0 0.0 0.0 <br> Space Heating 1.3 0.1 0.1 <br> Pumps 0.0 60.0 60.0 <br>
Fans - Interior 42.2 137.7 137.7 <br> Fans - Car park 0.0 0.0 0.0 <br> Interior Lighting 530.5 530.5 530.5 <br> Exterior Lighting 0.0 0.0 0.0 <br>
Service Water Heating 0.0 0.0 0.0 <br> Receptacle/Process Equipment 146.3 146.3 146.3 <br> Data Centre Equipment 0.0 0.0 0.0 <br> Elevators and Escalators 0.0 0.0 0.0 <br>
Total Site Energy 1467.9 1926.6 1590.2<br><br>I have the energy for the baseline, the proposed with COP = 3.1, and then trying COP = 5. It seems that even if we drastically increase the COP of the chiller plant in the proposed VAV system, we still can't get any energy savings. Is this realistic, an artifact of the simulation, or just an error on my part? <br>
<br>Any guidance would be appreciated, <br><br>Marcus<br>-- <br>Marcus Jones, LEED AP, M.Sc. <br><i>Freelance energy consultant</i><br><i>Vienna, Austria</i></p></div></div></div></div><p class="MsoNormal"><br>_______________________________________________<br>
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