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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'>I'm curious how others have been interpreting G3.1.3.1 and when to lock out the compressors on PTHP units in the Baseline. I have been setting the minimum heat pump operational temperature (MIN-HP-T) in such a way as to allow the heat pump to operate at all hours and allow eQUEST to adjust the capacity of the heat pump with its own capacity curves. This allows the heat pump to run simultaneously with the supplementary electric heat, albeit at a reduced capacity.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p> </o:p></span></p><p class=MsoNormal>Realistically, no PTHP manufacturers allow their heat pumps to operate much below 35 deg F. I have heard from other modelers that they lockout the compressors at 40 deg F in the baseline. For those of you out there who take this approach, how do you justify it? Has the question come up in any LEED reviews?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The following is my rationale for not locking out the compressors at 40 deg F:<o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>ASHRAE 90.1-2007 section G3.1.3.1 states:<o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>“<b>G3.1.3.1 Heat Pumps (Systems 2 and 4).</b> Electric air-source heat pumps shall be modeled with electric auxiliary heat. The systems shall be controlled with multistage space thermostats and an outdoor air thermostat wired to energize auxiliary heat only on the last thermostat stage and when outdoor air temperature is less than 40°F.”<o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>So the section clearly references System 2 – PTHP’s. Then the question you could ask is what does “energize auxiliary heat only on the last thermostat stage” mean? From USGBC’s Advanced Energy Modeling for LEED guidelines, page 38:<o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><img width=635 height=446 id="_x0000_i1026" src="cid:image001.jpg@01CD7C54.4E748A90"><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>The guideline says to operate the compressor as low as 17 °F (low temperature rating condition using heat pump ARI 340/360 test procedure). Now PTHP’s are not rated per ARI 340/360 – they use ARI 310/380.<o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><o:p> </o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>From ARI 310/380-2004:<o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><img width=589 height=388 id="_x0000_i1025" src="cid:image002.jpg@01CD7C54.4E748A90"><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>17 °F is also utilized for PTHP’s.<o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>I've searched the CIR database and could not find any references to this specific section.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='font-family:"Franklin Gothic Demi","sans-serif";color:#632423'>Robby Oylear, </span><span style='font-size:10.0pt;font-family:"Franklin Gothic Demi","sans-serif";color:#632423'>PE, LEED AP</span><span style='font-family:"Franklin Gothic Demi","sans-serif";color:#632423'><o:p></o:p></span></p><p class=MsoNormal><i><span style='font-size:8.0pt;font-family:"Verdana","sans-serif";color:black'>Mechanical Engineer<o:p></o:p></span></i></p><p class=MsoNormal><i><span style='font-size:8.0pt;font-family:"Verdana","sans-serif";color:black'>Senior Energy Analyst<o:p></o:p></span></i></p><p class=MsoNormal><i><span style='font-size:8.0pt;font-family:"Verdana","sans-serif";color:black'><o:p> </o:p></span></i></p><p class=MsoNormal style='line-height:115%'><b><span style='font-size:8.0pt;line-height:115%;font-family:"Verdana","sans-serif";color:#632423'>D</span></b><span style='font-size:8.0pt;line-height:115%;font-family:"Verdana","sans-serif";color:#1F497D'> </span><span style='font-size:8.0pt;line-height:115%;font-family:"Verdana","sans-serif";color:black'>206-788-4571</span><span style='font-size:8.0pt;line-height:115%;font-family:"Verdana","sans-serif";color:#BFAB7F'><o:p></o:p></span></p><p class=MsoNormal style='line-height:115%'><span style='color:#1F497D'><a href="http://www.rushingco.com/"><b><i><span style='font-size:8.0pt;line-height:115%;font-family:"Verdana","sans-serif";color:#632423'>www.rushingco.com</span></i></b></a></span><span style='font-size:7.0pt;line-height:115%;font-family:"Verdana","sans-serif";color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>