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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-IE link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>David,<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Thank you very much for your suggestion. I did put a water tank in between the load loop and the heat pump. The result I am getting is great. However, I remembered you mentioned that your company is developing a multi-stage air-water heat pump component. I think this is very applicable for my case. I am wondering if this component has been finalised? If it is, would be possible if I can obtain this component. As even though the simulation result is very good, I am still not setting up the system as identical as the actual system (the system I want to set up) is. I may encounter some difficult questions over the system set up in my final thesis defence. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I asked about the mathematical description of Type941 air-water heat pump. I think this is still in the writing stage. I am wondering that when this mathematical description will be released, would be possible if I can obtain a copy of this description as soon as it is complete? This is very important for my PhD thesis, it is not convincing without a full detailed maths description in the thesis.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Please find attached two examples of solar thermal systems using identical parameters with collector type538 and type71. The sum of Useful Energy Gain from type538 and type71 is 2669.41kWh and 1876.44kWh respectively. I don’t understand why the results are significantly different. Hope you could give me some advice and direction.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Thank you so much for all your help. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Zhe Li <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'> David BRADLEY [mailto:d.bradley@tess-inc.com] <br><b>Sent:</b> 19 October 2012 19:26<br><b>To:</b> Zhe Li<br><b>Cc:</b> trnsys-users@cae.wisc.edu<br><b>Subject:</b> Re: [TRNSYS-users] Air source heat pump system validation<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'>Zhe,<br> This is a problem with actual single stage heat pumps, not just a simulation problem. Single stage heat pumps cannot really modulate their output power so under low load conditions, they can overheat a fluid loop. One effective way of solving the problem is to put a water tank in between the load loop and the heat pump. It requires an additional pump but then the load loop draws water from and returns water to the tank. When the tank temperature drops, the heat pump loop turns on and heats the tank back up again. Under low load conditions, the load slowly draws the tank temperature down and the heat pump stays off.<br><br> I am not sure what the problem with Type538 might be. I'd be interested if you could send me a project showing the difference in result between the two.<br><br> As for the collector capacitance, often collector manufacturers will tell you the liquid volume of the collector. You can calculate a capacitance from the volume and from the specific heat of your working fluid. Without any better knowledge, though, we use a value of about 10 kJ/m2 of collector area. <br>Best,<br> David<br><br><o:p></o:p></p><div><p class=MsoNormal>On 10/18/2012 09:35, Zhe Li wrote:<o:p></o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p class=MsoNormal><span style='color:#1F497D'>David,</span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'>Thank you very much for your response a couple of days ago. I have been considering your advice and trying to make some changes in my simulation models. However, I have not been successful. I did identify the major problem, as you have explained, once the controller trigger the ON function, the heat pump runs without limiting the useful energy required for the thermal load, this results a massive energy overproduced especially for summer months. I am trying to write an equation to reduce the flowrate in order to prevent energy been overly produced. The whole validation I am carrying out against is a system without a buffer tank, hence I will have to set up an air source heat pump system without a buffer tank even though I understand it is more accurate to do so. In your experience, how would you do if you are in my situation? </span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'>Also come back to the solar thermal system. I remembered that you recommended flat plate solar collector type539 as it is the most robust collector as you mentioned. I have tried it, it worked pretty good. However, I would think evacuated tube solar collector type538 is also very robust and accurate, however the result I am getting is significantly larger than expected. Then I tried the simple version Type71 evacuated tube collector, it does give me decent result. The results difference between Type538 and Type71 is about 33% which I think it is huge. Would you recommend Type538 for general use even though I do think this type is quite sophisticated from what I have seen in Mathematic description in Tess model? </span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'>I have one final question, where could I get information for the capacitance of collector? I have tried varies manufacture website, none of them has given this value. If I leave the default value, is this going to affect my result by much?</span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'>Thank you very much for your help.</span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'>Zhe Li </span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'> </span><o:p></o:p></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'> David BRADLEY [<a href="mailto:d.bradley@tess-inc.com">mailto:d.bradley@tess-inc.com</a>] <br><b>Sent:</b> 16 October 2012 17:04<br><b>To:</b> Zhe Li<br><b>Cc:</b> <a href="mailto:trnsys-users@cae.wisc.edu">trnsys-users@cae.wisc.edu</a><br><b>Subject:</b> Re: [TRNSYS-users] Air source heat pump system validation</span><o:p></o:p></p></div></div><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'>Zhe Li,<br> I look at similar energy balances quite often so I suspect there is not a systematic problem but something wrong in the simulation. There are a few things to look at.<br><br>First, make sure that you have some thermal capacitance in the liquid loop. This will usually take the form of a buffer tank. The tank should have enough volume to store at least one timestep of liquid at whatever flow rate your pump is running. <br><br>Second, look at the controls on your flow loop. Type941 is basically an ON/OFF device; it does not meet a set point temperature but simply puts its entire current capacity into cooling down (or heating up) the liquid loop. Under low load situations, this can dramatically overheat or overcool the liquid loop; the tank above should help this a lot.<br><br>Third, make sure that you are using a reasonably short timestep (1 or 5 minutes). this will allow your system to be controller appropriately.<br><br>When you look at the energy balance, you have to also look at the beginning and ending temperature of the liquid loop. If it is significantly different than it was at the simulation start, you have to account for stored energy in your balance.<br>Kind regards,<br> David<br><br><br><br><o:p></o:p></p><div><p class=MsoNormal>On 10/16/2012 08:42, Zhe Li wrote:<o:p></o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p class=MsoNormal>Dear TRNSYS users,<o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>Thanks for your time. <o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>I am currently performing a simple validation of an air source heat pump system. The air-source heat pump is Type941, and I am using a defined thermal load (Type682) with an input file (Type9). However, the results I am getting for the Total Heat Transfer to Liquid from output option in air source heat pump component is between 2 and 3 times higher than the Heating Load Met from output option in thermal load. I cannot think of any reason why the generated energy is significantly higher than the load met. I would understand if the generated energy is a bit higher than the load met as there might be heat losses from connected pipes. <o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>Could anyone give me some advices? This is very important for me to continue my research project.<o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>Thanks very much in advance.<o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>Zhe Li<o:p></o:p></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman , serif","serif"'><br clear=all>Tá an teachtaireacht seo scanta ó thaobh ábhar agus víreas ag Seirbhís Scanta Ríomhphost de chuid Seirbhísí Faisnéise, ITBÁC agus meastar í a bheith slán. <a href="http://www.dit.ie">http://www.dit.ie</a><br>This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. <a href="http://www.dit.ie">http://www.dit.ie</a> <br><br><br><br></span><o:p></o:p></p><pre>_______________________________________________<o:p></o:p></pre><pre>TRNSYS-users mailing list<o:p></o:p></pre><pre><a href="mailto:TRNSYS-users@cae.wisc.edu">TRNSYS-users@cae.wisc.edu</a><o:p></o:p></pre><pre><a href="https://mailman.cae.wisc.edu/listinfo/trnsys-users">https://mailman.cae.wisc.edu/listinfo/trnsys-users</a><o:p></o:p></pre></blockquote><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman , serif","serif"'><br><br><br></span><o:p></o:p></p><pre>-- <o:p></o:p></pre><pre>***************************<o:p></o:p></pre><pre>David BRADLEY<o:p></o:p></pre><pre>Principal<o:p></o:p></pre><pre>Thermal Energy Systems Specialists, LLC<o:p></o:p></pre><pre>22 North Carroll Street - suite 370<o:p></o:p></pre><pre>Madison, WI 53703 USA<o:p></o:p></pre><pre> <o:p></o:p></pre><pre>P:+1.608.274.2577<o:p></o:p></pre><pre>F:+1.608.278.1475<o:p></o:p></pre><pre><a href="mailto:d.bradley@tess-inc.com">d.bradley@tess-inc.com</a><o:p></o:p></pre><pre> <o:p></o:p></pre><pre><a href="http://www.tess-inc.com">http://www.tess-inc.com</a><o:p></o:p></pre><pre><a href="http://www.trnsys.com">http://www.trnsys.com</a><o:p></o:p></pre><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><br clear=all>Tá an teachtaireacht seo scanta ó thaobh ábhar agus víreas ag Seirbhís Scanta Ríomhphost de chuid Seirbhísí Faisnéise, ITBÁC agus meastar í a bheith slán. <a href="http://www.dit.ie">http://www.dit.ie</a><br>This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. <a href="http://www.dit.ie">http://www.dit.ie</a> <o:p></o:p></span></p></blockquote><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><br><br><o:p></o:p></span></p><pre>-- <o:p></o:p></pre><pre>***************************<o:p></o:p></pre><pre>David BRADLEY<o:p></o:p></pre><pre>Principal<o:p></o:p></pre><pre>Thermal Energy Systems Specialists, LLC<o:p></o:p></pre><pre>22 North Carroll Street - suite 370<o:p></o:p></pre><pre>Madison, WI 53703 USA<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>P:+1.608.274.2577<o:p></o:p></pre><pre>F:+1.608.278.1475<o:p></o:p></pre><pre><a href="mailto:d.bradley@tess-inc.com">d.bradley@tess-inc.com</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre><a href="http://www.tess-inc.com">http://www.tess-inc.com</a><o:p></o:p></pre><pre><a href="http://www.trnsys.com">http://www.trnsys.com</a><o:p></o:p></pre></div><br clear=all> Tá an teachtaireacht seo scanta ó thaobh ábhar agus víreas ag Seirbhís Scanta Ríomhphost de chuid Seirbhísí Faisnéise, ITBÁC agus meastar í a bheith slán. <a href="http://www.dit.ie">http://www.dit.ie</a><br>
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