<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
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>
<br>
<div class="moz-cite-prefix">On 10/18/2012 09:35, Zhe Li wrote:<br>
</div>
<blockquote cite="mid:002401cdad3d$d881adc0$89850940$%25Li@dit.ie"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=ISO-8859-1">
<meta name="Generator" content="Microsoft Word 12 (filtered
medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
@font-face
{font-family:Consolas;
panose-1:2 11 6 9 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";
color:black;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
pre
{mso-style-priority:99;
mso-style-link:"HTML Preformatted Char";
margin:0cm;
margin-bottom:.0001pt;
font-size:10.0pt;
font-family:"Courier New";
color:black;}
span.EmailStyle17
{mso-style-type:personal;
font-family:"Calibri","sans-serif";
color:windowtext;}
span.HTMLPreformattedChar
{mso-style-name:"HTML Preformatted Char";
mso-style-priority:99;
mso-style-link:"HTML Preformatted";
font-family:Consolas;
color:black;}
span.EmailStyle20
{mso-style-type:personal-reply;
font-family:"Calibri","sans-serif";
color:#1F497D;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:72.0pt 72.0pt 72.0pt 72.0pt;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
<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 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? <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">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? <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 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?<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 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
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext"
lang="EN-US">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext"
lang="EN-US"> David BRADLEY
[<a class="moz-txt-link-freetext" 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 class="moz-txt-link-abbreviated" 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<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 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>
<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""><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
moz-do-not-send="true" 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 moz-do-not-send="true"
href="http://www.dit.ie">http://www.dit.ie</a> <br>
<br>
<br>
<o:p></o:p></span></p>
<pre>_______________________________________________<o:p></o:p></pre>
<pre>TRNSYS-users mailing list<o:p></o:p></pre>
<pre><a moz-do-not-send="true" href="mailto:TRNSYS-users@cae.wisc.edu">TRNSYS-users@cae.wisc.edu</a><o:p></o:p></pre>
<pre><a moz-do-not-send="true" 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""><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 moz-do-not-send="true" 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 moz-do-not-send="true" href="http://www.tess-inc.com">http://www.tess-inc.com</a><o:p></o:p></pre>
<pre><a moz-do-not-send="true" 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 moz-do-not-send="true"
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 moz-do-not-send="true" href="http://www.dit.ie">http://www.dit.ie</a>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI 53703 USA
P:+1.608.274.2577
F:+1.608.278.1475
<a class="moz-txt-link-abbreviated" href="mailto:d.bradley@tess-inc.com">d.bradley@tess-inc.com</a>
<a class="moz-txt-link-freetext" href="http://www.tess-inc.com">http://www.tess-inc.com</a>
<a class="moz-txt-link-freetext" href="http://www.trnsys.com">http://www.trnsys.com</a></pre>
</body>
</html>