<html>
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
Safwan,<br>
It is always a VERY good idea to do an energy balance and if it is
balancing to within 1kWh over a month then I think you can have
great confidence that your model is correct (of course that doesn't
necessarily mean that the model reflects reality but it is a good
first step). <br>
<br>
2- I found there was no way to calculate cooling load while running
the simulation, so I calculated it separately. any idea?<br>
<br>
this question gets to the heart of how TRNSYS is different from a
lot of other building modeling tools. Many tools calculate a space
load and then try to meet that load with the HVAC system model. It
is difficult in this case to write an energy balance because you
have to make the assumption that the HVAC system can deliver exactly
the amount of energy required by the load at all times. While TRNSYS
can operate in that manner, you can also use it to get a lot closer
to the way that a building actually operates. To do so you turn off
the automatic heating and cooling in TRNBuild and allow the building
temperature to float. Then you implement a thermostat model and
decrease the simulation time step to something on the order of 1
minute. You then implement your HVAC system and control it
(determine whether fans, pumps, and equipment) should be ON or OFF
based on your thermostat's output. The HVAC system outputs (air flow
rate, temperature, and RH) are inputs to VENTILATION types defined
in TRNBuild. You can then do your energy balance using the actual
amount of energy that was transferred by the equipment to the zone.<br>
<br class="" id="yui_3_16_0_1_1442841238647_7236">
3-When I come to (pipes, duct and fan loss) some of cold pipe will
gain heat instead of lost it, so should I add it to heat losses or
subtract it?<br class="" id="yui_3_16_0_1_1442841238647_7240">
<br>
you just need to be consistent about the sign of the terms in your
energy balance. In a water loop you might define energy into the
loop as positive (an energy gain) and energy out of the loop as
negative (an energy loss). If the liquid in a pipe is hotter than
the ambient then it will lose energy to the ambient and you take
that term to have a negative sign in your balance. If the liquid is
colder than ambient then it will gain energy from its surroundings
and you would take that as a term with a positive sign.<br>
regards,<br>
David<br>
<br>
<div class="moz-cite-prefix">On 09/21/2015 08:48, Safwan Kanan
wrote:<br>
</div>
<blockquote
cite="mid:278147867.851330.1442843286518.JavaMail.yahoo@mail.yahoo.com"
type="cite">
<div style="color:#000; background-color:#fff;
font-family:HelveticaNeue-Light, Helvetica Neue Light, Helvetica
Neue, Helvetica, Arial, Lucida Grande,
sans-serif;font-size:16px">
<div dir="ltr" id="yui_3_16_0_1_1442841238647_6212">Dear David,<br
class="" id="yui_3_16_0_1_1442841238647_7214">
<br class="" id="yui_3_16_0_1_1442841238647_7216">
I doing a simulation of a solar cooling system( collector,
absorption chiller and building) and everything seems fine but
I want to do an Energy balance for the whole system. So I
calculated as Energy in (Useful heat from
collector+Electricity consumed in the whole system such as
pumps ,fan,chiller and tower fan+Building cooling load which I
calculated separately assuming unlimited cooling power) and
for Energy out ( heat subtract in cooling tower+pipes, duct
and fan losses).<br class=""
id="yui_3_16_0_1_1442841238647_7218">
<br class="" id="yui_3_16_0_1_1442841238647_7220">
I found there was around one kWh difference during July of the
second year simulation time.<br class=""
id="yui_3_16_0_1_1442841238647_7222">
<br class="" id="yui_3_16_0_1_1442841238647_7224">
My questions are:<br class=""
id="yui_3_16_0_1_1442841238647_7226">
<br class="" id="yui_3_16_0_1_1442841238647_7228">
1-Do you think that's correct? if not correct me, please.<br
class="" id="yui_3_16_0_1_1442841238647_7232">
2- I found there was no way to calculate cooling load while
running the simulation, so I calculated it separately. any
idea?<br class="" id="yui_3_16_0_1_1442841238647_7236">
3-When I come to (pipes, duct and fan loss) some of cold pipe
will gain heat instead of lost it, so should I add it to heat
losses or subtract it?<br class=""
id="yui_3_16_0_1_1442841238647_7240">
Any idea I will appreciate that.<br class=""
id="yui_3_16_0_1_1442841238647_7242">
<br class="" id="yui_3_16_0_1_1442841238647_7244">
I look forward to hearing from you as soon as possible.<br
class="" id="yui_3_16_0_1_1442841238647_7246">
<br class="" id="yui_3_16_0_1_1442841238647_7248">
Regards,<br class="" id="yui_3_16_0_1_1442841238647_7250">
<br class="" id="yui_3_16_0_1_1442841238647_7252">
Safwan Kanan<br class="" id="yui_3_16_0_1_1442841238647_7254">
<br class="" id="yui_3_16_0_1_1442841238647_7256">
PhD student at the University of Manchester<br class=""
id="yui_3_16_0_1_1442841238647_7260">
Manchester<br class="" id="yui_3_16_0_1_1442841238647_7264">
M13 9PL<br class="" id="yui_3_16_0_1_1442841238647_7268">
UK<br>
</div>
<br>
</div>
</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>