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<DIV><FONT size=2 face=Arial><SPAN class=994143023-22122009>Hello
all,</SPAN></FONT></DIV>
<DIV><FONT size=2 face=Arial><SPAN
class=994143023-22122009></SPAN></FONT> </DIV>
<DIV><FONT size=2 face=Arial><SPAN class=994143023-22122009>I am using TRNSYS to
model a solar water heater based on a template deck provided by a well-respected
source. I am concerned about the calculation of heat transfer coefficient U for
input into the TYPE 33 (pipe) components. The TYPE 33 component spec requires U
based on inside surface area, so the following calculation seems correct to
me:</SPAN></FONT></DIV>
<DIV><FONT size=2 face=Arial>UP1 =
1/(1/hin+dpipe1/2/kinsul*ln(dpipeo/dpipe1)+dpipe1/dpipeo/hout)</FONT></DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2 face=Arial>(where hin and hout
are the internal/external surface heat transfer coeffs; dpipe1 is the internal
diameter; dpipeo the external diameter; and kinsul the thermal conductivity of
the pipe material).</FONT></SPAN></DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2 face=Arial>The result is used
in "UNIT 11" as follows:</FONT></SPAN></DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2 face=Arial>UNIT 11 TYPE 31
collector INLET PIPE<BR>PARAMETERS 6<BR>dpipe1 Lpipe1 UP1 1000 4.18
25</FONT></SPAN></DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2 face=Arial>However, a
calculation for another pipe elsewhere in the deck is:</FONT></SPAN></DIV>
<DIV><FONT size=2 face=Arial>UP3 =
1/(Dpipe3/2/k_insul3*ln(Dpipe03/Dpipe3)+Dpipe03/Dpipe3/hout)</FONT></DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2 face=Arial>(Dpipe3 is the
internal diameter; Dpipe03 the external diameter; k_insul3 the pipe material
thermal conductivity)</FONT></SPAN></DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=994143023-22122009>
<DIV><SPAN class=994143023-22122009><FONT face=Arial><FONT size=2><SPAN
class=564244100-23122009>T</SPAN>he result's application (in UNIT 21, below)
assumes that UP3 is based on the INTERNAL
area:</FONT></FONT></SPAN></DIV></SPAN></DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2 face=Arial>UNIT 23 TYPE 31 pipe
between solar preheater and gas booster<BR>PARAMETERS 6<BR>Dpipe3 Lpipe3 UP3
1000 4.18 25</FONT></SPAN></DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=994143023-22122009><FONT face=Arial><FONT size=2><SPAN
class=564244100-23122009>The general form of the equation looks reasonable,
assuming hin is very large in this instance. However, it appears to me that the
second term in the equation for UP3 has the ratio of diameters the wrong way
around. </SPAN>I would like to propose a correction of the calculation of
UP3 as:</FONT></FONT></SPAN></DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2 face=Arial>UP3 =
1/(Dpipe3/2/k_insul3*ln(Dpipe03/Dpipe3)+Dpipe3/Dpipe03/hout)</FONT></SPAN></DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2 face=Arial>Is anyone able to
confirm the correctness <SPAN class=564244100-23122009>of </SPAN>this, or
am I missing something obvious?</FONT></SPAN></DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2
face=Arial>Regards,</FONT></SPAN></DIV>
<DIV><SPAN class=994143023-22122009><FONT size=2 face=Arial>David
Ferrari</FONT></SPAN></DIV></DIV>
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