Hi Scott,<br><br>I'm not convinced that oversizing the fluid cooler would be the best way to go. It seems like the initial cost would be higher to the client and that you can achieve what you want with a right sized fluid cooler. If you need a certain gpm of cooling water to send to the chillers wouldn't the hp to accomplish that be the same using a larger motor running at part load as a right sized motor running at full load? I'd suggest using a right sized fluid cooler with a VFD for part load conditions.<br>
<br>The second strategy is what I know as wet bulb reset. I have attached a full discussion of it below. It is found in the Volume 2r Dictionary - Refrigeration Simulation. It is a shame this volume is called "Refrigeration" because it contains so much more and seems to get overlooked by modelers who aren't aware of that.<br>
<br>Let me know if you have any other questions.<br><br>Carol<br><title>Temperature Control in Cooling Towers</title><link rel="stylesheet" type="text/css" href="../Theme/nav.css"><link rel="stylesheet" type="text/css" href="../Theme/lf.css"><link rel="stylesheet" type="text/css" href="../LinksExt/C1H_HTML.css"><link rel="stylesheet" type="text/css" href="../LinksExt/DOE22Vol2-Dictionary.css">
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<h3><a name="_Toc226181961">Temperature Control in Cooling Towers</a></h3>
<p class="MsoBodyText">The supply temperature that a tower will attempt to achieve
is set by the attached CIRCULATION-LOOP through the COOL-SETPT-CTRL,
COOL-SETPT-T, COOL-<font style="background-color: rgb(49, 106, 197);" color="#ffffff">RESET</font>-SCH, COOL-SETPT-SCH, and LOOP-SETPT-RNG keywords (see
CIRCULATION-LOOP command). For open towers and fluid coolers only there is one
additional temperature control mode available that tries to achieve an optimal
compromise between tower fan energy and cooling compressor energy. You activate
this sequence by with COOL-SETPT-CTRL = LOAD-<font style="background-color: rgb(49, 106, 197);" color="#ffffff">RESET</font> in the attached
CIRCULATION-LOOP. The sequence is as follows:</p>
<p style="margin-left: 18pt;" class="MsoListBullet"><span style="font-family: Symbol;">· </span>The chiller load is determined on an
hourly basis. In the field, this would be accomplished either by a monitoring a
signal directly from the chiller control panel, or, perhaps more commonly, by
measuring the temperature rise across the chiller condenser, and comparing it to
the design temperature rise. For example, if the design condenser temperature
rise is 10F (5.6K), and the actual rise is 6F (3.3K), then the chiller load is
assumed to be 60%. (This assumes that the condenser is constant flow.)</p>
<p style="margin-left: 18pt;" class="MsoListBullet"><span style="font-family: Symbol;">· </span>The tower air flow (and fan speed)
required to reject a given chiller load is essentially linear with load (open
towers) or drops off faster than the load (fluid coolers). Rather than
controlling a variable-speed tower fan on the basis of leaving tower temperature
as is conventionally done, this algorithm will vary the tower fan speed directly
on the basis of chiller load. For the example given above, the tower fan will
run at 60% speed when the chiller load is 60%. The leaving tower temperature
then floats with both <font style="background-color: rgb(49, 106, 197);" color="#ffffff">wet</font>-<font style="background-color: rgb(49, 106, 197);" color="#ffffff">bulb</font> temperature and chiller load. This concept gives
priority to minimizing tower energy consumption, but still achieves chiller
energy savings as the leaving tower temperature floats.</p>
<p style="margin-left: 18pt;" class="MsoListBullet"><span style="font-family: Symbol;">· </span>To further increase chiller
efficiency, it can be recognized that the tower fan power varies approximately
as the cube of the air flow (and load), and that the majority of the energy
savings are achieved when the fan is close to full speed. Once the fan speed has
been reduced to 70% or so, additional tower fan energy savings will be
negligible compared to the potential chiller savings that might be achieved by
reducing the approach to the <font style="background-color: rgb(49, 106, 197);" color="#ffffff">wet</font>-<font style="background-color: rgb(49, 106, 197);" color="#ffffff">bulb</font>. </p>
<p style="margin-left: 18pt;" class="MsoListBullet"><span style="font-family: Symbol;">· </span>Keywords are provided to allow you to
experiment with this concept. For example, at 50% load the default fan speed
will be 50%. You might want to investigate what happens if the tower fan is not
allowed to drop below 65% speed at 40% load.</p>
<p style="margin-left: 18pt;" class="MsoListBullet"><span style="font-family: Symbol;">· </span>Maximum and minimum condenser
temperature limits are included. For example, you might not want the leaving
tower temperature to ever exceed 85F (29.4C) or to drop below 65F (18.3C). The
fan speed algorithm described in (2) and (3) will be overridden to ensure that
these limits are not exceeded.</p>
<p style="margin-left: 18pt;" class="MsoListBullet"><span style="font-family: Symbol;">· </span>Two-speed tower fans use a variation
of this algorithm. As before, the tower will cycle between low and high speed to
maintain the tower setpoint. However when the leaving temperature drops below
the setpoint, the fan will not cycle between off and low speeds. Instead, the
fan will remain on low speed unless the leaving temperature drops all the way
down to MIN-TWR-WTR-T, at which point it will cycle between off and low to
prevent the tower temperature from dropping any further.</p>
<p class="MsoBodyText">This control sequence is not applicable to single-speed
fans. It applies to both CW loops as well as WLHP loops. Maximum energy savings
might be achieved for WLHP loops, as these systems typically have a lower
cooling COP than chillers, and the heat rejection commonly uses a fluid cooler
which has a higher fan horsepower than an equivalent open tower. </p>
<p class="MsoBodyText">When using the LOAD-<font style="background-color: rgb(49, 106, 197);" color="#ffffff">RESET</font> control sequence, you can try experimenting with the
values of the MIN-<font style="background-color: rgb(49, 106, 197);" color="#ffffff">RESET</font>-PLR, MIN-VFD-SPEED, MAX-<font style="background-color: rgb(49, 106, 197);" color="#ffffff">RESET</font>-SPEED to optimize
the energy efficiency of the system.</p>
<p class="MsoBodyText">The LOAD-<font style="background-color: rgb(49, 106, 197);" color="#ffffff">RESET</font> tower keywords are illustrated in <a href="javascript:TL_7380.HHClick()">Figure 36</a> and are as follows: </p>
<hr noshade size="1">
<p class="RelatedHead">Subtopic help for this Topic:</p>
<p class="MsoNormal"><a style="text-decoration: none;" href="javascript:RT_1609.HHClick()"><img alt="" src="../button.gif" align="absMiddle" border="0">MIN-<font style="background-color: rgb(49, 106, 197);" color="#ffffff">RESET</font>-PLR</a></p>
<p class="MsoNormal"><a style="text-decoration: none;" href="javascript:RT_1610.HHClick()"><img alt="" src="../button.gif" align="absMiddle" border="0">MIN-VFD-SPEED</a></p>
<p class="MsoNormal"><a style="text-decoration: none;" href="javascript:RT_1611.HHClick()"><img alt="" src="../button.gif" align="absMiddle" border="0">MAX-<font style="background-color: rgb(49, 106, 197);" color="#ffffff">RESET</font>-SPEED</a></p>
<p class="MsoNormal"><a style="text-decoration: none;" href="javascript:RT_1612.HHClick()"><img alt="" src="../button.gif" align="absMiddle" border="0">CIRCULATION-LOOP:COOL-SETPT-T</a></p>
<p class="MsoNormal"><a style="text-decoration: none;" href="javascript:RT_1613.HHClick()"><img alt="" src="../button.gif" align="absMiddle" border="0">CIRCULATION-LOOP:MIN-<font style="background-color: rgb(49, 106, 197);" color="#ffffff">RESET</font>-T</a></p>
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</div><br><br><div class="gmail_quote">On Wed, Jul 14, 2010 at 11:37 AM, Scott Hackel <span dir="ltr"><<a href="mailto:shackel@ecw.org">shackel@ecw.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div link="blue" vlink="purple" lang="EN-US">
<div>
<p class="MsoNormal">Hello –</p>
<p class="MsoNormal">I’d like to model the energy savings from oversizing a
fluid cooler / closed circuit cooling tower … My general understanding of
this application is that the tower can be oversized to create energy savings in
two possible ways: 1) allowing the tower to run at part load, thus saving fan
energy assuming a variable speed fan and/or 2) sizing the tower such that the
average approach during operation is smaller, and therefore condenser water
temperatures are lower.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Has anyone had experience with modeling energy savings in
eQUEST from an oversized tower? I’ve done this successfully in
Trane TRACE, but have not had success using the obvious paths in eQUEST –
in this case 1) increasing the capacity ratio of the tower (from 1 to 1.2 –
1.5) and 2) decreasing the design approach (from 7 to 5). Any thoughts
would be helpful, thank you.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal"><span style="color: navy;">S</span><span>cott Hackel, P.E., </span><span style="font-size: 10pt;">LEED AP</span></p>
<p class="MsoNormal"><span style="font-size: 7.5pt;"> </span><u><span style="font-size: 10pt;"></span></u></p>
<p class="MsoNormal"><span style="color: navy;">Energy
Engineer</span></p>
<p class="MsoNormal"><b><span style="color: navy;">Energy
Center of Wisconsin</span></b></p>
<p class="MsoNormal"><span style="font-size: 2pt; color: navy;"> </span></p>
<p class="MsoNormal"><span style="font-size: 10pt; color: navy;">455 Science Drive, Suite 200</span></p>
<p class="MsoNormal"><span style="font-size: 10pt; color: navy;">Madison, WI 53711</span><span style="font-size: 12pt; font-family: "Times New Roman","serif"; color: navy;"></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; color: navy;">608.238.8276 x129</span></p>
<p class="MsoNormal"><u><span style="font-size: 10pt; color: navy;"><a href="mailto:shackel@ecw.org" target="_blank"><span style="color: navy;">shackel@ecw.org</span></a></span></u></p>
<p class="MsoNormal"><u><span style="font-size: 10pt; color: navy;"><a href="http://www.ecw.org/" target="_blank"><span style="color: navy;">www.ecw.org</span></a>
</span></u></p>
<p class="MsoNormal"><b><span style="font-size: 13pt; font-family: "Times New Roman","serif";"> </span></b></p>
<p class="MsoNormal"><b><span style="font-size: 10pt; color: navy;">The Buildings Team</span></b><b><span style="font-size: 10pt; color: navy;"><br>
</span></b><span style="font-size: 10pt; color: navy;">Design decisions through energy, economics and emissions analysis.<br>
<a href="http://www.ecw.org/Buildings" title="http://www.ecw.org/Buildings" target="_blank"><span style="color: navy;">www.ecw.org/Buildings</span></a></span><span style="font-size: 10pt; font-family: "Times New Roman","serif"; color: navy;"> </span></p>
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<br></blockquote></div><br><br clear="all"><br>-- <br>Carol Gardner PE<br>
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