The commands you need are under the condenser water (CW) loop. If you click on the CW loop, and then on the Controls tab, you will see the Setpoint Control box which defaults to fixed. When you look at the pull down menu, however, you will see the option to select Load Reset. Load Reset, when accessed from the CW loop, allows the tower to be controlled using wet bulb reset. The way that the developers set it up, as described below, is to get the best of both worlds (thanks, Steve!), savings from cooling tower VFDs first and wet bulb reset second.<br>
<br>
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<div id="d2h_breadcrumbs" class="d2h_breadcrumbs"><a class="d2h_breadcrumbsNormal" href="volume2dictionary.htm">Volume 2: Dictionary</a><span class="d2h_breadcrumbsLinkSeparator"> > </span><a class="d2h_breadcrumbsNormal" href="hvaccomponents.htm">HVAC Components</a><span class="d2h_breadcrumbsLinkSeparator"> > </span><a class="d2h_breadcrumbsNormal" href="heatrejection1.htm">HEAT-REJECTION</a></div>
<h3>Temperature Control in Cooling Towers</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 = <font style="background-color: rgb(49, 106, 197);" color="#ffffff">LOAD-RESET</font> in the attached CIRCULATION-LOOP. The sequence
is as follows:</p>
<p style="margin-left: 36pt;" class="MsoListBulletCxSpFirst"><span style="font-family: Symbol;">· </span>The
chiller <font style="background-color: rgb(49, 106, 197);" color="#ffffff">load</font> 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 <font style="background-color: rgb(49, 106, 197);" color="#ffffff">load</font> is
assumed to be 60%. (This assumes that the condenser is constant flow.)</p>
<p style="margin-left: 36pt;" class="MsoListBulletCxSpMiddle"><span style="font-family: Symbol;">·
</span>The tower air flow (and fan speed) required to reject a given chiller
<font style="background-color: rgb(49, 106, 197);" color="#ffffff">load</font> is essentially
linear with <font style="background-color: rgb(49, 106, 197);" color="#ffffff">load</font>
(open towers) or drops off faster than the <font style="background-color: rgb(49, 106, 197);" color="#ffffff">load</font> (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 <font style="background-color: rgb(49, 106, 197);" color="#ffffff">load</font>. For the example given above, the tower fan will run
at 60% speed when the chiller <font style="background-color: rgb(49, 106, 197);" color="#ffffff">load</font> is 60%. The leaving tower temperature then floats with
both wet-bulb temperature and chiller <font style="background-color: rgb(49, 106, 197);" color="#ffffff">load</font>. 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: 36pt;" class="MsoListBulletCxSpMiddle"><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 <font style="background-color: rgb(49, 106, 197);" color="#ffffff">load</font>), 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 wet-bulb. </p>
<p style="margin-left: 36pt;" class="MsoListBulletCxSpMiddle"><span style="font-family: Symbol;">·
</span>Keywords are provided to allow you to experiment with this concept. For
example, at 50% <font style="background-color: rgb(49, 106, 197);" color="#ffffff">load</font> 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% <font style="background-color: rgb(49, 106, 197);" color="#ffffff">load</font>.</p>
<p style="margin-left: 36pt;" class="MsoListBulletCxSpMiddle"><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: 36pt;" class="MsoListBulletCxSpLast"><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 <font style="background-color: rgb(49, 106, 197);" color="#ffffff">LOAD-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 <font style="background-color: rgb(49, 106, 197);" color="#ffffff">LOAD-RESET</font> tower keywords are illustrated in <a>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;"><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;"><img alt="" src="../button.gif" align="absMiddle" border="0">MIN-VFD-SPEED</a></p>
<p class="MsoNormal"><a style="text-decoration: none;"><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;"><img alt="" src="../button.gif" align="absMiddle" border="0">CIRCULATION-LOOP:COOL-SETPT-T</a></p>
<p class="MsoNormal"><a style="text-decoration: none;"><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>
</div><br><br><div class="gmail_quote">On Fri, Nov 19, 2010 at 9:33 AM, Bishop, Bill <span dir="ltr"><<a href="mailto:wbishop@pathfinder-ea.com">wbishop@pathfinder-ea.com</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="blue" lang="EN-US">
<div>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy;">There is even more information in DOE-2
Help under </span></font><a>Volume
2: Dictionary</a><span> > </span><a>HVAC
Components</a><span> > </span><a>HEAT-REJECTION</a><span> > </span><a>Temperature
Control in Cooling Towers</a>. <font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy;">However, I don’t
see any commands that let you control the loop or tower using wet-bulb temp,
only the dry-bulb temp using OA-RESET.</span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy;">Bill</span></font></p>
<p class="MsoNormal"><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<div>
<p class="MsoNormal"><b><font size="2" color="black" face="Franklin Gothic Medium Cond"><span style="font-size: 10pt; font-family: "Franklin Gothic Medium Cond"; color: black; font-weight: bold;">William</span></font></b><b><font size="2" color="black" face="Franklin Gothic Medium Cond"><span style="font-size: 10pt; font-family: "Franklin Gothic Medium Cond"; color: black; font-weight: bold;"> Bishop, PE</span></font></b><b><font size="2" color="black" face="Franklin Gothic Medium Cond"><span style="font-size: 10pt; font-family: "Franklin Gothic Medium Cond"; color: black; font-weight: bold;">, BEMP, LEED<sup>®</sup>
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Engineers & Architects LLP</span></font></b><b><font size="2" color="black" face="Franklin Gothic Medium Cond"><span style="font-size: 10pt; font-family: "Franklin Gothic Medium Cond"; color: black; font-weight: bold;"></span></font></b></p>
<p class="MsoNormal"><font size="1" color="black" face="Arial"><span style="font-size: 9pt; font-family: Arial; color: black;">Mechanical Engineer</span></font></p>
<p class="MsoNormal"><font size="1" color="black" face="Arial"><span style="font-size: 5pt; font-family: Arial; color: black;"> </span></font></p>
<p class="MsoNormal"><span style="margin-left: 367px; margin-top: 17px; width: 60px; min-height: 58px;"><img src="cid:image001.jpg@01CB87E6.016F72A0" height="58" width="60"></span><font size="1" color="navy" face="Arial"><span style="font-size: 9pt; font-family: Arial; color: navy;">134 South Fitzhugh Street</span></font><font size="1" color="navy"><span style="font-size: 9pt; color: navy;"><span> </span></span></font><font size="1" color="navy" face="Arial"><span style="font-size: 9pt; font-family: Arial; color: navy;">Rochester</span></font><font size="1" color="navy" face="Arial"><span style="font-size: 9pt; font-family: Arial; color: navy;">, NY 14608</span></font><font size="1" color="navy"><span style="font-size: 9pt; color: navy;"><br>
</span></font><font size="1" color="navy" face="Arial"><span style="font-size: 9pt; font-family: Arial; color: navy;">T: (585) 325-6004 </span></font><font size="1" color="black" face="Arial"><span style="font-size: 9pt; font-family: Arial; color: black;">Ext. 114</span></font><font color="navy"><span style="color: navy;"><span> </span></span></font><font size="1" color="navy" face="Arial"><span style="font-size: 9pt; font-family: Arial; color: navy;">F: (585) 325-6005</span></font><font size="1" color="black" face="Arial"><span style="font-size: 9pt; font-family: Arial; color: black;"></span></font></p>
<p class="MsoNormal"><font size="1" color="black" face="Arial"><span style="font-size: 9pt; font-family: Arial; color: black;"><a href="mailto:wbishop@pathfinder-ea.com" target="_blank">wbishop@pathfinder-ea.com</a><span> </span></span></font><font size="1" color="black" face="Arial"><span style="font-size: 9pt; font-family: Arial; color: black;"><a href="http://www.pathfinder-ea.com/" target="_blank">www.pathfinder-ea.com</a></span></font></p>
<p class="MsoNormal"><font size="5" color="green" face="Webdings"><span style="font-size: 18pt; font-family: Webdings; color: green;">P</span></font><font color="green"><span style="color: green;"><span> </span></span></font><font size="1" color="green"><span style="font-size: 7.5pt; color: green;">Sustainability
– the forest AND the trees.</span></font><font size="5" color="green" face="Webdings"><span style="font-size: 18pt; font-family: Webdings; color: green;"> P<span> </span></span></font><font color="green"><span style="color: green;"></span></font></p>
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<div class="MsoNormal" style="text-align: center;" align="center"><font size="3" face="Times New Roman"><span style="font-size: 12pt;">
<hr size="2" align="center" width="100%">
</span></font></div>
<p class="MsoNormal"><b><font size="2" face="Tahoma"><span style="font-size: 10pt; font-family: Tahoma; font-weight: bold;">From:</span></font></b><font size="2" face="Tahoma"><span style="font-size: 10pt; font-family: Tahoma;">
<a href="mailto:equest-users-bounces@lists.onebuilding.org" target="_blank">equest-users-bounces@lists.onebuilding.org</a>
[mailto:<a href="mailto:equest-users-bounces@lists.onebuilding.org" target="_blank">equest-users-bounces@lists.onebuilding.org</a>] <b><span style="font-weight: bold;">On Behalf Of </span></b>Carol Gardner<br>
<b><span style="font-weight: bold;">Sent:</span></b> Friday, November 19, 2010
11:53 AM<br>
<b><span style="font-weight: bold;">To:</span></b> Chris Jones<br>
<b><span style="font-weight: bold;">Cc:</span></b>
<a href="mailto:equest-users@lists.onebuilding.org" target="_blank">equest-users@lists.onebuilding.org</a><br>
<b><span style="font-weight: bold;">Subject:</span></b> Re: [Equest-users]
Condenser loop control?</span></font></p>
</div><div><div></div><div class="h5">
<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size: 12pt;"> </span></font></p>
<p class="MsoNormal" style="margin-bottom: 12pt;"><font size="3" face="Times New Roman"><span style="font-size: 12pt;">The commands you are
looking for are for the cooling tower. See below.<br>
<br>
Carol</span></font></p>
<div style="border-width: 1pt medium; border-style: solid none; border-color: rgb(153, 153, 153) -moz-use-text-color; padding: 0in;">
<div>
<div>
<p><font size="3" face="Times New Roman"><span style="font-size: 12pt;"> </span></font></p>
</div>
</div>
</div>
<div style="overflow: auto;" valign="bottom">
<div>
<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size: 12pt;"><a href="http://volume2dictionary.htm" target="_blank">Volume 2: Dictionary</a><span> > </span><a href="http://hvaccomponents.htm" target="_blank">HVAC
Components</a><span> > </span><a href="http://circulationloop2.htm" target="_blank">CIRCULATION-LOOP</a><span> > </span><a href="http://looptemperaturecontrol.htm" target="_blank">Loop Temperature Control</a></span></font></p>
</div>
<h5><b><font size="2" face="Times New Roman"><span style="font-size: 10pt;">COOL-SETPT-CTRL</span></font></b></h5>
<p><font size="3" face="Times New Roman"><span style="font-size: 12pt;">Code word specifies the loop temperature control
sequence:</span></font></p>
<p><font size="3" face="Times New Roman"><span style="font-size: 12pt;">FIXED
specifies that the loop supply temperature is controlled to a fixed value,
specified by the COOL-SEPT-T</span></font></p>
<p><font size="3" face="Times New Roman"><span style="font-size: 12pt;">OA-<font color="white"><span style="color: white; background: none repeat scroll 0% 0% rgb(49, 106, 197);">RESET</span></font>
specifies that the loop supply temperature is <font color="white"><span style="color: white; background: none repeat scroll 0% 0% rgb(49, 106, 197);">reset</span></font> on outdoor air
according to the COOL-<font color="white"><span style="color: white; background: none repeat scroll 0% 0% rgb(49, 106, 197);">RESET</span></font>-SCH.</span></font></p>
<p><font size="3" face="Times New Roman"><span style="font-size: 12pt;">SCHEDULED
specifies that the loop supply temperature is controlled to a schedule
specified by the COOL-SETPT-SCH.</span></font></p>
<p><font size="3" face="Times New Roman"><span style="font-size: 12pt;">LOAD-<font color="white"><span style="color: white; background: none repeat scroll 0% 0% rgb(49, 106, 197);">RESET</span></font>
specifies that the loop supply temperature is <font color="white"><span style="color: white; background: none repeat scroll 0% 0% rgb(49, 106, 197);">reset</span></font> so that the valve of
the worst-case coil is fully open. The minimum <font color="white"><span style="color: white; background: none repeat scroll 0% 0% rgb(49, 106, 197);">reset</span></font> temperature for a
cooling-type loop is MIN-<font color="white"><span style="color: white; background: none repeat scroll 0% 0% rgb(49, 106, 197);">RESET</span></font>-T. LOAD-<font color="white"><span style="color: white; background: none repeat scroll 0% 0% rgb(49, 106, 197);">RESET</span></font> is applicable to any loop serving a
chilled-water coil (CHW, PIPE2). It is also applicable to a condenser-water
loop; here this control mode will enable the cooling tower temperature to float
with the load and <font color="white"><span style="color: white; background: none repeat scroll 0% 0% rgb(49, 106, 197);">wet</span></font>-<font color="white"><span style="color: white; background: none repeat scroll 0% 0% rgb(49, 106, 197);">bulb</span></font>
temperature as described in the cooling tower sections. </span></font></p>
<p><font size="3" face="Times New Roman"><span style="font-size: 12pt;">
Since a WLHP loop also uses a cooling tower, LOAD-<font color="white"><span style="color: white; background: none repeat scroll 0% 0% rgb(49, 106, 197);">RESET</span></font> is applicable to the
heat-rejection side of a WLHP loop. It does not apply, however, to the heating
setpoint of a WLHP loop. </span></font></p>
<p><font size="3" face="Times New Roman"><span style="font-size: 12pt;">
This mode maximizes the efficiency of the primary equipment and minimizes the
loop's thermal losses (but at the expense of pumping energy in a variable-flow
loop). Refer to LOOP-FLOW-<font color="white"><span style="color: white; background: none repeat scroll 0% 0% rgb(49, 106, 197);">RESET</span></font> for information on how to minimize the
pumping penalties associated with this control scheme.</span></font></p>
</div>
<p class="MsoNormal" style="margin-bottom: 12pt;"><font size="3" face="Times New Roman"><span style="font-size: 12pt;"> </span></font></p>
<div>
<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size: 12pt;">On Fri, Nov 19, 2010 at 5:26 AM, Chris Jones <<a href="mailto:cj@enersave.ca" target="_blank">cj@enersave.ca</a>> wrote:</span></font></p>
<div>
<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size: 12pt;">I believe that the CONT-SETPT-CTRL = VARIABLE provides similar control?</span></font></p>
<div>
<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size: 12pt;"><br>
<br>
At 08:16 AM 19/11/2010, Brian Fountain wrote:</span></font></p>
</div>
<blockquote style="margin-top: 5pt; margin-bottom: 5pt;" type="cite">
<div>
<p class="MsoNormal" style="margin-bottom: 12pt;"><font size="2" face="Calibri"><span style="font-size: 10pt; font-family: Calibri;">In DOE-2.1e, you had the option of
condenser loop control by wet-bulb reset. I cannot figure out how to do
that in DOE-2.2. Any suggestions or was this option lost in the combining
of systems & plants.<br>
<br>
<br>
</span></font></p>
</div>
<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size: 12pt;">_______________________________________________<br>
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</blockquote>
<p style="margin-bottom: 12pt;"><font size="3" face="Times New Roman"><span style="font-size: 12pt;"><br>
Chris Jones<br>
14 Oneida Avenue<br>
Toronto, ON
M5J 2E3.<br>
Tel. 416-203-7465<br>
Fax. 416-946-1005</span></font></p>
</div>
<p class="MsoNormal" style="margin-bottom: 12pt;"><font size="3" face="Times New Roman"><span style="font-size: 12pt;"><br>
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</div>
<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size: 12pt;"><br>
<br clear="all">
<br>
-- <br>
Carol Gardner PE</span></font></p>
</div></div></div>
</div>
</blockquote></div><br><br clear="all"><br>-- <br>Carol Gardner PE<br>
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