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<tt>Perhaps it would help to clarify how DOE-2.2 (the simulation engine
behind eQUEST) calculates hourly energy input for boilers and chillers.<br>
<br>
For boilers, the hourly energy input is:<br>
Hourly Energy = Cap(hour) * HIR * HIRf(plr)<br>
<br>
So while the HIRf(plr) may increase as part load decreases, which is
not uncommon for standard atmospheric boilers, the energy use will
certainly decrease with plr because the required output of the boiler
for the hour decreases.<br>
<br>
For chillers, DOE-2 uses the following relationship to calculate the
electricity input to the chiller each hour:<br>
<br>
Caphour = Capacity * CAPf(t1,t2)<br>
PLR = Load / Caphour<br>
dT = t2 – t1<br>
Elechour = Caphour * EIR * EIRf(t1,t2) * EIRf(PLR,dT) / 3413 Btu/kW<br>
<br>
where<br>
<br>
Caphour hourly capacity, Btuh (this is dependent on condenser
and evaporator conditions for that hour)<br>
Capacity rated capacity, Btuh<br>
CAPf(t1,t2) correction to capacity for temperatures, curve CAP-FT<br>
t1 leaving chilled-water temperature, °F<br>
t2 condenser temperature, °F<br>
PLR Part load ratio<br>
Load Hourly load, Btuh<br>
dT Temperature differential across chiller, °F<br>
Elechour electric input to the chiller, kW<br>
EIR rated electric input ratio<br>
EIRf(t1,t2) correction to EIR for temperatures, curve EIR-FT<br>
EIRf(PLR,dT) correction to EIR for part-load ratio and dT, curve
EIR-FPLR<br>
<br>
Again, the primary factor affecting chiller energy use is the cooling
capacity needed for that hour. Just because you don't have access to
the dual function information doesn't mean you shouldn't be accounting
for it in the simulation. Chiller performance is dependent on all
operating conditions including load, condenser conditions and
evaporator conditions.<br>
<br>
For a more complete discussion on these simulation concepts, refer to
the DOE-2 documentation included with the eQUEST installation. Look in
Dictionary:HVAC Components:Boiler:Boiler Energy Consumption and
Dictionary:HVAC Components:Chiller:Chiller Energy Consumption.<br>
<br>
Kevin Madison<br>
Madison Engineering PS<br>
Seattle WA<br>
USA<br>
</tt><br>
Taylor Keep wrote:
<blockquote
cite="mid:MDAEMON-F200710041858.AA5833843pd80003835671@gard.com"
type="cite">
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<title>eQuest Default f(PLR) Skepticism</title>
<!-- Converted from text/rtf format -->
<p><font face="Arial" size="2">eQuest models boiler and chiller
plants with default part load curves that I think may be incorrect. As
I understand it, the f(PLR) curves are used as a direct multiplier on
the HIR for boilers and EIR for chillers, with full load (1.0 PLR)
corresponding to a 1.0 multiplier. If this is true, the f(PLR) curve
should increase at part load for atmospheric boilers (atmospheric
boilers become somewhat less efficient at part load). The default
atmospheric boiler curve decreases almost linearly down to zero! I am
having a tough time wrapping my head around this.</font></p>
<p><font face="Arial" size="2">On the chiller side, the default
f(PLR) is a bi-quadratic function using both dT and PLR as variables,
so it is f(PLR,dT). Since I never have this dual function information
in my general chiller selections, I have been using a standard f(PLR)
function quoted at a fixed dT from the manufacturer. The curve I get
from a McQuay 400-ton chiller selection is quadratic, with decreasing
EIR down to 50% load and increasing EIR below 50% load. I seriously
doubt that the eQuest default corresponds with this entry because
changing the function produces a huge change in performance.</font></p>
<p><font face="Arial" size="2">Do any of you have any thoughts or
suggestions about the accuracy of default f(PLR) curves? Should I scrap
my "improved," real curves - they are drastically changing the model
performance?!?!</font></p>
<p><font face="Arial" size="2">Taylor</font>
</p>
<br>
<p><font face="Arial" size="2">________________________________________________________</font>
<br>
<font face="Arial" size="2">Taylor Keep</font>
<br>
<font face="Arial" size="2">Mechanical, LEED® AP</font>
<br>
<font face="Arial" size="2"><u> </u></font>
<br>
<font face="Arial" size="2">Arup </font>
<br>
<font face="Arial" size="2">901 Market Street Suite 260</font>
<br>
<font face="Arial" size="2">San Francisco, CA 94103</font>
<br>
<font face="Arial" size="2">tel: 415 946 0279</font>
<br>
<font face="Arial" size="2">fax: 415 957 9096</font>
<br>
<font face="Arial" size="2"><a class="moz-txt-link-abbreviated" href="mailto:taylor.keep@arup.com">taylor.keep@arup.com</a></font>
<br>
<a moz-do-not-send="true" href="file://www.arup.com"><u><font
color="#0000ff" face="Arial" size="2">www.arup.com</font></u></a>
</p>
<br>
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