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<DIV dir=ltr align=left><SPAN class=828301914-05102007><FONT face=Arial
color=#0000ff size=2>Actually Kevin didn't get the boiler hourly energy equation
quite right. The actual equation is:</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=828301914-05102007><FONT
face="Courier New"></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=828301914-05102007><FONT
face="Courier New">Hourly Boiler Energy = DesignCapacity * HIR *
HIRf(plr)</FONT><BR></DIV></SPAN><SPAN class=828301914-05102007><FONT face=Arial
color=#0000ff size=2></FONT></SPAN>
<DIV dir=ltr align=left><SPAN class=828301914-05102007><FONT face=Arial
color=#0000ff size=2>The part of this that Kevin didn't explain is that the
boiler HIRf(PLR) curve includes the PLR which explains why the curve is nearly
linear. The value that the performance curve returns is actually
</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=828301914-05102007><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=828301914-05102007><FONT face=Arial
color=#0000ff size=2>(HIRadj) * PLR</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=828301914-05102007><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=828301914-05102007><FONT face=Arial
color=#0000ff size=2>HIRadj = the </FONT></SPAN><FONT
face=Arial><FONT color=#0000ff><FONT size=2><SPAN class=828301914-05102007><FONT
face=Arial color=#0000ff size=2>multiplier that indicates how the full load
HIR changes with respect to part load. If the boiler efficiency
at a given part load goes down, HIRadj > 1. If the boiler efficiency
goes up at a given part load HIRadj<1. HIRadj is really the ratio
HIR-partload over
HIR-fullload. </FONT></SPAN></FONT></FONT></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=828301914-05102007> </SPAN></DIV>
<DIV>P<SPAN class=828301914-05102007>LR = hourly load on the boiler / total
capacity of the boiler</SPAN></FONT></FONT></FONT></DIV>
<DIV><SPAN class=828301914-05102007><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=828301914-05102007><FONT face=Arial color=#0000ff size=2>To
create a curve that describes boiler HIR at various part loads you will
need to divide the performance curve output at each part load point by
the part load value and then multiply by the full load
HIR.</FONT></SPAN></DIV>
<DIV><SPAN class=828301914-05102007><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=828301914-05102007><FONT face=Arial color=#0000ff size=2>Taylor
- You should double check your "custom" chiller curves I'm pretty sure from what
you describe they are not correct. The Vol6 -New Features user
manual does a good job describing how the chiller curves work. I suggest
you review this. You can use the Excel function "LINEST" to create the
necessary coefficients for a bi-quadratic curve from manufacturers chiller
data. Typically you will need to request data for a specific chiller from
the chiller rep. The hardest data to get is the chiller capacity data
at various CHW/CW temperatures. Remember total chiller capacity is
different than the rated 100% part load point, most chillers can provide 10-20%
extra capacity. </FONT></SPAN></DIV>
<DIV><SPAN class=828301914-05102007><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=828301914-05102007><FONT face=Arial color=#0000ff size=2>I have
had good experience creating custom chiller curves for DOE2.2 and I think the
default curves in eQuest are representative of the various chiller types.
Obviously if you are evaluating a specific chiller you should try to create
custom curves.</FONT></SPAN></DIV>
<DIV><SPAN class=828301914-05102007><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=828301914-05102007> <FONT face=Arial color=#0000ff
size=2>Mike</FONT></SPAN></DIV>
<DIV><SPAN class=828301914-05102007><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=828301914-05102007><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> BLDG-SIM@gard.com
[mailto:BLDG-SIM@gard.com] <B>On Behalf Of </B>Kevin Madison<BR><B>Sent:</B>
Thursday, October 04, 2007 9:46 PM<BR><B>To:</B>
BLDG-SIM@gard.com<BR><B>Subject:</B> [BLDG-SIM] eQuest Default f(PLR)
Skepticism<BR></FONT><BR></DIV>
<DIV></DIV><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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<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
href="file://www.arup.com" moz-do-not-send="true"><U><FONT face=Arial
color=#0000ff size=2>www.arup.com</FONT></U></A> </P><BR><PRE>____________________________________________________________
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