[BLDG-SIM] eQUEST Condensing Boiler Curve

[Brandon Nichols]

Mark,
 
I think the basic problem with the curve as you have defined it is that,
for a given flow rate, delta-T is dependent on firing rate, and thus the
value of the leaving water temperature cannot be assumed and must be
calculated.  This however can easily done, using the given firing rate
for each entering water temperature value.
 
That being said, the Aerco curve as presented I think is somewhat
ambiguous, and requires a few engineering assumptions to solve
definitively.
 
As I know this is bound to come up very soon in one or more of the
projects I've got sitting in front of me, I spent a little time today
reasoning this out and have published the results in my ongoing ELCCA
Exchange blog:
 
 
http://elcca-exchange.blogspot.com/2006/12/equest-boiler-curve-example.h
tml
 
 
If you wouldn't mind, please let me know how the curve fit data works...
I don't have a live project just yet with a condensing boiler to test it
on.
 
 
Regards
 
Brandon Nichols, PE
Mechanical
HARGIS ENGINEERS
600 Stewart St
Suite 1000
Seattle, WA 98101
d | 206.436.0400 c | 206.228.8707
o | 206.448.3376 f | 206.448.4450
www.hargis.biz



  _____  

From: BLDG-SIM at GARD.COM [mailto:BLDG-SIM at GARD.COM] On Behalf Of Mark
Nieman
Sent: Thursday, December 21, 2006 9:42 AM
To: BLDG-SIM at GARD.COM
Subject: [BLDG-SIM] eQUEST Condensing Boiler Curve



Using eQUEST v.3.6, I've taken a stab at creating a performance curve
for an Aerco KC1000 condensing boiler. I've defined BOILER:HIR-FT =
"Aerco-KC1000-HIR-fEWT&LWT" as shown below. This boiler is being used
for a water source heat pump condenser water loop with a CT/HX & two
condensing boilers, piped in a primary loop configuration.

"Aerco-KC1000-HIR-fEWT&LWT" = CURVE-FIT       
   TYPE             = BI-QUADRATIC-T 
   INPUT-TYPE       = DATA 
   INDEPENDENT-1    = ( 180, 180, 180, 80, 80, 80, 100, 100, 100, 120,
120, 
         120, 140, 140, 140, 160, 160, 160 ) 
   INDEPENDENT-2    = ( 180, 90, 135, 90, 135, 180, 90, 135, 180, 90,
135, 
         180, 90, 135, 180, 90, 135, 180 ) 
   DEPENDENT        = ( 1, 1.023, 1.019, 1.151, 1.077, 1.065, 1.102,
1.047, 
         1.038, 1.053, 1.026, 1.017, 1.033, 1.017, 1.012, 1.023, 1.017, 
         1.007 ) 
   .. 

Question: Is this a proper curve for this equipment? Any comments and
critiques would be much appreciated. Part of my difficulty is that
HIR-FT is a Bi-Quadratic-T or Bi-Linear-T curve that needs two
temperatures (EWT & LWT) to define the HIR ratio modifier. When looking
at the curves, it's stated as thermal efficiency vs. EWT (return water
temperature) on several different curves based on fire rate of the
boiler. Basically, I assumed a LWT based on firing rate (90F=25%,
135F=75% & 180F=100%). I'm not sure if this is reasonable or not. Per
the manual, the DEPENDENT variable is the ratio of the actual efficiency
(based on the curves) / rated efficiency (at full fire, full load).
INDEPENDENT-1 = EWT, INDEPENDENT-2 = LWT.

The link to the data sheet is here: 
http://www.aerco.com/cgi-bin/docsserv.cgi?idDocument=344
<http://www.aerco.com/cgi-bin/docsserv.cgi?idDocument=344>  

Mark Nieman, PE, CEM 
Sr. Energy Engineer 
McKinstry Essention 
Direct: (206) 832-8152 
Cell: (206) 510-4760 
FAX: (206) 832-8552 
http://www.mckinstry.com <http://www.mckinstry.com>  
"For The Life Of Your Building" 

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