[BLDG-SIM] eQUEST Condensing Boiler Curve

["Brandon Nichols" <BrandonN@xxxxxxxxxx>]

Title: eQUEST Condensing Boiler Curve

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.html

 

 

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@xxxxxxxx [mailto:BLDG-SIM@xxxxxxxx] On Behalf Of Mark Nieman
Sent: Thursday, December 21, 2006 9:42 AM
To: BLDG-SIM@xxxxxxxx
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

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
"For The Life Of Your Building"

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