[BLDG-SIM] Boiler Standby Loss and Cycling Times

[Brandon Nichols]

Standby losses

"About 1.5%-2.0% of the rated boiler fuel input is lost to the engine
room. While this loss is small when boilers operate at or near their
rated capacity, it can be significant where boilers operate frequently
at low loads. For example, imagine a boiler rated at 10 GJ/hr fuel
input, but operating at a 2 GJ/hr level. The standby loss of 2% of 10
GJ/hr is 200 megajoules per hour. This is the reason why plants with
large seasonal variations in steam-use install small boilers to operate
during the summer rather than operate large boilers year round. "

This from the State of Victoria's sustainability web site... Google
"firetube standby losses boiler optimisation" and the article should be
at the top of the list.  So 1.6% standby loss for a firetube boiler
sounds right in the ballpark, and jibes with everyday experience...to
me, STANDBY-TIME as defined translates directly to standby losses as a
percentage of full load capacity. 
 
Condensing boilers on the other hand, should have near-zero standby
losses since they don't need to stay warm to avoid thermal shock.  It
was tough to quickly find manufactures documentation confirming this,
but a call to our local Cleaver-Brooks rep who in turn called the
factory came back with an estimate of about 0.25%, i.e. 0.0025, that he
will attempt back up with a published reference tomorrow.  
 
Thanks for bringing up this topic Sean, the default standby time in my
eQuest simulations is 0.027 for firetubes... a number that definitely
needs to be changed when running a condensing boiler as the parametric
comparative.
 
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 Be I. can youhalf
Of Sean Henry
Sent: Thursday, March 08, 2007 11:56 AM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Boiler Standby Loss and Cycling Times



Dear BLDG-SIM users:

In modeling boilers, standby losses obviously need to be accounted for.