[Bldg-sim] Boilers sized by eQuest

[Steven Savich]

Yu,

Have a look at the PS-H report for your boilers.  It's likely that eQuest
oversized the boilers dramatically.  You could look at the percentage of
time the main boiler spends above the 50% of full load bin and if the number
of hours is not significant, limit the boiler capacity accordingly.

You can also control the boiler staging with an equipment control
(EQUIP-CTRL keyword).  Have a look at the DOE2 help files for instructions
on how to set one up.  An excerpt: "This command allows you to override the
default load allocation routines (in which the program automatically selects
the mix of equipment with a combined capacity most closely matching the load
but preventing an overload condition)."

Hope this helps,
Steven

 

Steven Savich
Systems West Engineers
411 High Street
Eugene, OR  97401-2427
(541) 342-7210
(541) 342-7220 (fax)


-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of yizhao1 at vt.edu
Sent: Friday, July 11, 2008 12:10 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Boilers sized by eQuest


Hi -
My model let eQuest to size the boiler capacity based on 'secondery' demand
to
see how large the size of the boiler will be. There are 2 equally sized
boilers. I made the capacity and capacity ratio of each boiler default
(blank).
The output report shows the rated capacity for each boiler is 4.037 MBtu/h,
and
boiler A works at all spectrum of part load for most hours when heating is
needed, while the boiler B only work several hours at very low part load
percent. The peak load for boiler A is 4.125 MBtu/h, the peak load for
boiler B
is only 0.058 MBtu/h.

Since boiler B works less efficiently, I try to downsize the boiler capacity
to
reduce equipment cost and heating energy use. If I input a capacity ratio of
<0.5 for each boiler, eQuest will give out a warning that the hot water loop
heating capacity is less than the secondary demand. However, the percent of
hours outside throttling range was not affected.

Is the warning a concern? Or any alternative way to reduce the size of the
boiler and make them 'work' more efficiently in eQuest?

Many thanks in advance.


Yu
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