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J u l y 2 00 4 ASH RAE Jo ur na l 5 5

New Software for 

Calculating

SeasonalEfficiency for BoilersBy David C. Bixby, Member ASHRAE; Martha J. Hewett, Member ASHRAE; and Ron M. Nelson, Ph.D., P.E., Member ASHRAE

David C. Bixby  is manager, Technical Services, with

 the Gas Appliance Manufacturers Association, in

 Arlington, Va., and a member of ASHRAE SPC 155P.

Martha J. Hewett is assistant director of research

& engineering with the Center for Energy and En-

 vironment, Minneapolis, and chair of SPC 155P. Ron

M. Nelson, Ph.D., P.E., is professor of mechani-

cal engineering at Iowa State University in Ames,

Iowa, and the principle investigator on RP-1196.

 About the Authors

user-friendly, Windows-based software tool has been devel-

oped to calculate the application seasonal efficiency (ASE) of 

commercial space heating boiler systems, based on the tests and

calculation procedures specified by ASHRAE Standard 155P, Method

of Test for Rating Commercial Space Heating Boiler Systems.

The standard, which is nearing comple-

tion by Standard Project Committee

(SPC) 155P, is unique in that the tests and 

calculation procedures result in an appli-

cation-specific seasonal efficiency rating

for a particular system configuration in a

 particular building type and climate lo-

cation. This represents a first in North

America for any kind of commercial

heating system.

 Why the Software?

The software was developed to facili-

tate the standard’s application-specific

approach. Given the complexity of com-

mercial boiler systems and the resulting

complexity of Standard 155P, only the

most experienced could be expected to

use the standard without this software.

The software will greatly facilitate de-

termination of boiler system energy in-

 put and ASE for commercial buildings

 by manufacturers’ representatives, de-

sign engineers, utility staff and others

to compare options for building owners.

It also will help boiler manufacturers

use the standard in sensitivity analyses

for designing new boiler products and 

control strategies.

The research project that resulted in the

software was recommended by SPC

155P, and sponsored by ASHRAE TC

6.1, Hydronic and Steam Equipment and 

Systems. Ron Nelson, Ph.D., P.E., Mem-

 ber ASHRAE, of Iowa State University

is the project’s contractor.

How “Friendly” Is It?

Designers can use the software’s user-

friendly interface to:

• Select building load profiles from the

library by building type and climate

location;

• Import customized load profile data

from one or more common file formats;

A

The following article was published in ASHRAE Journal, July 2004. © Copyright 2004 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. It is presented for educational purposes only. This article may not be copied and/or distributed electronically or inpaper form without permission of ASHRAE.

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5 6 A SHRA E J o ur na l a s h r ae . o r g J u l y 20 0 4

• Specify the sizing of the boiler relative to the building de-

sign load;

• Input boiler rating data or select data from a database of rating information;

• Specify the sequencing and control of the boiler system;

and 

• Specify desired outputs.

Inputs are saved until deleted, allowing the user to change

 just a few inputs without reentering inputs that are unchanged.

Several alternative systems can be evaluated in separate win-

dows at the same time.

Output options include:

• A convenient summary of user inputs and selections;

• Application seasonal efficiency;

• Annual energy input and output; and • Graphical and tabular output and input load profiles.

The output format anticipates use of the software for sensi-

tivity analysis or for comparison of options. An option to per-

mit comparisons by tabulating or graphing the outputs listed 

 previously for multiple scenarios and an option to write the

results of several scenarios to file will

 be provided. The software accepts both

I-P and SI inputs, and produces I-P or SI

outputs as selected by the user. Internal

computations are in I-P.

 Why Commercial Boilers?

Boilers are estimated to account for 

42% of space heating energy use in the

commercial and multifamily sectors in

the U.S. Significant energy savings could 

 be achieved in commercial and multi-

family buildings by optimizing the se-

lection of commercial boiler systems in

new buildings and at the time of boiler 

replacement. Currently, however, com-

mercial boilers and all other types of 

commercial heating equipment are rated 

only in terms of steady-state efficiency

at full load (derived from either a flue

loss test or a thermal efficiency test),

which does not provide a meaningful indication of relative

operating costs.

 Addressing All Parameters

The efficiency of space heating in commercial and multi-

family buildings depends in part on the part-load efficiency of 

the individual boilers used. However, it also depends signifi-

cantly on the design of the boiler system, for example, whether 

single or multiple boilers are used, whether multiple boilers

are staged or gang-fired, whether staged boilers have primary/

secondary pumping or not, and whether reset and/or cutout

control are used. It depends as well on the load profile of the particular building in which the boiler system is used and how

oversized the system is relative to the building design load. All

of these parameters are addressed in 155P and its software.

 We’ve Got the Bins!

Determination of the ASE using Standard 155P and the soft-

ware required bin-based calculations. The building load data

can be chosen from a library of five building types in eight

climate locations, or may be obtained from a building-specific

hourly simulation program. One-hundred and one bins were

constructed, including a zero load bin and bins from 1% to

100% of the maximum hourly load. The total energy output tothe building in each bin was determined by binning the load 

data. In any bin, various boilers in the system may be operat-

ing at steady-state high fire, modulating, operating at steady-

state low fire, cycling, idling, off but experiencing through-flow,

or isolated. The status of each boiler in each bin and its contri-

 bution to the energy output required by

the building is determined based on the

system sizing and the system control

strategy. The input required of each boiler 

in each bin is determined based on its out-

 put and its part load efficiency in that

mode at the average water temperature

associated with that bin.

 When Will the Software be Ready?

 Not until later this year. It is expected 

that another ASHRAE Journal article will

appear near the public review period for 

Standard 155P that will cover the stan-

dard itself, including how the software

will be made available by ASHRAE.

 Acknowledgments

The building load profiles developed 

for 155P could not have been accom-

 plished without the valuable contribution

of Battelle Pacific Northwest National Laboratories, supported 

 by the U.S. Department of Energy (DOE). Likewise, valida-

tion testing essential to development of the standard was con-

ducted by Intertek/ETL Semko with funding from the National

Institute of Standards and Technology, supported by DOE, from

the Gas Research Institute (now the Gas Technology Institute),

and from the New York State Energy Research and Develop-

ment Authority. Several producer members of the committee

also conducted validation testing.