ASHRAE Journal - April 2013 - 72

EnErgy ModEling

Modeling and 90.1
By Jared A. Higgins, P.E., Member ASHRAE

Two Paths: ECB and PRM

M

any consider Standard 90.1-2010 to be the energy bible. But,
when I’m working with people new to energy modeling, they have

questions about the energy cost budget method and the performance
rating methods found in the standard. They want to know the differences
between them, their requirements and when they are used. So, I decided
this was the perfect topic for my first column on energy modeling.

Energy Cost Budget Method
The energy cost budget method is Standard 90.1’s alternative approach to the standard’s prescriptive compliance path. It uses
a computer simulation program to evaluate
the design energy cost of a proposed building design compared to that of the energy
cost budget of a baseline design (as determined in Section 11 of the standard). This
method may be used to evaluate compliance
of proposed designs with the exception of a
design without a mechanical system.
This approach allows you to trade off
certain energy related design variables
between the different building components, assuming the standard’s mandatory provisions are met. An example
would be a building designed with a
higher interior lighting power density
than allowed by the standard, but which
has a more efficient air-conditioning and
heating system. If the simulation analysis
determines that the designed building’s
energy cost will be lower than that of
the baseline building, the building has
achieved compliance even though the
lighting power density was greater than
allowed in the standard.
Table 11.3.1 of the standard shows
the modeling requirements for calculating both the design energy cost and the
energy cost budget buildings. The requirements include aspects such as space
72

ASHRAE Journal

use classifications, schedules, building
envelope, lighting, HVAC zones, HVAC
systems, service hot-water systems, and
miscellaneous loads. Additionally, Table
11.3.2A provides the requirements of
the budget building HVAC system to be
modeled.

Performance Rating Method
We have determined the energy modeling method used for achieving compliance with the standard. If we want to
rate the energy efficiency of building
designs that exceed the requirements
of the standard, we use the performance
rating method (PRM), found in Standard 90.1-2010’s Normative Appendix
G. This approach also simulates performance between a proposed building
design and a baseline building design.
However, instead of verifying that the
proposed design results are within the
range of compliance, the performance
rating method determines a percentage
improvement between the two buildings
performances. The PRM is the method
used for the whole building energy
simulation option of the Energy and
Atmosphere Credit 1, Optimize Energy
Performance, for LEED New Construction & Major Renovations-2009.
Table G3.1 in Standard 90.1-2010 lists
the modeling requirements for calculatashrae.org

Standard 90.1-2010 sets minimum
energy requirements for buildings. Each
section contains mandatory provisions
that must be met. The standard also
contains two energy modeling methods:
the energy cost budget (ECB) method
and the performance rating method
(PRM).
In addition to compliance of the mandatory provisions, the standard further
lays out requirements for compliance
by means of a prescriptive path, in
which the building design has to comply
with additional energy reduction measures. The alternative approach to the
prescriptive compliance path is known
as the energy cost budget method
(ECB). The performance rating method
(PRM) is used to quantify performance
that exceeds the requirements of Standard 90.1.
Both the ECB and PRM allow tradeoffs between building components,
but the mandatory provisions identified throughout the standard are still
required to be met.
ing both the proposed building design
as well as the baseline building design
performance. Table G3.1.1A lists the
baseline building HVAC system types
and Table G3.1.1B provides the HVAC
system descriptions.
Although this is a very high level
description of both energy modeling
methods, I hope you understand when
each methods is used and where to find
more information.
Jared A. Higgins, P.E., leads the mechanical engineering and energy services
group for Parkhill, Smith, & Cooper, Lubbock, Texas. He is an ASHRAE certified
Commissioning Process Management
Professional.
April 2013



ASHRAE Journal - April 2013

Table of Contents for the Digital Edition of ASHRAE Journal - April 2013

ASHRAE Journal - April 2013
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Ground-Coupled Heat Pump and Energy Storage
Fan Efficiency Requirements for Standard 90.1-2013
Technology Award Case Studies:
Geothermal for 5 Ecosystems
Holistic HVAC Design
Standing Columns
Engineer’s Notebook
Data Centers
Emerging Technologies
IAQ Applications
Refrigeration Applications
Special Products
People
International Column
Energy Modeling
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - April 2013 - ASHRAE Journal - April 2013
ASHRAE Journal - April 2013 - Cover2
ASHRAE Journal - April 2013 - 1
ASHRAE Journal - April 2013 - 2
ASHRAE Journal - April 2013 - Contents
ASHRAE Journal - April 2013 - Commentary
ASHRAE Journal - April 2013 - 5
ASHRAE Journal - April 2013 - Industry News
ASHRAE Journal - April 2013 - 7
ASHRAE Journal - April 2013 - 8
ASHRAE Journal - April 2013 - Letters
ASHRAE Journal - April 2013 - Meetings and Shows
ASHRAE Journal - April 2013 - 11
ASHRAE Journal - April 2013 - 12
ASHRAE Journal - April 2013 - 13
ASHRAE Journal - April 2013 - Ground-Coupled Heat Pump and Energy Storage
ASHRAE Journal - April 2013 - 15
ASHRAE Journal - April 2013 - 16
ASHRAE Journal - April 2013 - I1
ASHRAE Journal - April 2013 - I2
ASHRAE Journal - April 2013 - I3
ASHRAE Journal - April 2013 - I4
ASHRAE Journal - April 2013 - 17
ASHRAE Journal - April 2013 - 18
ASHRAE Journal - April 2013 - 19
ASHRAE Journal - April 2013 - 20
ASHRAE Journal - April 2013 - 21
ASHRAE Journal - April 2013 - 22
ASHRAE Journal - April 2013 - 23
ASHRAE Journal - April 2013 - Fan Efficiency Requirements for Standard 90.1-2013
ASHRAE Journal - April 2013 - 25
ASHRAE Journal - April 2013 - 26
ASHRAE Journal - April 2013 - 27
ASHRAE Journal - April 2013 - 28
ASHRAE Journal - April 2013 - 29
ASHRAE Journal - April 2013 - 30
ASHRAE Journal - April 2013 - 31
ASHRAE Journal - April 2013 - Geothermal for 5 Ecosystems
ASHRAE Journal - April 2013 - 33
ASHRAE Journal - April 2013 - 34
ASHRAE Journal - April 2013 - 35
ASHRAE Journal - April 2013 - 36
ASHRAE Journal - April 2013 - 37
ASHRAE Journal - April 2013 - 38
ASHRAE Journal - April 2013 - 39
ASHRAE Journal - April 2013 - Holistic HVAC Design
ASHRAE Journal - April 2013 - 41
ASHRAE Journal - April 2013 - 42
ASHRAE Journal - April 2013 - 43
ASHRAE Journal - April 2013 - 44
ASHRAE Journal - April 2013 - 45
ASHRAE Journal - April 2013 - 46
ASHRAE Journal - April 2013 - 47
ASHRAE Journal - April 2013 - Engineer’s Notebook
ASHRAE Journal - April 2013 - 49
ASHRAE Journal - April 2013 - 50
ASHRAE Journal - April 2013 - 51
ASHRAE Journal - April 2013 - 52
ASHRAE Journal - April 2013 - 53
ASHRAE Journal - April 2013 - Data Centers
ASHRAE Journal - April 2013 - 55
ASHRAE Journal - April 2013 - 56
ASHRAE Journal - April 2013 - 57
ASHRAE Journal - April 2013 - 58
ASHRAE Journal - April 2013 - 59
ASHRAE Journal - April 2013 - Emerging Technologies
ASHRAE Journal - April 2013 - 61
ASHRAE Journal - April 2013 - 62
ASHRAE Journal - April 2013 - 63
ASHRAE Journal - April 2013 - IAQ Applications
ASHRAE Journal - April 2013 - 65
ASHRAE Journal - April 2013 - 66
ASHRAE Journal - April 2013 - Refrigeration Applications
ASHRAE Journal - April 2013 - Special Products
ASHRAE Journal - April 2013 - People
ASHRAE Journal - April 2013 - International Column
ASHRAE Journal - April 2013 - 71
ASHRAE Journal - April 2013 - Energy Modeling
ASHRAE Journal - April 2013 - 73
ASHRAE Journal - April 2013 - Products
ASHRAE Journal - April 2013 - 75
ASHRAE Journal - April 2013 - 76
ASHRAE Journal - April 2013 - 77
ASHRAE Journal - April 2013 - 78
ASHRAE Journal - April 2013 - Classified Advertising
ASHRAE Journal - April 2013 - Advertisers Index
ASHRAE Journal - April 2013 - Cover3
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