ASHRAE Standard 90.1
One of ASHRAE’s premier standards, ASHRAE Standard 90.1-2022, is titled “Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings” and establishes the minimum requirements for buildings serving commercial, educational, health care, public, mid and high-rise residential, and other purposes. It includes the criteria for how to construct these buildings to reduce energy consumption during operation. For modelers, it is important because it includes several performance methods, including two explicitly intended for whole-building energy modeling:
- Energy Cost Budget Method
- Performance Rating Method
These may both be used to show compliance with the standard itself, and the second method is also used by beyond-code programs such as USGBC’s LEED. In addition, 90.1 includes specific criteria for various building components that are often used by modelers as modeled values even when these two methods are not used.
ASHRAE Standard has been developed and updated regularly since the 1980s, generally on a three-year basis, and the stringency has increased substantially over that time:
Purpose and Scope
The purpose and scope of the 2022 version of the standard is:
1. PURPOSE
1.1 To establish the minimum energy efficiency requirements of buildings other than low-rise residential buildings, and sites for design, construction, and a plan for operation and maintenance; and utilization of on-site renewable energy resources.
2. SCOPE
2.1 This standard provides
a. minimum energy-efficient requirements for the design and construction, and a plan for operation and maintenance of
new buildings and their systems,
new portions of buildings and their systems,
new systems and equipment specifically identified in this standard that are part of a site,
new systems and equipment in existing buildings, and
new equipment or building systems specifically identified in this standard that are part of process applications,
b. criteria for controlling systems in the building or on the site that modify energy usage based on communication with energy suppliers to facilitate the use of low-emissions energy sources, and
c. criteria for determining compliance with these requirements.
2.2 The provisions of this standard do not apply to
a. single-family houses and related incidental structures, multifamily structures of three stories or fewer above grade, manufactured houses (mobile homes), and manufactured houses (modular) or
b. buildings that use neither electricity nor fossil fuel.
2.3 Where specifically noted in this standard, certain other buildings or elements of buildings or sites shall be exempt.
2.4 This standard shall not be used to circumvent any safety, health, or environmental requirements.
The 90.1-2019 edition did not include “sites” in the title, purpose, or scope since the term was added for the 90.1-2022 version.
Contents
The table of contents for ASHRAE Standard 90.1-2022 is shown below, with items of particular interest to modelers shown with an asterisk and bold text.
- 1 Purpose
- 2 Scope
- 3 Definitions, Abbreviations, and Acronyms
- *4 Administration and Enforcement
- 5 Building Envelope
- 6 Heating, Ventilating, and Air Conditioning
- 7 Service Water Heating
- 8 Power
- 9 Lighting
- 10 Other Equipment
- 11 Additional Efficiency Requirements
- *12 Energy Cost Budget Method
- 13 Normative References
- Normative Appendix A: Rated R-Value of Insulation and Assembly U-Factor, C-Factor, and F-Factor Determinations
- Informative Appendix B: (Retained for Future Use)
- Normative Appendix C: Methodology for Building Envelope Trade-Off Option in Section 5.6
- Informative Appendix D: (Retained for Future Use)
- Informative Appendix E: Informative References
- Informative Appendix F: U.S. Department of Energy Minimum Energy Efficiency Requirements,
- Test Procedures, and Definitions
- *Normative Appendix G: Performance Rating Method
- Informative Appendix H: Additional Guidance for Verification, Testing, and Commissioning
- *Informative Appendix I: Using Other Metrics in Conjunction with Appendix G Performance Rating Method when Approved by the Rating Authority
- *Normative Appendix J: Sets of Performance Curves
- Informative Appendix K: Informative Figures—Thermal Bridges
- Normative Appendix L: Mechanical System Performance Rating Method
- Informative Appendix M: Addenda Description
- Annex 1: Reference Standard Reproduction—ASHRAE Standard 169
These highlighted sections are described further below.
Section 4
Section 4, Administrative and Enforcement, includes subsection 4.2.1.1 New Buildings, which describes the use of BEM modeling with Appendix G as a compliance path and how to calculate the Performance Cost Index Target and includes the table on Building Performance Factors used in that calculation. Subsection 4.2.1.2 shows how this same approach can also be used for additions to existing buildings. Subsection 4.2.1.3 shows how some changes to this approach can be used for alterations of existing buildings.
Section 12
Section 12 Energy Cost Budget Method is a method to show compliance with the standard that requires the modeling of the design and the modeling of the budget building and compare the annual energy cost between the two and compliance is met as long as the cost for the design is less than the annual cost for the budget. The budget building is the design building modified to
- Meet the prescriptive requirement of the rest of the standard
- Use specific HVAC systems
Table 12.5.1 is a two-column table that includes many of the modeling rules and is broken down into the following rows:
- Design Model
- Additions and Alterations
- Space Use Classification
- Schedules
- Building Envelope
- Lighting
- Thermal Blocks – HVAC Zones Defined
- Thermal Blocks – HVAC Zones not Defined
- Thermal Blocks -Multifamily Residential Buildings
- HVAC Systems
- Service Water Heating Systems
- Miscellaneous Loads
- Refrigeration
- Modeling Exceptions
- On-Site Renewable Energy
HVAC system selection for the budget system design follows Figure 12.5.2 and Table 12.5.2 and requires one of 11 different systems depending on the condenser cooling source being water or ground versus air or none and a heating system classification based on fossil fuel, heat pump, or electric resistance, and if it is single zone residential or non-residential or something else. The 11 different systems include:
- Variable air volume with parallel fan-powered boxes
- Variable air volume with reheat
- Packaged variable air volume with parallel fan-powered boxes
- Packaged variable air volume with reheat
- Two-pipe fan coil
- Water-source heat pump
- Four-pipe fan coil
- Packaged terminal heat pump
- Packaged rooftop heat pump
- Packaged terminal air conditioner
- Packaged rooftop air conditioner
Appendix G
Appendix G Performance Rating Method was originally intended to assess beyond code programs such as LEED but has been modified through several versions to also allow compliance with the standard. Similar to the Energy Cost Budget Method, it requires a model of the proposed building and the baseline building performance. The baseline building performance is a “stable baseline” since it is based on the criteria from the 90.1-2004 edition. This means that subsequent updates to the standard do not trigger changes in the way building energy models are constructed for Appendix G in order to help users and developers of BEM software. Many of the rules again are shown in a large multi-page table called Table G3.1 with the following sections:
- Design Model
- Additions and Alterations
- Space Use Classification
- Schedules
- Building Envelope
- Lighting
- Thermal Blocks – HVAC Zones Defined
- Thermal Blocks – HVAC Zones not Defined
- Thermal Blocks -Multifamily Residential Buildings
- HVAC Systems
- Service Water Heating Systems
- Receptacle and Other Loads
- Modeling Limitations to the Simulation Program
- Exterior Conditions
- Distributive Transformers
- Elevators
- Refrigeration
- On-Site Renewable Energy
An overview of the baseline HVAC System Types are described in Table G3.1.1-3 and Table G3.1.1-4. The selection of the systems depends on the type of building, building floor space, number of stories, and climate zone, and the process is described in Section G3.2.1.1. The baseline HVAC system types include 13 different systems:
- Packaged terminal air conditioner
- Packaged terminal heat pump
- Packaged rooftop air conditioner
- Packaged rooftop heat pump
- Packaged rooftop VAV with reheat
- Packaged rooftop VAV with parallel fan power boxes and reheat
- VAV with reheat
- VAV with parallel fan-powered boxes and reheat
- Warm air furnace, gas-fired
- Warm air furnace, electric
- Single-zone VAV
- Hot water single-zone system
- Electric resistance single-zone system
The major sections of Appendix G are described below
G1 General includes the scope, a list of the requirements in the rest of the standard that must be met by the proposed building, the calculation procedure, and the compliance documentation that must be submitted.
G2 Simulation General Requirements include requirements for the simulation software, such as the software is tested according to ASHRAE Standard 140, the weather data that should be used, how renewable energy should be modeled, how annual energy costs should be calculated, and the exceptional calculation method for when the simulation program cannot model a component used in the building.
G3 Calculation of the Proposed Design and Baseline Building Performance is the bulk of Appendix G and includes the tables described above and many sections related to specific modeling requirements for HVAC components. This section also includes how to include in the model purchased (district) energy, air leakage, and calculation of unmet loads. Section G3.3 describes a special methodology for the calculation of performance for other alterations, which is based on the criteria in the rest of the standard (instead of 90.1-2004) for tradeoffs. Many tables are used in this section of Appendix G to describe details of the model for the baseline building, including HVAC equipment performance, lighting, and envelope criteria based on 90.1-2004.
Appendix I
Informative Appendix I: Using Other Metrics in Conjunction with Appendix G Performance Rating Method when Approved by the Rating Authority is designed to help rating authorities, whether they are jurisdictions or beyond-rating programs, that want to use Appendix G with metrics other than annual energy cost. The metrics covered by the section include site energy, carbon emissions, and source energy. It describes changes that can be made to the text of Sections 3, 4, and Appendix G. The most significant change described is how to alter the building performance factors and how they should be calculated depending on the new metric. It specifically includes example language for the changes related to site energy as an example.
Appendix J
Normative Appendix J: Sets of Performance Curves include specific performance curves that can be used to model chillers in the baseline or budget building for the Section 12 Energy Cost Budget Method or Appendix G Performance Rating Method. It consists of a large number of tables of performance curve coefficients that are typically used in BEM software.
Adoption
In the United States, Title II of the Energy Conservation and Production Act requires that each state update the provisions of their commercial building codes regarding energy to the latest version of ASHRAE Standard 90.1 after the U.S. Department of Energy shows that it saves energy compared to the previous version. Some states do not have building energy codes and leave that up to local jurisdictions, while other states have not updated their building energy codes as quickly as desired. The following map shows the states which are meeting that rule.
EnergyCodes.gov Resources
The USDOE Office of Energy Efficiency and Renewable Energy provides a website with many resources for energy codes, and the page on ASHRAE Standard 90.1 Performance Based Compliance is especially important for modelers.
https://www.energycodes.gov/performance_based_compliance
The page briefly describes the Energy Cost Budget and Performance Rating methods and includes links to a number of useful tools, including
- Compliance forms (and companion tool)
- Reference Manuals for the Performance Rating Method
- Submittal review manual
- Adopter Toolkit
- Documents to support adoption
- Quality Control roadmap
Additional Resources
ASHRAE Landing page for Standard 90.1
ASHRAE Journal Series on Standard 90.1-2022 Updates
Standard 90.1 at ASHRAE Bookstore
Energycodes.gov page on Performance Based Compliance
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