Changes to ASHRAE 90.1, the North American standard for the energy performance of buildings, are about to be published at the end of 2001.

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has developed and published energy standards for buildings since 1975. The current edition is ASHRAE Standard 90.1-1999, Energy Standard for Buildings Except Low-Rise Residential Buildings. However, the society will publish the 2001 edition at the end of this year, and it contains some important revisions.

Standard 90.1 is a significant document, particularly in the United States where state codes must be at least as stringent as the 1989 version. ASHRAE 90.1-1999 is also used widely across Canada, although primarily as a standard for design, not as a mandatory code. It has already been included in the International Energy Conservation Code.

Compliance with the standard may be achieved by either of two ways: meeting the prescriptive requirements in the standard, or by using the Energy Cost Budget approach in Section 11. The Energy Cost Budget approach requires that the annual energy cost of a proposed building design not exceed the annual energy cost of a "budget building." The budget building must meet all prescriptive requirements of the standard for envelope insulation, HVAC, service water system, lighting and equipment efficiencies. The approach results in a customized energy cost budget for each proposed design.

The new revisions

After Standard 90.1-1999 was approved, ASHRAE placed it on continuous maintenance. Under this process the standard is maintained by a cognizant committee that considers any proposed changes. Each addendum is issued for public review and comment, and comments received are considered by the committee and submitted for board approval. Every three years, ASHRAE has committed to publishing a new edition of the standard incorporating all addenda approved to that time. ASHRAE Standard 90.1-2001 will be the first new edition of the energy standard since it went onto continuous maintenance.

The 2001 standard incorporates 34 addenda. Many of these clarify intent and improve readability, but do not change requirements. They will make the standard easier for the user to understand and apply. An important goal is for greater consistency in interpretation by building officials. By far the most important of these addenda is 'ao.'

Addendum 'ao' is a complete re-organization of Section 5, Envelope, which contains requirements for the thermal performance of roofs, walls, glazing, and other building envelope components. The details of the mandatory requirements have been relocated to the end of the section. This change permits the prescriptive envelope requirements, which vary by climate, to be closer to the beginning of the section. All types of opaque areas (roofs, above-grade walls, below-grade walls, floors, slab-on-grade floors, and doors) are itemized and the user can go directly to the applicable requirements. The somewhat complex requirements for "semi-heated" spaces are now dealt with by exception. Previously, the user had to wade through these requirements although they might not be applicable in a particular building.

• energy efficiency
• Standards: ASHRAE : new ASHRAE 90.1