ASHRAE’s Revised Standard 90.1 Features Upgraded U-Factors for Building Envelopes

ASHRAE has released an expanded and revised version of the ANSI/ASHRAE/IES Standard 90.1-2019, Energy Efficiency Standard for Buildings Except Low-Rise Residential Buildings, which includes more than 100 changes, including some pertaining to building facades and energy-saving measures.

Significant changes include:

  • Administration and Enforcement: Commissioning requirements were added to the standard for the first time. Section 4.2.5, “Verification, Testing, and Commissioning,” was expanded and requirements were outlined for commissioning in accordance with ASHRAE/IES Standard 202.
  • Building Envelope: For vertical fenestration, the categories of “nonmetal framed” and “metal framed” products were combined. Minimum criteria for SHGC and U-factor were upgraded across all climate zones. The air leakage section was revised to clarify compliance. Changes to the vestibule section refined the exceptions and added a new option and associated criteria for using air curtains.
  • Lighting: Lighting power allowances for the Space-by-Space Method and the Building Area Method were modified. According to ASHRAE, the model is more representative of real-world conditions with the inclusion of updated IES recommendations. A new simplified method for lighting (new Section 9.2) was added. Lighting control requirements for parking garages were updated. Daylight-responsive requirements and side-lighting requirements were updated.
  • Mechanical: New requirements were defined to allow designers the option to use ASHRAE Standard 90.4 instead of ASHRAE/IES Standard 90.1 requirements in computer rooms that have an IT equipment load larger than 10 kW. Pump definitions, requirements and efficiency tables are included in the standard for the first time.
  • Energy Cost Budget Method: Numerous changes were made to ensure continuity. The baseline was set for on-site electricity generation systems.
  • Performance Rating Method: Appendix G rules and the corresponding baseline efficiency requirement were clarified. Explicit heating and cooling COPs were provided without fan for the baseline packaged cooling equipment. Rules were added for modeling the impact of automatic receptacle controls. More specific baseline rules were set for infiltration modeling. Clarification was added for how plant and coil sizing should be performed. Building performance factors in Section 4 were updated.
  • Both Compliance Paths: Clearer and more specific rules were added related to how renewables are treated. Extensive updates were added to the rules for lighting modeling.

Code consultant Tom Culp provided an update on the revised code during the National Glass Association/Glass Association of North America 2019 Fall Conference. He said that one of the focuses of the new version would be a continued expansion of daylighting, including better controls and more spaces.

Items still in progress that did not make it into the 2019 version of ASHRAE 90.1 include limiting thermal bridges in opaque areas and at wall/window interface, a prescriptive requirement for on-site renewable energy and envelope trade-off limits of backstops.

Culp explained that when using the performance path to do tradeoffs, the proposed envelope backstops mean the following:

  • It must show compliance of overall building energy performance. This includes everything: the enveloped, HVAC, lighting, hot water, etc.; and
  • Proposed envelope performance must be no more than X% worse than the prescriptive envelope.

Culp stressed that the industry agrees it doesn’t want to see the use of poor performing windows, but there are concerns. For example, he explained that the measures go against the “philosophy of performance-based standards and integrated design … what matters is the overall building performance, not how you get there.”

Culp noted that there could be potential negative impact on window area for highly glazed buildings, as anything above 40% window-to-wall ratio (WWR) must be made up in performance path tradeoffs.

As far as window area, he said there have been no direct attacks in WWR in recent code cycles, but there is a growing indirect pressure on WWR. Backstops, he said, restrict the types of tradeoffs that can be used.

Culp added that with or without backstops the industry must continue to promote high performance glazing and framing as the solution.

In the 90.1 proposal, they proposed that envelope performance factors may not exceed the baseline envelope by more than 15% in multifamily, hotel/motel and dorm applications and 7% in all other buildings.

This provides flexibility in a number of ways. He said limits were established by modeling to allow about a 70% WWR with prescriptively compliant windows. He added that a 90% WWR with good orientation, shading and/or better windows could be a possibility.

To purchase Standard 90.1, visit www.ashrae.org/bookstore.

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