BUILDING SYSTEMS: Energy Standards

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.

Closing loopholes

Other significant changes to close loopholes are:

Section 4, Administration and Enforcement. Addendum ‘af’ adds new details to clarify requirements for alterations and additions to buildings. New cooling systems installed to serve previously uncooled spaces, for example, must comply with Section 6. Alterations to existing cooling systems are not permitted to decrease an existing economizer capability unless equipment efficiencies meet the requirements of 6.3.1. Both new and replacement piping and ductwork must comply with the relevant Section 6 requirements unless there is insufficient space or access to do so. Finally, alterations to existing walls and floors are exempted from meeting the current standard’s envelope insulation requirements if the existing structure has no framing cavities and the alteration is not creating any.

Section 5, Envelope. When Standard 90.1-1999 was being developed, there was no nationally recognized certification program covering U-factors in glazed wall systems (e.g. site-built curtain wall systems). Since then, the National Fenestration Rating Council has put in place a program covering these systems. Addendum ‘ag’ requires that U-factors for glazed wall systems be determined through this program (or some other equivalent program if or when one is developed).

Section 6, Heating, Ventilating and Air Conditioning. Addendum ‘j’ revises some chiller minimum efficiency values for consistency with revisions in the referenced efficiency test procedure. The new test procedure is ARI 550/590. Addendum “j” changes the Integrated Part-Load Value (IPLV) efficiencies for electrically operated chillers in Table 6.2.1C to correspond to the new parameters. For example, the minimum IPLV for a centrifugal chiller larger than 300 tons nominal capacity was changed from 6.10 to 6.40. In addition, Table 6.2.1H was replaced so that the required Coefficient of Performance (COP) values are consistent with those in Table 6.2.1C — previously they were not. Finally, new tables now list minimum Non-Standard Part-Load Values for centrifugal chillers that are rated at non-standard conditions.

Addendum ‘q’ removes all reference to enclosed parking garage ventilation systems. The standard had explicitly permitted, but did not require, controls to shut off garage exhaust fans, or to modulate flow volumes or stage their operation provided the carbon monoxide concentration does not exceed exposure limits. The standard project committee felt the omission does not change the standard, but would avoid a possible conflict with health and safety regulations in some jurisdictions.

The standard requires economizers in most situations, but includes exceptions to reflect situations where economizers would be impractical. Some examples of exceptions are:

small capacity fan-cooling units generally are not required to have economizers;

systems serving residential spaces, unless such systems are of quite large capacity (such as central systems serving several suites in a multi-unit facility), and

where the use of outdoor air for cooling will negatively affect open refrigerated cases in supermarkets.

Addendum ‘r’ closes a possible loophole in one such exception, stating that it only applies where “gas phase air cleaning” is required. The previous wording could have been interpreted to include any type of air filtration, which was not the intent.

Addendum ‘s’ ensures economizers will be permitted in VAV systems, even if local zone heating may increase; the rationale is that the overall energy benefit of the economizer will be greater than any increase in zone heating. Finally, addendum ‘ad’ is an “omnibus” addendum covering many minor revisions to Section 6.

Section 8, Power. Addendum ‘aa’ requires that maximum permitted voltage drops in electrical feeders and branch circuits be based on design loads, not on connected loads. This change makes enforcement easier — the design loads are documented. But it also increases stringency in the majority of cases where connected load is less than design load.

Section 9, Lighting. There are two ways the permitted interior lighting power allowance can be calculated, by the building area method or the space-by-space method. Addendum ‘ah’ permits the use of the building area method for any building (previously there were limitations on its use that, with further study, were not justified). When the building area method is used, addendum ‘ai’ requires that the maximum lighting power density for the most applicable building type listed in the “building types” table be used to calculate the interior lighting power allowance. The standard recognizes that there are space usage situations for which additional interior lighting (above that normally permitted by the standard) is needed. Examples are lighting installed specifically to highlight “fine merchandise” in retail stores for display and inspection, and lighting specifically installed to meet the needs of people using video display terminals as “the primary vi
ewing task.”

Addendum ‘w’ adds limitations for its use in highlighting merchandise in retail occupancies.CCE

Cedric Trueman, P.Eng. is principal of Trueman Engineering Services of Victoria, B.C. He is a voting member of the project committee responsible for ASHRAE Std. 90.1 and also chair of ASHRAE Technical Committee 9.6 Systems Energy Utilization. In Canada he is a member of the NRC/CCBEC Standing Committee on Energy Conservation in Buildings.