Volume 35, Number 10, October 2000



ASHRAE 90.1.99 Spells Good News for Glass and Glazing Contractors

 by Jim Benney

Last year, the American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE) approved a revision to ASHRAE 90.1-89, “Energy Efficient Design of New Buildings, Except for Low-Rise Residential.” The new standard, ASHRAE 90.1-99, includes numerous changes that will help glazing contractors and other standard users perform their jobs more efficiently—in every sense of the word.

Published earlier this year, the standard is an improvement over the 1989 version in terms of both increased energy efficiency and ease of use. It is estimated that buildings that meet the new ASHRAE standard will save 20 percent more energy than buildings constructed in accordance with the 1989 standard. It should be noted that ASHRAE 90.1-99 applies to all buildings except residential buildings with three habitable stories or less.

Specific improvements to the standard include the following:

• It is written in code enforceable language;

• Separate versions are available for both metric and inch-pound units;

• The requirements for the building envelope, the lighting and the HVAC systems are independent of each other (except in the case of the energy cost budget methodology);

• It addresses additions and alterations to existing buildings;

• It includes a simple prescriptive compliance path.


New Standard Provides Three Compliance Options

Compliance with the standard requires that all mandatory provisions must be met, after which, the building designer can choose to comply with one of three options:

• The building envelope option;

• The building envelope trade-off option;

• The energy cost budget method.

The prescriptive building envelope option recognizes the advances made in glazing performance over the last ten years by allowing vertical fenestration area up to 50 percent of the gross wall area. If a building has more than 50 percent glazing area (or more than 5 percent fenestration area in the roof) another compliance path must be used.

The prescriptive option has maximum requirements for U-factor and solar heat gain coefficient. These requirements are based on local climate and building orientation. Fenestration U-factors requirements range from 0.29 to 1.27, while SHGC requirements range from 0.14 to no requirement. In addition, the standard provides a credit for overhangs that provide shading.

There are also requirements for air leakage in windows and doors. Leakage shall not exceed 1.0 cubic feet per minute (per square foot of door area) for glazed swinging entrance doors and 0.4 cfm/ft2 for all other products (note that field glazed products are exempt from these air leakage requirements).

ASHRAE 90.1-99 also provides a building envelope trade-off option to assist in compliance. This option allows the performance of one envelope component to be improved to make up for another component that does not meet minimum requirements (note that this option cannot be used to trade off between the building envelope and the lighting or mechanical system). When utilizing the trade-off option, the visible transmittance of the fenestration systems must also be specified. This is used for determining the potential for daylighting.

Of special interest, is the availability of software for conducting these trade-offs. The ENVSTD program meets all the requirements of the building envelope trade-off option. ASHRAE published a users manual and the ENVSTD software earlier this year.

The analysis methodology is termed the energy cost budget method. It is used to evaluate the compliance of proposed building designs and is intended for use with simulation programs that model building efficiency. The models must report energy usage by lighting, internal equipment loads, and service water heating equipment, space cooling and heat rejection equipment, fans and other HVAC equipment. Using this approach, architects, builders, and designers can increase the amount of glass in buildings by utilizing high-performance glass products to control solar heat gain and take advantage of energy savings from daylighting.

It should be noted that all performance criteria (U-factor, solar heat gain co-efficient, emissivity, visible transmittance and air leakage) must be determined in accordance with the National Fenestration Rating Council (NFRC) standards as follows:

• NFRC 100 “Procedures for Determining Fenestration Product U-factors.”

• NFRC 200 “Procedure for Determining Fenestration Product Solar Heat Gain Coefficients at Normal Incidence.”

• NFRC 300 “Procedure for Determining Solar Optical Properties of Simple Fenestration Products.”

• NFRC 301 “Standard Test Method for Emittance of Specular Surfaces Using Spectrometric Measurements.”

• NFRC 400 “Procedure for Determining Fenestration Product Air Leakage.”

ASHRAE 90.1 also requires that all performance criteria “shall be determined by a laboratory accredited by a nationally recognized accredited organization, such as the NFRC and shall be labeled and certified by the manufacturer.”

IECC and DOE Likely To Adopt Standard

The International Energy Conservation Code currently references the “Energy Efficient Design of New Buildings, Except for Low-Rise Residential,” and it is anticipated that the 1999 edition will be accepted at the code hearings this fall. In addition, a ruling from the U.S. Department of Energy is expected later this summer approving the 1999 standard as a replacement for ASHRAE 90.1-89 in federal building standards and state energy codes.

Jim Benney is director of education at the NFRC. Prior to joining NFRC, he served as executive director of the Primary Glass Manufacturers Council and as NFRC vice chairman.


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