Achieving compliance with ASHRAE 90.1

ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings is one of the main drivers used in any building design. The 2016 edition hasn't been adopted by all jurisdictions, however engineers should understand the key elements of this important standard.

Jeff Boldt, IMEG Corp.; Michael Rosenberg, Pacific Northwest National Laboratory

Learning objectives

ASHRAE 90.1-2016: Energy Standard for Buildings Except Low-Rise Residential Buildings is an ANSI-approved, consensus-based standard that establishes minimum energy efficiency requirements for buildings. Provisions in the standard are meant to be technically feasible, cost-effective, and adoptable in the U.S. and international markets. The standard has progressively reduced building energy use since 1975, and the 2016 edition is no exception.

This looks at the latest changes to Standard 90.1 including provisions for:

Figure 1: The progression of energy savings in ASHRAE Standard 90.1 includes preliminary estimates for 2016. Courtesy: Pacific Northwest National LaboratoryMost changes in Standard 90.1 are reflected in the next edition of the International Energy Conservation Code (IECC), which for many years has permitted compliance with either the latest edition of the IECC or Standard 90.1. Also, states and other jurisdictions adopt different editions of IECC or Standard 90.1—most commonly IECC—so minimum requirements may vary by location.

Regardless of the minimum code in force, compliance with the latest version of ASHRAE 90.1 will save energy, and each change must meet the cost-effectiveness criteria based on standard engineering economics using a "scalar" method described in this document.

Formatting has changed significantly. In 2013, the standard was published in a two-column format and was 278 pages long. In 2016, the standard is in single-column format for easier reading on computer monitors, is 388 pages long, and has added shading of alternate columns and italicizing of defined terms.

ASHRAE Standard 169-2013: Climactic Data for Building Design Standards updated the climate maps throughout the world based on warming trends over the most recent 30 years of compiled weather data. Because many of the criteria in Standard 90.1 are determined by climate zone, including envelope insulation and many HVAC requirements, this can be particularly impactful. Approximately 10% of U.S. counties moved to a warmer climate zone. A perfect example is Wisconsin, where the southern 40% of the state and most of the population was moved from Climate Zone 6A, under which Green Bay falls, to 5A—the same as Chicago. This means less insulation is required for construction in those areas. The standard also added climate zones 0A (hot and humid) and 0B (hot and dry) because Climate Zone 1 is about as hot as Miami, and there are warmer places on our planet. IECC-2018 did not change its climate zones, so different requirements will exist depending on the chosen compliance path (90.1 or IECC prescriptive) in many locations. 

Envelope requirements

Prescriptive continuous air barrier design and installation are still an option in Standard 90.1, but whole-building air-leakage testing was added as a new prescriptive alternative. In the testing option, the leakage must be ≤0.4 cfm/sq ft of envelope (including the roof and bottom floor) at 0.3 in. of water-pressure differential (which is about the velocity pressure of a 25-mph wind) per ASTM E779 or ASTM E18.

This is better performance than studies of large numbers of buildings have measured (e.g., "Airtightness of Commercial and Institutional Buildings: Blowing Holes in the Myth of Tight Buildings," by Andew K. Persily, presented at the Thermal Envelopes Conference VII in 1998) (~1.5 cfm/sq ft in this reference), so acceptance testing cannot be ignored, nor will sloppy or "normal" construction pass this test. If the building fails, evaluation and additional sealing is required and must reduce leakage to ≤0.6 cfm/sq ft. Searching for and sealing leaks is required, but not the deconstruction of the envelope unless the leakage still exceeds 0.6 cfm/sq ft after repairs are made. The fallback threshold of 0.6 cfm/sq ft was established as a compromise to gain acceptance for this new provision.

For those familiar with the standard 15-mph wind-equivalent infiltration value that is commonly used in heating-load calculations, multiply these infiltration rates by about 0.5 (Q = C*ΔP0.65). Buildings larger than 50,000 sq ft can test only portions of the building. If testing is not done, an air barrier installation and verification program is required in addition to prescriptive air-sealing requirements, which was the only alternative in prior editions of ASHRAE 90.1.

Window U-values were reduced Standard 90.1-2016 for Climate Zones 6 through 8 (cold climates). Solar heat-gain coefficients (SHGC) were reduced in Climate Zones 4 and 5. Shading-projection factor multipliers were eliminated for north-facing glass, and formulas were added that limit the amount of glass facing east and west multiplied by its SHGC.

Figure 2: The definitions for energy-recovery efficiency have been updated in ASHRAE 90.1-2016. Courtesy: IMEG Corp.HVAC and refrigeration requirements

Integrated energy efficiency ratio (IEER) minimum ratings are now required for most direct expansion (DX) commercial air conditioning equipment efficiency. In general, commercial equipment now must meet both energy efficiency ratio (EER), which measures efficiency at peak load and integrated energy efficiency ratio (IEER), annual load) efficiencies, while residential equipment must meet seasonal energy efficiency ratio (SEER) efficiencies, which rate efficiency over a range of outdoor air temperatures s. All are expressed in Btu/W*hr. 3.4 Btu/W*hr = 1.0 coefficient of performance (COP).

IEER = (2% * EERat 100% load) + (61.7% * EER75%) + (23.8% * EER50%) + (12.5% * EER25%)

Higher IEER values are required for most variable refrigerant flow (VRF) equipment.

Computer room units were divided into three classifications (75°F, 85°F, and 95°F) with different efficiency requirements due to trends toward higher computer room temperatures that permit much more use of economizers.

Efficiency requirements were added in the 2016 edition for pool dehumidifiers based on the recently developed AHRI Standard 920. These use the metric of moisture-removal efficiency (MRE), which is the ratio of the pounds of moisture removed to the energy input in kWh at a standard rating condition.

Two tables were added for dedicated outside-air systems (DOAS), one for those with energy recovery and one for those without. The metric used is integrated seasonal moisture-removal efficiency (ISMRE) per AHRI Standard 920. Like MRE, ISMRE is the ratio of the pounds of moisture removed to the energy input in kWh, but instead of at a single standard rating condition, it is a seasonal value based on a weighting of four different rating conditions.

Hotels and motels with more than 50 guest rooms must now have automatic setup/down of at least 4°F for temperature setpoints and turn off fans or close dampers for ventilation and exhaust systems within 30 minutes of all occupants vacating. Captive key cards are acceptable for detecting occupancy.



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