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.

By Jeff Boldt, IMEG Corp.; Michael Rosenberg, Pacific Northwest National Laboratory January 22, 2018

Learning objectives

  • Know the latest updates to ASHRAE 90.1-2016: Energy Standard for Buildings Except Low-Rise Residential Buildings.
  • Realize what other codes and standards are affected by and rely on ASHRAE 90.1.
  • Review a case study of a hospital that traveled a path to compliance.

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:

  • The building envelope.
  • HVAC systems.
  • Power and lighting systems.
  • Whole-building energy performance.

Most 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.

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.

There is a new requirement to monitor energy use of new, large electric chilled-water plants. The threshold for water-cooled plants is 1,500 tons in Climate Zones 3C, 4C, and 5 through 8, and 1,000 tons in other climate zones. For air-cooled plants, the threshold is 860 tons in Climate Zones 3C, 4C, and 5 through 8, and 570 tons in other climate zones. There is no minimum plant-efficiency requirement, but the metric should be displayed in kilowatt per ton or COP. The intent is to give operators information to help them improve plant efficiency; with information that is easy to see, operators can experiment with setpoints, such as condenser temperature, to find the optimum combinations under all weather and load conditions. Because Standard 90.1 only regulates a building through design and construction, it would not be within the scope of the standard to require some operational efficiency, but providing the monitoring capabilities ensures that building operators will have a simple way to verify the performance of the plant.

In several places in the standard, the phrase "must be capable of" was replaced with "must be capable of and configured to automatically." This is intended to avoid the argument that "the direct digital control system is capable of doing that, but we didn’t program it because that’s not required."

Much like the requirements for variable air volume (VAV) systems, chilled- and heating-water systems must reset water temperature based on valve position, with some exceptions. These exceptions may include process loads requiring a minimum temperature and district chilled water where blending would reduce efficiency.

DX systems with air economizers must now include fault detection and diagnostic (FDD) systems. These systems require sensors for outside air (OA), supply air (SA), and (where needed) return air (RA) temperatures. There are specific requirements for the FDD features including not economizing when it should be, economizing when it shouldn’t, dampers not modulating, etc.

New language requires that relief fans with motors larger than 0.5 hp have variable speed or four or more stages (presumably ≥4 fans because using two two-speed fans is probably more expensive today than a variable frequency drive or electrically commutated motor).

ASHRAE 90.1 previously stated that systems shall provide a means to relieve excess outdoor air during air-economizer operation to prevent over-pressurizing the building. In the 2016 edition, this has been changed to: "Relief air rate shall be controlled to maintain building pressure either directly or indirectly through differential supply-return airflow tracking. Systems with constant-speed or multispeed supply fans shall also be allowed to control the relief system based on outdoor-air damper position."

Parallel-flow, fan-powered VAV units now need controls that turn off the terminal fan when neither heating nor ventilation is required. In addition, the terminal fan must be used as the first stage of heating and during warmup without primary air or instead to provide heating with primary air.

Hydronic variable-flow system requirements were modified to include heating systems. Also, the motor horsepower at which variable flow systems are required (including the requirement to use <30% of peak power at 50% flow) was changed from >10 hp in all climate zones to a series of values in a table that vary based on the climate zone and whether the system is for heating or cooling. Turndown must be to ≤25% flow or minimum equipment flowrate, with some exceptions.

Chilled-water systems now must have ≥15°F ΔT and ≥57°F leaving-water temperature, with several exceptions.

The definitions for energy-recovery efficiency have been updated:

  • Enthalpy recovery ratio: Change in the enthalpy of the outdoor-air supply divided by the difference between the outdoor air and entering exhaust air enthalpy, expressed as a percentage.
  • Sensible energy-recovery ratio: Change in the dry-bulb temperature of the outdoor-air supply divided by the difference between the outdoor air and entering exhaust air dry-bulb temperatures, expressed as a percentage.

A major change was made in the 2016 edition regarding transfer air that is intended to minimize conditioning of make-up air that could have been supplied from transfer air that otherwise would have been exhausted. This states that transfer air is conditioned supply air delivered to any space with mechanical exhaust and shall not exceed the greater of one of the following: 

  • The supply flow required to meet the space heating or cooling load.
  • The ventilation rate required by the authority having jurisdiction, the facility environmental health and safety department, or ASHRAE Standard 62.1.
  • The mechanical exhaust flow minus the available transfer air from conditioned spaces or return-air plenums on the same floor, not in different smoke or fire compartments, and that at their closest points are within 15 ft of each other. Available transfer air is that portion of outdoor ventilation air that is not required to satisfy other exhaust needs, is not required to maintain pressurization of other spaces, and is transferable per applicable codes and standards and to the class of air-recirculation limitations in ASHRAE Standard 62.1. 

Safety exceptions

Service-water heating: A new requirement was added in Standard 90.1-2016 to insulate at least the first 8 ft of branch piping connected to recirculated, heat-traced, or impedance-heated piping. IMEG Corp. initiated this change after the firm had an issue on a project in which a value-engineering proposal deleted insulation between the recirculated mains and the fixtures, which was required in specifications but not in Standard 90.1 and possibly the IECC (wording is conflicted). Unfortunately, this resulted in too little heating capacity because numerous small, uninsulated, metal pipe branches make excellent cooling fins. Justifying this for Standard 90.1 required heat-transfer calculations for bare and insulated pipes connecting to mains, followed by cost-effectiveness analysis to determine the length that just met the criteria.

Lighting: In the 2010 and 2013 editions, the lighting changes concentrated on controls to turn off unneeded lighting. In the 2016 edition, both interior and exterior lighting-power density (LPD) limits were lowered, primarily because of improved efficacy and availability of LED sources. The average reduction in the space-by-space method was 26%. In the building-area method, the average reduction for all building types is 12%. Exterior lighting-power limits were reduced by an average of 30%. In retail lighting, the added allowances for display and decorative lighting were both reduced by about 25% because of advances in LED technology.

A slight relaxation of the code was to allow open-plan office areas to automatically come fully on if control zones are limited to 600 sq ft. Larger zones still must either be turned on manually or to no more than 50% power automatically.

The requirement to reduce exterior and parking-ramp lighting power by a minimum of 30% during unoccupied periods has been increased to 50%.

Dwelling units must now have 75% of permanently installed lighting fixtures use lamps with an efficacy of at least 55 lumens/W or have fixture efficacy of at least 45 lumens/W. This limits the use of Edison screw fixtures that also could accept incandescent lamps in 4-story and taller multifamily buildings. There is an exception for lights with dimmers or automatic control.

Lighting alterations must now comply if they involve more than 20% (formerly 10%) of the connected lighting load.

Other equipment: The Department of Energy (DOE) increased required efficiencies for most electric motors, and ASHRAE 90.1 simply reprints that data.

Elevator design documents must now list the usage category between 1 (seldom used) and 6 (extremely high usage) per ISO 25745-2 and energy efficiency class between A (very efficient) and G (very inefficient) per ISO 25745-2, Table 7. There is no minimum requirement for the energy efficiency class. The intent is to give designers time to become familiar with the standard before setting a minimum efficiency level. The documentation requirements also make them aware that there is a test and a rating standard for elevators and that they can specify high-efficiency equipment. It is even possible to specify efficiency higher than the minimum for Category A. Efficiency class calculations include both standby and moving energy, so a seldom-used elevator with very efficient lighting might reach Class A even with an inefficient movement system. 

Appendix G

One of the most important changes in 2016 is the addition of a whole-building simulation-based compliance path via Appendix G. Previously, Appendix G was used only for "beyond-code" programs, such as U.S. Green Building Council LEED, ASHRAE Standard 189.1, and the International Green Construction Code (IgCC), meaning a project needing to comply via whole-building performance and going for a beyond-code rating could potentially have to create two or more completely different baseline models in addition to the proposed building design model.

Previously, one baseline model was required for compliance and a completely different baseline model was required for a beyond-code program. Now that Appendix G is approved for compliance, only the proposed building model and a single baseline building model are required, thus saving time and cost that could be better spent on improving the efficiency or amenities of the building.

This change also means that a project choosing an inherently more efficient HVAC system, reducing the percentage of glass, reducing fan power, increasing thermal mass, or building a tighter envelope will get credit for those improvements, which was not the case under previous editions’ energy-cost budget method. (See case study linked below)

Another change is that the compliance requirements are now based on improvement over a stable baseline set at approximately the stringency level of the 2004 standard. This means that code compliance and beyond-code programs using the same modeled baseline simply require different levels of improvement over that stable baseline, and each new edition of Standard 90.1 only needs to revise the target improvement. LEED v4 now includes a pilot credit based on this method.

For example, an office building in Chicago that just complies with Standard 90.1-2016 with an improvement of 40% over the baseline (varies based on the number of unregulated loads in the building) would qualify for six points under Energy and Atmosphere Credit 1 using the new LEED pilot credit. LEED v4 references 90.1-2010, so just complying with 90.1-2016 shows substantial energy savings. ASHRAE 90.1-2016 will also be the basis of the upcoming edition of the IgCC and ASHRAE Standard 189.1.

This new approach should make it more economical for software developers to produce products, because they don’t need to change the rules for the baseline calculations with each new issue of 90.1. 

Jeff Boldt is a managing principal and director of innovation and quality at IMEG Corp. and a voting member of the ASHRAE 90.1 and 189.1 committees. 

Michael Rosenberg, a senior research scientist at Pacific Northwest National Laboratory, has worked in the building energy field for more than 20 years upgrading building energy codes, training code officials and design professionals, designing high-performance buildings, analyzing complex building systems, and developing and administering beyond-code energy programs.

Acknowledgements: This article relied heavily on a presentation developed by co-author Michael Rosenberg and fellow SSPC-90.1 committee members Drake Erbe, Leonard Sciarra, Richard Lord, and Eric Richmond. 


Learn more about ASHRAE 90.1 changes in an article linked below.