What's new in ASHRAE 90.1-2013

Nearly 150 addenda were proposed for ASHRAE Standard 90.1-2013.


This article has been peer-reviewed.The changes in ASHRAE Standard 90.1-2013 are not as radical as the changes made in 2010, which reduced the energy consumption of minimally compliant designs by approximately 30% compared to 90.1-2004. But while the 2013 edition does not result in as large a drop in energy use as was seen three years ago, the changes in this latest version still are significant. 

ANSI/ASHRAE/IES Standard 90.1 is a continuous maintenance standard, which means that the committee meets frequently (usually four times per year in person) to develop and vote on changes (addenda). Changes to ASHRAE standards can be proposed by committee members, subcommittee members, or members of working groups, or can be suggested by anyone through the continuous maintenance proposal (CMP) process. Once a change passes in the committee, it is released for public review. If it successfully completes the public review, it is then part of the next edition of Standard 90.1 and ASHRAE proposes the changes also to be made in the International Energy Conservation Code (IECC). Some of the changes discussed in this article already are incorporated into the 2012 edition of the IECC because of the offset in publication dates between IECC and 90.1. 

More than 120 addenda were approved for 90.1-2013. Following are the more significant changes (excluding lighting) for 2013. 

Envelope changes 

Addendum bb is one of the most significant changes. It increases the insulation values required for most opaque elements in buildings in most climate zones (see Figure 1). For example, in my location (Madison, Wis.), opaque steel-framed nonresidential walls changed from U-0.64 (R13 + R-7.5 continuous insulation) to U-0.049 (R-13 + R-12.5 continuous insulation). This basically changes the requirement from 2 in. of continuous insulation (usually polystyrene or polyisocyanurate board) to 3 or 4 in. of continuous insulation, depending on the product. This addendum also increases the minimum insulation values for roofs and skylights.

Figure 1: Addendum bb of ASHRAE 90.1-2013 is one of the most significant changes. It increases the insulation values required for most opaque elements in buildings in most climate zones. Courtesy: ASHRAE

Addendum dm limits the size of vestibules to minimize the use of fully conditioned spaces as “vestibules.” It also sets a minimum spacing of 16 ft between motorized doors in vestibules in buildings with more than 40,000 sq ft of floor area on the vestibule floor. 

Addendum bg requires that storm windows that are added must be low-E if the existing glazing is not low-E. This applies to panels added to either the interior or exterior of existing glazing. 

Addendum bw revises the fenestration orientation rules and adds a compliance option. Either:

  • East- and west-oriented glazing must each be less than 25% of the total glazing, or
  • East- and west-oriented glazing, multiplied by their solar heat gain coefficients (SHGC), must each be less than the total building sum of glazed area multiplied by each area’s SHGC.  

Several exceptions exist, including one for buildings where the east and west glazing do not exceed 20% of the east and west gross wall area and the SHGC factors are not more than 90% of the criteria in Tables 5.5-1 through 5.5-8. This is basically a passive solar requirement that promotes buildings that are longer east to west than north to south. If your building is planned to be long north to south relative to east to west, it can severely restrict glazing on the east and west facades. 

Addendum ca requires that heating for vestibules and air curtains include automatic controls configured to shut off the heating system when outdoor air temperatures are above 45 F. Vestibule heating systems shall also be controlled by a thermostat in the vestibule with a setpoint limited to a maximum of 60 F. 

Addendum da relaxes infiltration requirements for high-speed nonswinging doors intended for vehicular access and material transportation, if they have a minimum opening rate of 32 in. per second. It also exempts building products from infiltration rating requirements if the building completes a whole building air leakage test per ASTM E 779 with a leakage of under 0.4 cfm/sq ft at 0.3 in. w.g.

Mechanical changes 

Addendum g increases the efficiency requirements for many types of commercial refrigerators and freezers. 

Addendum aa requires direct digital control (DDC) for many situations, including:

  • New building air handling systems, and zones served by them
  • New building chilled water plants and all coils and terminal units served by them
  • New building heating water plants and all coils and terminal units served by them
  • Alteration or addition to zone terminal units, such as variable air volume (VAV) boxes, when the central system has DDC
  • New air handling units (AHUs) or fan-coils when served by air handling, chilled water, or heating water systems with DDC
  • Chiller plants over 300 MBH capacity with all new chillers
  • Boiler plants over 300 MBH capacity with all new boilers.

Addendum y adds efficiency requirements for small electric motors. These match upcoming Dept. of Energy requirements, and have the same effective date of March 9, 2015. 

Addendum af requires multiple-cell heat rejection equipment (cooling towers, dry-coolers, etc.) with variable speed fan drives to operate the maximum number of fans that comply with manufacturer’s requirements, and control all fans to the same speed instead of staging them on and off. This allows the maximum heat transfer surface to be used, reducing tower fan power significantly. Also, open-circuit cooling towers used on water-cooled chiller systems that are configured with multiple or variable speed condenser water pumps shall be designed so that all open-circuit cooling tower cells can be run in parallel with the larger of either the flow that is produced by the smallest pump at its minimum expected flow rate, or 50% of the design flow for the cell. 

Addendum aj requires that motors for fans that are 1/12 hp or greater and less than 1 hp be electronically commutated motors or have a minimum motor efficiency of 70% when rated in accordance with Dept. of Energy 10 CFR Part 431. These motors also shall have the means to adjust motor speed for either balancing or remote control. Belt-driven fans may use sheave adjustments for airflow balancing in lieu of a varying motor speed. 

Addendum am requires that boiler systems comply with minimum turndown ratios at various capacities of:

  • ≥ 1,000,000 Btuh = 3 to 1
  • > 5,000,000 Btuh = 4 to 1
  • > 10,000,000 Btuh = 5 to 1. 

The system turndown requirement may be met through the use of: multiple, single-input boilers; one or more modulating boilers; or a combination of single-input and modulating boilers. 

Addendum ap permits an alternative compliance path for computer rooms by demonstrating a power usage effectiveness (PUE) below climate-specific values that vary from 1.3 to 1.61, based on ASHRAE 90.1-2013 Appendix G simulation. This allows innovative cooling techniques to be used that may not fit in with the prescriptive requirements for computer rooms. 

Addendum aq requires multistage or modulation of direct expansion (DX) cooling systems.

  • For systems more than 65,000 Btuh but less than 240,000 Btuh, a minimum of three stages of cooling is required with a maximum first-stage displacement of 35% of total displacement or variable speed reducing capacity to 35% or less.
  • For systems with capacity of 240,000 Btuh or greater, a minimum of four stages of cooling is required with a maximum first-stage displacement of 25% of total displacement or variable speed reducing capacity to 25% or less.  

Addendum aq prohibits false loading of cooling systems by trimming the economizer or by engaging hot gas bypass when more than the first stage of mechanical cooling is operating. It also requires at least two stages of cooling for systems that are controlled directly by space temperature with capacity greater than 75,000 Btuh, and effective Jan. 1, 2016, 65,000 Btuh. It also requires systems that control cooling capacity based on space temperature to reduce fan speed to less than 66% at low cooling load, and systems that control space temperature by modulating airflow to reduce fan speed to less than or equal to 50% at low cooling load. There are exceptions for units with fan motors less than 1 hp and where more flow is required to comply with ventilation codes. 

(Figure 2, left). The addendum basically is a passive solar requirement that promotes buildings that are longer east to west than north to south. Figure 3 shows the ASHRAE 90.1-2013 glazing orientation. Courtesy: KJWW Engineering Consultants(Figure 2, left). The addendum basically is a passive solar requirement that promotes buildings that are longer east to west than north to south. Figure 3 shows the ASHRAE 90.1-2013 glazing orientation. Courtesy: KJWW Engineering Consultants

Addendum ar deals with commercial refrigeration equipment, with some exceptions. It requires automatic closing doors or other methods of infiltration minimization for commercial coolers and freezers; minimum R-values of R-25 for coolers and R-32 for freezers; light source efficacy of at least 40 lumens/W; minimum glazing requirements for reach-in coolers; maximum power limits for anti-sweat heaters; controls for anti-sweat heaters based on relative humidity (RH) or condensation, and electrically commutated (EC), permanent-split capacitor (PSC), or 3-phase fan motors. This also includes requirements for remote condensers. 

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John , PA, United States, 01/31/14 09:02 PM:

Interesting Map, in Washington state there is a region in the cascades that are mapped as Zone and the olympic mountains that have low tempertures, lots of snow etc, that are shown as Zone 4 and 5 and should be AZones 6, if not Zone 7.
ERNEST , CT, United States, 02/20/14 07:55 PM:

Big changes for Data Centers, too. Strong case for economizers to help meet the PUE requirements. See Part 6.6.
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