Top ten overlooked ASHRAE 90.1-2013 requirements

As energy efficiency is a growing concern, understanding ASHRAE 90.1 requirements for energy-efficient buildings is vital.
By Cory Duggin, PE, LEED AP BD+C; TLC Engineering for Architecture, Brentwood TN February 13, 2018

Learning objectives

  • Explain ASHRAE 90.1-2013 requirements for energy-efficient buildings.
  • Explore the requirements for the 2015 IECC.


Figure 1: The Witte Museum’s Mays Family Center was designed to save 16% on energy costs compared to the energy efficiency requirements in ASHRAE 90.1-2007. Courtesy: Luis Ayala, TLC Engineering for ArchitectureEnergy efficiency is a growing concern, and many associations are adopting more requirements for energy-efficient buildings. ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings and the International Energy Conservation Code (IECC) are codes that address the design of energy-efficient buildings. The following are requirements in ASHRAE 90.1-2013 that tend to get overlooked during a building project.

1. Commercial refrigeration equipment requirements. Requirements for commercial refrigeration equipment were introduced in ASHRAE 90.1-2013, Sections 6.4.5 and 6.4.6. The minimum efficiency requirements (Tables 6.8.1-12 and 13 in Section 6.8) are only mandatory for refrigerated display cases (Section 6.4.6). The mandatory walk-in coolers and freezers requirement (Section 6.4.5) does not mention these efficiency tables. Section 6.5.11 sets the new prescriptive requirements for refrigeration systems.

2. Fan-power limitation. ASHRAE 90.1’s prescriptive fan power limitation (Section 6.5.3.1) is a mandatory requirement in the IECC (Section C403.2.12), so it may be favorable to use ASHRAE 90.1’s performance-based compliance path for projects with design limitations that cause the fan-power limitation to be exceeded.

3. Prescriptive window-to-wall ratio. The prescriptive maximum window-to-wall ratio (WWR) is 40% in ASHRAE 90.1-2013, Section 5.5.4.2.1, so buildings can comply prescriptively with ASHRAE 90.1-2013 and have more glass than those complying with 2015 IECC, that has a prescriptive maximum WWR limit of 30% (C402.4.1, without exceptions).

4. Exhaust-air energy recovery. Fan systems that exceed the total supply-airflow and outdoor-airflow percentage threshold outlined in Section 6.5.6.1 may choose to trade off the added efficiency of exhaust-air energy recovery via the performance-based compliance path in ASHRAE 90.1-2013. However, the threshold is a mandatory requirement in 2015 IECC (Section C403.2.7), which means there is no alternative for compliance.

5. Performance-based compliance path. Section C401.2(3) of the 2012 IECC added the requirement that the design energy cost must be less than or equal to 85% of the standard reference design to compensate for differences between the prescriptive requirements and the standard reference design. Section 11 of ASHRAE 90.1-2010 and 2013 only requires the design energy cost to be less than or equal to the energy cost. If a project can implement the more stringent mandatory requirements of ASHRAE 90.1, its performance compliance path (Section 11) may be easier to comply with than the IECC.

Figure 2: The Witte Museum’s Mays Family Center is a new 17,000 sq ft facility designed to house traveling exhibits and serve as an event venue. Courtesy: Luis Ayala, TLC Engineering for Architecture6. Maximum net kitchen hood-exhaust flow rate. The maximum net exhaust flow rate in cubic feet per minute (CFM) per linear foot of hood is set in ASHRAE 90.1, Table 6.5.7.1.3 of Section 6.5.7.1. The requirements are divided up by hood type and appliance duty rating. It is a prescriptive requirement, thus can be traded off on the performance compliance path.

7. Requiring commissioning for HVAC systems. ASHRAE 90.1 and the IECC differ on how they define when HVAC systems are required to be commissioned. ASHRAE 90.1-2013, Section 6.7.2.4, states that projects with greater than 50,000 sq ft of conditioned floor area must be commissioned. However, in the 2015 IECC, Section C408.2 states that systems with less than 480,000 Btu/h do not require commissioning.

8. Electrical energy monitoring. New buildings must have meters installed to separately monitor total electrical energy, HVAC systems, interior lighting, exterior lighting, and receptacle circuits. (Section 8.4.3 of ASHRAE 90.1-2013)

9. Mandatory exterior and interior lighting controls. Since the lighting-power allowance (Sections 9.2.2.1 and 9.2.2.2 of ASHRAE 90.1) is a prescriptive requirement, many assume the lighting controls are too. Some of the largest changes to ASHRAE 90.1-2013 related to the lighting controls, which are all mandatory. In Section 9.6, Table 9.6.1 breaks down which interior lighting control types are required for each space, by space type. Section 9.4.1.4 specifies the exterior lighting control types and schedules required, such as façade and landscape lighting that must be shut off between midnight and 6 a.m.

10. Room-geometry adjustment. Each revision of ASHRAE 90.1 reduces the maximum allowable lighting-power density (LPD) for some spaces. As the maximum LPD goes down, it can be difficult to light some geometries to levels recommended by the Illuminating Engineering Society of North America. The room geometry-adjustment section allows spaces with a room-cavity ratio above the threshold in Table 9.6.1 of Section 9.6 to have their maximum LPD increased by 20%.



Cory Duggin is the energy-modeling wizard at TLC Engineering for Architecture Inc., providing building-performance simulation efforts across the 375-plus-person firm through both direct project involvement and by supporting project teams on specific and unique modeling issues. He is a member of the Consulting-Specifying Engineer editorial advisory board.