Keeping up with Standard 90.1

ANSI/ASHRAE/IES Standard 90.1-2010 includes some big changes, including its title, purpose, and scope.

By Carol Marriott, PE, LEED AP, Carol Marriott Consulting, Maple Grove, Minn. January 18, 2011

ANSI/ASHRAE/IES 90.1-2010 certainly provides a significant improvement over previous versions. To stay up-to-date you can follow the committee in its work on the next edition (2013) by signing up for its listserv to get notifications of upcoming meetings and notifications of public review drafts.

The Standing Standard Project Committee 90.1 (SSPC 90.1) has been hard at work for the past six years making significant strides in the energy efficiency provisions of 90.1. Its goal was to create a 2010 standard that would be used to build buildings that are 30% more efficient than buildings built to the 2004 version of the standard. As ASHRAE 90.1 is under continuous maintenance, the updates are published as addenda and incorporated into the document as supplements between editions. There have been 153 addenda incorporated into ASHRAE 90.1 since the 2004 version, 109 of which have been processed since the 2007 version of 90.1.

The Dept. of Energy (DOE) will perform its analysis to determine exactly how much savings has occurred, but it is clear that a lot has changed in 90.1. This article highlights some of the significant changes. Further reading of the document to understand the direct implications is required and encouraged.

Title, purpose, and scope

Perhaps one of the biggest changes in 90.1 is the change to its title, purpose, and scope. SSPC 90.1 has debated for many years as to how to broaden its scope to include more energy-saving technologies. ASHRAE 90.1 previously focused on the energy use in commercial buildings, meaning that process, industrial, and manufacturing loads were previously excluded from 90.1. The reasoning behind the exclusion is the difficulty of addressing process loads; that is, it is very difficult to define a set of regulations for manufacturing loads.

How do you write a standard for energy efficiency that is equally fair for a semiconductor manufacturing plant as for an automobile manufacturing plant? Despite the difficulty, why should some loads be excluded from energy efficiency provisions when in a culture of energy efficiency, it makes sense to start including them? Do you include the refrigeration load in a grocery store? Do you include the process load in a dry cleaning facility?

SSPC 90.1 came up with a way to address some loads that were previously excluded by including the “minimum energy-efficient requirements for the design, construction, and a plan for operation and maintenance of new equipment or building systems specifically identified in the standard that are part of industrial or manufacturing processes” (ANSI/ASHRAE/IES 90.1-2010). This doesn’t mean that all process, industrial, and manufacturing loads are now included in 90.1, but if the standard calls out a particular load, it is now included.

A good example of this is data centers. The change in title, purpose, and scope allowed 90.1 to expand its reach into data centers. Almost every building has one today, and yet due to business requirements, the focus has been on the operation, not the efficiency, of those systems. An advantage to including data centers is that designers now have a baseline upon which to begin their designs.


Within the envelope section of ASHRAE 90.1, a continuous air barrier is now a mandatory requirement for all buildings. Specific materials and assemblies have been listed and deemed compliant with the new minimum air leakage requirements; materials or assemblies not listed will need to be tested according to the appropriate testing standard to show compliance.

One of the prescriptive changes to the envelope section is the requirement for minimum skylight fenestration area for some space types, including buildings four stories or fewer. This change helps to promote daylighting energy savings for many spaces through the use of automatic lighting controls in the daylit area. There is also a new prescriptive provision to encourage better oriented vertical fenestration. Buildings will find it easier to comply with the standard by providing more fenestration on southern exposures than east and west exposures (northern exposures in the Southern Hemisphere). There are, of course, exceptions to every rule, and some spaces may be excluded, including those with permanent shading devices. It is important to note that prescriptive requirements can be traded for other efficiency strategies using the Building Envelope Trade-Off Option or the Energy Cost Budget Method.


The HVAC section of ASHRAE 90.1 has increased efficiency for most products in 2010. Air conditioners serving computer rooms, variable refrigerant flow (VRF) systems, water source heat pumps, and closed-circuit cooling towers were added to the HVAC minimum efficiency tables. Evaporatively cooled unitary equipment was separated from water-cooled equipment, and an integrated energy efficiency ratio (IEER) was introduced for these products, with new efficiencies effective June 1, 2011. Air-cooled chiller efficiencies were updated. In addition to updated efficiencies, water-cooled chillers with a variable frequency drive (VFD) have a separate path with a much more stringent integrated part load value (IPLV). The scope surrounding centrifugal chillers has also expanded to cover many more centrifugal chiller applications that must meet ASHRAE 90.1.

In the prescriptive requirements, energy recovery has been expanded significantly for 2010. This will mean more buildings will require energy recovery systems. For example, an office HVAC system located in Miami or Minneapolis with 5,500 cfm of supply air and 30% outdoor air would be required to have energy recovery with an effectiveness of at least 50%.

The prescriptive economizer requirements have increased in stringency dramatically from the 2007 requirements. Buildings with fan-cooling units ≥54,000 Btu/h (≥16 kW) will require an economizer unless they are in climate zone 1a or 1b. Economizers for computer rooms are now defined in ASHRAE 90.1, and there are separate requirements for other HVAC system types.

To encourage better design practices, maximum piping system design flow rates have been added, transfer air for kitchen exhaust is encouraged, and energy recovery or turn down are encouraged for laboratory exhaust.


The lighting section has a number of updates. It includes:

  • New exterior lighting zones
  • New lighting power density (LPD) values based on the most recent technology and modeling
  • Automatic controls for daylit areas
  • An expanded scope to include more alteration projects.

Exterior lightings requirements have always had tradable and nontradable surfaces. New for 2010 is the introduction of zones. Five lighting zones have been introduced that essentially allow for more lighting in well-lit areas and less lighting in lower-lit areas. To describe the effect, consider a uniform exterior lighting provision set based on available technologies. It is possible that a compliant building in a large brightly lit urban area would appear dim compared to surrounding buildings, possibly resulting in security concerns. The same building in a rural setting using it is fully allotted lighting power allowance may appear overly bright. As a co-developer of ASHRAE 90.1, IES developed a requirement with lighting zones 0 through 4 to define the location type from an undeveloped national park to a commercial district in a major urban center for use in the standard.

The lighting power density tables (space-by-space and building area method) were updated based on new lighting technology availability and better modeling tools. One of the new developments in the space-by-space method is the addition of room cavity ratio (RCR), which essentially takes the room configuration into account and allows the designer to adjust the lighting power accordingly.

Automatic daylighting controls were added for 90.1-2010, to coincide with the changes in the envelope provisions for minimum skylight area. Daylighting control requirements were also added for primary side-lighted areas.

The scope of the lighting section of 90.1 has been expanded to include more alterations applications. If less than 10% of the connected lighting load is being altered, the new requirements will not apply. This presents a much more stringent level than the previous 50% value.

– Marriott, the owner of Carol Marriott Consulting, has more than 10 years of experience in HVAC systems, energy applications, and sustainability. She is a member of ASHRAE and currently serves on the Standards committee as its vice chair. She has previously served as vice chair of SSPC 90.1 and Chair of Technical Committee 5.5 Air-to-Air Energy Recovery.

Other resources