What's new in ASHRAE 90.1-2013


Addendum as has two requirements:

  • Humidification systems using dispersion tube hot surfaces in the airstreams of ducts or AHUs shall be insulated with a product with an insulating value of at least R-0.5. This requirement was added because modern short-dispersion humidifiers have very large hot surface areas that act as heating coils, regardless of whether heat is needed. (Heat gains as high as 5 F have been recorded on my company’s projects.)
  • Preheat coils shall have controls that stop their heat output whenever mechanical cooling, including economizer operation, is occurring. This requirement seems innocuous, but it has large implications for some types of coils, such as face and bypass and integral face and bypass (IFB) steam coils. This addendum essentially requires that the control valve be closed when no heat is needed, regardless of the outside air temperature. This violates the recommendations of many manufacturers of IFB coils. I have personally seen heat gain as high as 13 F across IFB coils with completely closed clam-shell dampers in applications such as hospital operating room air handlers that have their heating coils sized for purge mode. This requirement means that those manufacturers will need to either revise their recommendations or redesign their products to operate with modulating steam/water or at least permit zero flow.  

The energy implications of these requirements of this addendum are huge for laboratories, hospitals, and other building types that require heating of high percentages of outside air. I have seen at least three hospitals operating at 100% outside air to reach design supply air temperatures of about 53 F in outdoor temperatures around 38 F because of the heat gain from IFB coils and short dispersion humidifiers. 

Addendum au eliminates the fan power credit for sound attenuators in systems serving spaces with design background noise goals above NC35. It also reduces fan power limits for systems without central cooling, without central heating, and with electric heat.

Addendum av restricts the exceptions for data center economizers by eliminating some types of computer rooms from the exemptions to this requirement.

Addendum az increases the minimum efficiency for open circuit cooling towers by 5% and requires that the towers meet the minimum efficiency with the impact of accessories and options included. 

Addendum ba requires that any conditioned space with door openings to the outdoors be provided with controls that, when any such opening is open:

  1. Disable mechanical heating or reset the heating setpoint to 55 F or lower.
  2. Disable mechanical cooling or reset the cooling setpoint to 90 F or greater. Mechanical cooling may remain enabled if outside air temperature is below space temperature.


  • Building entries with automatic closing devices
  • Any space without a thermostat
  • Alterations to existing buildings 

Addendum bi reconciles 90.1 with future Dept. of Energy requirements for small air conditioning unit efficiencies. 

Addendum bn adds requirements for metering of electric and other fuels to new buildings. It also allows up to 10% of loads for some categories to be “mismetered.” For example, if VAV boxes are in an area with no appropriate circuits, they could wire controls to another circuit. This addendum also requires whole building monitoring of natural gas, fuel oil, propane, steam, chilled water, and hot water.

Recording, including energy demands, is required at least every 60 minutes and to be reported hourly, daily, monthly, and annually. 

Electrical monitoring is required in new buildings for:

  • Total electrical energy
  • HVAC systems
  • Interior lighting
  • Exterior lighting
  • Receptacle circuits.

Up to 10% of load for each of b through e may be accounted for in other electrical loads. There are some exceptions.

The system shall be capable of maintaining all data collected for a minimum of 36 months and creating user reports showing at least hourly, daily, monthly, and annual energy consumption and demand.

Exceptions to and

  • Buildings or additions less than 25,000 sq ft
  • Individual tenant spaces less than 10,000 sq ft
  • Dwelling units
  • Residential buildings with less than 10,000 sq ft of common area
  • Fuel used for on-site emergency equipment. 

Addendum bo requires service water heating efficiency to be at least 90% for systems greater than 1 million Btuh. There are solar and heat recovery exceptions. 

Addendum bs reduces the occupant density that triggers the need for demand control ventilation from 40 people per 1,000 sq ft to 25 people per 1,000 sq ft. It also reduces the outside airflow rate in the exception to this requirement from 1,200 cfm to 750 cfm. 

Addendum bt adds requirements for energy recovery for systems with 10% to 29% outside air and deletes requirements for climate zones 3B, 3C, 4B, 4C, and 5B. 

Addendum cd defines piping as “the pipes or tubes interconnecting the various parts of a fluid distribution system including all elements that are in series with the fluid flow such as pumps, valves, strainers, and air separators, but not including elements that are not in series with the fluid flow such as expansion tanks, fill lines, chemical feeders, and drains.” It also requires piping (not just pipes) to comply with the sizing and insulation requirements that previously only applied to “pipes.” 

Addendum ch increases the minimum efficiencies for air and water-cooled chillers by an average of 8.3%. 

Addendum ck, also known as VAV Dual Max, makes separate limitations on reheat for systems with direct digital controls. The most significant change is that the former exception allowing reheat of up to 30% of the peak airflow rate is changed to a maximum of 20% in the dead band between heating and cooling. The first stage of heating must be modulating the zone supply air temperature setpoint up to a maximum setpoint while the airflow is maintained at the dead band flow rate. The second stage of heating modulates the airflow rate from the dead band flow rate up to the heating maximum flow rate of 50% of peak cooling airflow. 

Addendum cl updates the minimum Institute for Energy and Environmental Research (IEER) ratings for unitary air conditioning and condensing units, and becomes effective on Jan. 1, 2016. 

Addendum cy adds a table and more stringent energy recovery airflow rate triggers for systems that operate more than 8,000 hours per year.

Addendum de modifies the requirements for water economizers used primarily on computer room applications. Rather than using a fixed dry or wet bulb for the design of the water economizer where 100% of the expected cooling load is met, the design point is now variable by climate zone. The effect is to reduce the amount of oversizing of the cooling towers or dry coolers in such applications, which can result in control problems when the computer rooms are lightly loaded during the first few years of operation. 

Addendum di prohibits use of fossil fuel or electricity to produce relative humidity above 30% in the warmest zone served by the humidification system or to reduce relative humidity below 60% in the coldest zone served by the dehumidification system. There are exceptions for systems serving zones that are required to maintain special humidity conditions, such as some museums and hospitals.

Addendum dn reduces the allowable capacity of hot gas bypass systems to 15% of full capacity for systems with capacities up to 20 tons, and 10% for systems larger than 20 tons. 

Addendum dv requires preventing fluid flow through chillers and boilers that are off. If constant speed pumps are used, there must be at least one per chiller and boiler.

Addendum dw revises the acceptable options for economizer high limit control. It completely removes the fixed enthalpy option and allows fixed dry-bulb control for all climate zones where economizers are required.

Appendix G and other changes 

Addendum b requires escalators and moving walks to automatically slow to the minimum speed permitted by ASME A17.1/CAS B44 (the ASME elevator safety code), when not conveying passengers. While this has been common practice in other countries, it was illegal in the U.S. until recent revisions to the ASME Elevator Safety Code were completed.

Appendix G is used to predict energy savings in designs that exceed the requirements of 90.1. Appendix G has updates to align with many of the addenda listed above. 

For example, Addendum cn updates the Appendix G baseline for laboratories to permit modeling with 100% outside air if a code or accreditation standard prohibits recirculating air. 

This article covered many of the changes to 2013 edition of ASHRAE Standard 90.1. While not as momentous or controversial as the changes in 2010, 90.1-2013 is another significant step forward in the energy efficiency of the 90.1 code. The Standing Standard Project Committee (SSPC) will be working toward additional energy saving requirements for the 2016 version, including pursuing the concept of subsystem and system efficiencies. With the expansion in the scope of Standard 90.1 in 2010 to include additional building types and processes, expect changes in those areas in the future.

Jeff Boldt is a principal and the Director of Engineering at KJWW Engineering Consultants. He has more than 30 years of experience in mechanical, fire protection, and acoustical design. He is a voting member of ASHRAE Standard 90.1, and a member of ASHRAE Standard 189.1.

For more information

Full wording of the changes to all ASHRAE Standards addenda are available for free at https://www.ashrae.org/standards-research--technology/standards-addenda, or simply by searching online for “ASHRAE addenda.”

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