Requirements for the building envelope, lighting, mechanical systems, and the energy cost budget are among the updates in the new version of ASHRAE 90.1.
90.1-2013 incorporates 110 addenda to the previous version, which was released in 2010. The major changes include:
Envelope: Revised opaque and fenestration assemblies for most climates, including double-glazing and a minimum visible transmittance/solar heat gain coefficient ratio to ensure both good daylighting and minimum solar gain.
Lighting: Improvements to daylighting and associated controls, space-by-space lighting power density limits, toplighting thresholds, and revised requirements and format for controls.
Mechanical: Increased efficiencies are required for heat pumps, packaged terminal air conditioners, single-package vertical heat pumps, and evaporative condensers. Fan efficiency requirements appear for the first time. Control revision has been added and features stipulations like direct digital controls.
Energy Cost Budget: The new version clarifies how to use the prescriptive provisions when modeling building energy use.
Alternate Efficiency Path: An alternate path to compliance (a concept introduced in the 2010 edition) is now offered for data centers. It requires users to calculate the power usage effectiveness (PUE) rating, commonly employed in datacom applications to measure how much energy is used for computing vs. overhead.