A Quick Rundown on ASHRAE 90.1

By Jim Crockett April 1, 2006

The first thing to keep in mind about ASHRAE 90.1 is that it is not exclusively an HVAC guideline. A joint standard by ASHRAE, the Illuminating Engineering Society and the American National Standards Institute, it is broken into 12 chapters: Purpose; scope; administration/enforcement; definitions; building envelope; HVAC; service water heating; power; lighting; other equipment (principly motors); energy cost budget method; and normative references.

The purpose of the standard, according to Sachin Anand, P.E., LEED AP, a project manager and mechanical team leader for CCJM Engineers, Ltd., Chicago, is to provide minimum requirements for the energy-efficient design of buildings except low-rise residential buildings.

Anand regularly conducts seminars on how to comply with the standard and recently participated in a webcast on the subject.

The standard’s goal, he said, is the implementation of efficient systems that minimize system losses, maximize equipment efficiencies and utilize free heating and cooling. A pair of compliance paths are acceptable: the simplified/prescriptive path and the energy cost budget method. The latter is based on overall building performance where all of the standard’s mandatory provisions must still be met, but the energy cost budget method, according to Anand, allows trade-offs between measures and is useful for optimizing design.

Regarding lighting, the guide applies to all interior and some exterior lighting and includes exit signs with exceptions for life-safety lighting. Basically, it promotes energy-efficient and high-efficacy light fixtures that still meet IES light levels for the type of application. Controls also play a major role and must be combined into building space models to calculate lighting power densities.

Power is not a huge part of the standard, said Anand, so as not to compete with standards already established in existing electrical codes. That said, it does regulate voltage drop in feeders and branch circuit conductors (2% and 3%).

Finally, 90.1 is a component of LEED certification, but LEED is not part of the standard. Because of obvious synergy, Apendix G, Anand said, was added as an informative guide for rating energy efficiency of building designs that exceed 90.1’s requirements. It also provides guidelines for awarding credit for advanced design strategies.