Update to I2SL Laboratory Modeling Guideline Using ASHRAE 90.1-2019

Michael Walsh, R.G. Vanderweil Engineers, LLP

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In 1999, I2SL (formerly Labs21) issued Laboratory Modeling Guidelines using ASHRAE 90.1-1999 to specifically address modeling of laboratory mechanical systems using the Energy Cost Budget Method. The guideline was needed to address items in the energy code that were developed for more typical commercial buildings rather than the specific needs of laboratory facilities. Items that required modification from the base code include changes to fan power limitations, fume hood exhaust, operational schedules, HVAC budget systems, and supply to room delta T as examples. In 2004, the guideline was updated to address modeling in accordance with ASHRAE 90.1-2004 Appendix G - Performance Rating Method. This method of assessment is used by rating systems such as LEED. In addition to developing the guideline, I2SL (Labs21) continued to work with ASHRAE to correct some of the issues identified in the modeling guide which was updated to remove items addressed by ASHRAE and identify any remaining issues with ASHRAE 90.1-2007.

While I2SL (Labs 21) and ASHRAE continued to refine ASHRAE 90.1 in the 2010 and 2013 in regard to laboratory design, more recent changes in 2013 addenda, 2016 and 2019 versions of Appendix G have driven the need for an update to the Energy Modeling Guide. This presentation will outline the latest update to the I2SL (Labs 21) Energy Modeling Guideline based on the 2019 edition of ASHRAE 90.1 to identify recommended approaches to address critical issues that affect laboratory energy modeling.

Learning Objectives

  • Understand challenges of ASHRAE 90.1-2019 in regard to laboratory energy modeling;
  • Learn how modeling of diversity factors can better reflect actual energy use;
  • Identify how to challenge current ventilation rates in compliance with current ASHRAE 62.1 and NFPA 45 when seeking code variances below code values; and
  • Identify ASHRAE Laboratory Ventilation System Classification and associated recommended ventilation rates.


Michael is a Principal and HVAC Technical Director at Vanderweil promoting innovative and sustainable HVAC system design solutions. He has spent 33 years focusing on the design of energy efficient HVAC systems to serve over 7,500,000 square feet of space including animal facilities, BSL-2 & BSL-3 labs, biomedical research, public health, interdisciplinary science and forensic laboratories. Michael is an ASHRAE, I2SL and an International Code Council member.


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