Bill Bahnfleth, PhD, PE – Penn State Professor & ASHRAE Past President on Mechanical Systems and COVID-19

Air Date: 5-22-2020|Episode 586

This week we welcome back Bill Bahnfleth, PhD, PE to discuss the new ASHRAE Pandemic Task Force and Mechanical Systems and COVID-19. Dr. Bahnfleth is the Chair of the task force along with being a Penn State Professor and ASHRAE Past-President. We are thrilled to have him join us again in spite of his busy schedule.

William Bahnfleth is a professor of architectural engineering at the Pennsylvania State University (Penn State) in University Park, PA, where he has been employed since 1994. Previously, he was a Senior Consultant for ZBA, Inc. in Cincinnati, OH and a Principal Investigator at the U.S. Army Construction Engineering Research Laboratory in Champaign, IL. He holds BS, MS, and PhD degrees in Mechanical Engineering from the University of Illinois, where he also earned a bachelor of music degree in instrumental performance. His is a registered professional engineer. At Penn State, Dr. Bahnfleth teaches undergraduate courses in HVAC fundamentals, HVAC system design, and controls and graduate courses in chilled water systems, hot water and steam systems, and indoor air quality. His research interests cover a wide variety of indoor environmental control topics including chilled water pumping systems, stratified thermal energy storage, protection of building occupants from indoor bioaerosol releases, ultraviolet germicidal irradiation systems, and others. He is the author or co-author of more than 170 technical papers and articles and 14 books and book chapters. He consults on the design of chilled water thermal energy storage systems and has been involved in more than 20 projects world-wide.

Dr. Bahnfleth is a fellow of ASHRAE, the American Society of Mechanical Engineers (ASME) and the International Society for Indoor Air Quality and Climate (ISIAQ). He has served ASHRAE in a variety of capacities, including Student Branch Advisor, Chapter Governor, Technical Committee and Standing Committee Chair, and as Director-at-Large, Vice President, Treasurer, and 2013-14 Society President. His honors include a 1st place ASHRAE Technology Award, Transactions Paper Award, Distinguished Service and Exceptional Service Awards, The Louise and Bill Holladay Distinguished Fellow Award, the E.K. Campbell Award of Merit and the F. Paul Anderson Award. He is also a recipient of the Penn State Engineering Alumni Society’s World-Class Engineering Faculty Award.

Z-Man’s Blog:

ASHRAE Pandemic Task Force, Mechanical Systems and Covid19

Bill Bahnfleth, PhD, PE is a professor at Penn State University, a past president of ASHRAE and chairman of the ASHRAE Pandemic Task Force.

Nuggets mined from today’s episode:

Dr. Bahnfleth learned about Covid19 in March 2020 while in Mexico on a school trip when there were only 1500 known infections in the US.

Center County, PA where PSU is located has fewer than 100 cases of Covid19. PSU has a diverse building stock ranging from brand new buildings to some over 100 years old. PSU’s building stock relies upon a variety of different heating and cooling systems.

Like many other colleges and universities, Penn State did the maintenance which was necessary and deferred some of the remaining.

PSU has a student body of 45K-50K. How to handle education delivery in the fall remains an ambiguous situation?

PSU’s facilities staff are relying upon Bill for Covid19 compliance guidance.

ASHRAE is providing important information on Covid19 at no charge.

ASHRAE formed a task force to provide Covid19 mitigation guidance and asked Bill to chair it. Over a 15-18 month period, the task force will work on: dealing with the first Covid19 wave, preparing for the next Covid19 wave and thinking about future needs.

ASHRAE has 57K members and 100s of technical committees. There are 17 members on the task force. An additional 120 people are working on current teams. ASHRAE, is working with other groups (e.g. BOMA, AIA). It’s a huge investment of time.

  • Communications and advocacy at federal, state, local level.
  • Literature review
  • Filtration & disinfection
  • Building readiness (healthcare, long term healthcare, residential, commercial, schools, transportation & assembly)

CDC guidance on Covid19 has been inconsistent and confusing. CDC’s original guidance was that Covid19 was spread at short range and by fomites. (Common sense considerations prevent most fomite related transmission.) Now CDC is talking about aerosol transmission without calling it aerosol transmission.

The task force is careful not to miss lessons learned from the bioterrorism (e.g. anthrax) following 9/11. The task force has the opportunity to capture today’s sense of urgency to provide help & guidance for the future.

Bioterrorism, pandemics and extreme weather event related power failures result in acute IAQ problems.

  • Following hurricanes, loss of life in Florida nursing homes due to lack of air conditioning.
  • Guanzhou China 2020, 9 people were infected by someone without symptoms while dining in a restaurant. Not much environmental investigation. Transmission by large droplets at short distance. Dilution and distance likely minimized risks for others.
  • Yuguo Li, Evidence for probable aerosol transmission of SARS-CoV-2 in a poorly ventilated restaurant. Fan coil unit installed high over tables. Other tables not infected. Servers not infected. High concentration of infection in small area. Very low ventilation rate of .75-1 liter per second when rate of 5-10 liter per second is normal.
  • High SARS-CoV-2 Attack Rate Following Exposure at a Choir Practice — Skagit County, Washington, March 2020

No one has demonstrated evidence that Covid19 gets spread by HVAC systems. HVAC systems dilute and filter out viruses. Viral spread via HVAC system is highly unlikely.

According to ASHRAE and other HVAC organizations it is worthy to take precautions against airborne transmission pathogens via HVAC systems. HVAC systems circulate, filter, provide ventilation and comfort. Increasing ventilation through adjusting the systems or opening windows and addition of UV are beneficial.

Considerations for reopening closed buildings and transportationinclude:cleaning, filtration, disinfection, and Legionella.

Air cleaners are the future. According to EPA, ozone not good for air treatment.There is some evidence that hydroxyls some evidence can work on eliminating pollutants and pathogens inside the device. We need evidence that they can emit and distribute hydroxyl radicals beyond the device.

ASHRAE position document on infectious aerosols.

  •  Non-healthcare buildings should have a plan for an emergency response.
  •  The following modifications to building HVAC system operation should be considered:
  • Increase outdoor air ventilation (disable demand-controlled ventilation and open outdoor air dampers to 100% as indoor and outdoor conditions permit).
  • Improve central air and other HVAC filtration to MERV-13 (ASHRAE 2017b) or the highest level achievable.
  • Keep systems running longer hours (24/7 if possible).
  • Add portable room air cleaners with HEPA or high-MERV filters with due consideration to the clean air delivery rate (AHAM 2015).
  • Add duct- or air-handling-unit-mounted, upper room, and/or portable UVGI devices in connection to in-room fans in high-density spaces such as waiting rooms, prisons, and shelters.
  • Maintain temperature and humidity as applicable to the infectious aerosol of concern.
  •  Bypass energy recovery ventilation systems that leak potentially contaminated exhaust air back into the outdoor air supply.
  • Design and build inherent capabilities to respond to emerging threats and plan and practice for them. (Evidence Level B

Permanent improvement to IAQ improves performance in workplaces and schools.

According to WHO PM2.5 causes 4 million deaths per year. MERV 13/MERV 14 will save lives.

Is it safe? ERV wheels can pose a hazard.

1980s recommended 40%-60% RH. Recent studies in healthcare find: dry air results in smaller particles & increases particle travel distance, viability of pathogens is better at low humidity and dry mucus membranes are more prone to infection.

GPC 42P – Proposed Guideline Authorized June 29, 2016 (St. Louis). SSPC 62.1 is responsible for the development of this guideline. Editorial change to the title approved July 31, 2018.
Enhanced Indoor Air Quality in Commercial and Institutional Buildings

The purpose of this guideline is to recommend measures that exceed minimum requirements for improving indoor air quality in commercial and institutional buildings.   These measures are intended to provide enhanced indoor air quality that is acceptable to human occupants and that minimizes adverse health effects.


2.1 This guideline applies to spaces intended for human occupancy within commercial and institutional buildings except those within dwelling units in residential occupancies in which occupants are non-transient.

2.2 This guideline provides recommendations related to certain sources, and for ventilation and air-cleaning-system design, installation, commissioning, and operation and maintenance.

Indoor Environmental Quality- Global Alliance

REHVA is the Voice of European HVAC Designers and building services engineers

Z-Man signing off


By what mechanism does Ultraviolet Germicidal Irradiation kill or inactivate microorganisms?

Ultraviolet germicidal irradiation (UVGI) is a disinfection method that uses short-wavelength ultraviolet (ultraviolet C or UV-C) light to kill or inactivate microorganisms by destroying nucleic acids and disrupting their DNA, leaving them unable to perform vital cellular functions.

Doug Kohnen, Eratech