William Parry Bahnfleth

William Parry Bahnfleth
Pennsylvania State University | Penn State · Department of Architectural Engineering

PhD, PE, FASHRAE, FASME, FISIAQ

About

163
Publications
89,957
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3,280
Citations
Introduction
My interests broadly relate to control of indoor environmental quality and its impact on energy use of buildings and the utility systems that serve them. Current areas of interest and activity include chilled water system design and operation (variable primary flow pumping systems and water-side free cooling) control of indoor microorganisms with optical radiation (conventional 254 nm UVC and other wavelengths produced by low pressure Hg vapor lamps and emerging LED technology) and monetization of indoor air quality effects.
Additional affiliations
August 1994 - present
Pennsylvania State University
Position
  • Professor
Description
  • Mechanical Systems Group Assistant Professor 1994 Associate Professor with tenure 2000 Professor 2005

Publications

Publications (163)
Article
Full-text available
The question of whether SARS‐CoV‐2 is mainly transmitted by droplets or aerosols has been highly controversial. We sought to explain this controversy through a historical analysis of transmission research in other diseases. For most of human history, the dominant paradigm was that many diseases were carried by the air, often over long distances and...
Article
Full-text available
Several research studies have ranked indoor pollution among the top environmental risks to public health in recent years. Good indoor air quality is an essential component of a healthy indoor environment and significantly affects human health and well-being. Poor air quality in such environments may cause respiratory disease for millions of pupils...
Preprint
Full-text available
A database of bacterial ultraviolet (UV) susceptibilities is developed from an empirical model that correlates genomic parameters with UV rate constants. Software is used to count and evaluate potential ultraviolet photodimers and identifying hot spots in bacterial genomes. The method counts dimers that potentially form between adjacent bases that...
Article
Full-text available
A method is described for inactivation of pathogens, especially airborne pathogens, using ultraviolet (UV) radiation emitted directly into occupied spaces and exposing occupants to a dose below the accepted actinic exposure limit (EL). This method is referred to as direct irradiation below exposure limits, or DIBEL. It is demonstrated herein that l...
Article
As advanced control sequences are developed to improve the operational efficiency of buildings, it is important to better understand the implications of uncertainty on system design and specification, and its propagation through system components to various performance measures. This paper describes the detailed development of a testbed for perform...
Article
Full-text available
Some infectious diseases, including COVID-19, can undergo airborne transmission. This may happen at close proximity, but as time indoors increases, infections can occur in shared room air despite distancing. We propose two indicators of infection risk for this situation, that is, relative risk parameter (Hr) and risk parameter (H). They combine the...
Article
Full-text available
The evolution of SARS-CoV-2 virus has resulted in variants likely to be more readily transmitted through respiratory aerosols, underscoring the increased potential for indoor environmental controls to mitigate risk. Use of tight-fitting face masks to trap infectious aerosol in exhaled breath and reduce inhalation exposure to contaminated air is of...
Article
Maintaining control system performance over the lifespan of a building offers great potential for increasing system operation efficiency. Programming the building monitoring system with control loop performance assessment (CLPA) indices provides a way to identify poorly performing loops. This work further advances building control monitoring by dev...
Article
Full-text available
Coordination of efforts to assess the challenges and pain points felt by industries from around the globe working to reduce COVID-19 transmission in the indoor environment as well as innovative solutions applied to meet these challenges is mandatory. Indoor infectious viral disease transmission (such as coronavirus, norovirus, influenza) is a compl...
Technical Report
Full-text available
Many kindergarten through 12th grade (K-12) schools in the United States do not have good ventilation. This is a longstanding problem with demonstrably negative effects on student learning. We can and should act to fix this to ensure good indoor air quality for all students, educators, and school staff. During the COVID-19 pandemic, it is even more...
Article
Looking further than COVID-19, some of the key messages: 1. We from now on should include the risk of indoor respiratory infections in our design of buildings and its ventilation. 2. Treat the air quality in a similar way as we are used to for water and food quality. 3. ‘Visualize’ the air quality by displaying monitoring values (e.g. CO2 concentra...
Preprint
Full-text available
Some infectious diseases, including COVID-19, can be transmitted via aerosols that are emitted by an infectious person and inhaled by susceptible individuals. Most airborne transmission occurs at close proximity and is effectively reduced by physical distancing, but as time indoors increases, infections occur in those sharing room air despite maint...
Article
Full-text available
The Covid-19 pandemic has caused untold disruption and enhanced mortality rates around the world. Understanding the mechanisms for transmission of SARS-CoV-2 is key to preventing further spread but there is confusion over the meaning of “airborne” whenever transmission is discussed. Scientific ambivalence originates from evidence published many yea...
Article
Control sequences for air distribution and terminal systems in heating, ventilating, and air-conditioning (HVAC) aim to achieve a balance in the system outputs, i.e., maintain thermal comfort and indoor air quality (IAQ) with minimal energy use. ASHRAE Guideline 36 (G36) – High-Performance Sequences of Operation for HVAC Systems, is the result of A...
Article
Full-text available
During the rapid rise in COVID-19 illnesses and deaths globally, and notwithstanding recommended precautions, questions are voiced about routes of transmission for this pandemic disease. Inhaling small airborne droplets is probable as a third route of infection, in addition to more widely recognized transmission via larger respiratory droplets and...
Conference Paper
Full-text available
The effect of indoor environment parameters specified in national and international standards on simulated energy use of an educational spaces were assessed. Standards considered included those of EN, ISO, ASHRAE and ISHRAE. Eight different climatic locations were considered. Energy use to maintain IEQ parameters according to the highest category,...
Article
Quality of the indoor environment has become an important parameter to account for in new and existing buildings due to the increasing number of people spending most of their time indoors. Generally, the design and evaluation of indoor environments in buildings rely on appropriate guidelines and recommendations. National and international IEQ stand...
Article
The data from published studies were used to derive systematic relationships between learning outcomes and air quality in classrooms. Psychological tests measuring cognitive abilities and skills, school tasks including mathematical and language-based tasks, rating schemes, and tests used to assess progress in learning including end-of-year grades a...
Data
This spreadsheet demonstrates the Cluster Model of Ultraviolet Disinfection and can be used to fit any data set with or without a shoulder and with or without a tail. It will provide parameters defining the degree of clustering and will estimate the Intrinsic UV Rate Constant. It requires input in terms of the microbe mean diameter and must be used...
Article
Aims: To develop a new mathematical model derived from first principles to define the kinetics of ultraviolet disinfection and to explain the phenomenon known as tailing. The theory presented interprets tailing as the result of photoprotection due to cumulative Mie scattering effects in clustered populations of microorganisms. Methods and results...
Article
The human interaction with the building is a key cause of uncertainty when predicting energy consumption in buildings. Building occupants affect building energy use directly and indirectly by interacting with building energy systems, for example, by adjusting thermostats, switching lights on/off, using electrical devices and opening/closing windows...
Article
Full-text available
Wet cooling coil surfaces can provide opportunities for microorganism growth. This biological fouling (biofouling) increases airside pressure drop and decreases airside heat transfer coefficient. Ultraviolet germicidal irradiation is one method to eliminate biofouling. The current article reports field measurements of changes in pressure drop and h...
Article
Full-text available
Ultraviolet germicidal irradiation of cooling coil airside surfaces is used to mitigate biofouling caused by viable microorganisms captured from the air. However, few peer-reviewed studies have investigated its effectiveness. Part 1 of this study presents the results of field measurements of changes in coil performance after treatment with ultravio...
Conference Paper
Full-text available
Occupant behaviour has been shown to be one of the key driving factors of uncertainty in prediction of energy consumption in buildings. Building occupants affect building energy use directly and indirectly by interacting with building energy systems such as adjusting temperature set-points, switching lights on/off, using electrical devices and open...
Conference Paper
Full-text available
Occupant behaviour has been shown to be one of the key driving factors of uncertainty in prediction of energy consumption in buildings. Building occupants affect building energy use directly and indirectly by interacting with building energy systems such as adjusting temperature set-points, switching lights on/off, using electrical devices and open...
Article
Ultraviolet germicidal irradiation of cooling coils controls biofouling that increases airflow resistance and decreases heat transfer coefficient. Though lower in power than air disinfection systems, coil ultraviolet germicidal irradiation systems should provide some collateral air treatment benefit. This benefit is estimated through monetization o...
Article
The IAQ 2016 conference convened in Alexandria, Virginia, USA from September 12–14, 2016 was the 18th in the series inaugurated in Atlanta, Georgia in 1986 and was co-organized with the Air Infiltration and Ventilation Center (AIVC) as its 37th conference. The Indoor Air Quality Association (IAQA) and the Indoor Environmental Quality Global Allianc...
Article
A previous IEQ Applications column1 reviewed the then-current literature on the use of ultraviolet germicidal irradiation (UVGI) to control biological growth on cooling coils and other components of air-handling units. In addition to reducing potential sources of air contaminants, this technology has long been claimed to yield signifi cant energy u...
Article
Summary of the ASHRAE IAQ 2016 Conference held in Alexandria, VA, USA in September 2016
Article
Biological fouling (biofouling) on cooling coil surfaces acts as thermal insulation, impeding heat transfer from air to coil surfaces, decreasing airside heat transfer coefficient and degrading coil cooling capacity. It is also a common cause of low ΔT syndrome in chilled water distribution systems. The effects of a commercially available ultraviol...
Article
The natural ventilation potential to maintain acceptable indoor air quality (IAQ) and thermal comfort in gymnasia was investigated using a university multisport facility in northeastern United States as a case study building. A parametric modeling study was conducted considering the effects of opening configurations and control strategies during th...
Conference Paper
Ultraviolet Germicidal Irradiation (UVGI) of cooling coils is done to control biofouling that can increase their flow resistance and decrease their heat transfer coefficient. UVGI is also applied in air-handling units to improve indoor air quality (IAQ) by deactivating airborne microorganisms. A typical coil cleaning application delivers a smaller...
Article
Full-text available
A review of the effectiveness of dilution ventilation, filtration, and ultraviolet germicidal irradiation in mitigating five biological-weapon agents and Bioterrorism Defense
Article
Full-text available
A number of factors affect building indoor environmental quality (IEQ), principally thermal environment (temperature, humidity, and air movement), indoor air quality (IAQ), lighting, and acoustics. Most studies on comfort or preference and virtually all dealing with health and productivity focus on thermal environment and IAQ. However, a recent met...
Article
ASHRAE Journal is highlighting the 2013-14 Presidential theme "Shaping the Next - Our World, Ourselves, Our Work" (http://tinyurl.com/bahnfleththeme) by publishing groups of forward-looking essays about the future of areas of high importance to ASHRAE, our industry, and society. This third group of "Shaping the Next" essays considers the future of...
Article
This paper presents the impacts of UVGI systems on cooling coil performance in hot and humid climate. The purpose of this study is to investigate the effects of UVGI systems on pressure drop reduction and air-side heat transfer enhancement. Speed variation experiments were employed before and after UVGI operation to comparatively demonstrate the ef...
Article
William P. Bahnfleth, PH.D., P.E., ASHRAE president, shares his views on the steps that need to be taken to secure the future of ASHRAE and that of the industry. The certificate of consolidation, the document that created ASHRAE states that the purpose of this organization is to advance the arts and sciences of heating, refrigerating, air condition...
Article
This study uses ray-tracing software to calculate the fluence distribution in ultraviolet germicidal irradiation devices with different surface reflectivities and lamp configurations. Of five validation cases considered, one incorporating anisotropic duct surface reflectivity and wind-chill correction of lamp output gave the best agreement with pla...
Article
Multizone air and contaminant flow models of actual buildings may produce significant deviations from measured conditions for a variety of reasons. The extent to which the well-mixed space assumption is valid is perhaps the primary reason, but other modeling approximations and input data uncertainties, e.g., the leakiness of building components and...
Conference Paper
This paper proposes a methodology to calibrate multizone airflow models in existing buildings. The methodology has been demonstrated with the widely used multi-zone model CONTAM and applied to two buildings, one synthetic and one actual. The methodology builds on previous workwith thecalibration process enhanced by the use of carbon dioxide tracer...
Article
We designed, constructed, and characterized a new dual-collimation UV air-phase reactor. This new system is unique because it collimates UV energy from a single lamp in two directions simultaneously. This dual-collimation feature provides two distinct advantages over traditional single-collimation systems: 1) real-time UV dose (fluence) determinati...
Article
We developed, characterized, and tested a new dual-collimation aqueous UV reactor to improve the accuracy and consistency of aqueous k-value determinations. This new system is unique because it collimates UV energy from a single lamp in two opposite directions. The design provides two distinct advantages over traditional single-collimation systems:...
Conference Paper
Ultraviolet germicidal irradiation (UVGI) systems are known to be effective in the control of harmful microorganisms in the indoor environment. This paper addresses the modelling of induct airstream disinfection with a methodology that couples an energy model driven multizone airflow and contaminant transport model to simulate the deactivation of a...
Article
Ultraviolet germicidal irradiation (UVGI) is the use of ultraviolet radiation to inactivate microorganisms. UVGI systems predominantly use Ultraviolet C (UVC) radiation at a wavelength of ∼254 nm that is produced by low pressure mercury vapor or amalgam lamps. UVGI is applied in a variety of ways. Upper air systems disinfect air in rooms as it circ...
Conference Paper
Full-text available
Air cleaner effectiveness (ε) is the fractional change in concentration of an air contaminant resulting from the addition of an air cleaner to a system. Unlike component single-pass efficiency, it takes into account the aggregate effect of all contaminant removal mechanisms as well as the effects of air cleaner placement in the system. The usefulne...
Article
Quantifying the impact of chemical or biological releases on a building and its occupants is a necessary part of risk assessment. The most informative metrics for this purpose are absolute, "threat-based" measures of lost or preserved assets that are specific to the agent of interest. Practical application of threat-based metrics may be difficult b...
Article
Measures of the risk to building occupants posed by indoor contaminant exposures must account for the combined impact of concentration (C) and duration of exposure (t). A common assumption embodied in Haber's law is that the outcome of an exposure is proportional to C × t, i.e., the effects of concentration and duration are equivalent. However, it...
Article
Protecting the occupants of buildings from the ill effects of chemical, biological, or radiological agents is an important part of emergency response to accidental or intentional release events. A procedure to balance these competing requirements using a multizone modeling approach is outlined, the results are demonstrated for a prototype building,...
Article
This paper classifies and describes analysis methods, tools, and simulation programs that allow prediction of airborne chemical/biological dispersal and transport dynamics in indoor environments subject to different risk scenarios. These are the building blocks for related analytical treatment of the overall problem involving risk assessment, risk...
Article
Assessing and reducing vulnerability of building occupants to intentional indoor airborne releases of chemical and biological agents has acquired some importance in the past two decades. This paper reports on the evaluation and comparison of a set of available tools (described in the companion paper) that have been developed for practical and pragm...
Article
Literature on aerosol behavior in conventional heating ventilating and air conditioning duct systems that is directly applicable to modeling and simulation of deposition and resuspension of particulate matter is reviewed. Open literature discussing particle resuspension from duct surfaces is rare and most studies investigating particle deposition c...
Article
Ultraviolet germicidal irradiation (UVGI) uses UVC radiation produced by low pressure mercury vapor lamps to control biological air contaminants. Ambient air velocity and temperature have a strong effect on lamp output by influencing the lamp surface cold spot temperature. In-duct UVGI systems are particularly susceptible to ambient effects due to...
Conference Paper
Full-text available
A mathematical model is presented for the ultraviolet susceptibility of microbes based on evaluation of complete genomes. The genomes of 49 animal viruses and bacteriophages, and 33 bacteria, were analyzed using base-counting software to establish the frequencies of potential dimers. A total of 71 data sets represented 27 ssRNA viruses, while 77 da...
Article
Full-text available
A mathematical model is presented to explain the ultraviolet susceptibility of viruses in terms of genomic sequences that have a high potential for photodimerization. The specific sequences with high dimerization potential include doublets of thymine (TT), thymine-cytosine (TC), cytosine (CC), and triplets composed of single purines combined with p...
Article
Full-text available
The susceptibility of viruses to ultraviolet (UV) light has traditionally been defined in terms of the UV rate constant, also called a Z value, which is the slope of the survival curve on a logarithmic scale. The UV rate constant refers to either broad range UV in the UVB/UVC spectrum (200-320 nm) or, more commonly, to narrow-band UVC near the 253....
Article
Full-text available
In-duct ultraviolet germicidal irradiation (UVGI) systems treat moving air streams in heating, ventilation, and air-conditioning (HVAC) systems to inactivate airborne microorganisms. UVGI system performance depends on air temperature, velocity, cumulative operating time, variations in exposure time and other factors. Annual simulations of UVGI effi...
Article
Ultraviolet Germicidal Irradiation (UVGI) systems use 254 nm UVC radiation to inactivate microorganisms in the air and on surfaces. In-duct UVGI systems are installed in air-handling units or air distribution systems to inactivate microorganisms "on the fly" and on surfaces. The literature contains few investigations of the economic performance of...
Article
The output of low pressure mercury vapor lamps used in ultraviolet germicidal irradiation (UVGI) applications depends strongly on the lamp surface cold spot temperature. The objective of this study is to develop a model to predict the output variation of these lamps in flow conditions typical of ventilation systems. Experiments were performed to ac...