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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 in a phantasmagorical way. This miasmatic paradigm was challenged in the mid to late 19th century with the rise of germ theory, and as diseases such as cholera, puerperal fever, and malaria were found to actually transmit in other ways. Motivated by his views on the importance of contact/droplet infection, and the resistance he encountered from the remaining influence of miasma theory, prominent public health official Charles Chapin in 1910 helped initiate a successful paradigm shift, deeming airborne transmission most unlikely. This new paradigm became dominant. However, the lack of understanding of aerosols led to systematic errors in the interpretation of research evidence on transmission pathways. For the next five decades, airborne transmission was considered of negligible or minor importance for all major respiratory diseases, until a demonstration of airborne transmission of tuberculosis (which had been mistakenly thought to be transmitted by droplets) in 1962. The contact/droplet paradigm remained dominant, and only a few diseases were widely accepted as airborne before COVID-19: those that were clearly transmitted to people not in the same room. The acceleration of interdisciplinary research inspired by the COVID-19 pandemic has shown that airborne transmission is a major mode of transmission for this disease, and is likely to be significant for many respiratory infectious diseases.

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 occur at specific genomic motifs such as TT, TC, CT, & CC. Hot spots are identified where clusters of three or more consecutive pyrimidines can enhance absorption of UV photons. The model incorporates nine genomic parameters into a single variable for each species that represents its relative dimerization potential. The bacteria model is based on a curve fit of the dimerization potential to the ultraviolet rate constant data for 92 bacteria species represented by 216 data sets from published studies. There were 4 outliers excluded from the model resulting in a 98% Confidence Interval. The curve fit resulted in a Pearson correlation coefficient of 80%. All identifiable bacteria important to human health, including zoonotic bacteria, were included in the database and predictions of ultraviolet rate constants were made based on their specific genomes. This database is provided to assist healthcare personnel and researchers in the event of outbreaks of bacteria for which the ultraviolet susceptibility is untested and where it may be hazardous to assess due to virulence. Rapid sequencing of the complete genome of any emerging pathogen will now allow its ultraviolet susceptibility to be estimated with equal rapidity. Researchers are invited to challenge these predictions.ImportanceThis research demonstrates the feasibility of using the complete genomes of bacteria to determine their susceptibility to ultraviolet light. Ultraviolet rate constants can now be estimated in advance of any laboratory test. The genomic methods developed herein allow for the assembly of a complete database of ultraviolet susceptibilities of pathogenic bacteria without resorting to laboratory tests. This UV rate constant information can be used to size effective ultraviolet disinfection systems for any specific bacterial pathogen when it becomes a problem.

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 low-intensity UV radiation below exposure limits can achieve high levels of equivalent air changes per hour (ACHeq) and can be an effective component of efforts to combat airborne pathogens such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19). An ACHeq of 4 h−1 is presently achievable over a continuous 8 h period for the SARS-CoV-2 virus with UV-C light-emitting diodes (LEDs) having peak wavelength at 275 nm, and future improvements in LED technology and optics are anticipated to enable improvements up to 150 h−1 in the coming decade. For example, the actinic EL is 60 J/m2 at 254 nm, and human coronaviruses, including SARS-CoV-2, have a UV dose required for 90 % inactivation of about 5 J/m2 at 254 nm. Irradiation by 254 nm UV-C at the EL is expected to provide 90 % inactivation of these organisms in air in about 40 min when the UV-C is delivered at a constant irradiance over 8 h, or in about 5 min if the UV-C is delivered at a constant irradiance over 1 h. Since the irradiation is continuous, the inactivation of initial contaminants accumulates to 99 % and then 99.9 %, and it also immediately begins inactivating any newly introduced (e.g., exhaled) pathogens at the same rate throughout the 8 h period. The efficacy for inactivating airborne pathogens with DIBEL may be expressed in terms of ACHeq, which may be compared with conventional ventilation-based methods for air disinfection. DIBEL may be applied in addition to other disinfection methods, such as upper room UV germicidal irradiation, and mechanical ventilation and filtration. The ACHeq of the separate methods is additive, providing enhanced cumulative disinfection rates. Conventional air disinfection technologies have typical ACHeq values of about 1 h−1 to 5 h−1 and maximum practical values of about 20 h−1. UV-C DIBEL currently provides ACHeq values that are typically about 1 h−1 to 10 h−1, thus either complementing, or potentially substituting for, conventional technologies. UV-C DIBEL protocols are forecast herein to evolve to >100 ACHeq in a few years, potentially surpassing conventional technologies. UV-A (315 nm to 400 nm) and/or UV-C (100 nm to 280 nm) DIBEL is also efficacious at inactivating pathogens on surfaces. The relatively simple installation, low acquisition and operating costs, and unobtrusive aesthetic of DIBEL using UV LEDs contribute value in a layered, multi-agent disinfection strategy.

There is great disparity in the way we think about and address different sources of environmental infection. Governments have for decades promulgated a large amount of legislation and invested heavily in food safety, sanitation, and drinking water for public health purposes. In contrast, airborne pathogens and respiratory infections, whether seasonal influenza or COVID-19, are ad-dressed fairly weakly, if at all, in terms of regulations, standards, and building design and operation, pertaining to the air we breathe. We suggest that the dramatic growth in our understanding of the mechanisms behind respiratory infection transmission should drive a paradigm shift in how we view and address the transmission of respiratory infections to protect present and future generations from unnecessary suffering and economic losses. It starts with a recognition that preventing respiratory infection, like reducing waterborne or food-borne disease, is a tractable problem. See Additional URL below for 'free to read' PDF reprint.

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 critical importance for disease control. Administrative controls including the regulation of occupancy and interpersonal spacing are also important, while presenting social and economic challenges. Indoor engineering controls including ventilation, exhaust, air flow control, filtration, and disinfection by germicidal ultraviolet irradiation can reduce reliance on stringent occupancy restrictions. However, the effects of controls-individually and in combination-on reducing infectious aerosol transfer indoors remain to be clearly characterized to the extent needed to support widespread implementation by building operators. We review aerobiologic and epidemiologic evidence of indoor environmental controls against transmission and present a quantitative aerosol transfer scenario illustrating relative differences in exposure at close-interactive, room, and building scales. We identify an overarching need for investment to implement building controls and evaluate their effectiveness on infection in well-characterized and real-world settings, supported by specific, methodological advances. Improved understanding of engineering control effectiveness guides implementation at scale while considering occupant comfort, operational challenges, and energy costs.

The coronavirus disease 2019 (COVID-19) pandemic has caused untold disruption throughout the world. Understanding the mechanisms for transmission of severe acute respiratory syndrome coronavirus-2 (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 years ago which has generated mythological beliefs that obscure current thinking. This article collates and explores some of the most commonly held dogmas on airborne transmission in order to stimulate revision of the science in the light of current evidence. Six ‘myths’ are presented, explained and ultimately refuted on the basis of recently published papers and expert opinion from previous work related to similar viruses. There is little doubt that SARS-CoV-2 is transmitted via a range of airborne particle sizes subject to all the usual ventilation parameters and human behaviour. Experts from specialties encompassing aerosol studies, ventilation, engineering, physics, virology and clinical medicine have joined together to produce this review to consolidate the evidence for airborne transmission mechanisms, and offer justification for modern strategies for prevention and control of COVID-19 in health care and the community.

The question of whether SARS-CoV-2 is transmitted by droplets or aerosols has been very controversial. We sought to explain this controversy through a historical analysis of transmission research in other diseases. For most of human history, many diseases were thought to transmit through the air, often over long distances and in a phantasmagorical way, and often in error (e.g. malaria, cholera). Building on the germ theory of disease developed in the mid 19th century and on the demise of miasma theory, prominent public health official Charles Chapin in 1910 urged the public health community to focus on contact and droplet infection. However, he introduced a major error in the process: that ease of infection in close proximity is associated exclusively with large “sprayborne” droplets that fall to the ground quickly, and he deemed airborne transmission as very unlikely. This new paradigm became dominant, leading to systematic errors in the interpretation of research evidence on transmission. For the next five decades, no disease was accepted by the general medical and infection control communities as airborne, until tuberculosis (which had been misclassified as droplet) in 1962. Chapin’s paradigm remained dominant and only a few diseases were widely accepted as transmitted by aerosols before COVID-19: those that were clearly transmitted over long distances or time scales. Resistance to the idea of airborne spread of a respiratory infection is not new. In fact, it has occurred repeatedly over much of the last century and greatly hampered understanding of how diseases transmit.

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 direct contact with infected people or contaminated surfaces. While uncertainties remain regarding the relative contributions of the different transmission pathways, we argue that existing evidence is sufficiently strong to warrant engineering controls targeting airborne transmission as part of an overall strategy to limit infection risk indoors. Appropriate building engineering controls include sufficient and effective ventilation, possibly enhanced by particle filtration and air disinfection, avoiding air recirculation and avoiding overcrowding. Often, such measures can be easily implemented and without much cost, but if only they are recognised as significant in contributing to infection control goals. We believe that the use of engineering controls in public buildings, including hospitals, shops, offices, schools, kindergartens, libraries, restaurants, cruise ships, elevators, conference rooms or public transport, in parallel with effective application of other controls (including isolation and quarantine, social distancing and hand hygiene), would be an additional important measure globally to reduce the likelihood of transmission and thereby protect healthcare workers, patients and the general public.

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-ofyear grades and exam scores were used to quantify learning outcomes. Short-term sick leave was also included because it may influence progress in learning. Classroom indoor air quality was characterized by the concentration of carbon dioxide (CO2). For psychological tests and school tasks, fractional changes in performance were regressed against the average concentrations of CO2 at which they occurred; all data reported in studies meeting the inclusion criteria were used to derive the relationship, regardless of whether the change in performance was statistically significant at the examined levels of classroom air quality. The analysis predicts that reducing CO2 concentration from 2,100 ppm to 900 ppm would improve the performance of psychological tests and school tasks by 12% with respect to the speed at which the tasks are performed and by 2% with respect to errors made. For other learning outcomes and short-term sick leave, only the relationships published in the original studies were available. They were therefore used to make predictions. These relationships show that reducing the CO2 concentration from 2,300 ppm to 900 ppm would improve performance on the tests used to assess progress in learning by 5% and that reducing CO2 from 4,100 ppm to 1,000 ppm would increase daily attendance by 2.5%. These results suggest that increasing the ventilation rate in classrooms in the range from 2 L/s-person to 10 L/sperson can bring significant benefits in terms of learning performance and pupil attendance; no data are available for higher rates. The results provide a strong incentive for improving classroom air quality and can be used in cost-benefit analyses.

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 developing an approach to help prioritize control problems based on the severity of their system-level impact. CLPA indices were added to a Modelica-based small office building model programmed with advanced heating, ventilating, and air conditioning control sequences. An extensive set of unique simulations of different levels of loop detuning were implemented to generate a database that contains both system-level performance metrics and CLPA indices. A regression model was then developed that combines individual loop performance to assess the impact on system-level outputs. Loops of the zone with higher heat gains and the air handling unit supply air temperature loop produced the greatest system-level impact.

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 of simulated nonfatal illness spread in a group of commercial buildings. Benefits were quantified using appropriate metrics for each building type: work-loss days for office buildings, hospital acquired infections for healthcare facilities, and disability adjusted life years for schools. The pre-ultraviolet germicidal irradiation annual cost of occupant illness was the same order of magnitude as annual energy cost. Area-normalized cost was similar in magnitude for all buildings. The collateral air disinfection of coil surface ultraviolet germicidal irradiation reduced baseline illness costs by 3.5% or less, but the resulting cost savings exceeded the energy cost ...

Wet cooling coil surfaces can provide opportunities for microorganism growth. This biological fouling (biofouling) increases airside pressure drop and decreases airside heat transfer coefficient. U...

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 ultraviolet germicidal irradiation. Part 2 reports modeled energy use and indoor air quality impacts of coil irradiation, as well as results of a life-cycle cost analysis that combines energy, indoor air quality, capital, and maintenance costs. Life-cycle costs with coil ultraviolet germicidal irradiation are compared to life-cycle costs with mechanical coil cleaning. Models from the U.S. Department of Energy Commercial Reference Buildings set were used to predict the benefit of ultraviolet germicidal irradiation treatment of fouled coils for 7 buildings in 16 climate zones using pressure drop reduction estimates bounded by experimental results from Part 1 and results r...

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 micro-organisms. Methods and Results: Mie scattering effects at ultraviolet wavelengths are used to compute a shielding constant for each micro-organism based on the average projected diameter. An intrinsic rate constant, hypothesized to be a characteristic property of the microbial genome alone, is computed. The cluster model is fitted to tailing data from 30 ultraviolet inactivation studies and results are compared with the classic two stage multihit model. Conclusions: The cluster model demonstrates a statistically significant improvement in the mean adjusted R2 values of the tested data sets (P < 0·0001). Tailing in survival curves is the direct consequence of the Gaussian distribution of cluster sizes and the intrinsic rate constant is a real and critical parameter that defines ultraviolet susceptibility. Significance and Impact of the Study: The ultraviolet dose–response behaviour of micro-organisms can now be explained in terms of parameters that have physical meaning and provide deep insight into the disinfection process.

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 the summer months. The thermal accuracy of the model was verified using field measurements during August 2015. Performance metrics for IAQ and thermal comfort were the percentages of occupied hours during which ventilation rate met or exceeded ASHRAE Standard 62.1–2013 and temperature met adaptive thermal comfort criteria of ASHRAE Standard 55–2013, respectively. Wind direction was found having a major effect on cross ventilation rate. Wind and buoyancy driven forces could complement or oppose each other depending on the wind direction and opening position. Relative to the base case, larger net openings that were more evenly distributed performed better. Rooftop vents improved ventilation performance, particularly under unfavorable wind conditions. With improved opening configurations, the acceptable ventilation hours increased from 21.5% to 99.5% of occupied time for the maximum occupancy. The strictest temperature-controlled strategy had the best thermal performance. Thermal comfort conditions could be maintained during 85.3% of the occupied hours. However, the temperature rule largely shortened the opening operation time, and consequently decreased the acceptable ventilation hours to only 47.1%. Continuously natural ventilation during occupied time gave the longest combined IAQ-thermal acceptable hours, 73.9% of the occupied time, although it moderately decreased the thermal comfort hours to 74.2%.

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 ultraviolet germicidal irradiation system installed in a variable air volume system on the airside heat transfer coefficient, cooling coil capacity, and its potential to mitigate low ΔT syndrome were investigated via a field test. Energy-related measurements including chilled water supply/return temperature, water-/airflow rate and entering/leaving air temperature/relative humidity commenced 4 months before turning on ultraviolet lamps and continued for 10 months after ultraviolet germicidal irradiation intervention. The effects of the ultraviolet germicidal irradiation system were evaluated via a “before ultraviolet” and “after ultraviolet” comparison. After ultraviolet...

Biological fouling (biofouling) on wetted cooling coil surfaces decreases heat transfer efficiency, increases air-side flow resistance and may eventually lead to more energy consumption by fans and chiller plants. Applying ultraviolet germicidal irradiation (UVGI) systems in air handling units (AHUs) has the potential to clean coils, improve coil performance and save energy. In this study, the effectiveness of a coil irradiation system in improving coil performance and saving energy was investigated through a field test in a hot and humid climate. A commercially available coil irradiation system was installed downstream of a cooling coil in a variable air volume (VAV) AHU. The duration of the field test was 14 months, with four months before UVGI intervention and 10 months after UVGI intervention. The effectiveness of UVGI was evaluated via a “before UV” and “after UV” comparison of coil performance. The coil overall thermal conductance increased by 10% and the pressure drop decreased by 13%, with the improvement being most rapid over the first month after UVGI intervention. Fan energy use fell by 9% over the ten months of UVGI operation. Savings in fan energy were 39% greater than the energy used by the UV lamps.

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: 1) real-time UV dose (fluence) determination; and 2) simple actinometric determination of a reactor factor that relates measured irradiance levels to actual irradiance levels experienced by the microbial suspension. This reactor factor replaces three of the four typical correction factors required for single-collimation reactors. Using this dual-collimation reactor, Bacillus subtilis spores demonstrated inactivation following the classic multi-hit model with k = 0.1471 cm 2 /mJ (with 95% confidence bounds of 0.1426 to 0.1516).

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 ASHRAE research project 1455-RP intended to develop standardized sequences of operation to achieve more effective use of existing controls. This paper complements G36 by evaluating the influence of the uncertainty inherent in the control components (e.g. sensors and actuators) on the system outputs of a multiple zone variable air volume (VAV) system. The system outputs under study were zone air temperature, relative humidity, carbon dioxide (CO2) concentration, and site electricity use. To evaluate the effects of uncertainty in HVAC systems with advanced sequences of operation, this work applies a Monte Carlo uncertainty analysis to a detailed Modelica building energy model that has been programmed with G36 control sequences. Uncertainty models were integrated with the deterministic models of the building and the control sequence at small time scales to represent frequencies in which a real-world building automation system (BAS) samples its signals. The impact of uncertainty was quantified using annual simulations. Specification of the accuracy levels in the components of the control system were evaluated by the means of: 1) uncertainty analysis for low, medium, and high severities of accuracy in the components to identify relation between performance requirements and component accuracy, and 2) sensitivity analysis to identify the sensors and actuators where the impact of uncertainty on the system outputs is most influential.

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 standards specify indoor environmental conditions considered acceptable to most occupants. This publication reviews and critically compares the requirements for indoor thermal environment and ventilation for acceptable air quality across international standards such as ISO, EN and ASHRAE and national standards of China, India, Singapore, and Australia. The critical analysis of IEQ standards demonstrates that regional differences and diversity factors due to factors such as climate, building typology, demographics, and culture might not be appropriately addressed both in national and international standards, limiting the feasibility of universal indoor environmental criteria. In addition to that, most of the standards provide recommendations for various categories of thermal comfort and air quality by focusing on the perception of IEQ by occupants rather than productivity and wellness as quantitative criteria. The review shows that thermal comfort and air quality parameters are treated separately and without an integrated assessment of various environmental quality-related dimensions. Therefore, there is a need for a method to combine various indoor environmental factors into a combined indicator. (C) 2020 Elsevier B.V. All rights reserved.

The human interaction with the building is a key cause of uncertainty when predicting energy consumption of 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. The occupants’ daily activity profiles and occupancy patterns clearly shape the timing and magnitude of energy demand in households. Modelling energy-related human activities throughout the day, therefore, is a crucial task for prediction of energy use and, consequently, to reduce the gap between real and predicted building energy use. This study modelled data gathered in the diary-based Danish Time Use Survey (TUS) 2008/09 of 9640 individuals from 4679 households. Individuals’ daily activities were logged in 10-min time increments for 24 h, starting and ending at 04:00, during both weekdays and weekends. The aims of this study were to (i) profile energy-related daily activities of occupants during different seasons and weekdays/weekends (ii) investigate time-related characteristics of activities such as starting and ending times and durations, and (iii) profile occupancy patterns for weekdays/weekends for different household types. The outcomes provide valuable input for building energy simulation for bridging the gap between simulated and real energy consumption in the Danish residential sector; typical occupancy profiles for different household types for different days of the week are freely available online [1] .

In historical centres, the buildings are characterized by pitched roofs, sometimes not insulated, with low thermal inertia and coated in brick tiles with low solar reflection factor. So, the attics show high energy costs for heating and cooling. This paper analyses the energy saving obtainable by applying innovative surface finishes on interior and exterior surfaces of opaque envelope components of existing buildings. This simple and inexpensive retrofit action determines energy cost reductions for heating and cooling, but also benefits regarding indoor thermal comfort and useful life of buildings, because condensation problems and thermal shock are reduced; moreover, it preserves the architectural and chromatic characteristics of the building envelope. The analysis is performed by means of a building energy simulation code, considering typical HVAC systems for various Italian and European cities. A technical-economic and environmental investigation is also performed. Thermal energy needs of buildings for summer cooling can be reduced up to 60% by applying “cool paints” on the external surface of walls and roof, while internal low infrared emissivity coatings can reduce winter thermal requirements up to 12.5%. Significant primary energy savings for heating and cooling and reductions of greenhouse gas emissions (up to 60%) can be obtained, as well as a payback value of few years in most cases.

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 and costs to implement and operate the system depend greatly on the output of the UV lamps and the exposure time, which are affected by the temperature and the velocity of the air passing through the UVGI device. The type of HVAC system, the installation location of the UVGI device, and the climatic location of the building all have an impact on the air temperature and velocity the device experiences at a given time. The effects of installation location and climate were investigated using simulation of an induct UVGI device installed in a cooling-only VAV system operating in a hypothetical commercial building. The studied device was investigated at locations both upstream and downstream of the cooling coils of the VAV system in three climatically distinct U.S. locations. The results of the six resulting scenarios indicate that UVGI devices installed upstream of the cooling coils provide comparable if not better performance than those installed downstream. The results demonstrate the impact on performance and cost of the dynamic environment that a UVGI device could experience. It can also be observed that the generated heat of UVGI devices has a great impact on cooling and heating loads, and thus affects the overall operating cost. (C) 2013 Elsevier Ltd. All rights reserved.

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 consider only clean duct surfaces. There is a similar lack of studies on particle deposition and resuspension in mechanical components found in air distribution systems (e.g., heat exchangers, fans, dampers, etc.) and in duct flows where the turbulent velocity profile is not fully developed. An example calculation of penetration through a simple duct system illustrates the characteristics of results produced by the identified modeling methods.

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 the range of velocity and temperature conditions they may experience. An analytical model of the effect of ambient conditions on lamp surface temperature was developed for three common lamp types in cross flow from a convective–radiative energy balance assuming constant surface temperature. For one lamp type, a single tube standard output lamp, UVC output and cold spot temperature data were obtained under typical in-duct operating conditions. Over an ambient temperature range of 10–32.2 °C and an air velocity range of 0–3.25 m/s, measured cold spot temperature varied from 12.7 to 41.9 °C and measured lamp output varied by 68% of maximum. Surface temperatures predicted by the heat transfer model were 6–17 °C higher than corresponding measured cold spot temperatures, but were found to correlate well with cold spot temperature via a two-variable linear regression. When corrected using this relationship, the simple model predicted the cold spot temperature within 1 °C and lamp UVC output within ±5%. To illustrate its practical use, the calibrated lamp model was employed in a simulation of the control of a contaminant in a single-zone ventilation system by an in-duct UVGI device. In this example, failure to account for the impact of ambient condition effects resulted in under-prediction of average space concentration by approximately 20% relative to a constant output system operating at maximum UVC output.

Skylights can introduce considerable heat gains and losses that may offset the benefits of electric light savings and cause an increase in yearly net building energy use. The design of a toplight system needs to take into consideration different toplighting types, including aperture size and orientation, electric lighting control, and, most important, the local climate. This study examines the impacts of a variety of toplighting strategies and glazing types on the total yearly energy loads for a prototypical open office space situated in five different climates. Coordinated modeling with both an advanced daylight and electric lighting simulation program and a building thermal simulation program based on hourly weather data for an entire year enable the reliable estimation of annual lighting energy use in response to dynamically changing daylight conditions, and address the interaction between lighting energy and total building energy. This study shows that different toplighting strategies designed to meet...

The feasibility of wireless measurements for rapid tuning of a multizone airflow model was extensively investigated using a small-scale residential building as a test site. The main objective of the research was to provide fundamental information, such as measurement time and cost for various measurement techniques, needed for selecting an appropriate field measurement strategy. Potential advantages of the wireless measurement approach were evaluated. These include: portability and flexibility, fast equipment setup, time synchronized data collection, negligible interruption to the occupants’ activity during the measurement, and installation time and cost savings. Currently, the high equipment cost of the wireless approach, relative to more conventional techniques, may offset the noted advantages and be the highest barrier to the wide use of wireless sensors in field measurements. Consequently, conventional hand-held measurements can be more economical, but the stability of the building HVAC system operating status should be considered before selecting the hand-held measurement approach. System stability and the ambient and internal building load status to which it is responding have significant impact on the model tuning usefulness of this approach

Airborne concentration of micron-sized particulate matter (PM) is an important index of indoor air quality. While human activity is considered the main reason causing indoor particle resuspension, theoretical particle adhesion force models give predictions of adhesion force much larger than the disturbance forces introduced by human activity. This work suggests that the imperfect contact between particles and surfaces can greatly reduce the adhesion bond. Electrostatic detachment method is used to measure the actual adhesion force distribution of micron-sized particles to such common indoor flooring materials as vinyl and rubber. Comparisons are made between the theoretical predictions and experimental measurements. Factorial experiments are also designed to study the influence of particle type, flooring type and contact time on particle adhesion force.

The air-handler fan pressurisation method can be a practical way to estimate envelope leakage in large scale or tall buildings where a conventional blower door test is not practical. Standards such as CGSB 149.15 describe desirable test conditions and protocols for such tests. However, because of the variety of building air handling system constructions and site conditions, and limited time and budget available for testing, one may not be able to perform the test under the recommended standard conditions, especially when the system configuration and operation at the site are unfavourable. This study describes air-handler fan pressurisation tests performed for two existing buildings having problematic site conditions affected the ability to perform standard test protocols. Envelope leakage was measured with and without sealing of elevator shafts. Both buildings were found to have standard leakage flow rates that exceed typical levels, with or without elevator shaft leakage. This paper provides some insight into what should be done to ensure a successful air-handler fan pressurisation test by describing what was done to deal with undesirable site conditions which could occur in many buildings. Practical applications: This study shows that air-handler fan pressurisation tests can be performed even in problematic buildings by improving test conditions at the site by adjusting the system operation and by utilising site specific measurement techniques and instrumentation. The applicability of recently developed fan airflow and outdoor intake flow measuring sensors to the air-handler fan pressurisation test is also discussed. However, it also shows that perfect implementation of standard air-handler fan pressurisation test procedure may be difficult in real buildings for a reasonable cost. Published case studies providing methods for solving various practical problems at the test site are very rare. This paper is useful for engineers who are seeking practical information about the air-handler fan pressurisation.

This study presents and develops a controlled and characterized method to explore the influence of specific occupant activity on the aerosolization of allergen-containing particles. Indoor allergen-related diseases are primarily inhalation sensitized and developed, suggesting an aerobiological pathway of allergen-containing carrier particles from dust reservoir to occupant respiration. But the pathways are not well understood or quantified. The influence of occupant walking on particle aerosolization is simulated by a system in which complex floor disturbances are deconvoluted into aerodynamic and mechanical components. Time resolved particle size distributions are measured for particles resuspended from representative samples of flooring materials and different types of floor disturbances in an environmentally controlled experimental chamber. Results indicate aerodynamic disturbances, relative to mechanical, dominate the particle resuspension behavior. Dust type, dust load and floor type showed marginal influences on a normalized surface loading basis. Humidity effects were not clear since during experiments the floor samples may not have reached moisture partitioning equilibrium with the controlled air humidity. Average resuspension rates ranged from 10 −7 to 10 −3 min −1 , having phenomenological consistency with previous, large room or chamber investigations, suggesting the method can be utilized to develop a database for particle resuspension rates.

This paper presents results from the simulation of localized, short-duration bioaerosol releases in a hypothetical building similar to a dormitory or barracks using public domain multizone air flow and contaminant dispersion modeling software. The primary purpose of the modeling was to generate example exposure data to be used in the development of a comprehensive microbial risk assessment methodology. However, these results are also of intrinsic interest for what they reveal about the contribution of various building characteristics to risk from airborne contaminants. A variety of parameters were varied, including building construction, heating, ventilating, and air-conditioning (HVAC) system design, and release characteristics, among others. Results of these simulations demonstrate the variability of exposure possible under different scenarios and, more particularly, the impact that HVAC design decisions can have on risk. Although a single building and restricted set of scenarios was investigated, several general conclusions could be drawn regarding factors, such as HVAC zoning and filter maintenance, that intrinsically contribute to vulnerability reduction.

The prospect of biological attacks is a growing strategic threat. Covert aerosol attacks inside a building are of particular concern. In the summer of 2005, the Center for Biosecurity of the University of Pittsburgh Medical Center convened a Working Group to determine what steps could be taken to reduce the risk of exposure of building occupants after an aerosol release of a biological weapon. The Working Group was composed of subject matter experts in air filtration, building ventilation and pressurization, air conditioning and air distribution, biosecurity, building design and operation, building decontamination and restoration, economics, medicine, public health, and public policy. The group focused on functions of the heating, ventilation, and air conditioning systems in commercial or public buildings that could reduce the risk of exposure to deleterious aerosols following biological attacks. The Working Group's recommendations for building owners are based on the use of currently available, off-the-shelf technologies. These recommendations are modest in expense and could be implemented immediately. It is also the Working Group's judgment that the commitment and stewardship of a lead government agency is essential to secure the necessary financial and human resources and to plan and build a comprehensive, effective program to reduce exposure to aerosolized infectious agents in buildings.

Temperature distributions formed during charging of a 14 m (46 ft) water depth, 7 m (23 ft) radius stratified chilled water storage tank with double ring octagonal slotted pipe diffusers were recorded and analyzed. Prior to the beginning of each test, the tank was fully discharged and at a relatively uniform temperature. To the extent possible, inlet flow rate and temperature were held constant during each test. Six tests were performed for flow rates varying from 50% to 95% of design. Thermal performance was quantified using thermocline thickness, half-cycle figure of merit (FoM1/2) and equivalent lost tank height (ELH). The thermal performance for all tested charge flow rates was good by current standards (FoM1/2 > 90%, ELH

A parametric study was performed of the charging thermal performance of a full-scale pipe diffuser in a single cylindrical stratified chilled water storage tank by applying factorial experimental theory to the results of simulations performed with a validated computational fluid dynamics (CFD) model. Dimensional parameters having the potential to influence charging inlet performance were identified and formed into dimensionless groups using the method of repeating variables. Parameters included: the inlet Richardson number based on inlet slot width (Ri l ), inlet Reynolds number (Re i ), ratio of inlet width to diffuser height (l/hi ), ratio of inlet diffuser height to tank radius (hi/RW ), and ratio of diffuser radius to tank radius (RD/RW ). Thermal performance was measured in terms of equivalent lost tank height (ELH). A full 2k factorial experiment of thirty-two simulations was performed and analyzed. Parameter ranges were: 0.05-2 for Ri l , 500–5000 for Re i , 0.1–1 for l/hi , 0.005–0.05 for hi/RW , ...

As part of ASHRAE Research Project 1185, field data from the constant flow rate charging of a stratified chilled water storage tank with double-ring octagonal slotted-pipe diffusers serving a university chilled water system were compared with results of a transient axisymmetric computational fluid dynamics (CFD) model. Charge processes at flows near design flow rate and 50% of design were modeled. Laminar and turbulent simulations were performed for a range of slot dimensions. Performance of the model was assessed by direct comparison of temperature profiles and by comparison of common thermal performance metrics, including thermocline thickness, lost capacity, and equivalent lost height. The inlet Richardson number based on slot hydraulic radius was found to have the strongest effect on model results. The model Richardson number giving best agreement with the lost height of the field data for near design flow rate was roughly an order of magnitude greater than the Richardson number of the actual diffuser...

A dimensional analysis of an ultraviolet germicidal irradiation (UVGI) air disinfection system within a diffusely reflective enclosure is performed using the Buckingham pi theorem. The eight dimens...

This paper presents the results of research on the performance of air-cleaning and air-disinfection systems used for protecting buildings against intentional releases of biological agents. The air-cleaning technologies addressed include dilution ventilation, filtration, and ultraviolet germicidal irradiation. A 40-story commercial office building is modeled using typical occupancy levels and leakage rates for doors, walls, and floors. A steady-state single-zone model is used to predict steady-state conditions resulting from the use of various levels of air cleaning. A transient single-zone model is used to predict transient indoor concentrations from which inhaled doses and estimated casualties are predicted. A transient multizone model is used to evaluate contaminant dispersion and estimate potential casual- ties. Three design-basis attack scenarios are simulated using various biological weapon agents. Predicted casualties are estimated using an epidemiological model of the dose response curves for each of the agents. The effect of increasing levels of air cleaning is examined under the attack scenarios to evaluate their effectiveness. Results indicate that high levels of protection are possible for building occupants with moderate and affordable levels of air cleaning when filtration is combined with ultraviolet germicidal irradiation. Results also suggest that diminishing returns occur when increased levels of air cleaning are applied. It is hypothesized that the maximum useful size of any air-cleaning system is defined and limited by building physical characteristics alone.

An enclosed flow-through system using airborne ozone for disinfection and which removes the ozone with a catalytic converter was tested with a strain of Escherichia coli. Petri dishes containing the microorganisms were inserted in a chamber and exposed for 10-480 min to ozone concentrations between 4 and 20 ppm. Death rates in excess of 99.99% were achieved. Survival data is fitted to a two-stage curve with a shoulder based on the multihit target model. Ozone was removed from the exhaust air to nondetectable levels using a metal oxide based catalyst. The possibility of using ozone as an airborne disinfectant for internal building surfaces and catalytically removing the ozone on exhaust is demonstrated to be feasible. A model for the decay of Bacillus cereus under ozone exposure is proposed as an example for predicting the sterilization of buildings contaminated with anthrax. The potential for disinfecting airstreams and removing ozone to create breathable air is also implied by the results of this experiment.

A computational fluid dynamics (CFD) model has been developed to simulate the flow and heat transfer near a lower radial inlet diffuser in a cylindrical stratified chilled water storage tank during charging. The model was used to perform parametric simulations of inlet diffuser performance in full-scale tanks during thermocline formation, from which first-order correlation relating thermal performance to tank and diffuser design parameters were derived. Part 1 describes the development of the CFD model and its validation. Part 2 reports the results of the parametric study. The two-dimensional, transient model was implemented in a commercial finite element code. The model has been validated with field-measured data from two full-scale tanks. Laminar analysis predicted field-measured temperature profiles well, even under ostensibly transitional conditions, provided that variations in inlet temperature during the field tests were accurately modeled. These results suggest that turbulence has a secondary effec...

A comprehensive treatment of the mathematical basis for modeling the disinfection process for air using ultraviolet germicidal irradiation (UVGI). A complete mathematical description of the survival curve is developed that incorporates both a two stage inactivation curve and a shoulder. A methodology for the evaluation of the three-dimensional intensity fields around UV lamps and within reflective enclosures is summarized that will enable determination of the UV dose absorbed by aerosolized microbes. The results of past UVGI studies on airborne pathogens are tabulated. The airborne rate constant for Bacillus subtilis is confirmed based on results of an independent test. A re-evaluation of data from several previous studies demonstrates the application of the shoulder and two-stage models. The methods presented here will enable accurate interpretation of experimental results involving aerosolized microorganisms exposed to UVGI and associated relative humidity effects

During the 1980s and early 1990s, the use of cool thermal energy storage (TES) in commercial, institutional, and industrial facility air-conditioning systems became widespread in the United States. The growth of TES was driven by electric utility demand-side management (DSM) programs, which provided capital incentives and rate structures favorable to TES. The success of DSM and the pending deregulation of electric power production have all but eliminated external support for TES. Unless TES can adapt to the new economic climate, its use is likely to decline significantly. The market forces behind the TES boom and recent changes in these forces are reviewed. Strengths and weaknesses of TES are discussed relative to these redefined space conditioning market priorities. Potential future roles for TES are considered, and new developments in TES technology that may contribute to its sustainability are described. Although the future use of TES is likely to be focused more narrowly in its most competitive niches, it can survive and continue to play an important role in HVAC systems despite recent developments.

The bactericidal effects of high concentrations of airborne ozone were tested against Escherichia coli and Staphylococcus aureus. Petri dishes containing the microorganisms were inserted in a chamb...

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 meta-analysis showed that thermal comfort ranks only slightly higher in importance than acoustic comfort and IAQ (Frontczak & Wargocki 2011). Although not focused on acoustics, these prior studies do provide insight into appropriate methodologies. Perceived IEQ is the most widely studied since it is relatively simple to measure and can be compared to perception-based acceptability criteria. Some investigations go beyond formal surveys by including quantitative measures, such as overall productivity, student learning, and health. These data can be used for monetization of benefits and cost, where the typical finding in studies focused on the thermal environment and IAQ is as high as 10:1. Overall, the field of IEQ needs to move from perceived quality metrics to performance metrics, but more work is needed to establish sufficiently accurate quantitative measures. These advances will be especially beneficial to building occupants by providing better working environments both in terms of health and productivity.

Multizone network airflow analysis is used to analyze stack and mechanical system effects on the distribution of three representative biological agents in a prototype 40 story building. This approach relies on mass balances to compute airflow and contaminant transfer between the building zones. The analysis considers stack effects caused by cold outdoor temperatures, unintended positive and negative pressurization of the floor on which the release of the agent occurs, and three levels of contaminant removal using a combination filter/UVGI system. The results show that vertical shafts, such as stairwells and elevator shafts provide significant routes for contaminant transfer between floors, even when these floors are served by different air handling systems. Because the air moving through these pathways does not pass through an air handling system, this type of transport is not as easily reduced by filtering. However, commercially available filters were able to reduce contaminant concentrations substantially in zones that receive contaminants primarily due to recirculation through the air handling system.Copyright © 2002 by ASME