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Life-cycle cost simulation of in-duct ultraviolet germicidal irradiation systems
Abstract
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 UVGI. This study presents a simulation-based life- cycle cost analysis of in-duct UVGI in a hypothetical office building served by VAV systems. Three scenarios are considered: UVGI in the mixed air stream upstream of the cooling coil, UVGI downstream of the coil, and equivalent enhanced filtration without UVGI. The upstream location results in lower first and operating cost for UVGI due to a more favorable thermal environment for UV lamps. UVGI in either location is much lower in annualized cost than equivalent enhanced filtration. The methodology presented could serve as a model for an improved design process.
... However, its application can be complicated (e.g., when calculating the dose received by a microorganism following a tortuous path through a device with spatial variations in irradiance). Further on, three operational factors (air velocity, temperature and relative humidity) are identified critically affecting the in-duct UVGI performance [17][18][19][20]. ...
... The air temperature, air velocity, relative humidity, device geometry, and lamp characteristics (power, geometry, and wavelength) are critical for characterizing the UV inactivation efficiency and energy consumption. Previous research has addressed the energy simulation and life-cost analysis of an in-duct UVGI system from the perspective of lamp output, meteorological climate (cold, hot, and warm climate zones), and installation locations (downstream and upstream of the cooling coil for the conditioned supply air and unconditioned mixed air) [17,18,83]. The results show that installing the lamps downstream from the cooling coil (supply air) led to a stable air temperature and stable energy consumption for all three climate zones. ...
... This observation highlights the need to consider the individual particle inactivation performance in addition to the overall system disinfection evaluation. • In-duct UVGI system energy consumption predictions are discussed using the lamp output, meteorological climate, and installation locations in the HVAC system [17,18,83]. Based on previous studies, this paper introduces the humidity-amended UV rate constants and evaluates the corresponding energy consumptions under the monthly average environmental conditions for three meteorological climates. ...
The rapid increase in global cases of COVID-19 illness and death requires the implementation of appropriate and efficient engineering controls to improve indoor air quality. This manuscript focuses on the use of the ultraviolet germicidal irradiation (UVGI) air purification technology in HVAC ducts, which is particularly applicable to buildings where fully shutting down air recirculation is not feasible. Given the poor understanding of the in-duct UVGI system regarding its working mechanisms, designs, and applications, this review has the following key research objectives:
... Finally, the cost of retrofitting or installing additional HVAC equipment must eventually be considered. Lee et al. (2009) conducted a cost analysis in 2009 investigating the addition of a UVGI system or air filter upgrades. The analysis indicated that a UVGI system could cost as low as 21 % of the cost to upgrade to an equally efficient MERV 12 filter. ...
... • The lack of quality data from experiments Non-Thermal Plasma (NTP) (Narayanan et al., 2010;Lee et al., 2009;Moreau et al., 2008;López et al., 2019;Ma et al., 2008;Hernández-Díaz et al., 2021;Lai et al., 2016;Martin et al., 2008;Xia et al., 2019;Turgeon et al., 2014;Bisag et al., 2020;Sharma and Sharma, 2020;Schiappacasse et al., 2020) • Efficient method for the inactivation of bacteria and possibly some viruses. • Applicable to HVAC ducts as well as other standalone configurations. ...
COVID-19 forced the human population to rethink its way of living. The threat posed by the potential spread of the virus via an airborne transmission mode through ventilation systems in buildings and enclosed spaces has been recognized as a major concern. To mitigate this threat, researchers have explored different technologies and methods that can remove or decrease the concentration of the virus in ventilation systems and enclosed spaces. Although many technologies and methods have already been researched, some are currently available on the market, but their effectiveness and safety concerns have not been fully investigated. To acquire a broader view and collective perspective of the current research and development status, this paper discusses a comprehensive review of various workable technologies and methods to combat airborne viruses, e.g., COVID-19, in ventilation systems and enclosed spaces. These technologies and methods include an increase in ventilation, high-efficiency air filtration, ionization of the air, environmental condition control, ultraviolet germicidal irradiation, non-thermal plasma and reactive oxygen species, filter coatings, chemical disinfectants, and heat inactivation. Research gaps have been identified and discussed, and recommendations for applying such technologies and methods have also been provided in this article.
... In recent years, interest has grown in the potential for photochemical air filters, such as UV-C irradiation, to supplement or replace fine particle filtration for microbial control. These devices have the capacity of destroying or decomposing microorganisms and potentially volatile organic compounds (VOCs), and they may have energy performance benefits over conventional filters (Blatt 2006;Kowalski 2009;Lee et al. 2009). ...
... Microorganisms contained in the air passing through the UV field incur DNA damage proportional to the UV irradiance, time of exposure, and species of microorganism; with sufficient exposure, the damage may be lethal, rendering microorganisms inactive. The technology has also shown reduction of bacteria concentration on surfaces after UV-C has been installed within a ventilation system (Taylor et al. 1995), leading to applications for reducing bio fouling of cooling coils and the potential for improving system energy efficiency (Blatt 2006;Kowalski 2009;Lee et al. 2009). With increasing application of in-duct UV-C systems, it is important to accurately quantify the technology's performance, and appropriate analysis and test mechanisms must be set in place. ...
UV-C is becoming a mainstream air sterilization technology and is marketed in the form of energy-saving and infection-reduction devices. An accurate rating of device performance is essential to ensure appropriate microbial reduction yet avoid wastage of energy due to over performance. This article demonstrates the potential benefits from using computational fluid dynamics to assess performance. A computational fluid dynamics model was developed using discrete ordinate irradiation modeling and Lagrangian particle tracking to model airborne microorganisms. The study calculates the UV dose received by airborne particles in an in-duct UV system based on published EPA experimental tests for single-, four-, and eight-lamp devices. Whereas the EPA tests back calculated UV dose from measured microorganism inactivation data, the computational fluid dynamics model directly computes UV dose, then determines inactivation of microorganisms. Microorganism inactivation values compared well between the computational fluid dynamics model and the EPA tests, but differences between UV dosages were found due to uncertainty in microorganism UV susceptibility data. The study highlighted the need for careful consideration of test microorganisms and a reliable dataset of UV susceptibility values in air to assess performance. Evaluation of the dose distribution demonstrated the importance of creating an even UV field to minimize the risk of ineffective sterilization of some particles while not delivering excessive energy to others.
... However, UR-UVGI systems have demonstrated very high effective air change rates, without the limitation of series mechanical filters [17]. Nevertheless, an analysis of the impact of GUV in AHUs using the Wells-Riley model predicted that a typically sized system can reduce infection risk by as much as 50 % [28] and that even low-powered systems sized for coil maintenance produce an air-quality benefit [29]. ...
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.
... As for the operation and maintenance costs, they include the cost of electricity to operate the lamps, increased cooling load, and maintenance (lamp replacement). A study by Lee et al. [112] showed that the UVGI system in an office building added no more than 0.3% to the total energy consumption. ...
Airborne disease transmission in indoor spaces and resulting cross-contamination has been a topic of broad concern for years – especially recently with the outbreak of COVID-19. Global recommendations on this matter consist of increasing the outdoor air supply in the aim of diluting the indoor air. Nonetheless, a paradoxical relationship has risen between increasing amount of outdoor air and its impact on increased energy consumption – especially densely occupied spaces. The paradox is more critical in hot and humid climates, where large amounts of energy are required for the conditioning of the outdoor air. Therefore, many literature studies investigated new strategies for the mitigation of cross-contamination with little-to-no additional cost of energy. These strategies mainly consist of the dilution and/or the capture and removal of contaminants at the levels of macroenvironment room air and occupant-adjacent microenvironment. On the macroenvironment level, the dilution occurs by the supply of large amounts of outdoor air in a sustainable way using passive cooling systems, and the removal of contaminants happens via filtering. Similarly, the microenvironment of the occupant can be diluted using localized ventilation techniques, and contaminants can be captured and removed by direct exhaust near the source of contamination. Thus, this work answers ten questions that explore the most prevailing technologies from the above-mentioned fronts that are used to mitigate cross-contamination in densely occupied spaces located in hot and humid climates at minimal energy consumption. The paper establishes a basis for future work and insights for new research directives for macro and microenvironment approaches.
... While air disinfection may still occur as air passes by the UVG-CC system, the primary focus of UVG-CC is surface disinfection and, in turn, maintenance cost savings, and increased or prolonged system capacity due to cleaner heat exchanger surfaces, resulting in an overall system energy savings due to better heat transfer and reduced load on the chiller, pump, and/or fan. Life cycle cost simulations of UVGI in HVAC systems for air disinfection (requiring higher levels of irradiance than UVG-CC) found the annual energy cost of a UVGI system to be relatively small compared to a typical whole-building energy cost and, for comparison, found UVGI to be significantly more cost effective than the equivalent high efficiency filtration for removing microbial air contaminants [3]. The buildings sector accounted for 41% of primary energy consumption in the US in 2010 [4]. ...
Cooling coil surfaces are ideal sites for biofilm formation due to the presence of adequate nutrients (deposited particles) and moisture (condensate), causing adverse impacts on heating, ventilation and air-conditioning (HVAC) energy usage and performance. In this study, an HVAC test apparatus was built in our laboratory to investigate the hypothesis that ultraviolet germicidal coil cleaning (UVG-CC) of heat exchanger surfaces improves heat transfer effectiveness and reduces the static pressure drop across the coil. The test apparatus consisted of two parallel ducts, each with its own cooling coil. One coil was treated with UVG-CC while the other was the control and left untreated. Thermodynamic properties of the air and water flowing through both heat exchangers were monitored over the course of two years with sensors and a data acquisition system. Differences in static pressure drop and coil effectiveness between the UV-treated and control coil were compared across multiple modes of coil operation (defined by presence of condensate). The effectiveness of UVG-CC was drastically affected by the presence of condensation on coil fins. We observed a statistically significant difference in the heat transfer effectiveness between the UV-treated and control coils in wetted conditions while no difference was observed in dry conditions. Sensor accuracy, however, contributed to large uncertainty in our result. The average heat transfer of the UV-treated coil was 3.0–6.4% higher compared to the control coil, with an uncertainty of ±2.7%. UVG-CC, however, did not significantly reduce static pressure drop.
... Air cleaner effectiveness is frequently modelled with the well mixed assumption applied to conditioned spaces, and is therefore different than other measures with similar names that are concerned with the distribution of contaminant within a space (Novoselac and Srebric 2003). The concentration measure may have a variety of definitions as appropriate for the application, such as the steady state concentration of ozone with and without various air cleaner configurations (Nazaroff and Weschler 2009), or the steady state concentration of a biological contaminant (Lee 2009). Other concentration measures (e.g. ...
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 usefulness of ε in the analysis and application of air cleaners, as well as its shortcomings, is illustrated by the modeling of in-duct ultraviolet germicidal irradiation (UVGI) in a hypothetical two-zone building served by a constant volume system. The impact of design parameters such as the location of UVGI units, particulate filter efficiency, and the nature of contaminant release are investigated, with calculated ? values ranging from 5% to 90% depending on the nature of these parameters.
Germicidal ultraviolet light (UV) systems have been widely used in the field of healthcare to help disinfect equipment, surfaces, and air supply systems. Applications include disinfection of whole rooms (including operating rooms), walls and floors, medical equipment, and cooling coils. UV is a highly effective and predictable technology to ensure sterilization of almost any types of surfaces and to eliminate microbial growth. Public health agencies such as the Centers for Disease Control and Prevention in the USA (CDC) recommend UV use as an effective technology to disrupt pathogen transmission in building ventilation systems. The current rarity of UV disinfection stems from the fact that it has been erroneously assumed that air filters are sufficient to provide sterilized air. The last 25 years of data has shown that this is far from reality. When dealing with sub-micron bio-contaminants in the size range of 0.1–0.4 micron, even the best filtration technologies fail to stop them all. HEPA filter challenged with a concentration of one million viable particles per cubic meter at a flow rate of 1000 m³/h could allow as much as 500,000 particles every hour to go through. During the course of a single day, a total of 12 million bio-viable particles will penetrate the filter and contaminate the aseptic zone. Those uncaptured bio-contaminants particulates can be rendered innocuous by a proper use of UV germicidal irradiation (UVGI) technology. This chapter presents an overview of how germicidal UV can be used to sterilize a wide spectrum of microorganisms (e.g., bacteria, mold spores, and viruses) in air stream as well as on contaminated wall and objects.
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 efficiency and space concentration that accounted for these effects were performed for a hypothetical building served by a VAV system. The UVGI device was assumed to be located in the supply air stream and exposed to a near constant temperature, but variable flow. UVGI performance was compared with enhanced ventilation and infiltration. Large seasonal variations in UVC dose due mainly to the effect of airflow variation on residence time were observed. UVGI air treatment resulted in much lower predicted space concentrations of Staphylococcus aureus than ventilation according to ASHRAE Standard 62.1 and levels comparable to those achieved by high efficiency, but sub-HEPA, particulate filtration. Transient variations in space concentration due to lamp output variation were small, but adjustment of lamp output to the design operating condition was very important for modeling accuracy.
In this article a modified single fiber model of filtration is described and used to generate filter performance curves that can be fit to MERV data in the 0.3-10.0 micron size range and that can be extended down to the size range of viruses. Coupled with the summary of logmean diameters of airborne microorganism included here, these models will enable estimation of filtration rates for viruses and bacteria.
An estimate of the nationwide improvements in health and productivity potentially attainable by providing better indoor environmental quality (IEQ) in U.S. buildings is given. Such estimates include the potential reductions in three categories of health effects, the associated economic benefits, and the potential direct improvements in productivity not mediated through health. These risk factor reductions through practical measures are estimated from published data using engineering judgements.
This study estimated the health, energy, and economic benefits of an economizer ventilation control system that increases outside air supply during mild weather to save energy. A model of the influence of ventilation rate on airborne transmission of respiratory illnesses was used to extend the limited data relating ventilation rate with illness and sick leave. An energy simulation model calculated ventilation rates and energy use versus time for an office building in Washington, D.C. with fixed minimum outdoor air supply rates, with and without an economizer. Sick leave rates were estimated with the disease transmission model. In the modeled 72-person office building, our analyses indicate that the economizer reduces energy costs by approximately 6,000 and $16,000. This modeling suggests that economizers are much more cost effective than currently recognized.
How do you know when to upgrade filters responsible for indoor air quality – and which ones to choose? Marty Schloss, KBD/Technic takes us through a decision making solution that makes the process cleaner for everyone.
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 0–3.25m/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.
The effectiveness of any ultraviolet germicidal irradiation (UVGI) system is governed by the passage of airborne microorganisms through the UV ÿeld. This paper describes a new method for evaluating the perfor-mance of UVGI devices using computational uid dynamic (CFD) simulations. A microorganism inactivation equation is combined with a scalar transport equation to describe the concentration of airborne microorgan-isms in the presence of a UV ÿeld. The solution of this equation, in conjunction with the momentum and turbulent energy equations, allows the eeect of both the airrow and the UV ÿeld on the microorganism distri-bution to be examined. Solutions are shown for the airrow and microorganism concentration through a bench scale ow apparatus, at ÿve diierent UV intensities. The results from the CFD model are validated against the experimental data, obtained from the ow apparatus, for aerosolised Pseudomonas aeruginosa microorganisms. Good comparisons are seen, giving conÿdence in the application of the technique to other situations.
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