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Estimating the effects of ambient conditions on the performance of UVGI air cleaners
Abstract
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 commonly used mercury-based UV lamps have the output dependency on the lamp surface temperature (coldest spot) that controls the mercury vapor pressure and determines its UV output. Several studies have reported "wind-chill" effects, where low air velocity/high air temperature or high air velocity/low air temperature results in overheating or overcooling of the lamp, thus lowering its output and inactivation performance [1], [2]. Analogously, a high ventilation rate shortens the bioaerosol UV irradiating time, thus lowering the received UV dose and inactivation efficiency. ...
... In addition, humidity affects the radiation transport and the microorganism's susceptibility to UV irradiation. Although the humidity effect on the radiation transport was reported weak and negligible [1], [3], the considerate influence was observed for the microorganism's UV rate constant, characterized by the formation of bound water layer in bioaerosols that prevents UV irradiation on microorganisms and increases UV light scattering, thus affects the dose-response behaviours [4]. ...
... Thus, for the same type of UV lamps under the same ventilation condition, the r remains the same [8]. In this case, extracting the r from the same type cylindrical UV lamp (Philips TUV 25W -G25T8) in literature, where the lamp surface temperatures under different ventilation conditions were experimentally measured [1], the bulb wall temperature for the G24T6L UV lamp can be determined by rearranging Eq. (6) and using its lamp characteristics (Nu, A, D and Q total ) as: ...
Indoor airborne microorganism's transmission can be effectively mitigated using an induct ultraviolet germicidal irradiation (UVGI) system and adequate ventilation. However, quantifying the impacts of ventilation conditions (air temperature, velocity and humidity) on its inactivation performance is not clear, resulting in the uncertainties of a UVGI system's performance under different ventilation conditions. Therefore, a 3D Computational Fluid Dynamics (CFD) model combined with the r method for UV lamp output prediction, radiative transport equation (RTE), and UV dose equation were introduced in this study to characterize and predict an induct UVGI system inactivation performance. Further, the UVGI system design from the U.S. Environmental Protection Agency (EPA 600/R-06/051) was used to illustrate the effects of varying air temperature (15-30°C), velocity (1.5-3 m/s) and RH (20%-80%), and to predict its seasonal inactivation efficiencies for the cities in North America in light of COVID-19 mitigation.
... Thus, it is critical to identify the relationship between the HVAC operating conditions and the UV lamp working efficiency (lamp surface temperature). A previous study (Study 1 [23]) introduced empirical correlations of lamp output for three types of low-pressure mercury lamps under common HVAC operating conditions (air temperature: 5-35 • C; air velocity: 0.5-4 m/s). Three lamps, namely, cylindrical hot cathode (type 1), twin-tube hot cathode (type 2), and cylindrical cold cathode (type 3), were placed in the duct, both cross-facing and parallel-facing the airflow. ...
... However, discrepancies in the varying trends were observed. For instance, in Studies 1 [23] and 2 [24], where the air temperature increases from 15.5, 20.5-25.5 • C under U = 3 m/s, an increasing and then decreasing lamp irradiance was observed in Study 2 [24], which contradicts the mono-increasing trend observed in Study 1 [23]. For the type 1 lamp, both Studies 1 [23] and 3 [25] reported mono-increasing lamp irradiance with the air temperature varying from 15.5 to 30 • C at U = 3 m/s. ...
... However, discrepancies in the varying trends were observed. For instance, in Studies 1 [23] and 2 [24], where the air temperature increases from 15.5, 20.5-25.5 • C under U = 3 m/s, an increasing and then decreasing lamp irradiance was observed in Study 2 [24], which contradicts the mono-increasing trend observed in Study 1 [23]. For the type 1 lamp, both Studies 1 [23] and 3 [25] reported mono-increasing lamp irradiance with the air temperature varying from 15.5 to 30 • C at U = 3 m/s. ...
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:
... 10 The irradiance depends on the power rating of the UV source and on environmental factors. 17 Previous experimental studies of in-duct UV lamps in a turbulent flow in a full-scale duct examined only one environmental duct airflow condition. 8,9 This limited information is not practically useful for engineers designing new systems due to the varied air parameters in practical HVAC systems. ...
... 21 The ambient airflow velocity and temperature affect the UV lamp surface temperature and radiation output by influencing the mercury vapor pressure in the lamp. 17,22 The mercury vapor pressure can be decreased using amalgams instead of pure mercury. 21 Measurement of the UV lamp output as a function of the lamp surface (cold spot) temperature revealed that the lamp output first increased with the surface temperature and then decreased. ...
... 24 Although a few studies have measured the effect of surface temperature on the output of UV lamps, none have simultaneously measured the disinfection efficacy of UV lamps on airborne bacteria. 17,23,25 Many UV lamp manufacturers provide no information about UV performance, and even those that do tend to provide information for only one air condition. This can cause serious problems when a device is used in different environmental conditions. ...
In this study, we investigated the effects of environmental factors such as airflow velocity, relative humidity (RH), temperature and duct reflectance on the performance of in‐duct UVC lamps. Staphylococcus epidermidis, Pseudomonas alcaligenes and Escherichia coli were used as the test bacteria. The UV irradiance, disinfection efficacy and UV susceptibility constant (Z value) of the test bacteria were experimentally determined. The results showed that the UV disinfection efficacy decreased as the airflow velocity and RH increased. The maximum UV disinfection efficacy was obtained at temperature of 20‐21℃ compared with the performance at lower temperature (15‐16℃) and higher temperature (25‐26℃). When the RH increased from 50% to 90%, the Z values of airborne bacteria reduced by 40%, 60% and 38% for S. epidermidis, P. alcaligenes and E. coli, respectively. Besides, susceptibility constants had lower values under both cooling temperature (15‐16℃) and heating temperature (25‐26℃) compared with that under the temperature of 20‐21℃. It was observed that S. epidermidis generally had the highest resistance to the UV irradiance. The results also showed that the UV disinfection efficacy was lower in the duct with a black surface than in the clean duct.
... Details of the model are described in a previous paper by the authors. (Lau et al., 2009). ...
... The output measurement of lamp type 1 in cross flow was done separately and was published by Lau et al. (2009). In that paper, a different set of ten flow conditions were used. ...
... where T cs is the predicted cold spot temperature [°C], T amb is the air temperature [°C] and T Sur is the calculated average surface temperature [°C] from analytical heat transfer model (Lau et al., 2009). With the above regression model, the lamp output can predicted using the manufacturer's curve as shown in Figure 1. ...
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 account for the variability of the lamp cold spot temperature and output for three lamp types and two orientations. The cold spot temperature of lamps was lower in cross flow than in parallel flow under the same ambient conditions. Lamps in cross flow had output reductions of up to 70% compared to 50% for parallel flow. A calibrated semi-empirical model was predicted the lamp output well over a wide range of flow conditions with relative error of less than 8.5%.
... Due to the failure with the original sensors and disruption of installing new sensors, only data following the 1559-hour restarting of the test are included in the analysis. Lau et al. (2007) reported that UV-C germicidal low-pressure Hg lamps exhibited nearly linear reductions in output over time up to about 4000 hours. Since the reduction in output in the present study appeared to diminish gradually over time, a linear rate of degradation was also assumed in the present study as described below. ...
... The study results are supportive of the life rating with regard to warranty where there is no liability for exceeding performance ratings. The near linear output degradation over time exhibited in this study has been reported by others for this type of lamp (American Air & Water, Inc 2020; Lau et al. 2007). This implies that these UV-C lamps can have a longer useful life for applications like crop pest control, where dose can be maintained by increasing exposure times (e.g., reducing the speed of application) as the lamps age. ...
It is important in understanding the potential benefits of ultraviolet (UV-C) field applications for control of powdery mildew to know how long the lamps will last before replacement. We conducted a laboratory evaluation of a sample of low-pressure discharge germicidal UV-C lamps that have been used in field trials to control strawberry powdery mildew. None of the lamps tested failed to start after more than a year of operation. The degradation of UV-C output followed trends similar to those described by the manufacturer. Based on these measurement data and on the long history of this lamp technology, we predict that these lamps can continue to perform in the field after the manufacturer’s rated life of approximately 10,000 hours of continuous operation, by reducing the speed of application to deliver the prescribed UV-C dose. With protective sleeves, these low pressure discharge UV-C lamps can be expected to last for many years of service.
... It is also useful to note here that a beam irradiation flux of 270 W/m 2 at the lamp surface employed in our simulations of rapid decontamination is two orders of magnitude larger than the irradiance received from UVGI units installed in hospital rooms for air-borne micro-organism decontamination. For instance, the maximum irradiance at the lamp surface reported by Lau et al. 26 was 2.9 W/m 2 . Previous studies 26 have also investigated the effects of ambient conditions on the performance of UVGI air cleaners. ...
... For instance, the maximum irradiance at the lamp surface reported by Lau et al. 26 was 2.9 W/m 2 . Previous studies 26 have also investigated the effects of ambient conditions on the performance of UVGI air cleaners. Although, ambient room conditions were not monitored during the experimental portion of this study, other experimental campaigns have confirmed that the measurement variations with this UV device and radiometer (when the location and orientation are held constant) was within 2% if the measurements were made on two different days. ...
Experimental and modeling based assessments of employing reflective wall coatings towards improving the effectiveness of ultraviolet germicidal irradiation in unoccupied hospital rooms were carried out. Measurements of incident radiative fluxes on different surfaces were made in a control room as well as a room whose walls were painted with a nanostructured UV-C reflective wall coating. Employing the reflective paint resulted in up to a 20% increase in the incident radiative fluxes on some surfaces that were directly exposed to the radiation and nearly a 10-fold increase on surfaces that were not directly exposed. Spatially and directionally well-resolved simulations of radiative transfer within the rooms were carried out employing the finite volume radiation model. The measured enhancement in radiative fluxes predicted numerically agreed in general with experimental observations. The volume-averaged incident radiation increased by 60% in the presence of UV reflective walls. Ray effects or the preferential streaming of radiation in the numerical calculations was more pronounced in the control room and was minimized by increasing the angular resolution of the calculations even further. However in the room with UV reflective walls, the diffuse reflections caused the intensity distributions to become more isotropic and minimized the impacts of ray effects.
... The lamp considered in this study is a widely used single-ended twin-tube high-output hot cathode lamp (Philips TUV PL-L 60W HO) for which a validated polynomial cross-flow performance model was developed by Lau et al. [11]. Fig. 2 shows contours of predicted relative output (actual lamp output as a fraction of the maximum output) as a function of air temperature and velocity. ...
... Study lamp ambient condition response characteristics, in which contours are relative to maximum lamp output[11]. ...
... Consequently, the maximum output of the high output lamp occurs at a higher velocity than the standard output lamp. Figure 2. Wind chill effect on two germicidal lamp types a 21˚C air stream (Philips, 2006) Figure 3. Study lamp ambient condition response characteristics (Lau, et al. 2009) The lamp considered in this study is a widely used single-ended twin-tube high-output hot cathode lamp (Philips TUV PL-L 60W HO) for which a validated polynomial cross-flow performance model was developed by Lau, et al (2009). Figure 3 shows contours of predicted relative output (actual UVC as a fraction of maximum UVC) as a function of air temperature and velocity. ...
... Consequently, the maximum output of the high output lamp occurs at a higher velocity than the standard output lamp. Figure 2. Wind chill effect on two germicidal lamp types a 21˚C air stream (Philips, 2006) Figure 3. Study lamp ambient condition response characteristics (Lau, et al. 2009) The lamp considered in this study is a widely used single-ended twin-tube high-output hot cathode lamp (Philips TUV PL-L 60W HO) for which a validated polynomial cross-flow performance model was developed by Lau, et al (2009). Figure 3 shows contours of predicted relative output (actual UVC as a fraction of maximum UVC) as a function of air temperature and velocity. ...
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.
... UVC intensity is the most important factor for determining the germicidal efficiency of an Fifth sampling of microbes (internal inspection of the EH element) ID-UVGI system, because exposure time can easily be controlled by adjusting the system operation time. Therefore, UVC intensity was measured to predict the germicidal efficiency of the system using UVC sensors at six points (a-f) on the surface of the EH elements for each upstream and downstream side, as shown in Figure 2. Lau et al. (2009) measured the change of UVC lamp output in various conditions of air velocity and temperature. They found that the output of a UVC lamp could decrease drastically as air velocity increased and air temperature decreased, which caused the lamp surface temperature to drop. ...
... The surface temperatures of the UVC lamps in both operating and nonoperating conditions of the AHU were measured using an infrared thermography camera (Ti25, Fluke Corp., USA) with an accuracy of ±2 • C and were correlated with the UVC intensities measured by the UVC sensors. Another infrared thermography camera was effectively used to measure the surface temperature of the UVC lamps (Lau et al. 2009). The lowest temperature, i.e., the cold spot temperature, on the lamp surface faces the direction of airflow; however, the temperature of the lamp side was measured in these tests because it was impossible to measure the cold spot temperature on the downstream side. ...
Humidifiers have been used not only to maintain a comfortable indoor environment, but also to prevent respiratory diseases from worsening due to extremely low humidity. Some evaporative humidifiers (EH) that were considered to be energy efficient have been reported to have problems with microbial contamination. In this study, the microbial contaminations of an EH were verified, and both the germicidal effects and limitations of in-duct ultraviolet germicidal irradiation(ID-UVGI) systems against the contaminations were investigated. A numbers of bacteria and fungi were isolated from the surfaces and drain water of the EH, and airborne microbes that were likely dispersed from the contaminated EH were also detected. Based on the results of monitoring microbes for approximately six months for an ID-UVGI operation, it was found that microbial contamination was reduced but that microbes could still consistently be isolated from the surfaces and drain water. This was likely due to internal contamination of the EH in locations beyond the reach of the ultraviolet C-band (UVC) irradiation. Methods to overcome the limitations of this ID-UVGI system for EH disinfection are thus required.
... Additionally, the sterilization efficiency of low-pressure mercury UV lamps varies with temperature changes, making it essential to understand and consider these characteristics. Typically, the air temperature in HVAC systems ranges from 5 to 35 °C, with air velocities of 0.5~4 m/s [25,26]. In this study, air temperatures ranged from 25 to 28 °C, and air veloc-ity was approximately 0.5 m/s in a system utilizing geothermal energy in summer. ...
A simulated system was created to evaluate an air circulation-type geothermal ventilation system, focusing on measuring microbial contamination levels on the surface of the heat exchange unit. Additionally, this study examined sterilization methods using UV lamps on the surface of the heat exchanger. The fungal concentration on the surface of the heat exchanger showed a tendency to increase over time. Although direct comparison is challenging due to the varying concentrations of outdoor air fungi at different measurement times, the surface fungal concentration was highest at a minimum airflow rate of 150 m3/h compared to other conditions. However, since the adhesion of contaminants from outdoor air to the surface of the heat exchanger is influenced not only by airflow but also by outdoor temperature and relative humidity conditions, future research needs to consider these factors. According to the ATP measurement results, microbial contamination was evaluated as “slightly dirty” after 24 h and “dirty” after 48 h of operating the experimental apparatus. Therefore, it is advisable to clean the internal surfaces of the geothermal ventilation system every 1–2 days. The results of the sterilization experiments using UV lamps indicated that irradiation for approximately 30 min inactivated 94.5%-to-96.1% of microorganisms derived from outdoor air. However, since the sterilization dose varies depending on the type of microorganism, it is necessary to determine the optimal irradiation time based on the target microorganisms and the UV lamp’s irradiation intensity.
... The distribution of UV radiation inside a duct is influenced by both the system's design (duct dimensions and materials and lamp configurations and arrangements) and its operating conditions (duct airflow temperature and velocity) [5]. As for environmental conditions, like supply air velocity, temperature, and relative humidity (RH), they impact the efficiency of the in-duct UVGI system in several ways: (i) air velocity determines the UV exposure time and UV lamp output [5]; (ii) temperature regulates the UV lamp output [6][7][8]; and (iii) temperature and RH affect the survivability, infectivity, and UVC susceptibility of airborne microorganisms [9][10][11][12]. Furthermore, bioaerosol characteristics, including their composition, size, and the contained microorganism species, determine the received UV radiation and how effectively it is utilized: (i) bioaerosol compositions (suspending media) and bioaerosol particle size impact UV absorption properties [9,13,14], (ii) potential cell aggregations in the bioaerosol particles increase resistance to UV inactivation [9,15], and (iii) different microorganisms exhibit varying levels of susceptibility to UV radiation [6,16]. ...
Ultraviolet germicidal irradiation (UVGI) technology has garnered substantial attention in disinfecting airborne microorganisms during and beyond the COVID-19 pandemic. Given that UVGI inactivation performance varies in complex in-duct environments, this study examines the effects of bioaerosol particle size and relative humidity (RH) on the inactivation efficiencies of an in-duct UVGI system. MS2 bioaerosols, with phosphate-buffered saline as suspending media and subjected to a bioaerosol drying process, were used in UVGI tests. At any given RH condition (25 %, 40 %, or 60 % RH), lower UV rate constants were presented for larger bioaerosols (2.1–7 μm) in comparison to smaller ones (0.65–2.1 μm). For humidity, the UV rate constant initially increased and then decreased as RH increased from 25 % to 60 %, peaking at 40 % RH, irrespective of the particle size. Notably, the absence of the bioaerosol dryer altered this trend, where the inactivation efficiency decreased with the increase in RH. In conclusion, our findings suggest that a higher UV dose is required to mitigate hazards from larger bioaerosols in very humid environments. In addition, this work proposes a comprehensive flowchart, a beneficial tool for engineers and designers, which facilitates the effective design and implementation of UVGI technology in controlling bioaerosol hazards.
... Researchers have investigated the critical factors that influence the efficacy of UVGI. From several previous investigations, the complexity of estimating the antimicrobial efficacy of UVGI can be attributed to environmental factors such as relative humidity (Ko et al., 2000;Lau et al., 2009), temperature , and airflow pattern . Additionally, various researchers have reported the influence of UV fluencethe product of UV irradiance (W/m 2 ) and exposure time (s) - (Jensen, 1964;Tseng and Li, 2005;First et al., 2007;McDevitt et al., 2007McDevitt et al., , 2008McDevitt et al., , 2012Rudnick and First, 2007;Cutler et al., 2012;Verreault et al., 2015;Lin et al., 2017;Welch et al., 2018;Buonanno et al., 2020;Nunayon et al., 2020a), location of the UVGI system (Li et al., 2010;Sung and Kato, 2011;Nunayon et al., 2022), and source of pathogens (Nunayon et al., 2022) on the efficacy of UVGI systems. ...
... It was well known that UV irradiance highly depends on the mercury vapor pressure of a UV lamp [39]. The air temperature can affect the surface temperature and the radiation output of a specific wavelength by influencing the mercury vapor pressure in the UV lamp [2,40]. Additionally, UV irradiation could undoubtedly be attenuated with increased distance [41]. ...
The increased threats of pathogenic bioaerosol make air disinfection in heating, ventilation, and air conditioning (HVAC) systems crucial to occupants’ health. To satisfy the high efficiency, superspeed, and wide temperature range of HVAC air disinfection, UV irradiation (UV254/ UV185+254) and its combination with micro-static electricity were studied in two full-scale ducted ventilation systems. UV254 could efficiently disinfect S.albus (>99%) at high temperatures (31±2 °C) and low airflow rates (1.2 m s⁻¹) but was weakened at lower temperatures and higher airflow rates. Its combination with micro-static electricity could remarkably overcome these adverse factors and realize efficient disinfection within the retention time of 0.21 s. Especially for the relatively stubborn B.subtilis var. niger, the combination process improved the disinfection efficiency to 82% at 16±2°C and the airflow rate of 2.4 m s⁻¹, while UV254 was only 52.9%. Since the UV185+254 disinfection was more effective than that of UV254, the UV185+254-based combination could further enhance the B.subtilis var. niger to 93.1%. Besides the disinfection stability, the combination process has advantages in pressure drop (around 50 Pa), energy consumption (e.g., 0.115 kW·h km⁻³), and equipment costs (1,500- 3,000 CNY), making it potentially cost-effective for air disinfection in HVAC systems.
... Finally, for simulating the impact of in-duct UVGI treatment of air on the viruses, the built-in Penn State UVGI model in CONTAM [78,79] was used as an in-duct air disinfection system fitted to the return air side of the AHU. The UVGI susceptibility constant of 0.021 m 2 /J was used for a hypothetical mercury vapor system with 253.7 nm effective wavelength [80]. ...
The dispersion of indoor airborne contaminants across different zones within a mechanically ventilated building is a complex phenomenon driven by multiple factors. In this study, we modeled the indoor dispersion of airborne SARS-CoV-2 aerosols within a US Department of Energy detailed medium office prototype building using CONTAM software. The aim of this study is to improve our understanding about how different parts of a building can experience varying concentrations of the airborne viruses under different circumstances of release and mitigation strategies. Results indicate that unventilated stairwells can have significantly higher concentrations of airborne viruses. The mitigation strategies of morning and evening flushing of conditioned zones were not found to be very effective. Instead, a constant high percentage of outdoor air in the supply mix, and the use of masks, portable HEPA air cleaners, MERV 13 or higher HVAC air filters, and ultraviolet germicidal irradiation disinfection were effective strategies to prevent airborne viral contamination in the majority of the simulated office building.
... Ultraviolet germicidal irradiation (UVGI) is generated using low pressure mercury vapor. Within the UV-C band of the electromagnetic spectrum (100-290 nm), more than 90% of the output irradiation is at a wavelength of 253.7 nm [8,9]. UVGI has been applied in disinfection and sterilization for treating water, disinfecting surfaces, and preventing the spread of disease through the air [3,10]. ...
This study examined the use of high dosages of ultraviolet germicidal irradiation (UVGI) (253.7 nm) to deal with various concentrations of air pollutants, such as formaldehyde (HCHO), total volatile organic compounds (TVOC), under various conditions of humidity. A number of irradiation methods were applied for various durations in field studies to examine the efficiency of removing HCHO, TVOC, bacteria, and fungi. The removal efficiency of air pollutants (HCHO and bacteria) through long-term exposure to UVGI appears to increase with time. The effects on TVOC and fungi concentration were insignificant in the first week; however, improvements were observed in the second week. No differences were observed regarding the removal of HCHO and TVOC among the various irradiation methods in this study; however significant differences were observed in the removal of bacteria and fungi.
... The UVGI output power from a lamp in an airstream depends on the ambient temperature and airspeed and the orientation of the lamp to the airflow (typically crossflow). Correlations for several common lamp types were developed from experimental data by Lau, et al. (2009). For a typical hot cathode, standard output germicidal lamp in crossflow, the fraction of maximum output as a function of air temperature and speed is: ...
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 UV dose than an air treatment system, but should provide some collateral air treatment benefit. To date, this effect has not been studied. In this investigation, the benefit of air treatment provided by a cooling coil irradiation system is estimated via simulations employing a subset of the DOE Commercial Reference Buildings library. Benefits were quantified in terms of changes in appropriate measures for each building type: work-loss days (WLD) for office buildings, disability adjusted life years (DALY) for schools, and hospital acquired infections (HAI) for healthcare facilities. UVGI sized for coil cleaning results in a 0% to 7% average reduction in the measure of interest for each building type. This reduction is negatively related to the average outdoor air fraction in each building type, i.e., incremental benefit of UVGI decreases with increasing outdoor air fraction. Combining WLDs with US Gross National Income to monetize annual savings for office buildings yields 3.11/m² for Small, 0.91/m² for Medium, and 0.23/m² for Large types. Combining DALYs with US Gross National Income to monetize savings for Primary and Secondary Schools results in a wide range: 0.62/m² due to the large range of values one might reasonably assign to a DALY. In hospitals, reduction in airborne HAIs resulted in estimated savings of 0.40/m².
... The value of k was set to 0.0002996 cm 2 /µJ, the median of species-averaged virus values tabulated by Kowalski (2003). Lamp output variation was modeled using Equation 8 ( Lau et al. 2009) which applies to a typical hot cathode, standard output, cylindrical germi- cidal lamp in crossflow. The derating factor accounts for vari- ation in output due to cooling ("wind chill") as a function of air temperature and velocity. ...
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 to operate the coil ultraviolet germicidal irradiation systems by as much as a factor of 20. The effectiveness of air cleaning methods already in place, such as ventilation and filtration, directly influences the incremental benefit of additional air cleaning measures.
... taken fromLau et al. (2009) for a single-tube lamp in crossflow:f DR = 5.79 + 5.66T air − 20.3U air − 0.0701T 2 air + 4.01U 2 air ,(9)where f DR is the power derating factor [dimensionless], T air is the air temperature [°C], and U air is the air velocity [m/s]. ...
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 reported in literature. Indoor air quality benefits were estimated using a stochastic implementation of the Wells-Riley equation to predict infection rates and monetized metrics appropriate to the various occupancies considered. Using lower estimates of ultraviolet germicidal irradiation energy use impact, ultraviolet germicidal irradiation was economically superior to mechanical cleaning only when collateral air treatment benefits were considered. At the higher level of estimated improvement, ultraviolet germicidal irradiation was superior even without consideration of air quality impact.
... The output of a germicidal lamp depends on its thermal environment. Lau et al. (2009) studied the relationship of lamp output to airstream conditions (temperature and velocity) and developed regression models of the fraction of peak output as a function of air temperature and velocity for several types of lamps -Lau's "Type 1" lamp is used here, which is a 25 W single-tube hot cathode lamp. These factors may be used to determine the number of lamps needed to provide a desired dose for specified design conditions as well as the output of a UVGI device under off-design conditions. ...
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 anthrax spores. An example based on a 1,900 m2 commercial building with a forced-air heating, ventilating, and air-conditioning system is used to illustrate the application of the methodology. Representative releases of anthrax are simulated under different conditions to study the variation of effectiveness of UVGI during transient conditions. The practical application of the approach is discussed.
... Either increasing or decreasing the CS temperature decreases the output of the lamp significantly. Lau et al. (2009aLau et al. ( , 2009b) validated with experimental results the relationship between CS and lamp output. ...
Ultraviolet germicidal irradiation (UVGI), typically utilizing 254 nm radiation from low pressure mercury vapor lamps, is being applied in HVAC systems to inactivate infectious airborne microorganisms in health care, security, and general air quality applications. Simulation can play a useful role in the design of application-appropriate systems. A key requirement for accurate modeling is consideration for the impact on lamp UV output of the temperature and velocity of the air stream to which it is exposed. Lamp output varies greatly with the vapor pressure of the plasma it contains, which is highly dependent upon lamp surface cold spot temperature. A model of a single zone HVAC system serving an office space was constructed and was used to simulate the effects of UVGI device location, weather conditions, filter efficiency, and operating cycle on control of generic vegetative bacteria-like and fungal spore-like air contaminants. UVGI device modeling included a model of variable lamp output based on predicted average lamp surface temperature. It was found that lamp output could vary by more than 50% across the range of conditions considered with variations in average contaminant concentration during occupied hours as large as 13%. Operation of UVGI only during occupied hours produced similar occupied hour concentration to continuous operation, but much larger unoccupied hour concentrations. Filtration was found to complement UVGI well by removing the larger spore-like contaminant for which UVGI was less effective than for bacteria.
... Either increasing or decreasing the CS temperature decreases the output of the lamp significantly. Lau et al. (2009aLau et al. ( , 2009b validated with experimental results the relationship between CS and lamp output. ...
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 planar irradiance measurements (mean error –3%, standard deviation 9%). The ray-tracing software was used as a validated design tool to evaluate two typical in-duct ultraviolet germicidal irradiation devices (Cases 6 and 7). Four identical UVC lamps were modeled inside a rectangular duct. The lamps were either arranged in parallel or cross flow, and spherical irradiance values along the flow path were compared. Without accounting for the thermal effect on lamp output, an ultraviolet germicidal irradiation device placed in a cross flow would give a higher average UV irradiance. This benefit would be practical when a sufficient straight run is provided in a ventilation system. However, a lamp in parallel flow would produce a more uniform UV irradiance field near the center of the device. Changing the thermal conditions would have significant impact on lamp outputs. Arranging lamps in a parallel flow would provide a higher total irradiance at low temperature and high flow conditions, especially for lamps with outputs lower than the simulated lamps and lamps without sleeves.
... Lamp output was calculated using the model of Lau, et al. (2009) for every hourly air temperature-velocity pair from the energy simulation so that worst-case design conditions could be identified. Relative UVC output for the location downstream of the coil (supply air) was nearly constant over the entire year with a value slightly above 30% while median monthly output for the upstream location varied between roughly 40% and 80%, with the highest values in the summer and the lowest values in the winter. ...
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.
Ultraviolet germicidal irradiation (UVGI) as an engineering control against pathogenic microbes necessitates a clear understanding of operational parameters and environmental effects on inactivation rates. Here, we investigated the variation laws of ultraviolet-C (UV-C) irradiance under the influence of distance, ambient conditions of temperature, and relative humidity (RH) in a dark chamber using 30-W low-pressure mercury lamps, and all data were analyzed with curve fitting methods. UV-C irradiances in each plane were measured as the distance adjusting between 0.5 and 1.2 m, and a threshold of 70 μW/cm² was utilized to calculate the effective irradiation area. For the temperature and RH, UV-C irradiances were measured at 1 m perpendicular from the lamp axis at the lamp midpoint, with the ambient temperature increasing from 15.5°C to 40°C and RH adjusting from 10% to 97%. Results showed that the UV-C irradiance and effective irradiation area exhibited a notable decrease as the distance increased, both corresponded to polynomial 2nd order fits. The UV-C lamps operate at maximum efficiency at 20°C. Temperature above or below the optimum value will decrease UV output, especially when the ambient temperature exceeds 38°C and the irradiance decreases by 16% compared to the observed maximum. However, the impact of RH on radiant power is negligible with the UV-C irradiance maintaining an overall steady state (84–91 μW/cm²) in the 10%–97% RH range. The use of the measurement and modeling techniques demonstrated in this study may help understand various ambient conditions that influence the irradiance of UV-C and improve reliability and working performance of UVGI systems through better design.
The COVID-19 (SARS-CoV-2) pandemic increased the focus on preventing contamination with airborne pathogens (e.g. viruses, bacteria, and fungi) by reducing their concen tration. Filtration, UV or ionization technologies could contribute to air purification of the indoor environment and inactivation of microorganisms. The aim of this study was to identify the relevant literature and review the scientific evidence presented on the efficacy of filter and germicidal technologies (e.g. non-physical technologies) in air purification applications used to capture and inactivate microorganisms and airborne viruses (e.g. SARS-CoV-2, rhinovirus, influenzavirus) in practice. A scoping review was performed to collect literature. Adopting exclusion criteria resulted in a final number of 75 studies to be included in this research. Discussion is presented on inactivation efficiencies of ultraviolet germicidal irradiation (UVGI) and ionization applications in laboratory studies and in practice. Specific attention is given to studies relating the use of UVGI and ion-ization to inactivation of the SARS-CoV-2 virus. Based on the consulted literature, no unambiguous conclusions can be drawn regarding the effectiveness of air purification technologies in practice. The documented and well-controlled laboratory studies do not adequately represent the practical situation in which the purifier systems are used.
Indoor airborne microorganism’s transmission can be effectively mitigated using an in-duct ultraviolet germicidal irradiation (UVGI) system and adequate ventilation. However, quantifying the impacts of ventilation conditions (air temperature, velocity and humidity) on its inactivation performance is not clear, resulting in the uncertainties of a UVGI system’s performance under different ventilation conditions. Therefore, a 3D Computational Fluid Dynamics (CFD) model combined with the r method for UV lamp output prediction, radiative transport equation (RTE), and UV dose equation were introduced in this study to characterize and predict an in-duct UVGI system inactivation performance. Further, the UVGI system design from the U.S. Environmental Protection Agency (EPA 600/R-06/051) was used to illustrate the effects of varying air temperature (15–30 °C), velocity (1.5–3 m/s) and RH (20–80%), and to predict its seasonal inactivation efficiencies for the cities in North America in light of COVID-19 mitigation.KeywordsUVGIVentilation conditionsLamp outputUV rate constantCFD
Microorganism contamination in air conditioning systems can cause respiratory diseases in building occupants. This study aims to evaluate and predict the performance of an in-duct ultraviolet germicidal irradiation (ID-UVGI) system to reduce the microorganisms that can grow in the liquid desiccant and indirect/direct evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS). Bacteria and mold on the direct evaporative cooling (DEC) element and in the outdoor and supply air were monitored using a swab and Petrifilm for surfaces and impact sampler for air during the operation of the LD-IDECOAS. Microbial contamination was first verified in the air before performing the sterilization experiment. The experimental results showed that the airborne bacteria were reduced by 78.3% after the operation of the ID-UVGI system but there was almost no reduction in the airborne mold. The bacteria and mold concentration on the DEC surface were decreased by 99.7% and 96.7% respectively 3 h after the ID-UVGI operation. Even after the ID-UVGI system was operated for 6 days, the microbial contamination in the downstream water was not decreased significantly; the inside of the DEC element was suspected to be improperly sterilized. The operating times of the ID-UVGI system needed to inactivate the microorganisms were predicted from the UV–C intensity distribution by irradiation analysis. Legionella sp. and Penicillium sp. were predicted to be inactivated by 99.9% with UV–C exposures of 6 s and 15 min 57 s or less respectively when the LD-IDECOAS is operated at the highest air flow rate.
This study examined the use of high dosages of ultraviolet germicidal irradiation (UVGI) (253.7 nm) to deal with various concentrations of air pollutants, such as formaldehyde (HCHO), total volatile organic compounds (TVOC), under various conditions of humidity. We also estimated the emission of ozone as a secondary pollutant of UVGI as treatment. A number of irradiation methods were applied for various durations in field studies to examine the efficiency of removing HCHO, TVOC, bacteria, and fungi. The removal efficiency of air pollutants (HCHO and bacteria) through long-term exposure to UVGI appears to increase with time. The effects on TVOC and fungi concentration were insignificant in the first week; however, improvements were observed in the second week. No differences were observed among the various irradiation methods in this study regarding the removal of HCHO and TVOC; however significant differences were observed in the removal of bacteria and fungi.
Background and Aims
Ultraviolet (UV)‐C irradiation is used for the reduction of microbial spoilage in food. Its effectiveness for the treatment of white grape must has been investigated considering different microbial species and modification of must composition.
Methods and Results
Static and dynamic laboratory‐scale systems emitting at 254 nm were used for the treatment of Vitis vinifera cv. Chardonnay and cv. Crimson grape juices of variable turbidity. The must samples were singularly inoculated with a pure culture of wine spoilage strains belonging to three species, Dekkera bruxellensis, Acetobacter aceti and Lactobacillus brevis, and treated with UV‐C ranging from 300 to 1800 J/L. Cell counts and microbial reduction (derived from α values, according to the Weibull model), colour change, polyphenol oxidase (PPO) inactivation and formation of α‐dicarbonyl compounds were evaluated. After treatment at the maximum UV‐C dosage under static conditions, reductions of yeast counts of 4.91–5.99 log10 colony‐forming units (CFU)/mL and bacterial counts of 4.12–5.05 log10 CFU/mL were achieved, depending on the strain being tested. Polyphenol oxidase activity decreased by up to 7.8 ± 1.4% with variation attributed to must turbidity, which indicated that clarification of must before UV‐C treatment can lead to PPO inactivation. No significant variation in the colour or the concentration of α‐dicarbonyl compounds was detected. Results were confirmed for grape juice with the continuous flow apparatus.
Conclusions
The UV‐C systems achieved microbial reduction without formation of oxidative compounds, suggesting that the experimental conditions employed did not cause any noticeable oxidative phenomena.
Significance of the Study
The UV‐C treatment of grape juice can be considered a potential alternative to sulfur dioxide addition for processing of white must. Improved efficacy of treatment can be achieved by increasing the flow rate and by clarification of must, making the system potentially applicable under industrial conditions.
The ultraviolet (UV) lamp is the most critical component of any UVGI air or surface disinfection system. UV lamps come in many shapes, sizes, and UV output power levels, and they may produce different spectral bands of germicidal UV. All germicidal UV lamps will produce light wavelengths of either UVC (100–280 nm), UVB (280–320 nm), or both (UVC/UVB). Wavelengths of UVA (320–400 nm) are not germicidal and UVA lamps (i.e. blacklight and sunlamps) are not considered UVGI lamps and are not addressed in this chapter. UVGI lamps are commonly referred to as UV lamps and these terms are used interchangeably throughout this book. Various types of UV lamps are currently in use for air and surface disinfection applications, including standard medium pressure (MP) UV lamps which produce broadband UVC/UVB wavelengths, low pressure (LP) UV lamps that produce narrow band UVC wavelengths, microwave UV lamps, and light-emitting diodes (LEDs). Technically, UVC lamps are LP lamps that produce UVC wavelengths only, and the term is not necessarily accurate when applied to MP lamps that produce broadband UVC/UVB wavelengths although common usage doesn’t always make this distinction.
Airborne infectious diseases have been a concern in buildings for many years, even more so now with recent serious health threats such as H1N1, SARS, the Avian Flu and others. In-duct ultraviolet germicidal irradiation (UVGI) is currently being used to help control infectious airborne diseases in many buildings such as healthcare facilities. Many factors play into the effectiveness of these systems including the air and lamp properties. This study uses the Lighting Technologies Inc.'s ray-tracing (Monte Carlo Method) software, Photopia v3.0, to simulate two in-duct UVGI devices. The use of ray-tracing software is proposed because the software is capable of predicting spherical irra-diance values. With the prediction of the spherical irradiance, dose received by microorganisms could be more accurately estimated and the prediction of the survival rate of the microorganisms would also be improved. Four identical ultraviolet (UVC) lamps are modeled inside a rectangular HVAC duct with dimensions of 2′×2′×9′ (0.6m × 0.6m × 2.7m). The lamps are either arranged in parallel or cross-flow as these are the two most common configurations in the industry. This modelling approach for the UVC lamps adopted in this study was previously validated with experimental measurements. The simulated material of the duct surface and the supporting rods in the parallel flow configuration is perfectly diffuse aluminum. Spherical irradiance values in five locations along the length of the duct, before, between, and after the lamps, can be compared between the two configurations. The lamp configuration with higher average irradiance was identified and was used to indicate a more effective lamp configuration for in-duct UVGI systems under different thermal conditions. In conclusion, without accounting for the thermal effect on lamp output, a UVGI device placed in a cross flow would give a higher average UV irradiance for both centerline and edge flow paths that are considered in this study. This benefit would be practical when sufficient straight run is provided for the UVGI devices in ventilation systems. However, lamps in parallel flow would produce a more u nif orm UV irradiance field near the center for both pa ths. When considering the impact s due to th e thermal condition, arranging lamps in parallel flow would provide a higher average irradiance at high velocity and low temperature conditions.
Magnetic ballasts have limited the portability of mercury lamps for decades, while new electronic ballasts trade-off weight against cost and simplicity. We'll describe the lightest, most powerful, and economical UV equipment in the world today, for hand-held and floor curing applications. These systems work directly from standard 120/220-volt outlets without any heavy or costly power supplies. Lamps run at 300-500 watts/inch while curing widths from 20 to 60 inches. Purpose The purpose of this paper is two fold: To introduce a new ballast technology, known as the "Z" technology, which is the key to Super-Portable UV curing equipment, and to explain how this and other recent advancements are accelerating the emerging "Portable UV" curing industry.
This book is a comprehensive source for technical information regarding ultraviolet germicidal irradiation (UVGI) and its application to air and surface disinfection for the control of pathogens and allergens. The primary focus is on airborne microbes and surface contamination applications for hospitals, commercial facilities, and residential homes. All aspects of UVGI systems, including design methods, sizing methods, modeling, safety, installation, testing, guidelines, and disinfection theory are addressed in detail. An extensive database of over six hundred UV rate constant studies is included as well as tabular performance data for UV lamps and products. Providing this information in one single source simplifies the design and installation of UVGI systems, helps guarantee effective performance of new systems, and facilitates their use on a wide scale for the purpose of improving human health. This book is organized to provide systematic coverage of all related issues and will serve equally well as both a textbook and a handbook for general reference.
Unlabelled:
Staphylococcus aureus, Pseudomonas aeruginosa, and Legionella pneumophila have been detected in indoor air and linked to human infection. It is essential to adopt control methods to inactivate airborne pathogens. By passing bioaerosols horizontally into a UV device at two flow rates (Qs) and moving cells around a central UVC lamp at relative humidity (RH) of 12.7-16.7%, 58.7-59.6%, and 87.3-90%, the effects of swirling motion and 254-nm ultraviolet germicidal irradiation (UVGI) against bioaerosols were assessed under UV-off and UV-on settings, respectively. An inverse relationship between RH and UVGI effectiveness was observed for every test bioaerosol (r = -0.74 ∼ -0.81, P < 0.0001). Increased UV resistance with RH is likely associated with the hygroscopicity of bioaerosols, evident by increased aerodynamic diameters at high RH (P < 0.05). UVGI effectiveness was significantly increased with decreasing Q (P < 0.0001). Moreover, P. aeruginosa was the most susceptible to UVGI, while the greatest UV resistance occurred in L. pneumophila at low RH and S. aureus at medium and high RH (P < 0.05). Results of UV off show P. aeruginosa and L. pneumophila were more sensitive to air-swirling motion than S. aureus (P < 0.05). Overall, test bioaerosols were reduced by 1.7-4.9 and 0.2-1.7 log units because of the UVGI and swirling movement, respectively.
Practical implications:
The studied UV device, with a combination of swirling motion and UVGI, is effective to inactivate airborne S. aureus, P. aeruginosa, and L. pneumophila. This study also explores the factors governing the UVGI and swirling motion against infectious bioaerosols. With understanding the environmental and operational parameters, the studied UV device has the potential to be installed indoors where people are simultaneously present, for example, hospital wards and nursing homes, to prevent the humans from acquiring infectious diseases.
Mathematical models of the response of populations of microorganisms exposed to ultraviolet
germicidal irradiation (UVGI) are developed that include two-stage response curves and shoulder
effects. Models are used to develop a C++ computer program that is capable of predicting the
performance of UVGI air disinfection systems. The algorithms are based on models for 1) the
intensity field of UVGI lamps, 2) the intensity field due to UVGI reflective enclosures, and 3) the
kill rate of microorganisms to UVGI exposure as they pass through the modeled intensity field.
The validity of the UVGI lamp model is established by comparison with lamp photosensor data.
The validity of the overall predictive model is established by comparison of predictions with
laboratory bioassays for two species of airborne pathogens – Serratia marcescens and Bacillus
subtilis. First stage rate constants, second stage rate constants, and the defining shoulder
parameters are determined for Aspergillus niger and Rhizopus nigricans based on bioassay data,
and it is shown how predictions using only single stage rate constants can deviate significantly
from predictions using the complete survival curve. A dimensional analysis of UVGI systems
identifies nine dimensionless parameters responsible for determining the effectiveness of any
rectangular UVGI system. A factorial analysis of the dimensionless parameters based on data
output by the program identifies the most critical parameters and the inter-relationships that
determine UVGI system effectiveness. Response surfaces are generated using program output to
illustrate the inter-relationships of the dimensionless parameters. The optimum values of the
dimensionless parameters are summarized that result in optimized performance. Economic
optimization is demonstrated by a series of examples that calculate life cycle costs, and principles
of economic optimization are summarized. Conclusions are presented that will produce more
energy-efficient and effective designs and a proposed model for improved UVGI systems is
presented.
Installations of ultraviolet germicidal irradiation (UVGI) have been stimulated recently by a sudden rise in the incidence of tuberculosis. Hospitals, jails, and homeless shelters have been the most frequently equipped facilities because they are places where many tuberculosis cases are found, the buildings housing them tend to be old and not suited for economical increases in air exchange rates, and the work staffs have been apprehensive about transmission to themselves and their families. The diversity in structures currently being equipped with UVGI installations, plus the introduction of new designs of lamps and fixtures, have made it clear that an updated review of equipment performance factors and practical installation guidelines will be useful to interested parties. Illustrative examples are given of installations that have been made in a diverse set of facilities. In addition, representative figures are given to compare the cost of HVAC installations and UVGI installations that give an equivalent number of air changes based on equal levels of reduction in airborne microorganisms.
Editorial Note: In 1931 the CIE (Commission Internationale de l'Eclairage, or International Commission on Illumination) issued an historic set of standards on illumination and colorimetry. In the late 1940's it was becoming apparent that serious consideration needed to be given to a revision of some of the standards. Since then there has been persistent thought given to the revision of the concepts, terminology, testing procedures, etc., and from time to time some changes have been effected. The report herewith covers revisions for an international terminology.
The publication, in 1938, of an international vocabulary of electrical terms marked the first time that such a list of definitions had been produced upon which international agreement had been reached. Advances during and since World War II, however, have necessitated the current process of revision, work in which the United States, previously inadequately represented, is taking an active part.
Ultraviolet; UV; UVC; UVGI; HVAC; ductwork; mold; fungus; effectiveness; microbial; dose; irradiance; reflectance; bacillis; aspergillis
An investigation of the published results of heat transfer studies for both natural convection and crossflow forced convection is conducted. It is found that the wide dispersion in the experimental data for the heat transfer from smooth circular cylinders can be attributed to various factors associated with the experiments. Natural convection in horizontal and inclined cylinders is considered. The cases of a cylinder with cross flow and of a yawed cylinder are investigated in connection with studies involving forced convection.
A single comprehensive equation is developed for the rate of heat and mass transfer from a circular cylinder in crossflow, covering a complete range of Pr (or Sc) and the entire range of Re for which data are available. This expression is a lower bound (except possibly for RePr (less than 0.2); free-stream turbulence, end effects, channel blockage, free convection, etc., may increase the rate. The correlating equation is based on theoretical results for the effect of Pr in the laminar boundary layer, and on both theoretical and experimental results for the effect of Re.
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
Heat transfer and fluid flow phenomena involved in a cylinder in crossflow are described and explained using both experimental and analytical techniques. Specific cases of various fluids, ranging from air to water, transformer to aviation oil, are analyzed and correlated over a wide range of Reynolds and Prandtl numbers. The effects of physical properties, temperature difference, heat flux direction, viscosity, free-stream turbulence, and blockage factor on both local and average heat transfer for circular and elliptic cylinders are among the topics considered. Usually proprietary data is presented throughout which is applicable to every area of engineering that uses the cylinder either as a conduit for the coolant or heating fluid or as a thermal entity reacting with an ambient medium.
Ultraviolet air disinfection
- CIE
- CIE
ASHRAE Standard 62.1-2007: ventilation for acceptable indoor air quality
- ASHRAE
- ASHRAE
- Philips
Philips. Personal communication with J. Boch. 2007.
Estimating the effects of ambient conditions and aging on the performance of UVGI air cleaners
- J Lau
- W Bahnfleth
- J Freihaut
Lau J, Bahnfleth W, Freihaut J. Estimating the effects of ambient conditions and
aging on the performance of UVGI air cleaners. In: Proceedings of sixth indoor
air quality. Sendai, Japan: Ventilation & Energy Conservation in Buildings;
2007. p. 563-70.
UV Purification -Application Information
- Philips
Philips (2005) "UV Purification -Application Information" Philips
Properties data sheet of transparent fused Quartz
- Saint
Saint-Gobain_Quartz. Properties data sheet of transparent fused Quartz. 2003.
2: method of testing general ventilation air-cleaning devices for removal efficiency by particle size GA: American Society of Heating, Refrigerating and Air-Conditioning, Engineers, Inc.; 1999. Fig. 14. Supply air flow rate and UVGI device output for example application Case 2
- Ashrae Ansi
ASHRAE. ANSI/ASHRAE standard 52.2: method of testing general ventilation air-cleaning devices for removal efficiency by particle size. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning, Engineers, Inc.; 1999. Fig. 14. Supply air flow rate and UVGI device output for example application Case 2. J. Lau et al. / Building and Environment 44 (2009) 1362–1370
UV purification -application information. Philips
- Philips
Philips. UV purification -application information. Philips; 2005.
Defining the effectiveness of UV lamps installed in circulating air ductwork
- Arti
ARTI (2002) "Defining the Effectiveness of UV Lamps Installed in Circulating Air Ductwork"
ARTI-21CR/610-40030-01.
Heat Transfer of a Cylinder in Crossflow
- A Zhukauskas
- J Ziugzda
A. Zhukauskas and J. Ziugzda (1985) "Heat Transfer of a Cylinder in Crossflow", published by
Hemisphere Publishing Co.
Supply air flow rate and UVGI device output for example application Case 2
- Fig
Fig. 14. Supply air flow rate and UVGI device output for example application Case 2.
International Lighting Vocabulary
- Cie
CIE (1987) "International Lighting Vocabulary" Joint publication International Electrotechnical
Commission/International Commision on Illumination CIE 17.4 -1987.
Personal communication with J. Boch
- Philips
Philips (2007) "Personal communication with J. Boch."