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Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Building and Environment, Volume 67, September 2013, Pages 193–201
In-duct ultraviolet germicidal irradiation (UVGI) systems treat moving air streams in heating, ventilation, and air-conditioning (HVAC) systems to inactivate airborne microorganisms. UVGI system performance and costs to implement and operate the system depend greatly on the output of the UV lamps and the exposure time, which are affected by the temperature and the velocity of the air passing through the UVGI device. The type of HVAC system, the installation location of the UVGI device, and the climatic location of the building all have an impact on the air temperature and velocity the device experiences at a given time. The effects of installation location and climate were investigated using simulation of an in-duct UVGI device installed in a cooling-only VAV system operating in a hypothetical commercial building. The studied device was investigated at locations both upstream and downstream of the cooling coils of the VAV system in three climatically distinct U.S. locations. The results of the six resulting scenarios indicate that UVGI devices installed upstream of the cooling coils provide comparable if not better performance than those installed downstream. The results demonstrate the impact on performance and cost of the dynamic environment that a UVGI device could experience. It can also be observed that the generated heat of UVGI devices has a great impact on cooling and heating loads, and thus affects the overall operating cost.
Transmission of respiratory diseases by airborne pathogens is a major problem of indoor air quality (IAQ). Droplet residues generated by talking, coughing and sneezing can be suspended in the air for hours, entrained into HVAC ductwork, and distributed throughout a building . In-duct UVGI systems have been demonstrated to be an effective means to combat microbial contamination in AHU . In-duct UVGI systems can also be deployed to treat air streams as they pass through HVAC ductwork, and potentially reduce the respiratory diseases that are transmitted through the ductwork. Since air is being recirculated a number of times, an overall increase in removal rate is expected for in-duct air disinfection as compared to single pass system . This paper will focus on the performance and economics of in-duct UVGI system in treating air streams by taking the dynamic environmental conditions as experienced in the AHU of the VAV system into consideration.
نتیجه گیری انگلیسی
The results of this study show that both air temperature and air velocity play important roles in determining the UV dose delivered by a UVGI device through their influence on lamp output and residence time. The temperature at the supply air location (downstream of the cooling coils) was stable and in general much colder than at the mixed air location (upstream). Lamp output therefore may be much higher at the mixed air location most of the time. Due to higher lamp output, inactivation efficiency is also higher at the mixed air location in systems of this type. Therefore, a lower space concentration (for the presented hypothetical example) can be achieved at the mixed air location, since the airflow rate is exactly the same as that of the supply air location. As a result, a UVGI installation at the mixed air location costs less than one at the supply air location, and provides comparable if not better performance for all of the six scenarios studied in this paper. The performance of future UVGI system shall be studied with the help of simulation on a case-by-case basis. Current practice generally considers the rated power of the UV lamps as the total energy consumption without recognizing the impact of the heat generated by the UV lamps on the HVAC system. The generated heat has to be investigated with its impact on cooling, heating, and fan. Energy consumption studied in this paper suggests that the impact on the HVAC system is too significant to be ignored. An integrative investigation shall be performed by incorporating the UVGI system design with building energy simulation.