1、 Shiyu Rao is a graduate student in the Department of Architectural Engineering, Penn State University, University Park, PA. Donghyun Rim is an assistant professor in the Department of Archiectural Engineering, Penn State University, University Park, PA. Evaluating Air-side Economizer Use in Particu
2、late Air Pollution in Office Buildings in Multi-million Cities Shiyu Rao Donghyun Rim, Ph.D. Student Member ASHRAE Associate Member ASHRAE ABSTRACT Ambient particulate matter (PM) and ozone are critical to human health and well-being given their association with increased respiratory and cardiovascu
3、lar mortality. For urban office buildings in big cities, the use of economizers have been dramatically increased recently for energy saving and ventilation purposes. The objective of this paper is to examine outdoor-indoor transports of ozone and PM2.5 (particles smaller than 2.5 micron in diameter)
4、 for urban office buildings utilizing economizer operating modes. This study employs multi-zone contaminant transport model (CONTAM) for the prediction of outdoor-indoor pollutant dynamics in two cities: Los Angeles and Beijing. The model simulates infiltration of ambient ozone and PM2.5 into a DOE
5、reference building (medium office) based on outdoor climate condition, outdoor intake, and filtration efficiency. Seasonal variations are considered to capture the influences of high ozone levels during the summer in LA and elevated particle concentrations during the spring season in Beijing. The st
6、udy results show that outdoor-indoor pollutant transport varies significantly according to the ambient concentration, outdoor weather, season, and ventilation conditions. The indoor concentrations of ozone and particles in both cities are often higher than US EPA and WHO standards, implying that bui
7、ldings are a critical domain of air pollution control in big cities for reduction of human exposure to ambient air pollutants. The results of this study suggest that economizer flow rate and filtration efficiencies have significant influence on particulate matter transport and indoor concentrations.
8、 Comparisons between representative cities provide insights into particle entry into building under various weather and operation scenarios and strategies to maintain good indoor air quality in big polluted cities. INTRODUCTION . Human exposure to ambient ozone and particulate matter (PM) adversely
9、affect human health and well-being. Respiratory and cardiovascular mortality have been shown to increase in urban areas due to air pollution. In addition, the buildings consumes almost 41% of overall annual energy consumption in the US according to the annual report released by Department of Energy.
10、 The air-side economizers aimed at reducing energy usage and increasing ventilations have introduced to HVAC design and green building applications However, ambient ozone and particles can penetrate into buildings via economizer air paths influencing indoor air quality and inhalation exposure of occ
11、upants. According to epidemiological studies, mortality of lung cancer and myocardial infarction elevates in area of high ambient PM2.5 (particle diameter 2.5 micron in diameter) concentrations (Brook et al.2006). Furthermore, young adults exposed to high-level ozone have higher risks in acute arter
12、ial vasoconstriction (Jerrett et al. 2009). The objective of the study is to examine transports of ambient ozone and PM2.5 into urban office buildings considering outdoor air pollution and ventilation operating modes. METHODOLOGY In this study, the multi-zone contaminant transport model (CONTAM) is
13、employed for predicting outdoor-indoor pollutant dynamics in two metropolitan cities: Los Angeles and Beijing. These cities are selected based on degraded outdoor air quality and potential health implications for large populations (Hu and Jiang 2014). The CONTAM model built on a DOE reference buildi
14、ng (medium office) simulates infiltrations of ambient ozone and PM2.5, considering outdoor climate conditions, outdoor air fractions, and filtration efficiency (Ng et al. 2013). Building Description A medium-sized DOE reference office building is used to evaluate the indoor concentrations of ozone a
15、nd PM2.5 of outdoor origin. The modeled building contains 3 floors; each floor has an independent air handling unit (AHU) to serve all zones. A total of 6 zones are created per occupied floor. Restroom, elevator and stairs are separated from core zone in CONTAM (Ng et al. 2013).The common building s
16、ystems characteristics and other inputs are summarized in Table1. Another essential input utilized in simulation is deposition rates (h-1) of contaminants. The deposition rates of ozone and PM2.5 used in to this simulation are 4 h-1 and 0.5 h-1, respectively. (Ng. et al. 2013). And an associated sin
17、k model is employed to evaluate concentrations of ozone and particle for deposition onto indoor surfaces. Table 1. Modeled Building Charateristics Charteristics Inputs Total Area No. of CONTAM Zones 4982 m2 23 HVAC System Air Tightness at 4 Pa VAV 1.37 x 10 -4 m3/s/m2 Room Temperature Setting 20C Ou
18、tdoor Air Fraction 10% Filter Not installed Maximum Occupancy 52.39 Schedules 24/7 CONTAM Simulations A CONTAM model is developed to analyze air flows based on wind pressure and indoor-outdoor temperature differencs. The studied office buildings are set to locate in Changyang district, Beijing and G
19、lendoral-Laurel, Los Angeles County, where outdoor concentrations of ozone and PM2.5 are relatively higher than nearby regions. The hourly data of pollutant concentrations are acquired from the US Embassy in Beijing, and California Air Resource Board (CARB). Investigations of outdoor air intake rate
20、s and filtration efficiency are conducted to evaluate the sequential influences on ozone levels and PM2.5 that transport into building through an economizer. Assessments and parametric results analysis considering building air flow rates between Beijing and Los Angeles via varying efficiency of buil
21、t-in filter and seasons are presented in the following sections. RESULTS AND DISCUSSIONS This section consists of four major parts: 1) comparisons of ambient PM2.5 concentrations in Los Angeles and Beijing, 2) ozone concentrations in winter and summer in Los Angeles, 3) indoor PM2.5 concentration th
22、rough changing filter efficiencies of AHU, and 4) relationships between fractions of recirculation air and indoor contaminants concentrations. Ambient PM2.5 Concentrations in Los Angeles and Beijing Figure 1 presents outdoor PM2.5 concentrations in Beijing and LA during January, March, and July. The
23、 concentration reaches its daily peak between 11:00 am and 3:00 p.m. In Beijing, the concentration of PM2.5 in winter surpasses summer and spring seasons, and reaches the peak value in the middle of January. This trend is mainly caused by the lower air temperature close to the land cover that drives
24、 ambient particulate matter to lower regions of atmosphere. Moreover, PM2.5 concentration in Beijing is higher during March than July (Figure1a). Due to rised temperature and air mixing of fine particles, PM2.5 concenstration decreases significantly in summer. Figure 1b displays concentrations of PM
25、2.5 in Glendoral-Laurel, Los Angeles based on CARB database, which are 10 times lower than Beijing. In July, the aveage concentration of Beijing is 110.54g/m3, while the average concentration is 11.9g/m3 in Los Angeles. Hence, the results imply that Beijing are confronted with more challenges of hig
26、h concentrations of particulate matter, especially in cold seasons that pose threats on human respiratory health. Figure1 (a)PM2.5 concentraion of Beijing and (b) PM2.5 Concentration of Los Angeles Outdoor Ozone Level of Los Angeles Given the detrimental effects of ozone on the human cardiovascular
27、system and mortality rate (Brook, et al), examinations of ozone levels in Los Angeles are conducted through CONTAM. The deposition rates of ozone keeps at 4 h-1, and system does no have filters installed during the simulations. Figure 2 summarizes the simulation results of outdoor and indoor ozone c
28、oncentrations. Ozone level in Los Angeles fluctuates more intensively and oscillates in larger amplitude in summer. Despite the concentration differences, ambient and indoor ozone levels follow the similar pattern shown in Figure2. In this simulation, the percentage of the outdoor air is maintained
29、at default level, which is listed in Table 1. Results in figure 2(b) reveal that 40% decreases in winter and at least 50% decrease in summer compared to the original outdoor concentrations. Transport of ozone through infiltration and ventilation, especially in the summer season, illustrates that the
30、 controlling of indoor ozone level is another practice to maintain indoor air quality. It would be beneficial for cities under high ozone exposure, to employ an ozone filter in the economizer to reduce the mortality of cardiovascular diseases while saving energy. Figure2 (a) Outdoor ozone concentrat
31、ions in Los Angeles, and (b) Indoor simulated ozone concentrations of Medium Office in Los Angeles Impacts of AHU Filter Efficiency Beijing is selected as a target city to evaluate influences of AHU filter efficiency because of high ambient PM2.5 concentraitions. In this section, particle concentrat
32、ions of indoor environement are explored by varying AHU filter efficiencies and fraction of outdoor air. Figure 3 and 4 show simulated indoor concentrations of ambient PM 2.5 that transports into reference building under three difference circumstances. According to ASHRAE 52.2, MERV 8(30% to 35% eff
33、iciency) and 11(60% -65% efficiency) are typical selection of filters for commercial buildings. Performance of MERV 11 in capturing fine particles with a diameter range of 1 -10 micrometers surpasse MERV8. Hence, two single pass and simply constant efficiency filters with efficiency of 30% and 60% a
34、re created to assess impacts and importance of installing particulate filters for commercial buildings. It is assumed that two filters are working in 24/7 schedules. Additionally, AHU without filters can assist in reducing transports of PM2.5 by controlling percentage of outdoor air intake. In this
35、simulation, where the outdoor air schedule is designated to be 10% and 30% separately, the level of indoor PM2.5 is dramatically lowered compared with the original outdoor level. The consequences of altering efficiency of filter to 30% and 60% only present less than 30% reduction on average of indoo
36、r particles concentration. In most cases, due to indoor particle deposition and filtration, indoor concentrations are lower than the original outdoor concentrations. However, with regards of heavy polluted cities, such as Beijing, small percentages of outside air intake is not sufficient to ensure i
37、ndoor air quality. In January, even with 10% outdoor air, indoor PM2.5 concentrations are much higher than US EPA ambient PM2.5 standard (35 g/m3). AHU operating with additional filters would be required to control movements of particulate particles through mechanical ventilations. Figure3 Indoor PM
38、2.5 concentrations (w/ 10% outdoor air and 90% recirculated air) in the DOE reference medium office building in Beijing: a) Jannary b) March, and c) July Figure4 Indoor PM2.5 concentrations (w/30% outdoor air and 70% recirculated air) in the DOE reference medium office building in Beijing: a) Jannar
39、y b) March, and c) July. Table 2 lists reductions of PM2.5 in core zone under four scenarios compared to no filter situation, but same fraction of outdoor air. For any combination of filter selection and percentage of outdoor air, performances in July precede the other seasons. High efficency filter
40、s and more outdoor air intake casuses performance improvements to excel in reducting movements of comtaminants through ventilation. Table 2. Contaminants Reduction of Changes of Filters and Outdoor Air Fraction Filter/Outdoor Air Jan Mar Jul 60%Efficiency/10%OA 19.26% 27.71% 49.51% 30% Efficiency/10
41、%OA 9.63% 13.86% 33.07% 60% Efficiency/30%OA 37.28% 44.80% 56.71% 30% Effiicency/30% OA 18.64% 22.40% 28.35% Table3 lists the average PM2.5 concentrations of the whole scenarios simulated in Table2. Though more fraction of outdoor air brings about better improvements, less outdoor air causes lower i
42、ndoor concentrations of PM2.5. in absolute value. That is, the least concentration of PM2.5 in core zone appears if only 10% outdoor air cooperates with 60% efficiency filter. Hence, overall air quality of indoor spaces can be improved by control of outdoor air intake and selection of filters in dif
43、ferent seasons. Table 3. Average Indoor PM2.5 Concentration Comparison Matrix (Units: g/m3) Filter/Outdoor Air Jan Mar Jul 60%Efficiency/10%OA 50.26 37.95 11.88 30% Efficiency/10%OA 60.59 44.95 17.66 No Filter/10% OA 66.92 51.95 23.44 60% Efficiency/30%OA 50.73 38.70 19.58 30% Effiicency/30% OA 65.5
44、7 54.20 32.40 No Filter/30% OA 80.42 69.70 45.22 Outdoor Concentration 118.77 110.54 89.62 Recirculation with 30% Outdoor Air Building operations are one of essential factors of introduction of outdoor contaminants to the indoor environment. An exploration of fractions of recirculated and outdoor ai
45、r is conducted via CONTAM and the results are presented in following paragraphs. The AHU developed in CONTAM is controlled by flow controller, which consists of three components: flow control, building pressurization and fraction of outdoor air. In this simulation, only modify input values of flow r
46、ate controller from 0.1 to 0.3 to investigate consequences of 30% outdoor air. Figures 5 and 6 demonstrate indoor particulate concentrations of Beijing and ozone levels in Los Angeles of core zone under the scenarios of 10% and 30% outdoor air. As presented in the figure 5, the rises of fraction of
47、outdoor air result in increased concentrations of PM2.5 transport to core areas through the air handling system and distribution system. Besides, cities discussed in this paper, where the base productions of ozone and PM2.5 are higher than WHO and EPA standards. The results of ozone levels in Los An
48、geles shown in Fig6 conincide with trends of PM2.5 concentrations in Beijing, the Ozone level rises as more outdoor air introduced into AHU. Conversely, the curves of ozone levels overlap in spite of seasonal variations, and only differ in curve amplitudes. Therefore, percentages of outdoor air is t
49、he main source of indoor air pollution and a critical factor of reducing human exposures and health risks due to exposure. Figure 5 (a) 30% Outdoor Air in Jan of Beijng, (b) 30% of Outdoor Air in Mar of Beijing, and (c) 30% of Outdoor Air in July of Beijing. Thus, control of outdoor air fraction and correct selection of air handling system is a feasible and valid strategy in the summer season to maintain fine indoor air quality. Nevertheless, the amount of outdoor air is an effective source for saving process energy and it supports operation of building HVAC system andit is exemplif
