Development of the indoor air quality index for commercial buildings in Hong Kong

Abstract

Like most of the developed countries and metro area in the world, people spent most of their lifetime working in the indoor environments with mechanically ventilation facilities. The human exposure on various air pollutants changed its importance in nature from the outdoor origin to indoor. While the indoor environment was actually a confined space where air pollutants might not be able to dilute itself or exhausted to the adjacent environment effectively, the indoor air quality could only be controlled by either source management or relied on the performance of the ventilation system. As some of the ail pollution sources were basically originated from the building envelop that could not be removed or hard to mitigate, the remaining questions were how the indoor air quality be smartly monitored and how the information could be implemented for the system control to achieve the best air quality delivery. As indoor air pollutants were from various sources and with different nature, just to perform a representative measurement and label them with a representative standard guideline for health concern was considerably a difficult task. In search of the problems and the possible mitigation measures, the Hong Kong Environmental Protection Department HKEPD conducted an extensive indoor air quality consultancy study in 1995. The objective of the study was to evaluate the existing IAQ condition in typical commercial buildings in Hong Kong and to establish a realistic guideline for the building related industry to comply. From the results of the study, it was observed that most of the building was under-ventilated and the accumulation of indoor air contaminants was common and worth further investigation to avoid any possible hazardrous scenario. Based on the results, the HKEPD issued a draft document named "Guidance Note for the Management of Indoor Air Quality in Offices and Public Places" (GN) in l997 for public comment. The GN illustrated the common indoor air pollutants and their nature suggested with appropriate measurement methods. In reference with some international air pollutants exposure 1imits, the GN introduced a classification of IAQ in offices and public places with respect to three levels objectives, where level 1 represented a prestigious environment, level 2 represents a health and well maintained environment and level 3 was an acceptable work place in the sense of occupational safety. Although the GN laid out the guideline for the 12 parameters of air pollutants and thermal condition to be measured, it did not show clearly how these measurements and monitoring could be performed in such an intensive manner. To earn the credit from the EPD, the industry was in need of a simplified method on IAQ monitoring so that they could easily perceive the condition of the building premises and apply appropriate mitigation measures to finally achieve the honorable certification in a cost effective way. In order to participate in the certification program, an intensive IAQ measurement on 12 parameters for 8 hours per location was required. Such kind of operation involved large amount of survey instruments and required sophisticated knowledge that most of the traditional building services engineers might not be acquainted. The involved applications, calibration, regular rnaintenance, interpretation of data and the on site operation of the equipment would have already induced major difficulties to the building operators. The worst scenario of all was that the outcome of the measurement might not even be applicable to represent the real situation of the building environment since just the interpretation of data already required some experienced operators and supplementary data to go along with it. It implied that the operation cost for the fulfillment of the certification program was expensive and reluctant to some building managements. In view of these difficulties, a comprehensive survey, as this thesis based on, in compliance with the requirement stated in the GN has been performed to evaluate the IAQ condition in 120 commercial premises. The survey was performed not just to over view the IAQ conditions in these premises but also to evaluate the difficulties, the inadequacy and the representation of the involved measurement procedure. With such experience and the acquired results, a further in depth study was performed to develop a new IAQ index that was composed with fewer measurement parameters so that the evaluation of the IAQ condition in commercial buildings cou1d be more cost effective and spontaneous. From the measurement results determined from the 120 locations, it was observed that most of the premises fulfill the level 2 objective, about 15% exceeded the objective with some of the parameters, like the TVOC and airborne bacteria exceeded very much from the guideline suggested in the GN. All of the data was analyzed statistically and the most dominating parameters were extracted with respect to their variance in the results among all 120 sampling points and their ease of measurement comparatively among the other parameters, From which, the 12 parameters were reduced to 3 parameters that represented three major pollution sources namely the outdoor, human activity related and the building materials sources. These 3 parameters were defined as Carbon Dioxide, TVOC and the RSP. With respect to the suggested classification on IAQ condition in the GN, the 120 points measurement results on the 9 pollutant parameters were manipulated to form an IAQ index by a weighted factor method. In contrasts, the simplified measurement results of the three selected parameters were used to form another IAQ index with the same method. The two indexes were compared by linear regression. The results revealed that the three selected parameters could closely represent the situation determined by the full set 9 parameter measurement. The newly developed IAQ index was formed in a scale that 100 represented level 1 condition, 250 represented level 2 condition. For those beyond 250, it represented that it did not fulfill the certification program and require further survey and mitigation measures. Since all three selected parameters could be measured in a relatively easy to handle way by handheld electronic equipment. Linking the results to central management systems for on-line monitoring, could facilitate the central building management system for demand control ventilation and safety control facilities that lead to a more intelligent, energy conservative and cost effective way of management.