INDOOR AIR QUALITY AND ENERGY EFFICIENCY IN THE DESIGN OF BUILDING SERVICES SYSTEMS FOR SCHOOL CLASSROOMS

Transcription

1 INDOOR AIR QUALITY AND ENERGY EFFICIENCY IN THE DESIGN OF BUILDING SERVICES SYSTEMS FOR SCHOOL CLASSROOMS KL Tam * Architectural Services Department, the Government of Hong Kong Special Administrative Region, Hong Kong, China ABSTRACT Efficient energy utilization and indoor air quality (IAQ) inside office premises and other public places have become issues of increasing concern in the Hong Kong Special Administrative Region (HKSAR). The Government of HKSAR has launched a territory wide consultation in 1999 on the proposed Indoor Air Quality Management Programme for offices and public places. This paper briefly introduces the proposed Indoor Air Quality Management Programme and its proposed target objectives. It also outlines the design approaches taken to tackle the issues both from maintaining good air quality and energy efficient usage in school classrooms. There are approximately 1,200 public sector primary and secondary schools in Hong Kong, and each year around 20 new schools will be added to the list. Achievements including indoor air quality, lighting, thermal comfort and energy efficiency in classrooms will be presented. INDEX TERMS IAQ, Energy efficiency, Schools, Lighting, IAQ Management Programme. INTRODUCTION In early 70s, in response to the oil crisis, the ventilation rate had once been drastically reduced to as low as 2.5 l/s/person. Nevertheless, public sector buildings in Hong Kong had generally been designed to 7 l/s/person. This reduced and inadequate fresh air ventilation is often cited as the most significant cause of indoor air quality problems affecting the existing airconditioning building stock. In recent years, apart from energy efficiency, indoor air quality has also become an issue of increasing concern all over the world. Governments and their people are more concerned about the health hazard imposed by poor indoor air quality. Thus, various guidance notes have been issued and management programmes launched to facilitate the maintenance of good indoor air quality. In Hong Kong, a set of draft Guidance Notes for the Management of Indoor Air Quality in Offices and Public Places under the proposed Indoor Air Quality Management Programme was published in November 1999 for consultation. Most commonly, good indoor air quality requires control of airborne pollutants and introduction of adequate outdoor air to dilute indoor contaminants. Apparently, the latter measure would require more energy to treat (to clean, cool/heat and humidify/dehumidify) and distribute the increased amount of outdoor air into the room, thus the energy consumption of the heating, ventilation and air-conditioning (HVAC) system would significantly increase and the total energy efficiency performance of the HVAC system would degrade. However, this is not necessarily true. A case study of new school classrooms in Hong Kong is used to illustrate that, through appropriate design approaches, it is possible not only to fulfil the * Contact author tamkl1@archsd.gov.hk 661

2 apparently conflicting requirements of good indoor air quality and energy efficient HVAC system, but also to achieve other environmental conservation measures relating to lighting, thermal comfort and overall energy efficiency. METHODS This paper will briefly introduce the proposed Indoor Air Quality Management Programme launched in Hong Kong and its proposed target Indoor Air Quality Objectives. It is then followed by a case study on the design of new school classrooms in Hong Kong to illustrate how indoor air quality and energy efficiency can be tackled simultaneously to give a healthy, comfortable and sustainable built environment. INDOOR AIR QUALITY MANAGEMENT PROGRAMME To address the increasing public awareness about the issue of indoor air pollution, the Government of HKSAR launched in 1999 a public consultation on the proposed Indoor Air Quality Management Programme which is aimed to protect the health of the public in indoor environment and to promote public awareness of the importance of indoor air quality. The programme started with a publicity campaign to raise public awareness of indoor air quality and an Indoor Air Quality Information Centre to disseminate indoor air quality information, to be followed by a voluntary Indoor Air Quality Certification Scheme to invite owners and management of premises to participate in the Scheme. While the Scheme has yet to be finalized, the Government has taken the lead to adopt the proposed set of 2-level Indoor Air Quality Objectives as a common benchmark for evaluating and assessing indoor air quality of government buildings, as follows: - Level 1 represents very good indoor air quality that a high-class and comfortable building should have. Level 2 represents the indoor air quality that provides protection to the public at large including the very young and the aged. Table 1 lists out the indoor air quality parameters and their proposed 2-level Indoor Air Quality Objectives. For office buildings and public places, building owners and management of these premises as well as employers should endeavour to achieve at least Level 2 of the proposed Indoor Air Quality Objectives as their desired target. Table 1. Recommended Indoor Air Quality Objectives for Office Buildings and Public Places in Hong Kong Parameter Unit 8-hour average Level 1 Level 2 Carbon Dioxide (CO 2 ) ppm <800 <1,000 Carbon Monoxide (CO) g/m 3 <2,000 <10,000 Respirable Suspended Particulates (RSP) g/m 3 <20 <180 Nitrogen Dioxide (NO 2 ) g/m 3 <40 <150 Ozone (O 3 ) g/m 3 <50 <120 Formaldehyde (HCHO) g/m 3 <30 <100 Total Volatile Organic Compounds (TVOC) g/m 3 <200 <600 Radon (Rn) Bq/m 3 <150 <200 Airborne Bacteria cfu/m 3 <500 <1,000 Temperature o C <25.5 Relative Humidity % <70 Air Movement m/s <0.2 <

3 MEANS TO ACHIEVE INDOOR AIR QUALITY OBJECTIVES IN NEW SCHOOL CLASSROOMS Though the proposed Indoor Air Quality Certification Scheme is specifically developed for office buildings and public places with totally enclosed areas provided with mechanical ventilation and air-conditioning, we are looking into the feasibility to comply with the recommended Indoor Air Quality Objectives in Table 1 for new schools whenever practicable. Indoor Air Quality Objectives in those new school classrooms which are air-conditioned could be achieved through the followings: - Source control Low-emitting building components and finishes such as solid polymer worktops, wooden cupboards faced with plastic laminates and water-based paints have been carefully selected by the architects to reduce the generation of contaminants like volatile organic compounds (VOCs) from within the occupied space. Dilution ventilation Adequate outdoor air is provided to dilute the polluted indoor air. ASHRAE (American Society of Heating, Refrigeration and Air-Conditioning Engineers) Standard Ventilation for Acceptable Indoor Air Quality stipulates under its Ventilation Rate Procedure that in order to achieve acceptable indoor air quality in school classroom, the required rate of outdoor air of prescribed quality is 8 l/s/person (ASHRAE, 1999). Air cleaning Particulate filters are provided to remove particulate contaminants from both the outdoor air and recirculated air streams before they enter into conditioned space. ENERGY EFFICIENT DESIGN INTEGRATED WITH INDOOR AIR QUALITY OBJECTIVES Hong Kong is a densely populated city with very limited land resources. Thus it is not uncommon to find schools located in urban areas and surrounded by heavy traffic. In Hong Kong, it is government policy to provide noise mitigation measure in the form of window insulation and air-conditioning to those school classrooms which are adversely affected by traffic noise. In the current design, split-type air-conditioners are provided to noise-affected classroom and sufficient amount of outdoor air meeting ASHRAE Standard is also provided. In order to minimize the cooling/heating load from this outdoor air, air-to-air totalenergy fixed-membrane heat exchangers are provided in the classroom to recover the total (i.e. sensible and latent) heat from the exhaust air and to add it to the outdoor air. In summer, the hot and humid outdoor air is fed into the room after having been pre-cooled and predehumidified to a condition close to the indoor air; and similarly in winter, the cold and dry outdoor air is fed into the room after pre-heated and pre-humidified. As a result, the cooling load from outdoor air is reduced by 60% and the cooling or heating capacity of the airconditioners is reduced by 25%. OTHER ENVIRONMENTAL CONSERVATION ACHIEVEMENTS Environmental conservation in the built environment is a major design consideration. Apart from maintaining good indoor air quality, effort has also been made to achieve qualitylearning environment for students and teachers, such as good lighting and thermal comfort, at an energy efficient manner as follows: - 663

4 Lighting As school curriculums in Hong Kong become more information technology (IT) oriented, the lighting in classroom has to suit the visual environment required for display screen equipment (DSE). This is achieved, after taking due consideration of the advice given in CIBSE (The Chartered Institute of Building Services Engineers, UK) Lighting Guide 3: The Visual Environment for Display Screen Use (CIBSE, 1996), by the use of Category 2 fluorescent luminaires. It addition, the lighting system is energy efficient. Its components, the luminaires, T-5 fluorescent lamps and electronic ballasts, are all energy efficient products of the latest technologies. Furthermore, daylight dimming through the use of photo sensors and dimmable electronic ballasts is adopted for the row of lighting in parallel and adjacent to the windows so as to maximize the use of daylight in the classroom. Thermal comfort To minimize direct solar heat gain and consequently total cooling load, the school building is orientated as far as practicable with major facades facing north south direction and the building envelope is carefully designed so as to achieve an overall thermal transfer value (OTTV) of less than 18 W/m 2, which is well below the statutory limit of 30 W/m 2 in Hong Kong. Natural ventilation in classroom is enhanced by elevated school building design, large openable windows and sun-shading feature offered by the wide access balcony on one side and the a/c platform on the other side of classroom. For traffic noise-affected classrooms which are deprived of natural ventilation due to window insulation requirement, their occupants thermal comfort is not compromised. Cooling in summer and heating in winter is provided either by means of split-type air-conditioners or variable refrigerant volume (VRV) air-conditioning system with frequency inverter control for energy saving, both operated with environmentally friendly refrigerant which is chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) free and has zero ozone depletion potential (ODP). Of course sufficient outside air is provided to these classrooms through heat-recovery ventilators as described earlier. RESULTS Indoor air quality measurement was taken in a typical air-conditioned classroom of a new school. The measurement was taken when the classroom was occupied. The parameters measured are carbon dioxide, carbon monoxide and respirable suspended particles and the result is shown in Table 2. Table 2. Measured Indoor Air Quality Values of a Typical Air-Conditioned New School Classroom Parameter Unit Measured Value (8-hour average) Carbon Dioxide (CO 2 ) ppm 690 Carbon Monoxide (CO) g/m 3 1,198 Respirable Suspended Particulates (RSP) g/m DISCUSSION The result shown in Table 2 reveals that amongst the parameters measured in a typical airconditioned new school classroom, carbon dioxide and carbon monoxide can meet Level 1 whilst RSP can meet Level 2 of the proposed Indoor Air Quality Objectives. 664

5 CONCLUSION AND IMPLICATION From the above discussion, it can be demonstrated that through proper design and suitable selection of equipment, it is possible to integrate both the indoor air quality and energy efficiency together to provide a reasonably healthy, comfortable and sustainable built environment for schools. It also illustrates the general approach which might be applicable for other types of buildings. REFERENCES ASHRAE ASHRAE Standard , Ventilation for Acceptable Indoor Air Quality, Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. CIBSE CIBSE Lighting Guide 3, The Visual Environment for Display Screen Use, London: Chartered Institution of Building Services Engineers. 665