Cooling energy evaluation for high-rise residential buildings in Hong Kong

Based on the design of a typical high-rise public housing block in Hong Kong, the dependence of space cooling loads of residential flats on the constructions of external walls and partitions, and the location of thermal insulation layer in the walls and partitions, was studied by detailed simulation. The results show that insulating the envelope and the partitions would be effective in reducing the yearly space cooling load, by up to 38%, but could either increase (by up to 19%) or reduce (by up to 16%) the peak cooling demand, depending on the number and positions of insulation layers in the walls. Reducing the thermal capacity of the envelope and partitions (e.g. by reducing their thickness) would lead to large increases in the peak cooling demand, by more than 60% in the extreme case.     

Benchmarking Hong Kong and China energy codes for residential buildings

Mandatory energy codes to curb energy use of residential buildings have been formally launched in China for more than two decades but little has been publicized in literature. Similar codes are not available for residential buildings in Hong Kong, but most residential buildings in Hong Kong, especially public housing estates, are HK-BEAM certified to demonstrate their compliance with regulatory and basic design requirements. Given HK-BEAM is internationally recognized and there are doubts about the effectiveness of the China codes, how the energy efficiency of the HK-BEAM certified buildings compare with buildings in compliance with the China codes is of interest to most building designers and policy makers. This paper describes how the energy efficiency of a case study building in compliance with the China codes compare with the one in compliance with HK-BEAM. The energy simulation by HTB2 and BECRES reveal that the case study building in compliance with the China codes is 51.1% better in energy use. In the study, the relative impact of each compliance criterion on energy use and cooling load has been quantified by sensitivity analysis. The sensitivity values indicate that energy use is most sensitive to air-conditioning operation hours, indoor design temperature, coefficient of performance (COP) of the room air-conditioners (RAC) units, and the envelop characteristics. The results of this study indicate that a HK-BEAM certified building cannot satisfy the China codes requirements. This provides good reference to the policy makers, the building owners, and to the China and Hong Kong Governments when considering reciprocal recognition of building energy codes.     

A study of energy efficiency of private office buildings in Hong Kong

A benchmark study of the energy efficiency of private office buildings in Hong Kong was conducted in 2002 because energy efficiency was declining. In the study, private office buildings were divided into five user groups. For each group, a multiple regression model was developed to find the relationship between Energy Use Intensities (EUIs) and other factors, such as operating hours, for normalization and benchmarking purposes. In this paper we make use of the regression results to study the energy efficiency of private office buildings by different grades. In Hong Kong, office buildings are divided into three grades (A, B, and C) based on the quality of the facility, which is reflected in rental values; a Grade A office building denotes expensive luxury. We found that the EUI of Grade A office buildings is the highest, consuming over 50% of the total energy used in office buildings. Recently, the annual EUI of office buildings has improved even though Grade A floor space is increasing. This may be due to the promotion of the energy efficiency program launched in the last decade.     

京港携手共促建筑节能--记第9届北京-香港经济合作洽谈研讨会建筑节能专题研讨会

第9届北京-香港经济合作洽谈研讨会于11月28日在北京隆重召开，京港两地的政府官员、工商业人士就加强经济合作进行了广泛交流。会议分别就城市规划、交通、环保、建筑节能、环卫管理和防洪减灾控制5个方面进行了专题研讨。其中建筑节能专题是京港合作的新领域，因而受到了广泛关注。在此项专题研讨会上．京港两地代表在正在编制以建设资源节约、环境友好型社会为重要目标的“十一五”规划的背景下，对城市建设与管理中的建筑节能问题进行了充分交流。     

Advancement of solar desiccant cooling system for building use in subtropical Hong Kong

The solar desiccant cooling system (SDCS) had a saving potential of the year-round primary energy consumption as compared to the conventional air-conditioning system for full fresh air application in the subtropical Hong Kong. In order to further enhance its energy efficiency, advancement of the basic SDCS was carried out through a strategy of hybrid design. Six hybrid system alternatives of SDCS were therefore proposed, three for full fresh air design while another three for return air design for the building zone. Year-round performance evaluation of each solar hybrid desiccant cooling system was conducted for typical office application under different climatic and loading conditions. All the six hybrid system alternatives were found technically feasible, with up to 35.2% saving of year-round primary energy consumption against the conventional air-conditioning systems. Among the hybrid alternatives, recommendations were made on the SDCS hybridized with vapour compression refrigeration for full fresh air design; and the SDCS hybridized with vapour absorption refrigeration for return air design, since they had the saving potentials of both primary energy and initial cost. These two hybrid system alternatives used evacuated tubes, a more economical type of solar collectors compared to the PV or PVT panels.     

Outdoor design conditions for HVAC system design and energy estimation for buildings in Hong Kong

Outdoor design conditions are important for heating, ventilating and air-conditioning (HVAC) system design and energy estimation for buildings. A research study on the determination of outdoor design conditions for HVAC applications in Hong Kong is presented here. Methods for determining outdoor design conditions are examined and the existing data for Hong Kong are studied. New design data developed from the latest weather database compiled for Hong Kong are provided. The characteristics of the Hong Kong climate are studied from the 33-year long-term statistical distributions of its hourly dry-bulb and wet-bulb temperatures. Significance, properties and proper selection of outdoor design conditions for HVAC design are then discussed. It is hoped that designers can assess critically the outdoor design conditions they have taken for granted for their building design and evaluate suitable data for design weather based on their applications and risk levels.     

Influence of thermal insulation position in building envelope on the space cooling of high-rise residential buildings in Hong Kong

At the present time, thermal insulation is almost not used in fabric of tall residential buildings in Hong Kong, as their fabric slabs usually comprise concrete layer covered on each side by plaster layers. This study investigates into the influence of an existence of the thermal insulation layer in the outside walls on the yearly cooling load and yearly maximum cooling demand in two typical residential flats in a high-rise residential building by employing HTB2, detailed building heat transfer simulation software. During the investigations, the thermal insulation layer up to 15 cm thick was placed either at the inside, or at the outside, or at the middle part of the outside wall structure. Then, the concrete layer was up to 40 cm thick. The simulation predictions indicate that the highest decrease in the yearly cooling load of up to 6.8% is obtained when a 5 cm thick thermal insulation layer faces the inside of the residential flat. The highest decrease in the yearly maximum cooling demand of 7.3% is recorded when a 5 cm thermal insulation layer faces either the outside or the inside of the flat; this depends on the flat orientation. However, much weaker reductions in the yearly cooling load and yearly maximum cooling demand are found when the thickness of thermal insulation is increased above 5 cm and the thickness of concrete is increased above 10 cm.     

Energy performance of windows in high-rise residential buildings in Hong Kong

At the present time in Hong Kong in its hot and humid climate, a single pane, clear glazing is most often used in windows of tall residential buildings. During this study, we employed HTB2, detailed building heat transfer simulation software, to evaluate a decrease in the yearly cooling load (Q) and in the peak cooling-load (D) in two residential flats due to different glazing single pane types and different flat orientations. The investigated glazing types were clear glazing, tinted glazing, reflective glazing, and tinted and reflective glazing.     

An analysis of daylighting performance for office buildings in Hong Kong

Daylighting has often been recognized as a useful source of energy savings and visual comforts in buildings. Occupants expect good daylight in their working spaces. The quality and quantity of natural light entering a building depend on both internal and external factors. In Hong Kong, commercial building accounts for the major building energy use and electric lighting is one of the major electricity-consuming items. This paper studies the daylighting performance and energy implications for office buildings. A total of 35 commercial buildings have been selected in the survey. Key building parameters affecting daylighting designs are presented. Two typical office blocks were further analysed based on a lighting simulation program. The daylighting performance was evaluated in terms of daylight factor, room depth and glare index. It has been found that the daylighting performance for office buildings is quite effective. About one-third of the office areas that are near the perimeter regions have an average daylight factor of 5%. For inner region of deep plan offices, some innovative daylighting systems such as light redirecting panels and light pipe could be used to improve the daylighting performance. In general, the office building envelop designs are conducive to effective daylighting and proper daylight linked lighting controls could save over 25% of the total electric lighting use.     

Application of switchable glazing to high-rise residential buildings in Hong Kong

For typical high-rise residential building in Hong Kong, we evaluated the impact of using switchable glazing on energy use for space cooling. By using software EnergyPlus, it was found that application of switchable glazing would lead to a reduction in annual cooling electricity consumption by up to 6.6% where the actual amount depends on existence of overhangs, orientation of building wings, types and locations of rooms. Energy saving by this magnitude, however, cannot justify use of switchable glazing in residential buildings in Hong Kong, mainly because of the high glazing cost.     

Application of advanced glazing to high-rise residential buildings in Hong Kong

The energy saving that can be achieved by applying advanced glazing to a typical high-rise residential building in Hong Kong was evaluated using the simulation software EnergyPlus. It was found that application of low-e glazing would lead to a reduction in cooling electricity use by up to 4.2%. The saving due to application of low-e reversible glazing would be up to 1.9%; double-clear glazing up to 3.7%; and clear plus low-e glazing up to 6.6%. The achievable saving would depend on orientation of building wings, and type and location of rooms. The analysis suggests that for the high-rise public housing blocks in Hong Kong, the use of expensive advanced glazing would not be economically viable from the point of view of saving in cooling energy cost.     

The use of underground space in Hong Kong

In 1991, the Hong Kong Government adopted a policy of encouraging development in rock caverns, where such development is appropriate. The underground option has recently been selected for certain facilities considered environmentally unattractive for surface placement. The paper discusses technical aspects of some of the cavern schemes currently under construction. It also traces the history of cavern usage in Hong Kong and describes the Hong Kong Geotechnical Engineering Office's study of the potential use of underground space in Hong Kong.     

A survey of building envelope designs for commercial buildings in Hong Kong

Nearly 1 million m² of gross floor area is represented by the survey which identified four different building envelope designs. To enable judgements to be made on construction cost and time, a comparative study was carried out based on a 40-storey generic office building.     

香港办公建筑的环境评价方法概况

简要介绍了香港办公建筑的环境评价方法和过程，这一评价方法是参照建筑机构的环境评价方法，根据香港的具体环境条件而制定的，包括办公建筑的构造和楼宇设备系统等对全球环境，区域环境和室内环境的各种影响。     

Ventilation of air-conditioned residential buildings: A case study in Hong Kong

More and more studies reported that there were insufficient ventilation and excessive CO_2 concentration in air-conditioned residential buildings, but few solutions were provided. This study investigates the overnight evolution of CO_2 concentration in air-conditioned residential buildings and then focuses mainly on the evaluation of three ventilation strategies, including overnight natural ventilation, short-term mechanical ventilation and short-term natural ventilation. On-site measurements were conducted in a typical residential bedroom in Hong Kong in September. The indoor and outdoor CO_2 concentration, air temperature and relative humidity as well as the outdoor wind speed during the measurements were analysed. Ventilation rates were calculated based on the time series of CO_2 concentration. This study confirms that additional ventilation is usually needed in air-conditioned residential buildings. Overnight natural ventilation with even a small opening is associated with excessive energy consumption and deteriorated indoor thermal environment. Short-term natural ventilation strategies are inefficient and uncontrollable. Compared to the best short-term natural ventilation strategy, a reasonably designed short-term mechanical ventilation strategy requires only a 41% of ventilation period to complete one full replacement of indoor air and to reach a lower indoor CO_2 concentration. Nighttime case studies and a theoretical analysis suggest that a few several-minute mechanical ventilation periods could potentially maintain an acceptable indoor air quality for a normal sleeping period of 8 h.     

香港地区办公楼变风量空调系统节能分析

利用能耗模拟软件HTB2／BECON对香港地区两栋办公大楼能耗进行了定量分析，比较了CAV与VAV系统的风机能耗与总能耗，预测了两个系统全年的能耗与VAV系统的节能情况。     

Application of overhangs and side fins to high-rise residential buildings in Hong Kong

For a typical lone high-rise 20-storey residential building in Hong Kong, the extent to which cooling of its 10th-floor (mid-level) rooms depends on overhangs and side fins was evaluated. By using the software EnergyPlus?, it was found that the application of overhangs would reduce the electricity consumption by up to 5.3%. The highest reduction was obtained in rooms with windows unshaded by own-wing walls, face west, and have 0.75 m overhangs. By using the same software, it was found that the application of side fins to the building with overhangs would reduce the electricity consumption by up to 1.4%, where the highest values belong to windows facing either north or south (at west wing), with out-of-core side fins.     

中国绿色建筑与节能(香港)委员会——增进香港与内地绿色建筑交流合作

中国绿色建筑与节能(香港)委员会成立 2010年1月,中国绿色建筑与节能(香港)委员会(下简称"香港委员会")正式在香港注册,并且由中国绿色建筑与节能专业委员会委任刘少瑜教授担任第一届香港委员会主任,邹经宇教授和梁以德教授担任副主任,张智栋担任秘书长.     

Evaluation of adaptive thermal comfort models in moderate climates and their impact on energy use in office buildings

Thermally Activated Building Systems (TABS) are regarded as top-cooling systems rather than full air-conditioning systems. Therefore, adaptive thermal comfort models (ASHRAE55, ISSO74 or EN15251) are supposed to be applicable to TABS buildings, although the comfort model conditions are not necessarily satisfied. This paper investigates whether, for a moderate climate and with the heating and cooling set points chosen according to the adaptive models, the building’s energy use reduces. After all, applying adaptive models, if appropriate, is thought to lower energy use because higher maximum operative zone temperatures T_op,max are allowed, compared to the conventional ISO7730 model. For purpose of generality, a building with an ideal heating and cooling system is considered. Analysis of moderate climate weather data reveals a low energy reducing potential for the ASHRAE55 and ISSO74 model, because high reference outdoor temperatures hardly occur. EN15251 on the other hand, allows very high T_op,max and will lower the cooling need.A 2-zone building simulation demonstrates a higher cooling need for ASHRAE55 and ISSO74, compared to ISO7730. Because cooling is needed during the whole year, the lower winter T_op,max of these adaptive models causes these unexpected results. With real data of warmer years or varying gains, this conclusion holds.