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Though area in office buildings has expanded significantly in Hong Kong in the decade to 2013, increase in cooling energy use has been rather moderate. The factors and policy instruments that contributed to the impressive enhancement in energy usage efficiency are not available in published literature. Data of sixty-six office developments were examined to evaluate the role of policy instruments in bringing about the visible improvement. Numerical analyses reveal that use of chiller units with higher efficiency and fresh water cooling tower (FWCT) systems have contributed significantly to reduce cooling energy use of office space in Hong Kong. It is important to note that policies promulgated have played a key role in encouraging designers of office space to opt for energy efficient systems. The BEAM Plus certification for all public buildings has contributed the most (efficacy = 0.09) to the success in moderation of electricity consumption for cooling of office space. The FWCT scheme and the Building Energy Codes have had efficacies amounting to 0.076 and 0.026, respectively. Interestingly, the new OTTV requirement, used for regulation and monitoring of thermal performance of building envelopes, has had a negative rate of efficacy (0.018), implying that the government needs to review its appropriateness.

Residential buildings represent a predominant source of energy consumption in most subtropical cities. To enhance the energy performance of this sector, the use of reversible room air-conditioners (RRACs) for combined space heating and domestic hot water (DHW) production is proposed. The idea arises from the fact that in subtropical regions RRACs sized for cooling always have excessive heating capacities to allow a parallel production of DHW. In order to assess the techno-economic feasibility of the proposed initiative, a representative housing estate in Hong Kong consisting of 12,800 residential units was selected for an extensive simulation study. Results confirmed the technical viability of the proposed system. It was found that a wide adoption of the technology has the potential to reduce 7.7% of Hong Kong residential energy consumption and 744,192 t of CO2e emissions. The tolerable capital cost (TCC) approach was adopted for yearly economic viability analysis. The average TCC for individual residential units was found ranging from HK$2,241 to HK$26,286 depending on the household size, electricity price, and economic settings. This study provides preliminary evidence to confirm the viability of the proposed technology and opens a new way for residential energy savings in Hong Kong and elsewhere in the subtropical.

Increase in cooling energy usage of the residential sector in Hong Kong has been moderate in the most recent ten years (2004–2013). Factors and drivers responsible for this are of interest to policy makers in search of performance improvement but such information is not available in extant literature. This paper reviews the policy instruments introduced in Hong Kong during this period of time and examines the different engineering factors contributing to improvements in cooling energy efficiency. Whether the policy instruments have been instrumental in bringing about changes in engineering design and thus improvement in cooling energy efficiency is evaluated on the basis of the equipment and building envelope characteristics of 64 residential developments in Hong Kong. Different statistical analyses reveal that the use of more energy efficient room air-conditioning units (COP), smaller window-to-wall ratios (WWR) and walls with higher U-values are the engineering factors (WallU) that have contributed to moderation of growth of energy consumption; these were driven by policies introduced by the Hong Kong Government. Regarding the sensitivity of the three engineering factors, it was found that COP was the highest amounting to 0.455, followed in descending order by WallU and WWR. Their sensitivities were 0.289 and 0.006, respectively.

A novel dedicated outdoor air system (DOAS) comprising a multi-stage direct expansion coil to produce extra-low temperature (XT) outdoor air to handle the entire space cooling demand has been confirmed more efficient than conventional systems. To further enhance the performance of XT-DOAS, the optimum number of cooling stages and treated outdoor air temperature need to be determined. This process requires the development of a coil performance model that takes into account the extra-high and extra-low entering air temperatures at the first and the last cooling stages. In this study, factory test data and field measurement data were used to develop such a performance model. Different statistical analyses were employed to validate the developed model. Based on the developed model, energy and exergy analyses were conducted to evaluate use of XT-DOAS for space cooling of a typical office building in Hong Kong. EnergyPlus was employed for the energy analysis. The laws of thermodynamics were used for the exergy analysis. Their combined results indicate that for better energy efficiency and performance for air-conditioning of office buildings in subtropical region, the optimum configuration for XT-DOAS is two cooling stages with a treated outdoor air temperature of 7 °C. The model developed and the energy and exergy analyses described will contribute significantly to future research in this area.

The use of SEHRAC (storage-enhanced heat recovery room air-conditioner) for space cooling and free water heating has been confirmed effective but its overall performance will unavoidably be affected by the associated increase in water temperature in the heat recovery water tank. Measures to enhance the heat storage capacity of the water tank will thus be beneficial to the overall performance of SEHRAC. But virtually none has been done to date. For achieving this objective, the use of PCM (phase change material) in the water tank was proposed in this study. A prototype SEHRAC integrated with an expanded graphite/paraffin composite PCM was designed and setup in a test facility for laboratory experiments. Two identical sets of experiments with and without the use of PCM (wPCM and woPCM scenarios) under a range of outdoor temperature conditions were conducted. It was found that the wPCM scenario, as compared to the woPCM scenario, the overall coefficient of performance was 6.9%–9.8% higher and the heat retention time of the tank water was 21.1% longer. The results confirmed that the performance of SEHRAC could be improved by the use of PCM.

The use of storage-enhanced heat recovery room air-conditioner (SEHRAC) to supply hot water and provide space cooling for energy saving has been confirmed effective, but the heat recovery process can lead to significant refrigerant pressure fluctuations. Whether an expansion device can function properly despite the fluctuations is decisive to the successful use of SEHRAC. Capillary tube (CT) and thermostatic expansion valve (TEV) are the two most used expansion devices in SEHRAC, but a suitable type has never been identified in extant literature. In this study, laboratory experiments were conducted to enable a side-by-side comparison of the two expansion devices. A prototype SEHRAC, which could be switched between the CT and TEV systems, was designed and setup in a test facility for two identical sets of experiments. For each set of experiments, a series of tests under different outdoor temperatures were conducted. It was found that an overall better performance was achieved by the TEV system. The space cooling and water heating capacities were on average 16.3–19.4% and 18.5–23.4% larger than the CT system. The overall coefficient of performance was also found 12.5–20.9% higher. The results confirmed that TEV is preferred for use in SEHRAC.

Effectiveness of SEHRAC (storage-enhanced heat recovery room air-conditioner) for water heating in residential buildings in Hong Kong and elsewhere has been confirmed in previous studies. However, given these studies assumed a theoretical maximum recoverable heat, whether its use is still energy effective in practice, in particular under intermittent operation, is of concern. Intermittent operation of the SEHRAC can lead to significant fluctuations in operating conditions. Adding that capillary tube is often used as the expansion device to magnify the fluctuations, whether SEHRAC can still operate satisfactorily despite the fluctuations is another concern. To address these concerns, a prototype which can be switched between the combined CH (cooling and heating) mode and the CC (conventional cooling) mode was set-up for laboratory experiments. The results showed that the water heating objective can be achieved. The operating parameters also confirmed the satisfactory operation of SEHRAC. Energy performance of the CH mode was found better than the CC mode. A prediction model was developed for evaluating the use of SEHRAC. On wider application of SEHRAC, energy use of the residential sector in Hong Kong can be reduced by 9.1%. The experimental details described in this study would become an experiment protocol to enhance future research in this area.

Compared with conventional energy retrofit projects, Energy Performance Contracting (EPC) projects present a different risk picture to the contracting parties as its primary focus is to deliver promised energy savings to building owners (hosts). This study aims to identify the key risks inherent in EPC projects, and investigate the hosts’ concerns on the use of EPC, as well as propose practical measures to enhance the wider adoption of EPC. Two separate questionnaire surveys were conducted with respondents comprising ESCOs (n = 34) and hosts (n = 168) in Hong Kong. Results indicate that the key risks to ESCOs are possible payment default of hosts after installation, uncertainty of baseline measurement, and increase in installation costs in EPC projects. For hosts, their primary concerns in considering the use of EPC include possible long payback periods, project complexities and repayment ability. In addition, the respondents agree with three practical measures to enhance the adoption of EPC in future, including the promotion of successful projects, modification of government procurement practices, and government's backup of loans. The findings of this study provide useful pointers to key stakeholders of EPC projects for harnessing their risk perceptions and mitigating their concerns on this procurement approach.

China building energy codes (CBEC) have been introduced for over two decades but little has been publicized in literature. LEED on the contrary is the most publicized building environmental assessment scheme. To enable better understanding of the compliance standards of CBEC, this paper presents the energy performance assessment results (represented by energy and energy cost savings) of three office buildings in China (one in Beijing and two in Shanghai) using the current versions of CBEC and LEED. The energy and energy cost savings of the three buildings were predicted based on hour-by-hour simulations using the weather data and energy tariffs of Beijing and Shanghai where the three studied buildings are located, and their actual building and system characteristics. The study revealed that LEED in general sets more stringent requirements than CBEC in indoor design conditions, building envelope characteristics and air-conditioning system features. Amongst various building end uses, energy use for air-conditioning was found dominating the assessment results, and the use of energy efficient measures not forming part of the baseline criteria, could lead to 2 to 5% reduction in the overall building energy use. The two schemes were benchmarked against BEAM Plus and their weaknesses were also unveiled.

a b s t r a c t Storage-enhanced heat recovery room air-conditioner (SEHRAC) is considered one of the most effective measures to curb energy use in residential dwellings. However, little has been done on optimal design of the storage tank. For application in dense living environment like Hong Kong, another concern is whether or not the amount of recoverable heat can meet the household water heating demand. In this study, a typical residential estate in Hong Kong was chosen for supply and demand analysis. The analysis was based on hour-by-hour simulations using actual building characteristics and previously identified utilization patterns. It was found that with the use of SEHRAC, the daily cumulative recoverable heat far exceeds the daily household water heating demand. For optimal design of the storage tank, an air-conditioner model (REFMOD) was developed to enable ascertaining the operating parameters at the refrigerant side of SEHRAC. Other design requirements of the storage tank including the minimum required heat storage capacity and heat transfer effectiveness were determined. The potential energy and energy cost savings, as well as CO2 emission reduction for wider application of SEHRAC were estimated as 9.3% of the overall contribution of the residential sector in Hong Kong.

LEED and BEAM Plus have been formally launched for more than 10 years. They are the two most recognized building environmental assessment schemes in China. Previous works have been done on benchmarking the energy assessment of the two schemes. However, benchmarking was either based on their earlier versions of which substantial changes have been made, or focused on their assessment issues and metrics without making reference to actual building characteristics. This paper compares the energy performance assessment results of three new office buildings in China (one in Beijing and two in Shanghai) using current versions of LEED and BEAM Plus. The three office buildings were chosen for their similarities in design. The study revealed that despite the variations in different aspects between LEED and BEAM Plus, assessment results of the three studied buildings were comparable. Amongst various building end uses, energy use for air-conditioning was found dominating the assessment results. Comparison results also show that although different tariff systems are adopted in Beijing and Shanghai, the difference will not affect the assessment results as long as same tariff system is used for predicting the energy cost of the baseline and design cases.

Buildings are key target of policies that aim at promoting environmentally sustainable development. Amongst policy instruments that address environmental burdens incurred by buildings, labelling and certification schemes are arguably the most cost-effective. Since the first building environmental assessment scheme was launched in the 1990's, similar schemes have emerged in about 30 countries. These are mainly domestic schemes tailored to suit local contexts. Whilst most of these schemes take a voluntary, market driven approach, some have become a part of mandatory building approval requirements, though different certification schemes may co-exist in some regimes. Benchmarking the strengths and characteristics of different schemes has been advocated. In this connection, this paper provides a comprehensive review and comparison of the issues and metrics of five representative assessment schemes, namely, BREEAM, LEED, CASBEE, BEAM Plus and the Chinese scheme ESGB. Comparison of these five schemes shows that BREEAM and LEED are the most comprehensive. A two-phase certification method is adopted in LEED, CASBEE and BEAM Plus, which is considered preferable. Statistical analysis also reveals that there is a moderate degree of agreement amongst the five schemes on weights and ranks of weights allocated to five key assessment aspects. Through comparison, the weighting coefficients adopted by ESGB were found the most representative. Strengths and characteristics of the five schemes have been identified for reference of policy makers in developing their domestic schemes.

Desiccant cooling system for active humidity control and to conserve energy has been in commercial applications for over two decades. However, its use in humid wet markets has never been examined. A gas-fired desiccant cooling system has been installed in a wet market in Hong Kong. In this study, the annual energy saving in conjunction with the use of desiccant cooling system was investigated by in-situ measurements, site surveys and simulations. The verified computer model was used for further simulations. It was found that for the use of a minimum ventilation rate of 10.3 L/s/person, the use of desiccant cooling system as compared to conventional system saved 4% of the energy and could achieve the desired space conditions. A parametric study under various ventilation rates indicated that use of desiccant cooling system in wet markets in hot and humid Hong Kong would lead to energy and energy cost savings, as well as CO2 emission reduction amounting from 1% to 13%. The savings were more evident when wet markets were designed for a ventilation rate of 20 L/s/person. Furthermore, the actual occupancy profile, and lighting and small power densities determined in this study would be useful for future studies on wet market., Highlights • The study is motivated by an actual desiccant cooling system installed in a wet market in Hong Kong. • The study focuses on side-by-side comparison of the desiccant and conventional systems. • Desiccant cooling system can better achieve the desired space air conditions. • Desiccant cooling system can lead to energy, energy cost and CO2 emission savings. • The results are useful for wider application of alternative energy source for cooling of wet markets.

Natural ventilation in residential dwellings is very important for occupants’ health and comfort. Previous studies by the authors have concluded that natural ventilation performance in dwellings can be enhanced by positioning the two groups of window openings (bedroom windows and living room windows) in opposite directions or perpendicular to each other; and/or the use of side-hung windows. However, the buildings selected for those studies were located in an isolated site, for the purpose of focused evaluation of the influence of various configuration parameters and window types. However, in Hong Kong, buildings are tightly packed. In this study, the influence of urban environment was thoroughly considered. A residential estate was identified to represent typical characteristics of the urban environment in Hong Kong for CFD modelling and simulations. Bi-variate correlations and K-means cluster analyses were adopted to identify a set of probable local wind conditions, which took into account the co...

BREEAM, LEED, CASBEE, BEAM Plus and Chinese ESGB have been formally launched at different stages in the last twenty years. How well the certified and rated buildings compare with each other is always an interest of building designers and policy-makers. This paper presents a side-by-side comparison of energy use assessments of the five schemes. The comparisons are on the assessment method and criteria, default parameters, trade-offs allowed, performance scales, approved simulation tools, performance indicators and assessment results. Comparison results showed that all the five schemes are based on relative performance. It was also found that despite the variations in default parameters among the five schemes, market positions of certified buildings are comparable. LEED was found to be the most stringent and relatively less flexible in its assessment criteria. Nonetheless, the energy cost budget approach, adopted only by LEED, is able to fulfil emission reduction and cost saving objectives on the condition that a “fuel neutral” approach should be adopted.

The combined space cooling and hot water preheating system that utilizes the rejected condenser heat is considered one of the most cost effective energy conservation measures. However, simultaneous consumption characteristics are absent in public domain. Questionnaire surveys have been conducted to obtain the relevant information from 126 households residing in high-rise public rental residential buildings in Hong Kong, achieving a confidence level of 95%. The candidate households were selected by a convenience sampling approach, and the questionnaire was constructed using either forced-choice format or in numeric response format. The data obtained were verified by correlation analysis. Data collected includes the occupancy pattern, the installed air-conditioner and water heater characteristics, and the utilization pattern of air-conditioning and hot water. Based upon the collected data and site measurements, hourly, daily and monthly heat recovery and hot water heating demand profiles were established, as well as the correlation between tap water and outdoor air temperatures. The combined profiles enable the evaluation of the feasible use of the combined system, and for future sizing of hot water storage tanks. The potential energy and fuel cost saving associated with the use of the proposed combined system for typical public rental housing in Hong Kong was estimated to be 50%.

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.

Water-cooled air-conditioning systems (WACS) are widely used in the commercial sector for energy efficiency, but not in the domestic sector. It has been found that there are no mathematical models and energy simulation programs to enable detailed investigation and evaluation into the energy performance of water-cooled air-conditioners. To improve the applicability of water-cooled air-conditioners in the domestic sector, the development of a prediction model for energy performance analysis is needed. This paper addresses the development of an empirical model for predicting the operational performance and energy consumption for the use of water-cooled air-conditioners. The model consists of four sub-models which has taken into account the energy consumption of the condenser water system. A prototype WACS was set up and tested in an environmental chamber to validate the resultant model. The overall COP of the WACS was found to be greater than 3 at 90% rated capacity. The predictions from the model compared well with the experimental results, with RMS error within 11%.

The latest (4/04 and 5/04) versions of the Hong Kong Building Environmental Assessment Method (HK-BEAM), one covering new buildings and the other existing buildings, have been formally launched in 2005. The paper describes the building energy performance assessment method in these latest HK-BEAM versions. With the use of the energy budget approach, the assessment framework is applicable to a wide range of buildings that may comprise different mixes of premises types. The new scheme provides bonus credits for provisions that allow utilization of renewable energy sources. For existing buildings, it makes allowances for plant performance degradation and constraints to implementation of improvement measures in existing buildings. So far, the new assessment method has been applied to six building developments, including commercial complexes and residential developments. The assessment results are presented and discussed in the paper.

Within a given budget, selection of the optimal set of measures for enhancing the energy efficiency of a building is often based on the relative order of the feasible measures, prioritised according to either the life cycle cost saving or the economic benefit–cost ratio of the measures. A sensitivity analysis shows that, compared to the life cycle cost analysis, the benefit–cost ratio analysis is less susceptible to the influence of uncertainties in the estimates of the present value of the life cycle energy saving and cost. Where interactive measures are involved, the effects of some are dependent on the co-existence of other measures. The prioritisation determined according to the benefit–cost ratios of individual measures, each taken in the absence of all the others, can lead to the choice of a range of measures that is below optimal. Selection of the optimal set of energy efficiency enhancement measures requires a multistep approach, which is exemplified by the case study described in the paper.

Unlike cold climate regions, where natural ventilation is not preferred during winter, natural ventilation is always preferred in Hong Kong for cooling because of the subtropical climate. It also provides better indoor environment quality and energy conservation. Natural ventilation performance of a residential unit is affected by internal as well as external factors. External factors are often subject to constraints beyond the control of site planners and architects. Internal factors include opening configurations and window types, which site planners and architects are free to design the way they deem proper. However, little information is available about their precise impact. An earlier study by the authors on opening configurations identified the best and the worst out of twelve configurations. The best was with cross ventilation and the worst was with single-sided ventilation. In this study, the focus is on the influence of window types. CFD simulations were performed based on the best and w...

The Hong Kong Building Environmental Assessment Method (HK-BEAM), an environmental assessment method for air-conditioned office buildings, has been developed by the Real Estate Developers Association (REDA) for use in Hong Kong. Two versions of the scheme have been developed; one for new office premises and the other for existing office premises. HK-BEAM embraces a variety of issues related to the global, local and indoor environments. The efficient use of electricity forms a major part of the assessment. The basis for the energy performance assessment method, and the criteria for obtaining the relevant credits are described and discussed.