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Integrated Part Load Value (IPLV) has been adopted worldwide as a simple metric for regulating and evaluating chiller performance. There is no exception for Hong Kong. However, the weighting factors and working temperatures for the derivation of IPLV were developed for the US. They may not be appropriate for use in other countries/regions with different operating conditions. Europe and China therefore have developed their own formula but the formulation is based on simulations and details cannot be found in literature. This study adopts a carefully-designed methodology to develop a Hong Kong specific IPLV. The development was based on actual operating characteristics of 20 Grade A office buildings in Hong Kong. Representativeness of the 20 office buildings was verified by statistical analysis. Through in-situ measurements and site surveys, hour-by-hour operating data of the studied buildings were collected. Monte Carlo analysis and ASHRAE's bin method were employed to examine the massive volume of operating data. Regression analysis was employed to formulate the Hong Kong specific IPLV. The formulated IPLV was validated. It gives the highest weighting to 75% capacity (0.682), followed in descending order are 50% capacity (0.257), 25% capacity (0.049) and 100% capacity (0.012). In determining the working temperatures, a mathematical model to enable quick estimation of entering condenser water temperature for water-cooled chillers was developed. The results and methodology adopted in this study will be useful for reference of manufacturers, policy makers and researchers in searching for a reliable metric for performance evaluation of chillers should simulation is not practical.

Overcooling causes thermal discomfort and wastes energy. Effectiveness of a novel dedicated outdoor air system (DOAS) consisting of a multi-stage direct expansion coil to generate extra-low temperature (XT) outdoor air to handle the entire space cooling demand for better energy and humidity control has been confirmed in previous studies. In these studies, the terminal system was assumed using variable air volume (VAV) without reheating. The conventional VAV system without reheating has overcooling problem. This is associated with uncertain fluctuations of operating characteristics. However, virtually no study has been done to investigate its overcooling risk, and how it is compared with XT-DOAS. In this study, a rigorous probabilistic approach is proposed to account for the uncertain fluctuations of operating characteristics to assess their overcooling risks. Monte Carlo simulations with 10,000 interactions was used for risk analysis. A morphing method was employed to develop 10,000 weather files that could give an accurate prediction of future variations in yearly weather conditions. Reliable datasets were used to develop the probability distribution functions to account for the daily variations in use patterns. The most probable operating characteristics were input to EnergyPlus for hour-by-hour simulations. The annual cooling load profile formulated by the probabilistic approach was successfully validated by in-situ measurements. The probabilistic assessment results show that XT-DOAS has far less overcooling hours and lower long-term percentage of dissatisfied than the conventional VAV system. The results also indicate that the proposed probabilistic approach is useful for a robust system performance evaluation.

Cooling energy use of residential buildings in Hong Kong has been increasing in the past two decades. Natural ventilation is an effective means to reduce cooling energy use. To encourage wider and ...

Natural ventilation and the type of window used are closely related. Many works have already been done on identifying the window types that can enhance ventilation performance in residential buildings. However, window performance has been investigated either independently, without considering the interactive effects of other apertures (relative positions of windows and window orientations) or it has been examined based on very limited wind data sets. To fill this research gap, this study aims to evaluate the influence of window types on indoor ventilation performance of residential units in Hong Kong, taking into account the interactive effect and based on representative wind data sets. Air change per hour (ACH) was used to quantify natural ventilation. In this study, site measurement was conducted at a carefully selected residential unit to provide data for validation of the Computational Fluid Dynamics (CFD) settings. The validated settings were used for further CFD simulations. The Central Composite Design method and the Squeeze Theorem were used to determine the representative wind data sets. The Response Surface Regression method was used to develop a mathematical model for quantifying the interactive influence of different apertures on indoor ventilation and to enable quick estimation of ACH. The results lead to the conclusion that for all apertures, side hung (SH) window is the most effective design, followed in descending order by top hung (TH) window and sliding (SLD) window. The maximum achievable ACH for SH and TH windows were 124% and 97% higher than the SLD window. It was also found that if windows can be located only on the same side of a residential unit, SH windows and south facing TH windows should be preferred.

In Energy Performance Contracting (EPC) projects, Energy Service Companies (ESCOs) often provide guarantees on the energy savings of proposed retrofit measures based on a simplified engineering method. In order to assess the risk of saving shortfalls, there is a need to develop an evaluation method based on the probabilistic approach. This study focuses on a proposed probabilistic approach to evaluate the performance risks of common lighting retrofit measures such as replacement of existing lighting, installation of daylight-linked lighting controls and occupancy-based controls. The proposed approach considers the variations in the influential factors affecting energy performance, including daylight availability, occupancy rates, lamp conditions and lighting use patterns. Empirical data is used to develop the probability distribution functions of those influential factors. A hypothetical 40-storey office building with typical design features (such as regularly shaped open plan) in Hong Kong was modeled using EnergyPlus to demonstrate the application of this probabilistic approach. The results indicate that the variations in actual energy savings can be substantial in lighting retrofit projects, ranging from 1,267,000 kWh (43% of pre-retrofit consumption) to 1,927,000 kWh (65% ditto) with 90% statistical significance, posing risk on the achievement of guarantee savings in an EPC project setting.

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.

Sleep is a dominant part of our daily lives. People often have sleeping habits. Sleeping habit is referred as the preferred bedding system (type of bedding and sleepwear) and thermal environment. Thermal environment and cooling energy use are closely related. Many works have been done on sleep quality, sleeping habits, and the associated cooling energy use. However, it is noted that they are either separately or pairwise investigated. No investigations to date have been done to investigate their interactive effect. This study serves as a pilot study to fill the research gaps in investigating the interactive effect of sleep quality, sleeping habits and cooling energy use. Based on the use of three bedding systems and four temperature settings, 12 sleeping tests, each refers to one sleeping habit, were performed simultaneously in eight subjects. Sleepbot was employed to quantity sleep quality. Upon ascertaining the best sleep quality for different bedding systems, hour-by-hour energy simulations using EnergyPlus were conducted. It was found that for the use of light bedding systems, the associated drop in energy use would be 78.3% and 37.8% for female and male subjects respectively. Two prediction models, one relating energy use with thermal environment, and the other relating sleep quality with sleeping habit, have been established. The models can help quickly determine the tradeoff amongst sleep quality, sleeping habit and energy use.

The fresh water supply is finite, but the fresh water demand is infinite. A sustainable supply of fresh water is emerging as one of the most critical resource issues in the world. Hong Kong is one of the highest per capita fresh water users in the world. This has led to many government initiatives to promote water-saving habits in Hong Kong. However, after almost a decade of efforts, there has been no obvious reduction in consumption. Little has been done to identify the reason for this. Through the use of questionnaire surveys, site measurements, and controlled experiments, the aim of this study is to investigate the level of adoption of different water-saving habits, the most influential water-saving habits, and the barriers to the adoption of water-saving habits in residential buildings in Hong Kong. It was found that if the policies are targeted to break the identified barriers, then there is a potential for reducing the total domestic fresh water consumption in Hong Kong by 14.7%. It was also found that the knowledge of water scarcity and good water use habits are not the barriers to the adoption of water-saving habits in Hong Kong households. Rather, the government should draw public&rsquo, s attention to the environmental impact of water usage and the high fresh water consumption level of Hong Kong people to break the knowledge barrier and should re-examine the water tariff to break the motivation barrier. The results of this study provide useful information for decision makers in the context of water conservation in Hong Kong as well as elsewhere in the world.

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.

Transom window (TW) has been demonstrated to be effective in enhancing natural ventilation in high-rise residential buildings in tropical climates. However, virtually no work has been done to investigate whether a naturally-ventilated hybrid system (using enhanced ventilation created by TW supplemented with air-conditioning (AC)) is effective in reducing cooling energy consumption and providing the desired thermal comfort. For this purpose, cooling energy usage of an AC only system is compared with that of a hybrid system for achieving the same thermal comfort in high-rise residential buildings in Hong Kong. In this study, a carefully-designed methodology which involves the use of market survey, statistical analyses, site measurements, and integration of CFD and EnergyPlus simulations was adopted. Market surveys and statistical analyses were used to provide reliable input data for simulations. Site measurements of ventilation were used to assess the uncertainty of CFD simulation results. The integration of CFD and EnergyPlus simulations were for accurate predictions of natural ventilation performance (ACH) and air velocities achieved with TWs, hour-by-hour air temperatures, and hour-by-hour cooling energy use of the hybrid and the AC only systems. The simulated air velocities and temperatures were used for thermal acceptability analysis. It was found that depending on the TW design, average improvement in ACH ranges from 117% to 190%, and the associated cooling energy saving from hybrid system ranges from 22.2% to 22.7%. The results confirm the effective use of TW in reducing cooling energy use and providing thermal comfort in high-rise residential buildings in Hong Kong.

Demand controlled ventilation (DCV) to conserve energy while maintaining an acceptable indoor environment has been used for over 30 years. However, little work has been done on evaluating its energy saving potential in cooling dominant office buildings in subtropical climate. In this study, the energy saving potential of DCV system for use in six representative office buildings in Hong Kong was investigated by simulations. Simulation validation was done based on in situ measurements and site surveys. The findings show that, based on their original design conditions, the use of DCV could lead to 12.5–26.1% energy saving. To facilitate quick estimation of the energy saving potential of DCV system, further simulations were performed for the development of a simplified model. The simplified model relates the energy saving potential to key air-conditioning system and design parameters. Based on the simplified model, sensitivity analysis was conducted to quantify the influences of different parameters on the energy saving potential of DCV system. The developed model method can be used for prediction on the energy saving potential in a wider application of DCV in Hong Kong.

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 consisting of a multi-stage direct expansion coil and a zero-energy heat pipe to generate extra-low temperature outdoor air to avoid moisture-related problems was proposed in this study. The proposed system’s performance in achieving the desirable air conditions and better energy efficiency objectives is compared with a conventional direct expansion system for air-conditioning of a typical office building in Hong Kong based on simulation investigations. The simulations were carried out using equipment performance data of a pilot study, and realistic building and system characteristics. It was found that the proposed system, as compared to the conventional system, could reduce the annual indoor discomfort hours by 69.4%. An energy and exergy analysis was also conducted. It was revealed that the proposed system could reduce the annual air-conditioning energy use by 15.6% and the system exergy loss rate by 13.6%. The associated overall exergy efficiency was also found 18.6% higher. The findings of this study confirm that the proposed system is better than the conventional system in terms of both energy and exergy efficiency and the desirable air conditions.

A novel dedicated outdoor air system consisting of a multi-stage direct expansion coil to generate extra-low temperature outdoor air to avoid moisture-related problems and for desirable air conditions and better energy efficiency is proposed for investigation. In this study, the proposed system's (extra-low temperature-dedicated outdoor air system) performance in achieving the desirable air conditions and better energy efficiency objectives is compared with a conventional direct expansion coil system with variable speed compressor and fan used for air conditioning of a typical office building in Hong Kong. Through hour-by-hour simulations, using equipment performance data of a pilot study and realistic building and system characteristics, it was found that the extra-low temperature-dedicated outdoor air system, as compared to the conventional system, could reduce the annual air-conditioning energy consumption by 22.6%, the indoor discomfort hours by 31% and the condensation risk to zero hours. Root-mean-s...

Replacement of air-cooled chillers with water-cooled chillers for air-conditioning plants in existing buildings can yield a significant amount of energy savings, especially in a sub-tropical climate. However, due to variations in weather conditions and building operation patterns, the amount of actual energy saving is often uncertain in these retrofits. These uncertainties impose a risk of saving shortfalls when Energy Service Companies (ESCOs) guarantee building owners for a certain amount of energy savings in Energy Performance Contracting (EPC) projects. This study presents a probabilistic approach to estimating a range of possible energy savings with the associated confidence levels for chiller replacement in existing buildings, taking into account the annual variations in the influential parameters affecting energy savings. The influential factors include building cooling loads, system control and operation systems, as well as chiller plant characteristics. The proposed approach involves: the use of correlation analysis for identifying influential parameters; EnergyPlus for simulating energy use of chiller plant; and a Monte Carlo approach for simulating the probability of post-retrofit energy savings. A commercial building where the air-cooled chillers were replaced with water-cooled chillers is used to illustrate the proposed approach. Results show that the variations in annual energy savings for chiller replacement projects can be estimated with a defined degree of certainty. In the case study project, the possible annual energy savings during the post-retrofit period range from 1,149,000 kWh (37.6% of baseline consumption) to 1,504,000 kWh (49.2% of ditto) at 90% statistical significance. The risk mitigation measures for this type of energy retrofit are discussed as well.

It has been a common practice to place room air-conditioners (RACs) at overhead level for cooling of residential environments because this offers better air distribution performance and thus thermal comfort. However, now reversible RACs are gaining ground and they comprise both cooling and heating modes. Whether the same practice of locating RACs at overhead level should continue for reversible RACs has never been investigated. This study is the first ever attempt to identify the optimum positioning (position and level) for installation of reversible RACs in a representative bedroom. Computational Fluid Dynamics (CFD) and EnergyPlus simulations were integrated for the purpose and experiments were conducted in an environmental chamber to provide data for validation of the CFD settings. EnergyPlus simulations were used to determine the hour-by-hour cooling and heating demands based upon realistic operating and probable equipment characteristics. The probable equipment characteristics were ascertained by an extensive market survey and Monte Carlo analysis. The hour-by-hour cooling and heating demands were analysed by Central Composite Design method and the Squeeze Theorem for the formulation of the representative cooling and heating data sets for further CFD simulations. Further CFD simulations provide an accurate prediction of air temperatures and velocities for different installation positioning for thermal comfort analysis. Revised air diffusion performance indices (ADPIs) were developed to facilitate thermal comfort analyses for cooling and heating modes. It was found that slightly higher ADPIs can be obtained when the reversible RAC is installed at high level and on the longer side of the bedroom.

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.

Effectiveness of dry cooling and dedicated ventilation (DCDV) system for decoupling dehumidification from cooling to achieve the desired indoor condition and condensate-free objectives for air-conditioning of office environments in Hong Kong has been confirmed in previous simulation and experimental studies by the authors. However, our previous studies assumed a constant outdoor air and chilled water flow rates, and this is not always the case in practice. Whether this assumption could affect the effectiveness of DCDV system is the subject of present investigation. A prototype that could enable the variation of outdoor air and chilled water flow rates, as well as indoor and outdoor conditions, was set up for laboratory experiments. Our results have illustrated the effectiveness of DCDV system in achieving the intended condensate-free objective which was most affected by the space-sensible heat ratio and chilled water flow rate. Little influence was found to be introduced by the outdoor air flow rate and outdoor air conditions. The results, through sensitivity and statistical analysis, were found consistent with results of our previous studies.

Excessive lead has been found in drinking water in Hong Kong in tests carried out in 2015. Investigations have identified that the problem in public rental housing estates was caused by the problematic solders used in the plumbing, and recommendations on enhancing the quality control system and strengthening the relevant water quality standards have been proposed. The cause for the same problem happening in other premises where soldering has not been adopted for water pipe connections is left unidentified. Considering the unidentified cause and the recommendations made, this study aims to identify the gaps in practice followed in Hong Kong for safeguarding the water quality of new installations. A holistic review of governing ordinances and regulations, products and materials used and the testing and commissioning requirements adopted in Hong Kong and elsewhere in the world were conducted. Based on international practices and parametric analysis, it was found that there are gaps in practices followed in Hong Kong, which are directly and indirectly leading to the lead-in-water crisis. Recommendations for improvement in the quality control system, and the water quality standards including the allowable lead content and leaching limit for products and materials and the testing and commissioning requirements on plumbing installations have been made. The review and the identified gaps would become useful reference for countries in strengthening their relevant water quality standards.

Of the building environmental assessment methods currently in use, none are able to assess the energy performance of existing commercial buildings that comprise a mix of premises with differing energy use characteristics. This paper proposes a method that takes into account the inter-related energy use characteristics of the landlord and the tenants, which aims to provide for a more comprehensive and fairer assessment. The key features of the proposed method includes a tenants/landlord co-operative scheme, and the fact that it is based on total measured energy consumption for the whole complex. This includes consumption by tenants and that of the centralised services systems. The assessment criteria have been established using the surveyed data from an energy end-use database, together with a method to determine the shares of energy consumption by the central services systems amongst the various premises in the building complex. Obtaining full participation by the tenants encourages efficient and effective use of equipment that is part of the cooling load, which can benefit both the landlord and the tenants.

In the Hong Kong Building Environmental Assessment Method (HK-BEAM) for air-conditioned office premises, energy use for air-conditioning constitutes one major item of assessment. The current assessment method for existing offices is based on computer simulation predictions. Following a recent review of the HK-BEAM scheme, simplified models have been developed for use in the assessment as an alternative to the detailed simulation method. These models are multiple linear regression models relating the annual electricity use for air-conditioning, and the maximum electricity demand, in an office building to the key characteristics of the building envelope and the air-conditioning system. Use of these models can reduce the effort required for data collection and input, and will allow the assessors to more quickly complete an assessment. In addition, additional parametric studies can be performed within much less time, which will help assessors in formulating advice to developers/designers on measures that will lead to improved energy performance and thus higher credits. This paper summarizes the review findings and describes the approach taken in the establishment of the regression models. Comparison of predictions by the detailed computer simulation method and the alternative method showed that the latter could provide estimates close enough to the simulation predictions for the purpose of assessing the credits to be awarded to a building for its energy performance.