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Highlights • A CCHP system primed by Maisotsenko combustion turbine cycle was proposed. • Performance comparison with that based on conventional gas turbine cycle was made. • Dynamic system simulations were conducted using the TRNSYS platform. • Different climate regions were considered with the results compared. • The loading profiles affected the relative performances of the two CCHP systems. Abstract Buildings are the significant primary energy consumption and pollutant emission contributors in a modern city. Distributed multi-generation systems such as combined cooling, heating and power (CCHP) systems are considered an alternative to fulfil the energy saving requirements in the building sectors. In this study, a CCHP system primed with Maisotsenko combustion turbine cycle (MCTC) was considered with its performance compared with that primed with a simple gas turbine with recuperator (SGTR). With dynamic models of the CCHP systems constructed using TRNSYS, a design optimisation was conducted using genetic algorithm to determine the system component size and number based on the best year-round cost saving. A study case which consisted of building complexes in a district scale was used for investigation under two climatic conditions. The simulation results showed that the relative performances of both CCHP systems depended on the load profiles which differed from the situations when both prime movers were used solely for power generation. In a heating-dominated application, the performance of the MCTC-primed CCHP system was better than the SGTR-primed one only during the summer period and that the year-round performance was inferior to the latter one. Last but not the least, a parameter study was conducted which showed the benefit reduction of CCHP system with the decreasing of public grid price and increasing fuel gas price. [ABSTRACT FROM AUTHOR]

Water flow window has very good application potential in zero carbon buildings of the warm climate. In this study, the effects of water-flow window configurations were investigated, such as the water layer thickness and glazing height-to-width ratio (GHTWR). The effects of distribution header design on the thermal and flow characteristics were also analyzed. Its long-term dynamic thermal performance was examined through a self-developed simulation program, of which the FORTRAN code was previously validated through comparison with experimental data. In the current study, the one-dimensional thermal simulation modelling approach was further justified through CFD analysis. Then the overall thermal performance of the window system was evaluated from the aspects of useful water heat gain and the impact on space air-conditioning power consumptions. A water layer of thickness around 15–20 mm and a GHTWR of 0.4 were found desirable for the tested cases. While the size and distribution of the header openings would affect the localized water flow and temperature distribution, their effect on the laminar upward flow and the final temperature rise is not significant. [ABSTRACT FROM AUTHOR]

Highlights: [•] A generic fully air-conditioned office building with inclined walls was modeled. [•] Simulations were run under climatic conditions in three modern cities in China. [•] Reduction in cooling load can outweigh the increase in heating load for Hong Kong. [•] Inclined angle of 30° is appropriate for inverted pyramidal building in Hong Kong. [•] Building constructed with inclined walls is not encouraged in Shanghai and Beijing. [ABSTRACT FROM AUTHOR]

Highlights: [•] Building energy simulation program EnergyPlus was validated using experimental data of a DSF system. [•] A generic commercial building with DSF system was modeled using EnergyPlus. [•] A dataset of correction factors was derived for OTTV evaluation of commercial buildings with naturally ventilated DSF. [ABSTRACT FROM AUTHOR]

Highlights: [•] An experimental setup of a green roof system was established for measurement. [•] A generic office building constructed with a green roof was modeled using EnergyPlus. [•] Energy performance of a green roof system was evaluated under different future climatic conditions. [•] The cost payback period of a green roof system is estimated as about 10 years. [ABSTRACT FROM AUTHOR]

Abstract: Overall Thermal Transfer Value (OTTV) is a measure of average heat gain into a building through the building envelope. It is a widely adopted measure in many countries for enhancing energy-efficient building design. In the past decade, there is increasing application of green roof into commercial buildings for enhanced building insulation, leading to reduction in heat gain through the roof area as well as cooling requirement of a building. Since the current OTTV equations and coefficients were originally developed for buildings with traditional bare roof construction, building designers have difficulty to compute the OTTV for building constructed with green roof. The aim of this study is to revise the existing OTTV calculation method and derive a set of correction factors for OTTV evaluation of green roof integrated buildings. An experimental setup of a green roof system with sensors was installed on the rooftop of a commercial building. The measured data were used for validation of a building energy simulation program EnergyPlus incorporated with a green roof model Ecoroof. Four building cases with typical and traditional roof constructions were modeled using the validated computer simulation program. Through a series of parametric computer simulations, a correlation between OTTV and annual heat gain through the roof area was established with that a set of correction factors ranging from 0.03 to 0.99 was developed. Theses correction factors can be used by building designers to compute the OTTV of building constructed with green roof. The details of methodology and findings are reported in this paper. [Copyright &y& Elsevier]

Abstract: Solar energy application is a good alternative to replace primary energy source especially for large-scale installations. Heat pumps are also effective means to reduce primary energy consumption. This paper describes a case study with a new design of solar assisted heat pump (SAHP) for indoor swimming pool space- and water-heating purposes. The system design procedure was first presented. The entire system was then modeled via the TRNSYS simulation environment and the energy performance was evaluated based on the winter time operation schedule. Economic analysis with a range of collector areas was also performed. The simulation results show that the overall system COP can reach 4.5, and the fractional factor of energy saving is 79% as compared to the conventional energy system. The economical payback period is less than 5years. [Copyright &y& Elsevier]

Abstract: A correlation study of the ground temperatures up to a soil depth of 3m (for lawn condition) with the weather parameters has been performed making use of the observed data in the 4-year period 2006–2009. It is found that within the soil depth of 3m, which belongs to the surface and shallow zones, the ground temperature is strongly correlated to the dry bulb air temperature whereas its dependence on the relative humidity, rainfall, global solar radiation or wind speed is weak. A multivariable nonlinear regression model was then developed based on the soil temperature and weather data within the same four-year period. This model can be utilized to predict soil temperature at various depths underground. The required inputs of the model are the day number of the year, soil depth and dry bulb air temperature. The model has been validated by the data records of the same site in the previous years, as well as the data record from another site in more recent years. This regression model provides a simple, fast and accurate alternative method for the estimation of natural ground temperature. [Copyright &y& Elsevier]

Abstract: A solar hybrid cooling design is proposed for high cooling load demand in hot and humid climate. For the typical building cooling load, the system can handle the zone cooling load (mainly sensible) by radiant cooling with the chilled water from absorption refrigeration, while the ventilation load (largely latent) by desiccant dehumidification. This hybrid system utilizes solar energy for driving the absorption chiller and regenerating the desiccant wheel. Since a high chilled water temperature generated from the absorption chiller is not effective to handle the required latent load, desiccant dehumidification is therefore involved. It is an integration of radiant cooling, absorption refrigeration and desiccant dehumidification, which are powered up by solar energy. In this study, the application potential of the solar hybrid cooling system was evaluated for the high-tech offices in the subtropical climate through dynamic simulation. The high-tech offices are featured with relatively high internal sensible heat gains due to the intensive office electric equipment. The key performance indicators included the solar fraction and the primary energy consumption. Comparative study was also carried out for the solar hybrid cooling system using two common types of chilled ceilings, the passive chilled beams and active chilled beams. It was found that the solar hybrid cooling system was technically feasible for the applications of relatively higher cooling load demand. The annual primary energy consumption of the solar hybrid cooling system was lower than that of the conventional vapour compression refrigeration system up to 36.5%. Between the two options of chilled ceilings, the passive chilled beams were more energy-efficient to work with the solar hybrid cooling system in the hot and humid climate. Harnessing solar energy for driving air-conditioning would help in reducing the carbon emission, hence alleviating the climate change. [Copyright &y& Elsevier]

Abstract: The provision of balcony to the living room of a residential flat offers a number of merits including improved view enjoyment, enhanced ventilation and increased planting space. In addition, a balcony can act as an overhang and provide solar shading as well as electricity saving of the air-conditioning system. This paper reports the findings on the energy and environmental impact due to the provision of a balcony. In this study, a typical residential flat with balcony constructed at the living room was modeled and the energy performance was investigated with the use of the typical weather data set of a subtropical city, Hong Kong. The effects of balcony''s orientation and glazing material of window were also evaluated. It was found that the residential flats facing various orientations (N, E, S, W, NE, SE, SW and NW) can offer substantial energy saving in air-conditioning system due to the shading effect of balcony. The building case with southwest facing balcony and clear glass glazed window gave the highest saving percentage of 12.3% in annual air-conditioning consumption. In terms of cost payback period, the values were estimated as 25.9 years (based on extra construction cost of a balcony) and over 100 years (based on extra purchasing cost), respectively. On the other hand, the energy payback period was 22.4 years for this building case. The provision of balcony to the living room of residential flat was found environmentally feasible in Hong Kong. [Copyright &y& Elsevier]

Abstract: 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. [ABSTRACT FROM AUTHOR]

Abstract: Direct hot water production consumes about 4% of the total energy use in Hong Kong, and about 20% when considering only the domestic sector. For water heating the energy sources are mostly town gas, liquefied petroleum gas and electricity. The use of heat pump or solar water heating, particularly the solar-assisted heat pump options, is not popular. In this paper, the potential application of a unitary type direct-expansion solar-assisted heat pump (DX-SAHP) system was examined. A numerical model of the DX-SAHP system was first introduced. From the simulation results with the use of the Typical Meteorological Year (TMY) weather data of Hong Kong, the system was found achieving a year-average coefficient of performance (COP) of 6.46, which is much better than the conventional heat pump system performance. The potential use of DX-SAHP therefore deserves further evaluation. [Copyright &y& Elsevier]

Abstract: A significant amount of research and development work on the photovoltaic/thermal (PVT) technology has been done since the 1970s. Many innovative systems and products have been put forward and their quality evaluated by academics and professionals. A range of theoretical models has been introduced and their appropriateness validated by experimental data. Important design parameters are identified. Collaborations have been underway amongst institutions or countries, helping to sort out the suitable products and systems with the best marketing potential. This article gives a review of the trend of development of the technology, in particular the advancements in recent years and the future work required. [Copyright &y& Elsevier]

Abstract: In recent years, more and more attention has been paid on the application potential of solar cooling for buildings. Due to the fact that the efficiency of solar collectors is generally low at the time being, the effectiveness of solar cooling would be closely related to the availability of solar irradiation, climatic conditions and geographical location of a place. In this paper, five types of solar cooling systems were involved in a comparative study for subtropical city, which is commonly featured with long hot and humid summer. The solar cooling systems included the solar electric compression refrigeration, solar mechanical compression refrigeration, solar absorption refrigeration, solar adsorption refrigeration and solar solid desiccant cooling. Component-based simulation models of these systems were developed, and their performances were evaluated throughout a year. The key performance indicators are solar fraction, coefficient of performance, solar thermal gain, and primary energy consumption. In addition, different installation strategies and types of solar collectors were compared for each kind of solar cooling system. Through this comparative study, it was found that solar electric compression refrigeration and solar absorption refrigeration had the highest energy saving potential in the subtropical Hong Kong. The former is to make use of the solar electric gain, while the latter is to adopt the solar thermal gain. These two solar cooling systems would have even better performances through the continual advancement of the solar collectors. It will provide a promising application potential of solar cooling for buildings in the subtropical region. [Copyright &y& Elsevier]

Abstract: Double skin façade can be defined as a building façade covering one or several stories with multiple skins. The skins may be air tight or ventilated. With sophisticated study and design, buildings constructed with double skin façade can have better thermal performance than the conventional single skin façade. This paper reports the findings on the energy performance of double skin façade applied to a typical office building under the climatic condition in Hong Kong. An experimental setup was established and the measured data were used to verify the theoretical model developed via the EnergyPlus simulation program. The validated model was then used to evaluate the energy performance of double skin façade with various configurations including glazing type (clear, absorptive or reflective glass), glazing position (inner or outer pane) and glazing layers (single or double glazing material). The results indicate that a double skin façade system with single clear glazing as the inner pane and double reflective glazing as the outer pane can provide an annual saving of around 26% in building cooling energy, as compared to a conventional single skin façade with single absorptive glazing. However, the long payback period of 81 years makes the double skin façade system economically infeasible. Support and motivation are needed from the local government in order to foster successful and widespread application of the double skin façade system in buildings. [Copyright &y& Elsevier]

Abstract: A building-integrated photovoltaic/water-heating (BiPVW) system is able to generate higher energy output per unit collector area than the conventional solar systems. Through computer simulation with energy models developed for this integrative solar system in Hong Kong, the results showed that the photovoltaic/water-heating (PVW) system is having much economical advantages over the conventional photovoltaic (PV) installation. The system thermal performance under natural water circulation was found better than the pump-circulation mode. For a specific BiPVW system at a vertical wall of a fully air-conditioned building and with collectors equipped with flat-box-type thermal absorber and polycrystalline silicon cells, the year-round thermal and cell conversion efficiencies were found respectively 37.5% and 9.39% under typical Hong Kong weather conditions. The overall heat transmission through the PVW wall is reduced to 38% of the normal building facade. When serving as a water pre-heating system, the economical payback period was estimated around 14 years. This greatly enhances the PV market opportunities. [Copyright &y& Elsevier]

Abstract: In photovoltaic–thermal (PV/T) technology, the use of glass cover on the flat-plate hybrid solar collector is favorable to the photothermic process but not to the photovoltaic process. Because of the difference in the usefulness of electricity and thermal energy, there is often no straight forward answer on whether a glazed or unglazed collector system is more suitable for a specific application. This glazing issue was tackled in this paper from the viewpoint of thermodynamics. Based on experimental data and validated numerical models, a study of the appropriateness of glass cover on a thermosyphon-based water-heating PV/T system was carried out. The influences of six selected operating parameters were evaluated. From the first law point of view, a glazed PV/T system is found always suitable if we are to maximize the quantity of either the thermal or the overall energy output. From the exergy analysis point of view however, the increase of PV cell efficiency, packing factor, water mass to collector area ratio, and wind velocity are found favorable to go for an unglazed system, whereas the increase of on-site solar radiation and ambient temperature are favorable for a glazed system. [Copyright &y& Elsevier]

Abstract: PV ventilated glazing technology for application in warm climate provides energy saving opportunities through the reduction in air-conditioning load, the daylight utilization, and the green electric power generation. In a working environment, the use of semi-transparent a-Si glazing is deemed better than the one with non-transparent c-Si solar cells. This paper reports an evaluation of its integrated performance using a small office room in Hong Kong as an example. An energy model of a PV ventilated window system is first introduced. Based on this together with the TMY weather data of Hong Kong and the daylight simulation capability of the EnergyPlus program, the overall performance analysis have been executed for different window orientations. It was found that a solar cell transmittance in the range of 0.45–0.55 could achieve the best electricity saving. [Copyright &y& Elsevier]

Abstract: The rapid development and sales volume of photovoltaic (PV) modules has created a promising business environment in the foreseeable future. However, the current electricity cost from PV is still several times higher than from the conventional power generation. One way to shorten the payback period is to bring in the hybrid photovoltaic–thermal (PVT) technology, which multiplies the energy outputs from the same collector surface area. In this paper, the performance evaluation of a new water-type PVT collector system is presented. The thermal collection making use of the thermosyphon principle eliminates the expense of pumping power. Experimental rigs were successfully built. A dynamic simulation model of the PVT collector system was developed and validated by the experimental measurements, together with two other similar models developed for PV module and solar hot-water collector. These were then used to predict the energy outputs and the payback periods for their applications in the subtropical climate, with Hong Kong as an example. The numerical results show that a payback period of 12 year for the PVT collector system is comparable to the side-by-side system, and is much shorter than the plain PV application. This is a great encouragement in marketing the PVT technology. [Copyright &y& Elsevier]

Abstract: The provision of mechanical ventilation in a semi-confined public transport interchange is mandatory in Hong Kong. The authority recommends the general use of low-level-supply and high-level-exhaust airflow schemes that different from the traditional ventilation concept in that low-level emitted vehicle pollutants are best removed at source. Analyses of air quality at typical public transport interchange environments are conducted for the two airflow schemes. The CFD simulations are generalized by studying light and heavy traffic conditions with adjusted ventilation rates to match the change in vehicle emission levels to examine pollutant concentrations at passenger waiting areas and the elevated footbridges. While the conventional high-level-supply and low-level-exhaust scheme could perform better during light traffic loads, the difference diminishes with increased traffic loads during peak hours. On the other hand, the high-level exhaust scheme has an advantage of serving as a smoke extraction system during a fire outbreak. [Copyright &y& Elsevier]

Abstract: Accurate prediction of building energy performance requires precise information of the local climate. Typical weather year files like test reference year (TRY) and typical meteorological year (TMY) are commonly used in building simulation. They are also essential for numerical analysis of the sustainable and renewable energy systems. The weather year file of one city is often employed by the nearby cities for such purposes. In this paper, the developments of customized weather year formulation are reviewed. The key issues are discussed making reference to two neighboring cities, Hong Kong and Macau, using their weather data records over a century, and the typical weather year files developed. The findings support the preference of TMY over TRY. It is also suggested that the TMY selection process should include the most recent meteorological observations, and should be periodically reviewed to well reflect the long-term climate change. [Copyright &y& Elsevier]

Abstract: In order to improve the energy performance of the photovoltaic system, much effort has been spent on the research and development of hybrid PVT (photovoltaic-thermal) technology using water as the coolant. The fin performance of the thermal absorber is known to be one crucial factor in achieving a high overall energy yield of the collector. Accordingly, an aluminum-alloy flat-box type PVT collector was constructed, with its fin efficiency approaching unity. Its design is primarily for natural circulation and for domestic water heating purpose. Our test results showed that a high final hot water temperature in the collector system can be achieved after a one-day exposure. A numerical model of this photovoltaic-thermosyphon collector system was also developed and the model accuracy was verified by comparison with measured data. The energy performance of the collector system was then examined first, through reduced-temperature analysis, and second, as applying in the “hot summer and cold winter” climate zone of China. The numerical results are found very encouraging, and the equipment is capable of extending the PV application potential in the domestic sector. [Copyright &y& Elsevier]

Abstract: There is a growing, government-led trend of applying renewable energy in Hong Kong. One area of interest lies in the wider use of solar-energy systems. The worldwide fast development of building-integrated solar technology has prompted the design alternative of fixing the solar panels on the external façades of buildings. In Hong Kong, high-rise buildings are found everywhere in the urban districts. How to make full use of the vertical facades of these buildings to capture the most solar radiation can be an important area in the technology promotion. In this numerical study, the potential application of a centralized solar water-heating system in high-rise residence was evaluated. Arrays of solar thermal collectors, that occupied the top two-third of the south and west façades of a hypothetical high-rise residence, were proposed for supporting the domestic hot-water system. Based on typical meteorological data, it was found that the annual efficiency of the vertical solar collectors could reach 38.4% on average, giving a solar fraction of 53.4% and a payback period of 9.2 years. Since the solar collectors were able to reduce the heat transmission through the building envelope, the payback was in fact even shorter if the energy saving in air-conditioner operation was considered. [Copyright &y& Elsevier]

Abstract: Weather data can vary significantly from year to year. There is a need to derive typical meteorological year (TMY) data to represent the long-term typical weather condition over a year, which is one of the crucial factors for successful building energy simulation. In this paper, various types of typical weather data sets including the TMY, TMY2, WYEC, WYEC2, WYEC2W, WYEC2T and IWEC were reviewed. The Finkelstein–Schafer statistical method was applied to analyze the hourly measured weather data of a 25-year period (1979–2003) in Hong Kong and select representative typical meteorological months (TMMs). The cumulative distribution function (CDF) for each year was compared with the CDF for the long-term composite of all the years in the period for four major weather indices including dry bulb temperature, dew point temperature, wind speed and solar radiation. Typical months for each of the 12 calendar months from the period of years were selected by choosing the one with the smallest deviation from the long-term CDF. The 12 TMMs selected from the different years were used for formulation of a TMY for Hong Kong. [Copyright &y& Elsevier]

A numerical simulation using a validated computational fluid dynamics model is used to investigate and compare the performances of displacement and mixing ventilations (MVs), under different boundary conditions. A companion paper will report the results in terms of thermal comfort, while this paper investigates the indoor air quality (IAQ). The IAQ will be measured in terms of carbon monoxide, mean age of air and the three volatile organic compounds, toluene, benzene and formaldehyde, which are commonly found in indoor room furnishings. The case studies include offices, classrooms, retail shops and industrial workshops, under typical Hong Kong thermal boundary conditions. Compared with conventional MV, displacement ventilation may provide better IAQ in the occupied zone. [Copyright &y& Elsevier]

A numerical simulation using a validated Computational Fluid Dynamics (CFD) model of several types of buildings was used to investigate the difference between mixing and displacement ventilation (DV). The comparison of performances of displacement and mixing ventilations (MV) will be reported in two parts, one on thermal comfort and the other one on indoor air quality. This paper, i.e., Part I, compares the performances of floor-supply DV systems with traditional MV systems for offices, classrooms, retail shops and industrial workshops under a wide range of Hong Kong thermal and flow boundary conditions, such as a very high cooling load. Through proper design, DV can maintain a thermally comfortable environment that has a low air velocity, a small temperature difference between the head and ankle level, and a low percentage of dissatisfied people. [Copyright &y& Elsevier]

Due to the existence of nonlinear mobile boundary conditions in the pyrolysis process of charring materials, such as the insulating layers of wires and cables, the precise tracing of the pyrolysis surface and calculating the pyrolysis rate pose a great challenge for researchers when trying to model the process using partial differential models. In this paper, the direct numerical simulation method including a set of partial differential equations has been exerted to make detailed studies on the pyrolysis of materials with changeable residual layers. In the simulation, a movable domain model was transformed to a fixed domain model and a cyclic iterative method was adopted to predict the thermal interface location between pyrolysis zone and virgin material. Resulting numerical results show good correlations with the exact solutions and the results of an integral model. In addition, influences of the residue mass ratio of the charring layer on the evolution of pyrolysis rate of the polyethene material with the time were also investigated. [ABSTRACT FROM AUTHOR]

The effect of fish oil (FO) on lipolysis and apparent biohydrogenation of linoleic (C18:2n-6, LA), linolenic (C18:3n-3, LNA), eicosapentaenoic (C20:5n-3, EPA) and docosahexaenoic (C22:6n-3, DHA) acid was studied in 6 and 24h in vitro incubations with diluted sheep rumen contents (50ml) as inoculum and six substrates (0.50g) containing compound feeds based on barley, sugar beet pulp and soybean meal. Feeds containing sunflower oil (SO, 80g/kg DM) or linseed oil (LO, 80g/kg DM), as C18:2n-6 and C18:3n-3 source, respectively, were further enriched with three levels of fish oil (0, 20 and 40g/kg DM), whereas addition of lard (40, 20 and 0g/kg DM) ensured equal amounts of added fat (120g/kg DM) in all feeds. Lipolysis was determined by the difference in triacylglycerol before and after incubation, whereas apparent biohydrogenation was calculated by the decrease of free polyunsaturated fatty acids (PUFA).FO had no influence on the degree of lipolysis or apparent biohydrogenation of C18:2n-6 and C18:3n-3, or on lipolysis of EPA and DHA in the different incubations. Biohydrogenation of EPA and DHA, however, was reduced with increasing FO dose. Compared to C18:2n-6 and C18:3n-3, lipolysis as well as biohydrogenation of EPA and DHA were significantly lower. Although C18:2n-6 and C18:3n-3 disappeared to the same extent, the amount of stearic acid (C18:0), the end-product of their biohydrogenation, was significantly lower in substrates with FO supplementation. Higher amounts of t11C18:1 and t11c15C18:2 in incubations with these substrates suggest that FO mainly inhibits the final step of biohydrogenation of C18:2n-6 and C18:3n-3.Addition of FO to diets containing C18:2n-6 or C18:3n-3 could increase ruminal accumulation and, hence, duodenal flow of t11C18:1. This could result in a higher uptake by the tissues and more substrate for the endogenous synthesis of c9t11CLA. [Copyright &y& Elsevier]

Land reclamation has been a long-term government policy of expanding the Hong Kong urban areas along the waterfront. These flat pieces of land are ideal sites for the application of district-cooling technology. At a central refrigeration plant, chilled water is generated and supplied to a district to support the air-conditioning systems in buildings. Because of the large-scale production, together with the convenience of bringing in seawater for condenser cooling, the chiller plant is higher in efficiency than those in individual buildings. The customers can also use the building space of their own more effectively. In this paper, the technical requirements and the cooling scheme options in the context of the subtropical urban environment are discussed. A government-commissioned feasibility study of a proposed district-cooling site in Hong Kong, with an estimated 200 MW cooling-plant capacity is then described. The proposed system and the methodology in predicting the thermal demand and the energy consumptions are introduced. [Copyright &y& Elsevier]

The overall performance of any solar energy project depends very much on the availability of solar radiation and the orientations of solar collectors. Presented in this paper is a numerical analysis of the solar irradiation received at the coastal region of South China. This region, with latitudes from 20.5°N to 24°N, belongs to the subtropical monsoon climatic zone. The computations were based on the typical meteorological year (TMY) weather data of Macau, compiled as a result of the ASHRAE International Weather for Energy Calculations Project. The hourly data were applied to the ESP-r building simulation program with the adoption of the Perez solar model. The analyses estimated the solar irradiation received on inclined surfaces at different orientations and slopes, and for different periods of the year. It was found that a solar collector facing the south-west direction could be most desirable for a wide range of tilt angles, and for maximizing the annual yield. The trends of variations towards other directions, tilt angles, and shorter periods of the year are also explored. [Copyright &y& Elsevier]

District cooling technology is advantageous in warm and hot climatic regions, in that chilled water from a central refrigeration plant is delivered through a distribution network to groups of buildings. The technology is most suitable for new urban developments where system design and construction receive much freedom. With a focus on the energy use, this paper outlines an energy modelling methodology and decision approach to derive the most desirable scheme for a given project. The process involves a series of building design load computation, dynamic simulation, and plant energy consumption analyses for different phases of development. A proposed scheme for the South East Kowloon Development Project in Hong Kong is quoted as an example to illustrate the approach. [Copyright &y& Elsevier]

A district-cooling system (DCS) has been applied in a number of countries where chilled water from a central plant is delivered through a distribution network to groups of buildings in an urban district. Because of the expected considerable investment and lengthy payback period, well-planned and optimized system design and operation are crucial areas leading to the success of the implementation. Much saving can be achieved when the plant serves a group of buildings with diversifying daily cooling-load patterns. Among various design factors and solution schemes, one important planning decision is therefore to determine the desirable mix of building types, within the district of interest, to be served by the DCS. An approach to determine this optimal mix through the use of genetic algorithm (GA) was described in this paper. The thermal-load modeling technique and the objective function for optimization were derived. The case studies showed that the method was effective to give optimal or near-optimal solutions. [Copyright &y& Elsevier]

Although the performance of hybrid photovoltaic-thermal (PV/T) collector had been studied both experimentally and numerically for some years, the thermal models developed in previous studies were mostly steady-state models for predicting the annual yields. The operation of a PV/T collector is inherently dynamic. A steady-state model is not suitable for predicting working temperatures of the PV module and the heat-removal fluid during periods of fluctuating irradiance or intermittent fluid flow. Based on the control-volume finite-difference approach, an explicit dynamic model was developed for a single-glazed flat-plate water-heating PV/T collector. A transport delay fluid flow model was incorporated. The proposed model is suitable for dynamic system simulation applications. It allows detailed analysis of the transient energy flow across various collector components and captures the instantaneous energy outputs. [Copyright &y& Elsevier]

• The merit of humidified gas turbine cycle was investigated. • Two air saturator designs were considered for performance comparison. • Detailed heat and mass transfer analysis were employed for the air saturators. • Parametric studies were conducted under different operating conditions. • The Maisotsenko combustion turbine cycle offered higher energy efficiency. The urge for more energy-efficient power plant systems to relieve the energy crisis triggers the design for more advanced power cycles. The humidified gas turbine cycle is considered one of the potential choices, and the air saturator performance is critical to the energy merit of such kind of system. To understand more, the performances of humidified gas turbine cycles with two types of air saturator designs were compared in this study. Type 1 air saturator was a hybrid design which combined an indirect evaporative cooler with a Maisotsenko cycle while Type 2 was a conventional indirect evaporative cooler. Detailed heat and mass transfer analysis was taken into account in the air saturator modelling. Through system simulations, it was found that all the humidified gas turbine cycle systems offered higher system efficiencies than a simple gas turbine system with recuperator. Besides, parametric studies were conducted which highlighted the effects of system inlet air temperature, turbine inlet temperature, water injection rate, and part-load ratio on the performances of the different humidified gas turbine cycle designs. The employment of Type 1 air saturator offered 9.34% and 23.55% enhancement in the system efficiencies as compared to those using Type 2 air saturator under the design and 50% part-load ratio conditions respectively. This reinforced the benefit of applying Maisotsenko cycle to the air saturator design of humidified gas turbine cycle for the enhancement of system efficiency. [ABSTRACT FROM AUTHOR]

An all-variable-speed chiller plant has been advocated so that the chillers and their associated pumps can work at reduced speed during part-load conditions for energy saving purposes. In this new building project, the savings merit is certainly attractive. However, an existing chiller plant or retrofit project, which is constrained by the performance of installed equipment and the configuration of a hydronic circuit, may not benefit from the an ideal extent of savings. As such, an existing chiller plant serving a typical commercial building was used to evaluate this. Through year-round dynamic simulation, it is found that there were about 5%, 6%, and 8% energy savings of the whole chiller plant when applying variable flow control on secondary chilled water pumps only, both primary and secondary chilled water pumps, and all chilled and condenser water pumps, respectively. If constant-speed centrifugal chillers were substituted by the variable-speed ones, an additional 4% savings could be achieved, which was, however, less than that incurred from the associated pumps. The payback periods of different variable flow control strategies were well below 1 year, indicating the techno-economical feasibility for wider application in existing chiller plants in subtropical climates. [ABSTRACT FROM AUTHOR]

Abstract: The performance of solar cooling systems with building-integrated (BI) solar collectors was simulated and the results compared with those having the solar collectors installed conventionally on the roof based on the weather data in Hong Kong. Two types of solar collectors and the corresponding cooling systems, namely the flat-plate collectors for absorption refrigeration and the PV panels for DC-driven vapour compression refrigeration, were used in the analysis. It was found that in both cases, the adoption of BI solar collectors resulted in a lower solar fraction (SF) and consequently a higher primary energy consumption even though the zone loads were reduced. The reduction in SF was more pronounced in the peak load season when the solar radiation was nearly parallel to the solar collector surfaces during the daytimes, especially for those facing the south direction. Indeed, there were no outputs from the BI flat-plate collectors facing the south direction between May and July. The more severe deterioration in the system performance with the BI flat-plate type collectors made them technically infeasible in terms of the energy-saving potential. It was concluded that the use of BI solar collectors in solar cooling systems should be restricted only to situations where the availability of the roof was limited or insufficient when applied in sub-tropical regions like Hong Kong. [Copyright &y& Elsevier]

Abstract: In this study, improvement was made for the solar-electric compression refrigeration system by incorporating the ejector design to a conventional vapour compression chiller within the system. Through year-round dynamic simulation, the performances of the ejector-assisted vapour compression chiller (EAVCC) were evaluated under the intermittent and changing supply of solar energy in the subtropical climate. In addition, the effect of three common refrigerants, R22, R134a and R410A on the EAVCC was assessed and compared. It was found that the coefficient of performance of the chiller was increased and the total primary energy consumption of the system was decreased for all the three refrigerants, in which the degree of enhancement from R134a was the most significant. It was also noted that the effect of R410A on EAVCC was not apparent, and the overall system energy improvement was marginal. With appropriate ejector design and refrigerant selection of the solar-electric compression refrigeration system, the reduction potential of year-round primary energy consumption could be more than 5%. This would be certainly helpful in promoting the application of solar air-conditioning for building use in the subtropical climate. [Copyright &y& Elsevier]

Abstract: Although solar energy is able to power the heat-driven refrigeration, its contribution is quite limited due to the conventional cooling requirement. In building air-conditioning, it is common to supply low temperature chilled water, usually in 5–7°C. If this temperature can be elevated, it would enhance the effectiveness to harness solar energy and minimize auxiliary heating. Solar refrigeration would then be more effective through high temperature cooling, by providing 15–18°C chilled water instead. In such provision, radiant ceiling cooling can be coupled to handle the space cooling load, particularly space sensible load. And the space latent load and ventilation load are handled by a separate dehumidification provision, like the heat-driven desiccant dehumidification. Therefore, a solar hybrid air-conditioning system is formulated, using adsorption refrigeration, chilled ceilings and desiccant dehumidification. In this study, the year-round performances of the proposed solar hybrid air-conditioning systems were evaluated for two typical office types. The performance metrics include the solar fraction, coefficient of performance, solar thermal gain, primary energy consumption and indoor conditions. Comparative study was conducted for the hybrid air-conditioning system worked with the three common types of chilled ceilings, namely the chilled panels, passive chilled beams and active chilled beams. The solar hybrid air-conditioning system was also benchmarked with the conventional vapour compression refrigeration for office use. It is found that the proposed solar hybrid air-conditioning system is technically feasible through high temperature cooling. Among the three types of chilled ceilings, the passive chilled beams is the most energy-efficient option to work with the solar adsorption refrigeration for space conditioning in the subtropical city. [Copyright &y& Elsevier]

Abstract: A district cooling system is a sustainable means of distribution of cooling energy through mass production. A cooling medium like chilled water is generated at a central refrigeration plant and supplied to serve a group of consumer buildings through a piping network. Because of the substantial capital investment involved, an optimal design of the distribution piping configuration is one of the crucial factors for successful implementation of the district cooling scheme. In the present study, genetic algorithm (GA) incorporated with local search techniques was developed to find the optimal/near optimal configuration of the piping network in a hypothetical site. The effect of local search, mutation rate and frequency of local search on the performance of the GA in terms of both solution quality and computation time were investigated and presented in this paper. [Copyright &y& Elsevier]

Abstract: Energy management of heating, ventilating and air-conditioning (HVAC) systems is a primary concern in building projects, since the energy consumption in electricity has the highest percentage in HVAC among all building services installations and electric appliances. Without sacrifice of thermal comfort, to reset the suitable operating parameters, such as the chilled water temperature and supply air temperature, would have energy saving with immediate effect. For the typical commercial building projects, it is not difficult to acquire the reference settings for efficient operation. However, for some special projects, due to the specific design and control of the HVAC system, conventional settings may not be necessarily energy-efficient in daily operation. In this paper, the simulation-optimization approach was proposed for the effective energy management of HVAC system. Due to the complicated interrelationship of the entire HVAC system, which commonly includes the water side and air side systems, it is necessary to suggest optimum settings for different operations in response to the dynamic cooling loads and changing weather conditions throughout a year. A metaheuristic simulation–EP (evolutionary programming) coupling approach was developed using evolutionary programming, which can effectively handle the discrete, non-linear and highly constrained optimization problems, such as those related to HVAC systems. The effectiveness of this simulation–EP coupling suite was demonstrated through the establishment of a monthly optimum reset scheme for both the chilled water and supply air temperatures of the HVAC installations of a local project. This reset scheme would have a saving potential of about 7% as compared to the existing operational settings, without any extra cost. [Copyright &y& Elsevier]

The energy performances of three types of ventilation systems, namely the mixing, displacement, and stratum ventilation systems, are compared when applied to a traditional class, a study group, and an E-learning class in a school. A solid desiccant dehumidification cycle, coupled with a solar heat collecting system, is employed to faciliate the humidity control in the displacement and stratum ventilation systems. Meanwhile, a higher design coefficient of performance for the chillers is adopted in view of the possibility to apply the systems to the entire school. It was found that the stratum ventilation systems are the best among the three ventilation systems investigated, particularly when applied to a study group class and a E-learning class, which represent a trend in school education development. With promising results even without solar provision, the stratum ventilation systems could be a good choice for use in the schools in Hong Kong. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an investigation into the use of occupancy space electrical power demand to mimic occupants’ activities in building cooling load prediction by intelligent approach. The occupancy space electrical power demand is obtained from an intelligent networked building power monitoring system. It works as a prototype advanced metering infrastructure – a key feature in smart grid technology. The artificial neural network model adopted is the Levenberg–Marquardt algorithm. The input parameters include the usual external climatic data, hour-type/day-type and pretreated air unit operation schedule, and the occupancy space electrical power demand. The output is the electrical power demand of the building cooling system. Simulation studies are conducted for a university building in Hong Kong. The 2010 and 2011 yearly data is used to conduct simulations. The performance indices used in evaluating the prediction performance are the coefficient of correlation (R), coefficient of variation (CV) and mean absolute percentage error (MAPE). It is demonstrated that with the use of occupancy space electrical power demand as one of the model input parameters, the prediction accuracy of the building cooling load model can be improved. In summer season, the best MAPE and CV is 4.494% and 5.808% respectively for hourly prediction, and is 1.935% and 2.345% respectively for daily prediction. On daily peak cooling load prediction in summer season, the best MAPE and CV is 2.313% and 2.862% respectively. It is found that the variability in the prediction is modest in summer season. [Copyright &y& Elsevier]

Abstract: Stratum ventilation has been proposed to accommodate elevated indoor temperatures recommended by governments in East Asia. TRNSYS is used for computation of the space cooling loads, sensible and latent, as well as system energy consumption. Typical configurations of an office, a classroom and a retail shop in Hong Kong are investigated. Desiccant dehumidification with and without solar assistance is utilized for the air treatment under displacement ventilation and stratum ventilation, while simple reheating is adopted under mixed ventilation. Compared with mixing ventilation and displacement ventilation, stratum ventilation derives its energy saving potential largely from the following five factors: the reduction in ventilation, dehumidification and transmission loads, prolonged free cooling period and increased the COP of the chillers. For the office, the year-round energy saving is found to be substantial at 20% and 40% without the need for solar energy provision when compared with displacement ventilation and mixing ventilation respectively. For the classroom and retail shop, the year-round energy saving is at about 25% and at least 37% with the aid of solar energy provision when compared with displacement ventilation and mixing ventilation respectively. [Copyright &y& Elsevier]

Solar air-conditioning can have higher application potential for buildings through the strategy of high temperature cooling. In recent years, displacement ventilation (DV), which makes use of the indoor rising plumes from the internal heat gains, provides a more effective supply air option than the traditional mixing ventilation (MV) in terms of both thermal comfort and indoor air quality. As it is possible to raise the supply air temperature to 19°C for DV, it would enhance the competitive edge of the solar air-conditioning against the conventional vapour compression refrigeration. Through dynamic simulation, a solar-desiccant-cooling displacement ventilation system (SDC_DV) was developed for full-fresh-air provision, while a solar-hybrid-desiccant-cooling displacement ventilation system (SHDC_DV) for return air arrangement. The latter was further hybridized with absorption chiller (AB) to become SHDCAB_DV, or adsorption chiller (AD) to be SHDCAD_DV, in order to be wholly energized by the solar thermal gain. Benchmarked with the conventional system using MV, the SDC_DV had 43.3% saving in year-round primary energy consumption for a typical office in the subtropical climate; the SHDCAB_DV had 49.5% saving, and the SHDCAD_DV had 18.3% saving. Compared with their MV counterparts, the SDC_DV, the SHDCAB_DV and the SHDCAD_DV could have 42.4%, 21.9% and 30.3% saving respectively. [ABSTRACT FROM AUTHOR]

Abstract: Stratum ventilation has been proposed to cope for elevated indoor temperatures recommended by governments in East Asia. TRNSYS is used for computation of the space cooling load and system energy consumption. Typical configurations of an office, a classroom and a retail shop in Hong Kong are investigated. Compared with mixing ventilation and displacement ventilation, stratum ventilation derives its energy saving potential largely from the following three factors: the reduction in ventilation and transmission loads and increased COP of chillers. The year-round energy saving is found to be substantial at 25% and 44% at least when compared with displacement ventilation and mixing ventilation, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The effect brought about by the burning of cables and its effect on building fires poses many problems and challenges for researchers. One of the main reasons is that the numerical simulation of the pyrolysis process is especially difficult because of the presence of non-linear moving boundary conditions in the partial differential equations. This paper presents the results of a detailed numerical simulation of the pyrolysis process of materials with a volatile residue layer using partial differential equations. The movable region formula in this case was transformed to the fixed region formula, and a pre-evaluation iteration method was used for tracing the pyrolysis front. Numerical simulation results were found to compare well with those of the precise solution and integral model. The effects of the volatile char on the pyrolysis rate, varying with time were then obtained. [Copyright &y& Elsevier]