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Computer simulation plays an important role in investigating the thermal/energy performance of buildings and energy systems. In order to reduce the computational time and provide a consistent form of weather data, simulation run with multi-year weather files is generally avoided. In contrast, representative weather data is widely adopted. For developing typical meteorological year (TMY) weather files, Sandia method is one of the commonly adopted approaches. During the generation of TMY, different weighting factors are assigned to some key climatic indices. Currently, the values of weighting factors mainly depend on the researchers' judgement. As these weighting factors can express the relative importance of impact of a particular climatic index on the thermal/energy performance of an energy system, computer simulation using different TMYs may lead to different conclusions. Therefore, it is inappropriate to apply one single TMY for all energy systems. In this study, a novel TMY weather file generator has been developed to link up an optimization algorithm and an energy simulation program. Through four application examples (one air-conditioned building and three renewable energy systems), this weather file generator demonstrated its capability to search optimal/near optimal combinations of weighting factors for generating appropriate TMY for computer simulations of different energy systems. [ABSTRACT FROM AUTHOR]

In a residential building, a balcony of an upper floor can act as an overhang; and provide solar shading and reduction in electricity consumption of air-conditioner (A/C) for a flat on the underneath floor. However, some residential flats located on the lower levels may receive substantial self-shading effect from some adjacent flats in the same building block, leading to an insignificant shading effect from a balcony. As there is substantial amount of energy consumed and pollutant generated during the production and disposal of a balcony, it is vital to investigate the energy and environmental performance of residential flats installed with balconies at various floor levels. The objective of this study is to investigate an appropriate floor level of a residential building above which balconies should be incorporated. A 21-story residential building was modeled using EnergyPlus. Simulation results indicated that, for a west-facing flat, only the flats located on 15/F to 20/F can give acceptable environmental payback periods, ranging from 58.3 years to 40.7 years, i.e. within the lifespan (60 years) of a building. The corresponding annual savings in A/C consumption range from 234.9 MJ (2.60%) to 336.7 MJ (3.57%). The research methodology and findings are presented in this paper. [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: There are various architectural features of a residential building that can influence its indoor climate and electricity consumption, such as thermal insulation, window size, glazing material, albedo of building façade and orientation. In addition to these architectural features, shading effects (either by external objects or by the building itself) can also affect the thermal performance of a building. External shading effects are mainly caused by nearby trees or buildings, while shading effect imposed by the building itself usually depends on the layout design of the building, i.e. building shape and layout arrangement of the flats on each floor. Some flats in a building may receive a shading effect from adjacent flats located in the same building block. When architects or building designers conduct the layout design of a building, a number of factors such as building regulations, site limitations, scenic view, noise control, natural ventilation and daylight utilization will be considered. The thermal performance of a building is one of the major issues that should be taken into account. The objective of this study is to assess the thermal performance of residential buildings under the effect of adjacent shading in subtropical Hong Kong. A literature survey was carried out to identify typical layout designs of residential buildings from the past two decades. Building energy simulations were conducted for residential building blocks with different layout designs. It is found that adjacent shading effect has a substantial impact on the thermal performance of residential buildings. The findings are reported in this paper. [Copyright &y& Elsevier]

Abstract: In the past decade, the application of phase change material (PCM) wallboard in building façade has gained wide attention around the world. For successful application of PCM integrated building façade, a number of crucial factors including thermo-physical properties of PCM, outdoor climate condition, operating schedule of building, investment cost and tariff structure should be taken into account. In this study, a typical residential flat with PCM integrated external walls constructed in the living room and bedroom was modeled and the thermal/energy performance was investigated. The effect of PCM integrated wall''s orientation was also evaluated. Through computer simulations, it was found that the living room of a residential flat with west-facing integrated external wall could perform better. It gave a comparatively higher decrease in the interior surface temperature up to a maximum of 4.14%. Moreover, an annual energy saving of 2.9% in air-conditioning system was achieved. However, a long cost payback period of 91 years makes the PCM integrated building façade economically infeasible. On the other hand, the energy payback period was estimated as 23.4 years for this building case, indicating that the energy saving can surpass the embodied energy of PCM wallboard and mitigate the greenhouse gas emission. [Copyright &y& Elsevier]

Abstract: The concern on climate change leads to growing demand for minimization of energy use. As building is one of the largest energy consuming sectors, it is essential to study the impact of climate change on building energy performance. In this regard, building energy simulation software is a useful tool. A set of appropriate typical weather files is one of the key factors towards successful building energy simulation. This paper reports the work of developing a set of weather data files for subtropical Hong Kong, taking into the effect of future climate change. Projected monthly mean climate changes from a selected General Circulation Model for three future periods under two emission scenarios were integrated into an existing typical meteorological year weather file by a morphing method. Through this work, six sets of future weather files for subtropical Hong Kong were produced. A typical office building and a residential flat were modeled using building simulation program EnergyPlus. Hourly building energy simulations were carried out. The simulated results indicate that there will be substantial increase in A/C energy consumption under the impact of future climate change, ranging from 2.6% to 14.3% and from 3.7% to 24% for office building and residential flat, respectively. [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: 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: 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]

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]

Photovoltaic (PV) system is a commonly adopted renewable energy system in building application. In most of the assessments on PV system, there is no consideration on adjacent shading effect cast by surrounding buildings which may lead to over-estimation of PV energy generation and inaccurate calculation of energy payback time (EPBT). This paper investigates the effect of adjacent shading on energy generation and EPBT of PV system. A survey had been conducted to identify and select 25 existing commercial buildings with different degrees of adjacent shading (expressed in terms of sky view factors (SVF), ranging from 0.16 to 0.95) and orientations. Through computer simulations using EnergyPlus, it reveals the significance of adjacent shading effect on the PV energy generation as well as EPBT of building-integrated PV glazing system for the 25 selected buildings, in terms of two ratios, namely PV electricity energy ratio (0.18–0.84) and energy payback time ratio (1.17–5.74). Moreover, a correlation between SVF and PV electricity energy ratio was established (PVEE Ratio = 0.3867 SVF 2 + 0.4176 SVF + 0.0975) with which building professionals can evaluate the PV energy generated and EPBT of a building-integrated PV glazing system in building application, under adjacent shading effect. • Twenty five buildings with different sky view factors were identified and selected. • Building energy simulation program was validated by using published data. • Simulations were run to study the effect of adjacent shading on PV glazing system. • Large discrepancy in PV energy generated among cases with various sky view factors. • Correlation was developed for assessing PV system under adjacent shading effect. [ABSTRACT FROM AUTHOR]

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]

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]

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: 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: 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]