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Energy pile group is an important component of ground source heat pumps with foundation piles as ground heat exchangers. Among different energy piles, those with spiral pipes have a large heat exchange area between the pipe and the concrete, achieving good heat exchanging performance and wide applications. To analyze the influence of geometrical parameters (pile layout, pile spacing and pile depth) and external parameter (groundwater velocity) on the heat transfer of spiral-coil energy pile groups, a three-dimensional analytical model of spiral-coil energy pile groups with seepage is used, considering the thermal interaction among different piles, the geometry of spiral pipe and the velocity of groundwater. The soil temperature distribution in the energy pile group is studied under conditions with different factors (pile layouts: 3 × 2, L shape and line shape; pile spacing distances: 3, 5 and 7 m; pile depths: 10, 30 and 50 m; and groundwater velocities: 0, 1.2 × 10−6 and 2.0 × 10−6 m/s). The 3-year outlet fluid temperature of energy pile group affected by the above different factors under different inlet fluid temperatures and velocities or soil thermal exchange ratios is investigated. Results show that for the low fluid velocity inside the piles, the influence of above factors on the thermal performance of energy piles is more obvious. Large groundwater velocity, line shape pile layout, large pile spacing distance and short pile depth can alleviate the long-term temperature variation caused by unbalanced soil heat exchange. This work will facilitate the research, design and application of the energy pile group in ground source heat pumps. [ABSTRACT FROM AUTHOR]

With the growing prosperity of the offshore wind energy market and the approaching end of the lifetime of the first-generation offshore wind farms, the high decommissioning cost has attracted increasing attention all over the world. To decrease this cost, the spotential repowering strategies are applied into the wind farm optimization and investigated in this study. In the repowering optimization strategy, the wind turbine foundations are not dismantled immediately after their service lifetime, and the lifecycle of them is extended to two generations' service time. The costs of removing the first foundations and installing the second foundations are saved. With the layout optimization method, the wind loss caused by wake effect can be decreased, which improve the energy output of the wind farm in the whole lifetime. Levelised cost of energy (LCoE) is set as the criterion to evaluate the wind farm layout. Both aligned and optimized layouts are analyzed in this study. A case study in Sha Chau Island seawater area in Hong Kong is then discussed. The results reveal that Hong Kong has many advantages to exploit offshore wind power and the repowering optimization layout is practical for cost-saving. According to this study, the LCoE of an offshore wind power farm in Sha Chau Island seawater area could be decreased to 0.9130 HK$/kWh. [ABSTRACT FROM AUTHOR]

The use of pumps as turbines (PATs) in different applications has attracted increasing attention in recent years. Based on our previous research, the PAT could be used in water supply system of high-rise buildings for water head reduction and hydropower generation, but the efficiency is relatively low. Due to the high water head and low flow rate, PATs used in water pipelines are usually low specific speed turbines. According to the impeller inlet and outlet velocity triangles, the blades wrap angle of a centrifugal pump is not optimal for low specific speed turbines, so the impact of blades wrap angle on the PAT performance should be studied. In this paper, the impact is investigated by numerical and experimental methods. Firstly, a 3D model of an original PAT was built in CAD software, then the model was imported into the ICEM to generate grids and then imported into Ansys CFX for simulation. After simulation, a PAT prototype was tested in the lab test rig to validate the simulation results. The comparison between simulation and experimental results indicates that although some deviations exist, the simulation could provide an acceptable prediction of the PAT's performance. Finally, four PAT models with different blades wrap angles were developed to compare their performance in terms of both power output and water head reduction. The results show that the blades wrap angle does have effects on the PAT's efficiency and hydraulic loss, to achieve a good balance between water head reduction and power output. The model with -60° wrap angle has the best performance. [ABSTRACT FROM AUTHOR]

The heat storage device is proposed to avoid the frequent on–off state under partial load, large variation of the supply and return water temperature and long defrosting time of air-to-water heat pump with plate heat exchanger for heating. The heat storage device is composed of a water tank, the inner double-pipe heat exchanger, appendages and the electric heater. The energy storage can reduce on–off times of the compressor. The energy storage and the electric heater can make up the shortage of heating during defrosting. Performance test shows that on–off times for the heat storage device unit compressor under partial load is about four times per hour compared six times per hour for the plate heat exchange unit. Defrosting time is reduced by 78 s by heat storage device unit and 84 s by heat storage device with electric heater unit. More steady running parameters, inlet heating water temperature of heat storage device or heat storage device with electric heater unit is about 35°C, while that of plate heat exchanger reduces to 30.73°C. Therefore, the designed heat storage device can improve the unit performance and is suitable for the new projects with air-to-water heat pumps. [ABSTRACT FROM AUTHOR]

Climate change may seriously affect the energy consumption of buildings by influencing their air conditioning loads, especially the ventilation loads which vary directly with the local weather conditions. Research on how the ventilation load responds to climate change is of great significance, especially in coastline subtropical regions like Hong Kong. This paper investigated the impacts of climate change on buildings' ventilation load and building energy use in Hong Kong with the hourly meteorological data from 1950 to 2007. Results have been well validated by the simulation of a typical local hotel building during this period. The results show that climate warming increases both sensible and latent parts of the cooling ventilation load. The latent part, which occupies ∼80% of the total ventilation load, increases at a higher rate, about twice of that of the sensible one. Furthermore, it is found that the urban heat island (UHI) effect causes a much higher growth rate of the ventilation load at night, which is about three times compared with that in the daytime. The latent part of the cooling ventilation load at night, which is found to be the most sensitive component to the climate change, plays a most significant role in the energy consumption increase. The possible measures were thus suggested to avoid negative changes of the ventilation load. Besides, reducing the UHI effect by better urban planning also significantly benefits the local buildings with a long air-conditioning operation time. [ABSTRACT FROM AUTHOR]

In order to investigate the operation performance of ground-coupled heat-pump (GCHP) system, an analytical simulation model of GCHP system on short time-step basis and a computer program based on this model to predict system operating parameters are developed in this study. Besides, detailed on-site experiments on GCHP test rig installed in a temperate region of China are carried out. The temperature distributions of borehole as well as ground around borehole at different depths are evaluated. Operation parameters of GCHP system such as circulating water temperature, heat rejection into ground and system power consumption when the system operated in intermittent and continuous modes are investigated. The accuracy of proposed simulation model is validated by experimental data. The advantage of GCHP technology in energy efficiency over other conventional air-conditioning systems is proved to be obvious and the performance of GCHP system is found to be affected by its operation modes. [ABSTRACT FROM AUTHOR]

This paper reports the exergetic modeling and performance evaluation of a novel multi-functional solar-assisted heat pump (SAHP) system based on an experimental study. Comparisons between the multi-functional SAHP system and conventional hot water heating systems, i.e. electric water heater, gas-fired water heater and air source heat pump, are made with respect to energy and exergy efficiencies. The results show that the multi-functional SAHP system has the highest energy performance, average 2.98. In addition, the multi-functional SAHP system offers the highest exergy efficiency among the four kinds of hot water heating systems. [ABSTRACT FROM AUTHOR]

The application of building-integrated photovoltaic technology has developed very rapidly in recent years. This paper presents a review of the development of the BIPV applications in major countries around the world. It is found that demonstration projects can help the promotion of the technology at the beginning of any BIPV programmes, but the government energy policy and incentive strategies play a critical role for its sustainable development. Based on our experience of BIPV research and consultancy projects completed in Hong Kong, the past, current and future application of this technology is summarized. The future potential of BIPV contribution can be a substantial part of the demand. [ABSTRACT FROM AUTHOR]