• Energy Research

Abstract 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 Stratum ventilation (SV), a new indoor air distribution strategy, has been promoted for applications in different building premises in recent years. Compared to the conventional mixing ventilation (MV), the prominent advantage of SV is that indoor thermal comfort can be satisfied with a relatively high supply air temperature, hence less energy consumption in refrigeration. In solar air-conditioning, the energy performance can also be facilitated by high-temperature cooling. As such, the potential of SV to be involved in solar air-conditioning was evaluated. In this study, the solar air-conditioning systems included solar absorption cooling system (SAbCS), solar adsorption cooling system (SAdCS), solar desiccant cooling system (SDCS), hybrid solar absorption-desiccant cooling system (HSAbDCS) and hybrid solar adsorption-desiccant cooling system (HSAdDCS). Their performances using SV and MV were determined through year-round dynamic simulation. Compared to the counterpart using MV, SAbCS, SAdCS, SDCS, HSAbDCS and HSAdDCS associated with SV could have 35%, 54%, 59%, 29% and 44% saving in the annual primary energy consumption for building in subtropical climate respectively. Benchmarked with the conventional air-conditioning system, they could have primary energy saving up to 30%. Consequently, solar air-conditioning and SV can have synergetic merit in building application in hot and humid city.

AbstractThe year-round dynamic performances of various types of internal-combustion-engine primed trigeneration (ICEPT) systems were analyzed and compared with that based on a conventional system powered by the grid electricity when they were applied to a high-rise office building in Hong Kong. It was found that the employment of the ICEPT systems reduced the total energy demand from the building by at most 10.9%. However, the saving in the carbon dioxide emission varied widely with the prime mover used with a maximum of only 13.2% for a natural-gas-fueled ICEPT system. One major reason was the relatively lower carbon dioxide emission index from the local grid electricity. In this regard, the sufficient supply of natural gas or biofuels is necessary in order to reduce the carbon dioxide emission through the employment of ICEPT systems in Hong Kong.

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.

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 Solar cooling is a novel approach, which primarily makes use of solar energy, instead of electricity, to drive the air-conditioning systems. In this study, solar-assisted desiccant cooling system (SADCS) was designed to handle the cooling load of typical office in the subtropical Hong Kong, in which half of the building energy is consumed by the air-conditioning systems. The SADCS mainly consisted of desiccant wheel, thermal wheel, evaporative coolers, solar air collectors and gas-fired auxiliary heater, it could directly tackle both the space load and ventilation load. Since the supply air flow is same as the outdoor air flow, the SADCS has a feature of sufficient ventilation that enhances the indoor air quality. Although it is inevitable to involve the auxiliary heater for regeneration of desiccant wheel, it is possible to minimize its usage by the optimal design and control scheme of the SADCS. Through simulation–optimization approach, the SADCS can provide a satisfactory performance in the subtropical Hong Kong.

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.

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.

This paper presents a new clustering-based sensor fault detection and diagnosis (SFDD) strategy for chilled water system. For data clustering, k-means algorithm was used and the optimal quantity of clusters was determined by Davis-Bouldin value. With the cluster centroid dataset, the featuring centroid score (CS) was determined for the fault-free sensor reading dataset thus the threshold for fault detection could be set. The database for sensor fault detection was then formed. By characterizing the CS patterns of different types of sensor fault, the database for sensor fault diagnosis was generated accordingly. Various sensor fault types could be handled, including bias, drift, precision degradation and complete failure. In this study, the developed SFDD strategy was applied to the sensor of primary chilled water return temperature in a water-cooled chilled water system. With the databases of sensor fault detection and diagnosis, the real-time measured sensor readings can be examined. Once sensor fault is detected, the fault type can be confirmed within a day at soonest or 2 days at most. The smallest detectable absolute bias value, absolute drifting rate and precision degradation error could be down to 0.25 °C, 0.025 °C/h and 0.1 °C respectively, demonstrating robustness of the proposed SFDD strategy.