T.T. Chow

Global optimization of absorption chiller system by genetic algorithm and neural network

The optimal use of fuel and electricity in a direct-fired absorption chiller system is important in achieving economical operation. Previous work on the control schemes mainly focused on the component local feedback control. A system-based control approach, which allows an overall consideration of the interactive nature of the plant, the building and their associated variables is seen to be the right direction. This paper introduces a new concept of integrating neural network (NN) and genetic algorithm (GA) in the optimal control of absorption chiller system. Based on a commercial absorption unit, neural network was used to model the system characteristics and genetic algorithm as a global optimization tool. The results appear promising.

Building-integrated photovoltaic and thermal applications in a subtropical hotel building

Effective cooling of a PV panel is able to increase the electricity output of the solar cells. This paper describes a comparative study of three different options in applying large-scale building-integrated PV technology in a coastal city at the South China Sea. The computational model was based on a 260 m2 mono-crystalline silicon PV wall on a 30-storey hotel building. The numerical analysis was via the ESP-r building energy simulation software. The results showed that the different design options exhibit short-term electrical performance differences, but have similar long-term electricity yields. However, some design options perform much better in reducing the air-conditioning loads of the building.

Dynamic performance of hybrid photovoltaic/thermal collector wall in Hong Kong

Abstract This paper presents a computational thermal model that has been used for analyzing the annual performance of facade-integrated hybrid photovoltaic/thermal collector system for use in residential buildings of Hong Kong. In the study, the applications of EPV (film cell) and BPV (single silicon cell) panels in this hybrid photovoltaic/hot-water system were investigated. Simulation results based on test reference year data showed that the annual average electrical efficiencies of the hybrid EPV and BPV modules are, respectively, 4.3% and 10.3%, the corresponding annual average thermal efficiencies to hot water are 47.6% and 43.2%, and the reductions of space heat gain in summer season through the collector wall are 52.9% and 59.1%. The overall thermal efficiencies are 58.9% and 70.3% respectively, which are much better than the conventional solar collector performance.

Performance of ventilation system in a non-standard operating room

Abstract The ventilation system of a hospital operating room is to provide a comfortable and healthy environment for the patient and the surgical team. Thermal comfort can be achieved by controlling the temperature, the humidity, and the air movement. A healthy environment can be achieved by minimizing the risk of contamination through appropriate filtration and air distribution scheme. The design and construction of operating rooms in Hong Kong, including the upgrading of the older ones, have been based on the UK Health Building Notes and Health Technical Memoranda. Observations and field measurements in a case study found that the airflow and some design features were not fully complied with the specified requirements. A CFD analysis supported by field measurements was made to simulate the temperature distribution, airflow pattern and the contaminant dispersion. The study placed an emphasis on the health risk of the airborne bacteria released from the surgical team on the patient, and vice versa.

Domestic air-conditioner and integrated water heater for subtropical climate

The technology of using a heat pump for space conditioning and domestic hot water heating in residences has been developed for half a century. The earlier air-to-water heat pumps and water-heating heat pumps suffered from drawbacks like high costs, unreliable operation, and inflexible applications. They were not well positioned in the market to attract customers. This paper introduces a novel air-conditioning product that can achieve the multi-functions with improved energy performance. The basic design principles and the laboratory test results are presented. The results showed that by incorporating a water heater in the outdoor unit of a split-type air-conditioner so that space cooling and water heating can take place simultaneously, the energy performance can be raised considerably.

Evaluation of thermal comfort conditions in a classroom with three ventilation methods.

UNLABELLED Thermal sensation is studied experimentally under mixing ventilation, displacement ventilation, and stratum ventilation in an environmental chamber. Forty-eight subjects participated in all tests under the same boundary conditions but different ventilation methods in the classroom. Thermal comfort analysis was carried out according to the designated supply airflow rate, room temperature, and relative humidity for the three ventilation methods. The thermal neutral temperature under stratum ventilation is approximately 2.5 °C higher than that under mixing ventilation and 2.0 °C higher than that under displacement ventilation. This result indicates that stratum ventilation could provide satisfactory thermal comfort level to rooms of temperature up to 27 °C. The energy saving attributable to less ventilation load alone is around 12% compared with mixing ventilation and 9% compared with displacement ventilation. PRACTICAL IMPLICATIONS The confirmation of the significantly elevated thermal neutral temperature can have a number of implications for both thermal comfort in an air-conditioned room and energy consumption of the associate air-conditioning system. With respect to the former, it provides scientific basis for the feasibility of elevated room temperatures, and with respect to the latter, it reveals considerable potentials for energy saving.

Hybrid solar: A review on photovoltaic and thermal power integration

The market of solar thermal and photovoltaic electricity generation is growing rapidly. New ideas on hybrid solar technology evolve for a wide range of applications, such as in buildings, processing plants, and agriculture. In the building sector in particular, the limited building space for the accommodation of solar devices has driven a demand on the use of hybrid solar technology for the multigeneration of active power and/or passive solar devices. The importance is escalating with the worldwide trend on the development of low-carbon/zero-energy buildings. Hybrid photovoltaic/thermal (PVT) collector systems had been studied theoretically, numerically, and experimentally in depth in the past decades. Together with alternative means, a range of innovative products and systems has been put forward. The final success of the integrative technologies relies on the coexistence of robust product design/construction and reliable system operation/maintenance in the long run to satisfy the user needs. This paper gives a broad review on the published academic works, with an emphasis placed on the research and development activities in the last decade.

Building-mix optimization in district cooling system implementation

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.

The Integrated Effect of Medical Lamp Position and Diffuser Discharge Velocity on Ultra-clean Ventilation Performance in an Operating Theatre:

The ventilation system of an operating theatre (OT) in a hospital needs to provide a comfortable and healthy surgical environment, particularly to minimise the risk of airborne infection. Engineering standards are available to outline specialised ventilation design and installation requirements based on knowledge accumulated from quality research and day-to-day practices. In this paper, the integrated effect of a reduction in supply air velocity and changed medical lamp positions on the ultra-clean ventilation performance of a standard OT environment is reported. The dispersion of infectious particles from both the surgical team and the patient were examined through computational fluid dynamic analysis. It was observed that variations in supply velocity and medical lamp configuration will only slightly affect the thermal comfort environment. However, they could have a serious effect on the movement of infectious particles and hence increase the cross infection risk.

Effect of building re-entrant shape on performance of air-cooled condensing units

Provision of split-type air-conditioners in high-rise residential buildings has become fashionable in Hong Kong. Building re-entrants are most popular for placing the outdoor condensing units. Heat energy dissipated by these condensing units induces a buoyant airflow. Inadequate displacement of air may lead to an elevated temperature environment at the re-entrant, which could significantly affect the condenser performance at the upper floors and subsequently result in a degradation of the overall capacity and efficiency of the air-conditioners. In recent years, some innovative building designers go for sustainable housing design. Re-entrants of various shapes thus evolve. One of their concerns is whether these various shapes would incur more difficulties in the airflow and thereby, would intensify the condenser heat dissipation problem. This paper describes some investigations on different re-entrant shapes making use of the computational fluid dynamics (CFD) techniques together with an energy evaluation model. The results show no evidence that the new re-entrant shapes will have adverse effects in comparison with the conventional design.