The global climate and environment are increasingly being affected by the vast amount of anthropogenic greenhouse-gas emissions generated by energy consumption in many parts of the world. Fast population growth and the rapid development of communities are two of the major factors behind the ever-growing demand for energy, which is further exacerbating emissions.
Energy consumed in the residential and commercial sectors for heating, cooling and water heating accounts for 20% of the world’s total energy consumption. In order to alleviate this problem, one of the viable options is the development of smart green buildings.
Green buildings aim to use resources efficiently both in regard to life-cycle effects and building performance in order to minimise their impact on the environment. Smart buildings feature integrated building technology systems along with construction and operational efficiencies that enhance management and occupant functions.
Given these characteristics, green buildings can benefit the environment, the economy and society as a whole from a variety of perspectives: biodiversity and ecosystems can be protected and enhanced, air and water quality can be improved, waste streams can be reduced, and natural resources can be conserved and restored.
Smart green buildings can also reduce overall operating costs, improve occupant productivity, enhance the asset value and profits, and optimise the life-cycle economic performance. They can also enhance the health and comfort of their occupants by improving the indoor air quality, minimising the strain on the local utility infrastructure and improving the overall quality of life.
I am delighted to introduce the seven papers of HKIE Transactions -- Special Issue on Energy Engineering with the Applications in Smart Green Buildings.
The study conducted by Hui and Chan aimed to eliminate the irritating dripping that results from high relative humidity by proposing directly compressed hot and humid air using the recently invented Hui turbine, instead of the displacement pressurisation of refrigerant. When compared with the usual Rankine cycle heat pump, the chill production from this cooling and dehumidifying process was more than doubled.
Liu et al. studied the thermodynamic performances of six different two-stage transcritical carbon dioxide (CO2) refrigeration systems with expanders. They found that among several design parameters, the gas cooler exit temperature and the low-stage compressor efficiency were the major factors which influence the coefficient of performance of the system.
Mui et al. investigated the cooling energy consumption needed for indoor environment quality acceptance in air-conditioned office buildings. The results of their study showed that the conventional constant air volume system with a fixed fresh air flow rate was less energy efficient than the demand-controlled ventilation system with indoor CO2 concentration. However, when the adaptive comfort temperature set-point adjustment was combined with the demand-controlled ventilation systems, the system had an energy-saving potential of 21.4%–24.3%.
The paper by Song et al. reviewed how to improve the frosting and defrosting performance of air source heat pump units when frost forms and accumulates on the surface of the coil.
Sun et al. analysed the optimal charge amounts in transcritical CO2 heat pump systems. The cooling and heating coefficients of performance using internal heat exchangers were increased by 8.3% and 0.7%, respectively compared to the cases where internal heat exchangers were not used.
Wang et al. invented a low-cost, non-toxic, simply-designed thermal switch in which paraffin wax is used as the phase change material. The heat transfer performance of the thermal switch, called the ON/OFF thermal conductance ratio, is approximately 30. Thermal switches can be integrated into buildings for the purpose of saving energy.
Lastly, Wijaya et al. from Singapore studied several technical measures to reduce the energy consumption and improve the energy efficiency of air conditioning and mechanical ventilation (ACMV) and lighting systems in the underground metro stations of Singapore. Examples of technical measurements of ACMV enable the optimised use of space in different public areas through increasing the chilled water temperature and adopting CO2 sensors. Light-emitting diodes (LEDs) were also used to reduce the lighting energy consumption by up to 50%.
These papers touch upon a number of interesting energy-related applications for smart green buildings that result in a number of new insights on this topic.
I would like to express my sincere gratitude to the authors, the members of the HKIE Transactions Committee, the Associate Editors, the reviewers and the HKIE Secretariat for their time and dedication in launching this special issue for the benefit of the engineering profession in Hong Kong.