Applying water cooled air conditioners in residential buildings in Hong Kong

The objective of this study is to conduct a realistic prediction of the potential energy saving for using water cooled air conditioners in residential buildings in Hong Kong. A split type air conditioner with air cooled (AAC) and water cooled (WAC) options was set up for experimental study at different indoor and outdoor conditions. The cooling output, power consumption and coefficient of performance (COP) of the two options were measured and calculated for comparison. The experimental results showed that the COP of the WAC is, on average, 17.4% higher than that of the AAC. The results were used to validate the mathematical models formulated for predicting the performance of WACs and AACs at different operating conditions and load characteristics. While the development of the mathematical models for WACs was reported in an earlier paper, this paper focuses on the experimental works for the AAC. The mathematical models were further used to predict the potential energy saving for application of WACs in residential buildings in Hong Kong. The predictions were based on actual building developments and realistic operating characteristics. The overall energy savings were estimated to be around 8.7% of the total electricity consumption for residential buildings in Hong Kong. Wider use of WACs in subtropical cities is, therefore, recommended.     

Application of an exhaust heat recovery system for domestic hot water

Typically, a great deal of heat is wasted in the drainage systems of large-scale public shower facilities, such as those in schools, barracks, and natatoriums. This paper enhances a heat pump system used in public shower facilities for exhaust heat recovery. The system consists of three sections for exhaust heat recovery: solar energy collection system, drainage collection system, and heat pump system. In the system, the energy from the solar energy collection system is used for the initial heating the shower's tap water. Afterwards, the drainage collection system collects the used shower water. Finally, the electric heat pump recycles the exhaust heat from the collected water to heat the shower's tap water. The operational practice of the system was presented. The drainage temperature and equipment capacity was optimized based on a practical example. The advantages of this heat pump system compared to gas-fired (oil-fired, coal-fired, electric) boilers are lower energy consumption, less pollution, and lower operating costs. Therefore, the system is superior in energy conservation and has a promising application prospect.     

Regenerative rotary heat exchanger for heat recovery in residential ventilation

Increased energy costs have brought about increased concern by building owners as well as governments about the operating costs and energy budgets for buildings and power plants. This growing energy conservation consciousness has brought a considerable interest in reclaiming waste heat from residential, commercial, industrial, and institutional ventilation systems. Based on theoretical considerations, the design and performance of a small rotary heat exchanger for residential houses is discussed in this paper. Laboratory results reveal a high sensible heat recovery maximum effectiveness of 85 percent with acceptable levels of pressure drop and cross leakage. Cost saving analysis indicates annual energy savings up to 15 percent, with even larger savings in the size of the heating and cooling equipment up to 42 percent. As expected the greatest savings could occur when large amounts of outside air are required for ventilation.     

Second-law performance of heat exchangers for waste heat recovery

Exergy change rate in an ideal gas flow or an incompressible flow can be divided into a thermal exergy change rate and a mechanical exergy loss rate. The mechanical exergy loss rates in the two flows were generalized using a pressure-drop factor. For heat exchangers using in waste heat recovery, the consumed mechanical exergy is usually more valuable than the recovered thermal exergy. A weighing factor was proposed to modify the pressure-drop factor. An exergy recovery index (η_II) was defined and it was expressed as a function of effectiveness (?), ratio of modified heat capacity rates (C^∗), hot stream-to-dead-state temperature ratio, cold stream-to-dead-state temperature ratio and modified overall pressure-drop factor. This η_II–? relation can be used to find the η_II value of a heat exchanger with any flow arrangement. The η_II−Ntu and η_II−Ntu_h relations of cross-flow heat exchanger with both fluids unmixed were established respectively. The former provides a minimum Ntu design principle and the latter provides a minimum Ntu_h design principle. A numerical example showed that, at a fixed heat capacity rate of the hot stream, the heat exchanger size yielded by the minimum Ntu_h principle is smaller than that yielded by the minimum Ntu principle.     

Study on performance of solar assisted air source heat pump systems for hot water production in Hong Kong

This paper reports the investigation results on application of the solar assisted air source heat pump systems for hot water production in Hong Kong. A mathematical model of the system is developed to predict its operating performance under specified weather conditions. The optimum flow rate from the load water tank to the condenser is proposed considering both the appropriate outlet water temperature and system performance. The effect of various parameters, including circulation flow rate, solar collector area, tilt angle of solar collector array and initial water temperature in the preheating solar tank is investigated, and the results show that the system performance is governed strongly by the change of circulation flow rate, solar collector area and initial water temperature in the preheating solar tank.     

Energy performance of residential buildings in Singapore

Energy consumption of buildings takes up about a third of Singapore's total electricity production. In this paper, we present a pioneering study to investigate the energy performance of residential buildings. Beginning with an energy survey of households, we established the air-conditioning usage patterns and modelled residential buildings for computer simulations. An ETTV equation for residential buildings was developed. Employing this equation, we demonstrated how to achieve improved energy efficiency in residential buildings. Two types of residential buildings, namely, point block and slab block, were modelled and parametric runs performed. ETTV impacts the energy consumption of residential buildings and thus lowering the ETTV will result in reduced building heat load. Results from the developed equation showed that a unit decrease in ETTV resulted in 4% and 3.5% reduction in annual cooling energy for point block and slab block residential buildings, respectively. In addition, a set of simple energy and load estimating equations were developed using computer simulation and local climatic data. These equations provided a means of estimating the annual cooling energy consumption of residential buildings in Singapore.     

Will energy regulations in the Gulf States make buildings more comfortable – A scoping study of residential buildings

Building envelope impacts upon energy consumption and indoor environment. The relationship between envelope components and indoor environment has become increasingly important, especially with the new emphasis on visual comfort, thermal comfort and indoor air quality. This paper examines the interaction between occupant thermal comfort and envelope component regulations in the Gulf States. The country chosen for this study is the Kingdom of Bahrain, the smallest country in the Gulf region. Simulation results and comparative studies were employed to investigate the impact of the current envelope component regulations on the internal environment. The paper focuses on residential buildings and concludes that the envelope component regulations contribute positively to the internal thermal performance. Although these envelope components are not generally the primary elements that impact upon internal thermal comfort there are circumstances when the components become very warm and occupants positioned close to them will experience discomfort. This paper shows that the thermal insulation regulation makes a small impact on thermal comfort, whereas the window regulation, particularly glazing, is more influential and that for most window areas, solar impacts are generally large.     

高温热管在小氮肥余热回收中的应用

将高温热管蒸汽发生器应用于小氮肥造气工艺，以取代原普通余热锅炉回收煤气工段的高温余热，解决了合成氨生产工艺中煤气降温的难题，取得了很好的经济效益和社会效益。     

A method of identifying and weighting indicators of energy efficiency assessment in Chinese residential buildings

This paper describes a method of identifying and weighting indicators for assessing the energy efficiency of residential buildings in China. A list of indicators of energy efficiency assessment in residential buildings in the hot summer and cold winter zone in China has been proposed, which supplies an important reference for policy makings in energy efficiency assessment in buildings. The research method applies a wide-ranging literature review and a questionnaire survey involving experts in the field. The group analytic hierarchy process (group AHP) has been used to weight the identified indicators. The size of survey samples are sufficient to support the results, which has been validated by consistency estimation. The proposed method could also be extended to develop the weighted indicators for other climate zones in China.     

Thermal performance analysis of plate heat exchanger with different configurations for the heat recovery system in buildings

Due to the scarcity of conventional energy sources, a lot of efforts need to be taken regarding energy conservation in the buildings, including heat recovery of air ventilation systems. The present paper focuses on new methods to improve the thermal performance of the heat recovery system by investigating the heat transfer characteristics and the flow development in a flat-plate heat exchanger (FPHE) using three different rib-grooved surfaces (trapezoidal, triangle and semi-circular), the numerical simulations were carried out for uniform wall heat flux equal to 290 W/m² for air as the working fluid, the Reynolds number varies from 500 to 2000 for three different channel heights. The numerical results indicated that, rib-grooved surfaces have a significant impact on heat transfer enhancement with an increase in the pressure drop through the channel. The effect of rib-grooved patterns on the heat transfer and the fluid flow is more significant in a narrow channel especially for trapezoidal and triangle corrugated surfaces, because they have sharp edges. Based on the present research, the FPHEs with the added rib-grooved surfaces are recommended to provide an efficient and compact heat recovery system. Moreover, it was found that by applying the new design, a considerable amount of energy and power could be saved.     

Developing sustainable residential buildings in Saudi Arabia: A case study

This paper assesses the energy and water consumption practices of existing housing in Saudi Arabia, with the ultimate aim of establishing guidelines for delivering sustainable residential buildings in the near future. In order to achieve this aim the current status of a typical Saudi residence (i.e. an apartment complex) is investigated in terms of energy and water consumption using simulation software packages. The paper then examines the prospects for applying various measures to the typical Saudi residence to manage energy and water use more sustainably. This research identifies several design-related faults common to Saudi Arabian house design. These faults contribute to an inefficient use of energy and domestic water resources. Finally, the paper puts forward a set of recommendations and guidelines, design-related and otherwise, to enhance the sustainability of future Saudi residential buildings.     

Sustainable renovation of residential buildings and the landlord/tenant dilemma

The landlord/tenant dilemma arises when the interests of landlords and tenants misalign and is one of the greatest barriers hindering the development of sustainable renovation of residential buildings in Europe. The aim of this research is to investigate how regulatory changes and contractual solutions can help solve the landlord/tenant dilemma in relation to sustainable renovation of residential buildings, and how the general awareness of sustainable renovation can be increased. Particular focus is on whether tools like energy performance contracting and energy labeling can help solve the landlord/tenant dilemma. The research was done in relation to the specific situation in Denmark, but theory, information and experiences from other countries were included. The results show that there are plenty of opportunities to overcome the landlord/tenant dilemma, but principal/agent problems can only be overcome with a package solution. In the Danish national context the package solution must consist of legislative changes, financial incentives and better dissemination of information. Therefore, an array of different tools must be integrated and used in cooperation to overcome the dilemma.     

Optimal waste heat recovery and reuse in industrial zones

Significant energy efficiency gains in zones with concentrated activity from energy intensive industries can often be achieved by recovering and reusing waste heat between processing plants. We present a systematic approach to target waste heat recovery potentials and design optimal reuse options across plants in industrial zones. The approach first establishes available waste heat qualities and reuse feasibilities considering distances between individual plants. A targeting optimization problem is solved to establish the maximum possible waste heat recovery for the industrial zone. Then, a design optimization problem is solved to identify concrete waste heat recovery options considering economic objectives. The paper describes the approach and illustrates its application with a case study.     

Seasonal variations in residential and commercial sector electricity consumption in Hong Kong

We present the energy use situation in Hong Kong from 1979 to 2006. The primary energy requirement (PER) nearly tripled during the 28-year period, rising from 195,405 to 566,685 TJ, about two-third of which was used for electricity generation. The residential and commercial sectors are the two largest electricity end-users with an average annual growth rate of 5.9% and 7.4%, respectively. The monthly consumption in these two sectors shows distinct seasonal variations mainly due to changes in the air-conditioning requirements, which are affected by the prevailing weather conditions. Principal component analysis of five major climatic variables—dry-bulb temperature, wet-bulb temperature, global solar radiation, clearness index and wind speed—was conducted. Measured sector-wide electricity consumption was correlated with the corresponding two principal components determined using multiple regression technique. The regression models could give a very good indication of the annual electricity use (largely within a few percents), but individual monthly estimation could differ by up to 24%. It was also found that the climatic indicators determined appeared to show a slight increasing trend during the 28-year period indicating a subtle, but gradual change of climatic conditions that might affect future air-conditioning requirements.     

电厂循环水余热回收供暖节能分析与改造技术

在电厂余热利用的基础上,通过回收冷却塔散失的热量,对循环水余热回收供暖进行了节能分析,结合电厂对循环水余热回收供暖的应用,阐述循环水余热回收供暖的节能措施以及实施后的节能效果。实践证明,电厂循环水余热回收供暖具有显著的节能和环保效果。     

Thermal comfort in residential buildings: Comfort values and scales for building energy simulation

Building Energy Simulation (BES) programmes often use conventional thermal comfort theories to make decisions, whilst recent research in the field of thermal comfort clearly shows that important effects are not incorporated. The conventional theories of thermal comfort were set up based on steady state laboratory experiments. This, however, is not representing the real situation in buildings, especially not when focusing on residential buildings. Therefore, in present analysis, recent reviews and adaptations are considered to extract acceptable temperature ranges and comfort scales. They will be defined in an algorithm, easily implementable in any BES code. The focus is on comfortable temperature levels in the room, more than on the detailed temperature distribution within that room.     

Cost optimal analysis of heat pump technology adoption in residential reference buildings

In European Union (EU) buildings consume approximately the 40% of total primary energy. Heat pump (HP) systems have proven to be an efficient and economically viable alternative to conventional systems to provide heating and cooling services in buildings. An effective penetration of this technology in the built environment is critical to achieve the ambitious goals set by the recent EU Directives on energy efficiency and energy performance of buildings. Although this technology is very versatile, its optimal design and management are related to specific climate, operational and economic conditions. The research presented aims to evaluate the performance of technical solutions for heating and cooling in residential buildings, using a “reference building” methodology. The comparison involves performance indicators such as primary energy consumption, CO₂ emission and net present cost.The potential improvements with respect to conventional baseline solutions are assessed and the performance gap between air-source and water-source HP systems is shown referring to realistic operational and climate conditions within the Italian territory. The research suggests the possibility of reducing this performance gap by concentrating future research effort on design and control optimization.     

某住宅小区中央空调冷凝热回收改造方案分析

本文分析了某住宅小区的生活热水使用情况,对原来的使用燃油锅炉方案进行改造.提出了两种冷凝热回收方案,分别从技术、经济、环境不同的方面进行比较,指出采用制冷剂循环中串联板式换热器的冷凝热回收方式更加合理.     

Latest concepts for combustion and waste heat recovery systems being considered for hydrogen engines

A more sustainable transportation calls for the use of alternative and renewable fuels, a further increase of the fuel energy conversion efficiency of internal combustion engines as well as the reduction of the thermal engine energy supply by recovering the braking energy. The paper presents two concepts being developed to improve the fuel conversion efficiency of internal combustion engines for transport applications. The first concept works on the combustion evolution to increase the amount of fuel energy transformed in piston work within the cylinder. The second concept works on the waste exhaust and coolant energies to be recovered through a power turbine downstream of the turbocharger turbine on the exhaust line and a steam turbine feed with the steam produced by a boiler/super heater made of the coolant passages and a heat exchanger on the exhaust line. The concepts work with hydrogen (and in this case a water injector is also necessary) as well as lower alkanes (methane, propane, butane). Preliminary simulations show improvement of top fuel conversion efficiencies to above 50% in the high power density operation. The waste heat recovery system also permits faster warm-up during cold start driving cycles.     

Modeling of fractal heat conduction of semi-coke bed in waste heat recovery steam generator for hydrogen production

With the steam obtained from the waste heat of high temperature semi-coke, the hydrogen production through gasification method is considered more commercial. In order to improve the efficiency of waste heat recovery, the fractional model for heat conduction of semi-coke bed in waste heat recovery process was established. The non-destructive CT was employed to obtain the inner morphology of semi-coke bed and the image binarization processing was used to segment the CT image. With the MATLAB program, the box-counting method was used to calculate the fractal dimension of semi-coke bed. The fractional model for heat conduction of semi-coke bed was established by the fractal theory. The results showed that, the CT image and bit binary image of semi-coke bed can really reflect the inner morphology of semi-coke bed, and the inner morphology of semi-coke bed can be regarded as a fractal medium. The fractal dimension of semi-coke bed is 1.7537, which is very close to golden mean, 1.618, this could be the optimal structure for the heat conduction of semi-coke bed under the condition of natural accumulation. The one-dimensional heat conduction fractional equation of semi-coke bed was established and it can be accurately solved by fractal complex transformation and traveling wave transformation.