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.     

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.     

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.     

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.     

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.     

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。     

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.     

Second law analysis of a diesel engine waste heat recovery with a combined sensible and latent heat storage system

The exhaust gas from an internal combustion engine carries away about 30% of the heat of combustion. The energy available in the exit stream of many energy conversion devices goes as waste. The major technical constraint that prevents successful implementation of waste heat recovery is due to intermittent and time mismatched demand for and availability of energy. The present work deals with the use of exergy as an efficient tool to measure the quantity and quality of energy extracted from a diesel engine and stored in a combined sensible and latent heat storage system. This analysis is utilized to identify the sources of losses in useful energy within the components of the system considered, and provides a more realistic and meaningful assessment than the conventional energy analysis. The energy and exergy balance for the overall system is quantified and illustrated using energy and exergy flow diagrams. In order to study the discharge process in a thermal storage system, an illustrative example with two different cases is considered and analyzed, to quantify the destruction of exergy associated with the discharging process. The need for promoting exergy analysis through policy decision in the context of energy and environment crisis is also emphasized.     

Assessment of technical and economical viability for large-scale conversion of single family residential buildings into zero energy buildings in Brazil: Climatic and cultural considerations

This paper addresses the viability of converting single-family residential buildings in Brazil into zero energy buildings (ZEBs). The European Union and the United States aim ZEBs implementation to address ‘peak oil’ and environmental concerns. However, literature shows no agreement on a consensual definition of ZEB. Seeking a Brazilian ZEB definition, this paper addresses PassivHaus and thermal comfort standards for hot climates, source metrics for ZEB, Brazil′s energy mix, residential energy end uses and Brazilian legal framework for residential photovoltaic (PV) generation. Internal Rate of Return for PV systems in two Brazilian cities is calculated under various scenarios. It shows grid parity was reached from April 2012 to November 2012 assuming residential electric tariffs of that period and the financial conditions given by the Brazilian government for the construction of new dams in the Amazon and the lowest rates offered by Brazilian banks to private individuals. Governmental decision to lower electric residential tariffs in November 2012 reduced the scope of grid parity. Later revocation of a tax exemption in April 2013 ended grid parity in Brazil. It concludes, conversely to developed countries, it is the volatile Brazilian energy policy, instead of economical barriers, the main obstacle for ZEB viability in Brazil.     

集中供暖热计量模式多样化的必要性分析

通过工程实例对我国节能建筑集中供暖热计量系统设计所存在的问题进行讨论。目前我国居住建筑集中供暖系统热计量设计模式单一,没有充分考虑我国国情和不同类型居住建筑的特点,加之我国的供热体制改革滞后,使得新建居住建筑的节能效果无法保证,还增加了工程建设费用。相关的技术规程予以补充和完善。     

炼油装置余热回收集中热水供应技术研究

为回收炼油装置丰富的低温余热用于生活区的集中供热,对余热资源和生活热水供应热负荷分别进行了综合标定和统计计算,在分析比较的基础上确定采用热管换热器回收余热和双管制生活热水集中供应系统方案,并对余热流股热回收的热管换热器进行了设计计算。集中热水供应系统的技术经济分析表明,该方案在技术上是可行的,节能效果和经济效益十分显著。     

Experimental investigation on heat recovery from diesel engine exhaust using finned shell and tube heat exchanger and thermal storage system

The exhaust gas from an internal combustion engine carries away about 30% of the heat of combustion. The energy available in the exit stream of many energy conversion devices goes as waste, if not utilized properly. The major technical constraint that prevents successful implementation of waste heat recovery is due to its intermittent and time mismatched demand and availability of energy. In the present work, a shell and finned tube heat exchanger integrated with an IC engine setup to extract heat from the exhaust gas and a thermal energy storage tank used to store the excess energy available is investigated in detail. A combined sensible and latent heat storage system is designed, fabricated and tested for thermal energy storage using cylindrical phase change material (PCM) capsules. The performance of the engine with and without heat exchanger is evaluated. It is found that nearly 10–15% of fuel power is stored as heat in the combined storage system, which is available at reasonably higher temperature for suitable application. The performance parameters pertaining to the heat exchanger and the storage tank such as amount of heat recovered, heat lost, charging rate, charging efficiency and percentage energy saved are evaluated and reported in this paper.