Life cycle analysis of enhanced condenser features for air-cooled chillers serving air-conditioned buildings

Air-cooled chillers are commonly used to provide cooling energy for air-conditioned buildings at the expense of considerable electricity. This paper examines the life cycle electricity cost of these chillers with the improved condenser features of condensing temperature control (CTC), evaporative pre-coolers (EC) and variable speed condenser fans (VSF). A validated model for an air-cooled screw chiller was used to ascertain how the individual and mixed features influence the annual electricity consumption of chillers in various operating conditions. It is estimated that the life cycle electricity cost savings range from HK$ 2,099,742 with EC to HK$ 6,399,564 with all the three features, with regard to a chiller plant serving an office building for 15 yr. The life cycle analysis reported here provides important insights into how to reap the benefits of energy efficient technologies for air-cooled chillers.     

Part load performance of air-cooled centrifugal chillers with variable speed condenser fan control

Air-cooled centrifugal chillers are commonly used in commercial buildings but their performance analysis is lacking. This paper investigates the part load performance of the chillers via a thermodynamic model. The model was validated using a wide range of operating data from an existing chiller with specific settings of outdoor temperature and condensing pressure in controlling the condensing temperature. The validated model was developed specifically to ascertain the maximum coefficient of performance of chiller (COP) together with the strategy for optimizing the condensing temperature under various operating conditions. It is found that the highest COP occurs at a part load ratio (PLR) of 0.71–0.84, depending on the outdoor temperature and the control of condensing temperature, rather than at full load. Yet the chillers operating at such part load conditions will cause extra energy used for the early staging of chilled water pumps. To minimize the overall chiller plant energy consumption, it is still preferable to implement chiller sequencing based on the full load condition than on the aforementioned PLRs. The results of this paper present criteria for implementing low-energy strategies for operating air-cooled chillers satisfying a given building cooling load profile.     

An integrated model for the design of air-cooled chiller plants for commercial buildings

Cooling load calculation is the first step in designing the air-conditioning system of a building. The calculated cooling capacity with appropriate buffer is then used to select the number and size of chillers in the system. N + 1 is a common formula used by designers to size the chiller plants in Hong Kong buildings, where N is the actual number of chillers required and 1 is a redundant chiller provided to ensure reliability. This paper reviews the problem of excess capacity and discusses the risk exposure of chiller systems without redundant chillers. The cooling load profiles of the chiller plants of four medium-sized commercial buildings in Hong Kong are reviewed. The risk exposure of chiller systems without redundant chillers can be minimized by applying risk-based preventive maintenance. The just-in-demand design reduces capital cost of the building and frees up funds for continuous energy measurement and improving the energy efficiency of chiller plant systems. This paper presents a model for designing chiller plants that improves the energy efficiency of the plant in a cost effective and thoughtful manner. It is designed with consideration of the life cycle of the plant and real-time continuous commissioning, monitoring, measurement, comparison and execution for better energy management.     

Modelling of the coefficient of performance of an air-cooled screw chiller with variable speed condenser fans

Air-cooled chillers are generally recognized as energy intensive equipment in air-conditioned buildings in the subtropical climate. This paper considers how the use of variable speed condenser fans enables these chillers to operate more efficiently. The thermodynamic model of an air-cooled screw chiller was developed using the simulation program TRNSYS and validated using the field data and specifications of the chiller. The staging of condenser fans and the control of their speed in various operating conditions were described. A comparison was made on the coefficient of performance of the chiller in the steady state with various control strategies: head pressure control with constant or variable speed condenser fans; condensing temperature control (CTC) with constant or variable speed condenser fans. Potential improvements in the chiller COP due to the use of CTC with variable speed condenser fans were discussed. The findings of this paper are useful in developing more energy efficient air-cooled chillers.     

An alternative approach for the energy and environmental rating of advanced glazing: An electrochromic window case study

The combined methodology for the rating of advanced glazing proposed in this work, aims to add the economical and the environmental aspect to the existing evaluation systems. Taking into account the special characteristics of the advanced glazing, a life cycle assessment (LCA) study and an eco-efficiency analysis have been combined to provide an alternative rating scheme, which has been applied to an electrochromic window as a case study. The proper graphical representation of the selected indicators leads to figures clearly depicting a rating result for the selected product. Such rating schemes can be useful for the consumers and also for the product manufacturers, requesting for additional necessary input apart from its typical technical characteristics only the product expected lifetime, its purchase cost and the energy required for its production.     

Indoor air quality and energy performance of air-conditioned office buildings in Singapore

An integrated indoor air quality (IAQ)-energy audit methodology has been developed in this study in Singapore, which provides a rigorous and systematic method of obtaining the status-quo assessment of an 'IAQ signature' in a building. The methodology entails a multi-disciplinary model in obtaining measured data pertaining to different dimensions within the built environment such as the physical, chemical, biological, ventilation, and occupant response characteristics. This paper describes the audit methodology and presents the findings from five air-conditioned office buildings in Singapore. The research has also led to the development of an indoor pollutant standard index (IPSI), which is discussed in this paper. Other performance indicators such as, the ventilation index and the energy index as well as the building symptom index (BSI) are also presented and discussed in the context of an integrated approach to IAQ and energy. Several correlation attempts were made on the various symptoms, indoor air acceptability, thermal comfort, BSI and IPSI, and while BSI values are found to correlate among them as well as with IAQ and THERMAL COMFORT acceptability, no such correlation was observed between BSI and IPSI. This would suggest that the occupants' perception of symptoms experienced as well as environmental acceptability is quite distinct from IAQ acceptability determined from empirical measurements of indoor pollutants, which reinforces the complex nature of IAQ issues.     

北京市《公共建筑节能评审标准》简介

北京市大型公共建筑单位建筑面积的全年耗电量高达100~350 kWh/(m2·a),是普通居民住宅的10~15倍,节能潜力达到30%~50%。不节能的原因之一是设计方案本身存在问题,强制性的节能设计标准没有得到执行。解决的途径是通过大型公共建筑的节能评审标准对设计方案进行节能审查和评估。所介绍的节能评审标准是对大型公共建筑能源需求、转换和消耗过程中建筑本身、能源转换和设备系统、可再生能源三个环节的多项指标给出定量的详细模拟计算结果,从而对设计方案的节能性给出全面评价,作为政府审批固定资产投资项目、鼓励和奖励节能设计的依据。     

An ETTV-based approach to improving the energy performance of commercial buildings

This paper aims to study the various parameters that affect the energy performance of commercial buildings in Singapore. The parameters are diverse, ranging from characteristics of construction of the walls and windows, to the various system settings and types within the building. Building energy performance is measured via two key indexes, namely, the Envelope Thermal Transfer Value (ETTV) and the annual cooling energy requirement (E_c). Parameters related to these two indexes are identified. An additional parameter, the solar absorptance of the wall, is further incorporated to calibrate the ETTV equation. A relative ranking on the functional parameters of ETTV has been performed to evaluate their effectiveness in lowering the ETTV of buildings. In addition, the impact of using cladding on ETTV is also studied. A correlation for E_c, expressed in the form of a simple linear equation, has been developed. This correlation accounts for the internal building loads, envelope loads, operating schedules and efficiency of the cooling equipment. Finally, ETTV and E_c have been employed to study the effects of chiller over-sizing and ventilation rates on building cooling energy. In the pursuit for better energy-efficient buildings, the approach presented in this paper contributes to the construct of sustainable energy-efficient built-environment.     

Application of energy rating methods to the existing building stock: Analysis of some residential buildings in Turin

The objective of this work is to contribute to the recent standardisation activity, finalized to apply the Energy Performance of Buildings Directive (EPBD). Through the energy assessment of some residential buildings in Turin (Italy), the work investigates the application of the calculation methods that have been specified in the recent European standard for the so-called “standard energy rating”. A comparison of the “calculated energy rating” with the “measured energy rating” is used to investigate the effect of user behaviour and weather conditions. Moreover, in order to draft the energy certificate and make an appropriate classification, the last part of the work investigates the way to find energy reference values of the building stock, through the study of the correlation between the input and the output data of an energy rating and the comparison of the analysed buildings.     

蒸发式空气加湿冷却器的性能及其在风冷冷水机组中的应用

通过对采用铝质孔板波纹填料的直接蒸发式空气加湿冷却器的测试,给出了蒸发冷却效率,空气阻力与迎面风速,淋水密度之间的关系式和曲线,并分析了该设备用于风冷冷水机组的效果和经济性。     

Development of energy performance benchmarks and building energy ratings for non-domestic buildings: An example for Irish primary schools

The EU Member States are in the process of implementing energy rating procedures for buildings. For non-domestic buildings in particular, devising a robust and cost effective energy rating method is not a simple task. The situation becomes more complicated where countries do not have a tradition of performing energy calculations or undertaking energy measurements in buildings.     

Development of a dynamic operational rating system in energy performance certificates for existing buildings: Geostatistical approach and data-mining technique

The operational rating system in building energy performance certificates(EPCs) has been used for systematically monitoring and diagnosing the energy performance in the operation and maintenance phases of existing buildings. However, there are several limitations of the conventional operational rating system,which can be subdivided into three aspects:(i) building category;(i i) region category; and(iii) space unit size. To overcome these challenges, this study conducted the problem analysis of the conventional operational rating system for existing buildings by using the statistical and geostatistical approaches. Based on the problem analysis, this study developed the dynamic operational rating(DOR) system for existing buildings by using the data-mining technique and the probability approach. The developed DOR system can be used as a tool for building energy performance diagnostics.To validate the applicability of the developed DOR system, educational facilities were selected as the representative type of existing buildings in South Korea. As a result, it was determined that the developed DOR system can solve the irrationality of the conventional operational rating system(i.e., the negative correlation between the space unit size and the CO2 emission density). Namely, the operational ratings of small buildings were adjusted upward while those of large buildings were adjusted downward. The developed DOR system can allow policymakers to establish the reasonable operational rating system for existing buildings, which can motivate the public to actively participate in energy-saving campaigns.     

An approach to evaluate the energy performance of buildings based on incomplete monthly data

The energy performance of buildings has become increasingly important in the general strive to reduce the overall energy use, which is manifested in the Energy Performance of Buildings Directive launched by the European Union. An important first step is of course to identify and address buildings that have an energy saving potential. In order to achieve this, robust methods for evaluation as well as reliable energy key figures are needed.     

新版《建筑灭火器配置设计规范》的灭火器配置基准

依据国内、外相关的国家消防工程设计规范和国家消防产品质量标准，结合我国40年消防科研工作的技术积累和实践经验，以灭火器配置基准的定额和灭火器灭火级别的换算为主题，从不同的角度与侧面翔实地论证了现行有效版国家标准《建筑灭火器配置设计规范》（GB50140-2005）的灭火器配置基准的设定依据及其与现行有效版国际标准接轨的技术基础。     

An analysis of daylighting performance for office buildings in Hong Kong

Daylighting has often been recognized as a useful source of energy savings and visual comforts in buildings. Occupants expect good daylight in their working spaces. The quality and quantity of natural light entering a building depend on both internal and external factors. In Hong Kong, commercial building accounts for the major building energy use and electric lighting is one of the major electricity-consuming items. This paper studies the daylighting performance and energy implications for office buildings. A total of 35 commercial buildings have been selected in the survey. Key building parameters affecting daylighting designs are presented. Two typical office blocks were further analysed based on a lighting simulation program. The daylighting performance was evaluated in terms of daylight factor, room depth and glare index. It has been found that the daylighting performance for office buildings is quite effective. About one-third of the office areas that are near the perimeter regions have an average daylight factor of 5%. For inner region of deep plan offices, some innovative daylighting systems such as light redirecting panels and light pipe could be used to improve the daylighting performance. In general, the office building envelop designs are conducive to effective daylighting and proper daylight linked lighting controls could save over 25% of the total electric lighting use.     

The new research centre of the Brazilian Petroleum Company in Rio de Janeiro,Brazil: The achievements in the thermal performance of air-conditioned buildings in the tropics

The study on the thermal performance of the air-conditioned buildings of the new research centre of the Brazilian Petroleum Company, in the tropical climate of Rio de Janeiro, was part of a bigger research and consultancy project involving environmental issues. The architectural design was the subject of a national competition in 2004, encompassing over 100,000 m². According to the design brief, out of the 10 buildings of the new research centre, 7 have to be either completely or partially air-conditioned, due to specific occupation requirements. The challenge for better thermal performance was related to systems’ energy efficiency, to the introduction of natural ventilation and to the notion of adaptive comfort, which were verified with the support of thermal dynamic simulations. At the early stages of the assessments, the potential for natural ventilation in the working spaces considering the mixed-mode strategy achieved 30% of occupation hours. However, the development of the design project led to fully air-conditioned working spaces, due to users’ references regarding the conventional culture of the office environment. Nevertheless, the overall architectural approach in accordance to the climatic conditions still showed a contribution to the buildings’ energy efficiency.     

An evaluation of the environmental burdens of present and alternative materials used for electricity transmission

This paper describes research using life cycle analysis assessment techniques to determine the environmental impacts associated with the use of present and possible alternative materials utilised in all aspects of high voltage electricity transmission. The study focuses on the National Grid system in England and Wales, where the majority of high voltage electricity is transmitted through steel and aluminium conductors supported above the ground by mild steel lattice type towers. A major aspect of the study is to address the effects of different corrosive environments to which the tower materials are exposed: namely rural, industrial and coastal locations.     

An improved assessment model of variable frequency-driven direct expansion air-conditioning system in commercial buildings for Taiwan green building rating system

Because of the superior performance of the multi-unit variable frequency-driven (VFD) direct expansion (DX) air-conditioning system, installing this kind of system in rental commercial buildings, dwelling houses, and schools is becoming more and more popular in Taiwan. Even though the features and characteristics of the multi-unit VFD DX system are different from those of the central system, it is still assessed by the conventional method used for evaluating the efficiency of all air-conditioning systems, which is designed mainly for central systems. This article explains the problems that occur when the current assessment method is applied to the multi-unit VFD DX system. An alternative assessment method is proposed.     

Optimization model for the selection of materials using a LEED-based green building rating system in Colombia

Buildings have a significant and continuously increasing impact on the environment because they are responsible for a large portion of carbon emissions and use a considerable number of resources and energy. The green building movement emerged to mitigate these effects and to improve the building construction process. This paradigm shift should bring significant environmental, economic, financial, and social benefits. However, to realize such benefits, efforts are required not only in the selection of appropriate technologies but also in the choice of proper materials. Selecting inappropriate materials can be expensive, but more importantly, it may preclude the achievement of the desired environmental goals. In order to help decision-makers with the selection of the right materials, this study proposes a mixed integer optimization model that incorporates design and budget constraints while maximizing the number of credits reached under the Leadership in Energy and Environmental Design (LEED) rating system. To illustrate this model, this paper presents a case study of a building in Colombia in which a modified version of LEED is proposed.