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Purpose – The operation of chiller systems could account for considerable electricity consumption in air-conditioned buildings in subtropical regions. The purpose of this paper is to consider using data envelopment analysis (DEA) to facilitate management of their energy performance. Design/methodology/approach – A system serving an institutional building was studied, which contains five sets of chillers, pumps and cooling towers. The building has a total floor area of about 25,000m2 and comprises classrooms, lecture theatres, offices and laboratories. The scale, technical and overall efficiencies defined in DEA were calculated based on the correlation between the output variable – system coefficient of performance (COP) – and the input variables – load factor and temperatures of chilled water and condenser water. The efficiencies were further examined to explain how outside air temperatures and controllable variables affect the system performance. Findings – The paper reveals that existing energy management gives a technical efficiency of 0.85 and fine-tuning the temperature-related variables could achieve an electricity saving of 14.8 per cent. Research limitations/implications – The improved COP predicted by DEA is related only to fine-tuning of the input variables concerned. An increase of COP by other advanced controls or system upgrades should be assessed based on robust system modelling techniques. Yet the extent of COP improvements helps investigate energy management opportunities requiring no or insignificant capital investment on existing systems. Practical implications – A systematic approach to performing energy management of a chiller system is proposed. The DEA helps examine which operating variable should be fine-tuned to achieve the highest possible performance. Originality/value – It is an under researched area to consider using scale and technical efficiencies in DEA to explain energy management of chiller systems and to estimate the highest achievable performance. [ABSTRACT FROM AUTHOR]

This study aims to present the fundamentals in which operation of a 100% outdoor air system integrates with indirect and direct evaporative cooling systems and to estimate its energy saving potential. The simulation of the proposed system is performed using a commercial equation solver program, and the annual operation energy saving potential with respect to a conventional variable air volume system is determined. This paper shows that significant operation energy savings (i.e. 21–51% less energy consumption) is possible principally by the pre-conditioning of supply air due to the waste heat recovery using the indirect evaporative cooler and the sensible heat exchanger units. By components, the proposed system shows a 16–25% less annual cooling coil load and an 80–87% reduced annual heating coil load with respect to the conventional variable air volume system, while there is no fan energy savings expected.Practical applications: This paper provides practical insight on how the evaporative cooling based 100% outdoor air system operates and how each essential component, such as the indirect evaporative cooler, cooling coil, direct evaporative cooler, heating coil and sensible heat exchanger should be controlled during the seasons for realising energy conservation benefits. The sequence of operation presented in this paper can be implemented to actual control logic. [ABSTRACT FROM AUTHOR]

Abstract: Reducing the energy consumption of air-conditioning systems is becoming increasingly important. This paper focuses on the air-conditioning system in Terminal 3 in Xi’an Xianyang International Airport, the first airport terminal to adopt radiant cooling in China. In the large spaces of this airport terminal, a temperature and humidity independent control (THIC) system has been adopted instead of a conventional nozzle air supply method, which significantly reduces the energy consumption of the air supply. The radiant floor is the main mechanism for indoor temperature control, while a liquid desiccant outdoor air processor combined with displacement ventilation is responsible for humidity control. Ice storage is adopted to reduce operating costs, and the supplied chilled water temperature can be as low as 3°C. This paper examines the performance of the THIC system in detail. The indoor environment is determined through measurements to be comfortable, and the on-site performances of key components in both the airport terminal and the cooling plant are investigated. The outdoor air processor supplies air of appropriate temperature and humidity ratio; two kinds of radiant floors are used for temperature control, both with measured cooling capacities of about 30–40W/m2; and the energy efficiency ratio (EER) of the cooling plant is 2.62. [Copyright &y& Elsevier]

Abstract: Evaluating a building’s performance usually requires a high number of sensors especially if individual rooms are analyzed. This paper introduces a simple and scalable model-based virtual sensor that allows analysis of a buildings’ heat consumption down to room level using mainly simple temperature sensors. The approach is demonstrated with different sensor models for a case study of a building that contains a hybrid HVAC system and uses fossil and renewable energy-sources. The results show that, even with simple sensor models, reasonable estimations of rooms’ heat consumption are possible and that rooms with high heat consumption are identified. Further, the paper illustrates how virtual sensors for thermal comfort can support the decision making to identify the best ways to optimize building system efficiency while reducing the building monitoring cost. [Copyright &y& Elsevier]

Highlights • In this paper, a novel energy-efficient AC system incorporating an independent evaporative condenser (EC) system is comprehensively investigated. • The most obvious phenomenon is the imbalanced cooling capacity of side A and side B as high and low efficiency working condition. • The COP value of high efficiency working condition is 4.0, almost the same as rated condition 4.3. • An economic model is applied to analyze the application feasibility and benefits of the EC-AC system against the conventional WC-AC system. Abstract Air conditioning system (AC) contributes significantly to the energy consumption of underground metros. In China, most metro stations are designed with water-cooling centralized air conditioning (WC-AC) system, it has been found that several serious problems are brought by this conventional system, such as large space occupying, water leaking, cooling tower noise and low system efficiency. In order to solve these problems, a novel energy-efficient AC system incorporating an independent evaporative condenser (EC) has been proposed and installed at Futong metro station in Beijing, China. A series of pilot measurements were conducted to analyze the cooling performance and energy consumption of this novel EC-AC system. During the testing period, the average refrigeration efficiency of COP, SCOP and ACOP in A and B side is up to 3.8/3.9, 3.4/3.4 and 2.5/2.3. At the same time, some operation problems such as unbalanced working condition have been identified during measurement. The research indicates that such EC-AC system could be a feasible solution to enhance the energy efficiency and reduce the operational costs and carbon emission in metro stations. [ABSTRACT FROM AUTHOR]

Abstract: In the last few years the solar-powered air-conditioning systems have been in intensive development and more often are considered as the viable application for the thermal solar systems in the regions of southern Europe. This is mainly due to the increasing higher electrical consumption in many countries (especially in Spain) which is moving from the winter to summer months due to expanding usage of cooling systems in this period of the year. In this paper we will analyze the behaviour of the solar-assisted air-conditioning system installed in the CIESOL building. This system consists mainly of flat-plate solar collectors and the simple effect LiBr–H2O absorption chiller. Different operation modes were analyzed. Coefficient of performance (COP) at various generator, absorber, condenser and evaporator temperatures is investigated and experimental results show that in practice it is easy to obtain values of about 0.6. The main goal of this paper is to describe the characteristics of the developing building and the solar-assisted air-conditioning system. Another useful purpose is to find the optimum conditions and operation parameters for the solar system through analyzing various systems'' operation strategies. [Copyright &y& Elsevier]

Abstract: Improving performance of existing air-conditioning system and minimizing its environmental effect are requested from global environmental issues. A new air-conditioning system using evapo-transpiration condenser has been proposed. Evapo-transpiration condenser is a condenser that uses transpiration by keeping condenser surface wet and water evaporation enhancing heat-transfer rate. In this paper, a prototype of the new system is tested and compared with the existing system in summer weather of Japan. Hourly-average condenser-temperature is achieved to be 5–10 °C reduction compared to that of the air-cooled condenser. Without any optimization in system operation, up to more than 30% hourly integral power consumption is saved at ambient temperature below 31 °C from this prototype. Besides, temperature of outlet-air from outdoor-unit is nearly the same as ambient temperature, while its relative humidity is slightly higher. Special maintenance is not necessary for the new evapo-transpiration condenser. [Copyright &y& Elsevier]

Abstract: Several studies show the potential benefits achievable by recurring to roof vegetation. Really, little literature investigates the economic feasibility of such solution. The paper verifies utility of green roofs, under environmental and energy point of views, by considering all the aspects that influence their performances. With reference to several climates, intensity of rainfalls, needs of irrigation and kind of building use, a large parametric analysis evaluates the technical and economical feasibility of green roofs applied to a modern office building, considering various vegetations and different external coatings. The scarce amount of rainfall – and thus the irrigation cost – can nullify the savings in energy demand for air-conditioning. Moreover, even if green roofs show satisfactory performance if monthly rainfalls do not imply significant additional watering – the economic investigation shows scarce convenience for well-insulated buildings, above all if the higher initial cost of a green roof, compared to traditional roofing coating, is computed. Finally, cool roofs, by means of high-reflective and high-emissive coatings, are suitable solutions in warm climates, strongly improving the summer performances, with low extra costs for installation and maintenance. [Copyright &y& Elsevier]

Abstract: Energy efficient HVAC solutions may be obtained by combining different energy sources – fossil and renewable – into single hybrid systems. This leads to a variety of system concepts with specific boundary conditions. As a consequence, the definition of a unique representation method and a standardized performance evaluation procedure is a challenging task. Currently, two international projects promoted by the IEA are dealing with the representation and the performance calculation of a particular category of hybrid systems, i.e. integrated solar assisted systems. The HPP Annex 34 “Thermally Driven Heat Pumps for Heating and Cooling”, whose goal is to reduce the environmental impact of heating and cooling by the use of thermally driven heat pumps, has solar cooling as one of the systems under investigation. The joint project between SHC and HPP Task 44/Annex 38 “Solar and Heat Pump Systems” is focused on different system combinations of solar thermal collectors and heat pumps. The scope of the present paper is to show a systematic methodology to represent and evaluate the energy performance of complex hybrid systems. The proposed approach is a joint effort of the on-going IEA activities and will be discussed regarding the mentioned solar hybrid systems. However, the final goal of the work is to provide a basis for a simple, fair and transparent comparison of all systems for heating and cooling, regardless of the technology. [Copyright &y& Elsevier]

Abstract: This paper presents the effect of operating water mist system to enhance the energy efficiency of air-cooled chillers under various operating conditions. A thermodynamic model for an air-cooled chiller with twin refrigeration circuits coupled with a water mist system was developed and validated by measured operating data. The validated model was used to investigate how the thermal properties of the entering condenser air and the performance of the air-cooled chiller varied under different operating schemes with water mist pre-cooling. Under the conventional head pressure control (HPC) with a designed water mist generation rate, the coefficient of performance (COP) increased by up to 21.3%. The chiller performance could be improved further under variable condensing temperature control (CTC). Under CTC, chiller COP was increased up to 51.5% with optimal water mist generation rate. The potential energy savings of these chillers serving a representative office building in subtropical climate was evaluated, and CTC coupling with optimal water mist generation rate would reduce the annual total electricity consumption for cooling by 14.1%. The water consumption of the water mist system was comparatively small, comparing with the total water losses for an open-loop cooling tower system with equivalent heat rejection capacity. [Copyright &y& Elsevier]

Liquid desiccant is an energy-saving, environmentally friendly and healthy means of air dehumidification. A liquid desiccant-based all-air air conditioning system is studied by simulation. Two different modes of air mixing between the return air and the fresh air are compared, that is mixing before and mixing after the liquid desiccant dehumidifier, respectively. System performance and total energy consumption of the two modes under different operation conditions are obtained. The results show that mixing air after dehumidification consumes less energy than mixing air before dehumidification. Coefficient of performance (COP) of the all-air system with air mixing after dehumidification is higher. The differences of COP and energy consumption between the two air mixing modes increase when the outdoor air temperature and relative humidity increase.Practical application: Liquid desiccant based all-air system is quite suitable for museums, libraries and computer centres where water is not allowed to enter the space for property safety and strict thermal-hygrometric control is necessary. The results of this paper provide guidelines on the selection of air mixing modes in liquid desiccant-based all-air systems, considering energy consumption and system COP. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the performance of the Heating,Ventilation, and Air Conditioning (HVAC) system in largebuildings is a prerequisite for optimizing their energy effincy. Fine grain performance analysis has not, to our knowledge, received adequate attention thusfar.To address this issue weevaluate the thermal comfort and the energyefficiencyof a relatively modernHVACsystemina largebuilding based onbuilding-wide high-fidelity environmental data collected via a wireless sensor network over 12 months. Access to fine grain information reveals temporal and spatial dynamics that help quantify thelevelof (non-)compliance with the system''s control objective and thebuilding''s thermal comfort standards. The paper moreover describes ThermoNet, our hybrid wireless sensor network for monitoring a legacy building,which usesdutycyclingandadaptivepower controltoachievehighdatayieldwithlowpower consumption. [Copyright &y& Elsevier]

Abstract: Hainan province is the only tropical and island province in China, with the unique climatic and geographical features. It has a different energy performance in public buildings from those in the inland areas. This paper investigated the current situation of energy consumption of the sampled public buildings, including 26 hotels, 24 office buildings and 7 department stores, through analyzing utility billing data, on-site survey and measurement, and site operational records. The breakdowns of energy consumption found out that the electricity dominated the energy consumption for all the sampled buildings and the air conditioning system played a key role in the energy consumption of major building services. By analyzing the main factors for building energy consumption, the annual average energy use indexes were calculated to be 141.63kWh/m2, 87.70kWh/m2, and 166.95kWh/m2 for hotels, office buildings and department stores, respectively. Besides, the comparison between Hainan province and other areas revealed that the building energy consumption of this tropical province was at a low level. Because indoor environment quality can influence the health and work efficiency of humans in buildings, field tests on the indoor environment quality were also carried out, and the performance of indoor environment quality was rated. [Copyright &y& Elsevier]

Abstract: Because of their excellent performance in local thermal environmental control, task/ambient conditioning (TAC) systems have attracted increasingly more research attention. However, the current applications of TAC systems are mainly for daytime activities, but seldom for nighttime. In fact, TAC systems may be best applied to a sleeping environment, since the subjects to be served by a TAC system are immobile during sleep. Therefore, there is a strong need for studying the operational and energy saving performance of TAC systems when applied to sleeping environments. This paper reports on an experimental study on evaluating the operational and energy saving performance of a novel bed-based TAC system. The experimental results and their analysis demonstrated that the use of the novel bed-based TAC system can help achieve energy saving, compared with the use of a full volume air conditioning (FAC) system. Considering the experimental limitations, the energy saving potential of the novel bed-based TAC system if used in an actual bedroom was studied through a theoretical analysis. It demonstrated that the novel bed-based TAC system would help achieve significant energy saving when used in real buildings. [Copyright &y& Elsevier]

Abstract: There are presently different types of air conditioning products in China such as room air conditioners, variable speed room air conditioners, unity air conditioners, multi-connected air-condition (heat pump) unit, chilled water air conditioning systems. For these air conditioning products, evaluation indexes have been created, respectively including energy efficiency ratio (EER), coefficient of performance (COP), seasonal energy efficiency ratio (SEER) and integrated part load value (IPLV), and their energy efficiency standards have been established. Based on thermodynamic perfectibility, this paper makes the compatible analysis of the energy efficiency and thermodynamic perfectibility gradient of energy efficiency standards for different air conditioning products. According to testing conditions of evaluation indexes, these air conditioning products are classified into two groups, the standard rating conditions group (EER, COP) and the variable working condition group (SEER, IPLV). The results show the thermodynamic perfectibility of different air conditioning products grade as the same level for energy efficiency standards in each group differ from one another. Besides, the average thermodynamic perfectibility gradient of energy efficiency levels for air conditioning product in the standard rating conditions group is basically the same, and that of variable speed room air conditioners and multi-connected air-condition (heat pump) unit are the highest and lowest, respectively. [Copyright &y& Elsevier]

Abstract: Buildings nowadays are increasingly expected to meet higher and more complex performance requirements: they should be sustainable; use zero-net energy; foster a healthy and comfortable environment for the occupants; be grid-friendly, yet economical to build and maintain. The essential ingredients for the successful development and operation of net zero- and positive-energy buildings (NZEB/PEB) are: thermal simulation models, that are accurate representations of the building and its subsystems; sensors, actuators, and user interfaces to facilitate communication between the physical and simulation layers; and finally, integrated control and optimization tools of sufficient generality that using the sensor inputs and the thermal models can take intelligent decisions, in almost real-time, regarding the operation of the building and its subsystems. To this end the aim of the present paper is to present a review on the technological developments in each of the essential ingredients that may support the future integration of successful NZEB/PEB, i.e. accurate simulation models, sensors and actuators and last but not least the building optimization and control. The integration of the user is an integral part in the dynamic behavior of the system, and this role has to be taken into account. Future prospects and research trends are discussed. [Copyright &y& Elsevier]

Abstract: This paper provides a comparative study of the performance of cross-flow and counter-flow M-cycle heat exchangers for dew point cooling. It is recognised that evaporative cooling systems offer a low energy alternative to conventional air conditioning units. Recently emerged dew point cooling, as the renovated evaporative cooling configuration, is claimed to have much higher cooling output over the conventional evaporative modes owing to use of the M-cycle heat exchangers. Cross-flow and counter-flow heat exchangers, as the available structures for M-cycle dew point cooling processing, were theoretically and experimentally investigated to identify the difference in cooling effectiveness of both under the parallel structural/operational conditions, optimise the geometrical sizes of the exchangers and suggest their favourite operational conditions. Through development of a dedicated computer model and case-by-case experimental testing and validation, a parametric study of the cooling performance of the counter-flow and cross-flow heat exchangers was carried out. The results showed the counter-flow exchanger offered greater (around 20% higher) cooling capacity, as well as greater (15%–23% higher) dew-point and wet-bulb effectiveness when equal in physical size and under the same operating conditions. The cross-flow system, however, had a greater (10% higher) Energy Efficiency (COP). As the increased cooling effectiveness will lead to reduced air volume flow rate, smaller system size and lower cost, whilst the size and cost are the inherent barriers for use of dew point cooling as the alternation of the conventional cooling systems, the counter-flow system is considered to offer practical advantages over the cross-flow system that would aid the uptake of this low energy cooling alternative. In line with increased global demand for energy in cooling of building, largely by economic booming of emerging developing nations and recognised global warming, the research results will be of significant importance in terms of promoting deployment of the low energy dew point cooling system, helping reduction of energy use in cooling of buildings and cut of the associated carbon emission. [Copyright &y& Elsevier]

Abstract: An experimental study on performance of digital variable multiple air conditioning system under part load conditions in hot summer and cold winter zone was conducted in this paper. The effects of outdoor air temperature and on-unit ratio on total power consumption in 1h, hourly heating performance factor or hourly energy efficiency ratio were analyzed by experiments. The variations of hourly heating performance factor (or hourly energy efficiency ratio) and total power consumption in 1h with part load value under different outdoor air temperature were obtained. The results indicate that digital variable multiple air conditioning system can keep economical and reliable operation under part load conditions. And it is necessary to study the index which may reflect the seasonal energy consumption of digital variable multiple air conditioning system. [Copyright &y& Elsevier]

Abstract: To maintain satisfactory comfort conditions in buildings with low energy consumption and operation cost, control of air-conditioner units is required. In this paper, nonlinear control of an air-handling unit (AHU) is investigated and compared for two control approaches: gain scheduling and feedback linearization. A nonlinear multi input–multi output model (MIMO) of an air-handling unit (AHU) is considered. Both indoor temperature and relative humidity are controlled via manipulation of valve positions of air and cold water flow rates. Using an observer to estimate state variables, a hybrid control system including regulation system for disturbance rejection and nonlinear control system for tracking objectives is designed. Achievement of tracking objectives is investigated for various desired commands of indoor temperature and relative humidity; including a sequence of steps and ramps-steps. According to results, more quick time responses with a bit more overshoot in tracking set-points/paths are achieved by using feedback linearization method (especially for temperature). However, valves position as input control signals are associated with less oscillation (and consequently less energy consumption) when the controller designed based on gain scheduling approach is used. Finally, it is shown through phase portrait of the system that the controller designed based on feedback linearization shows a robust performance in the presence of random uncertainty in model parameters. [Copyright &y& Elsevier]

Abstract: In conventional air-conditioning system, fresh air volume is always restricted to save energy, which sacrifices indoor air quality (IAQ) to some extent. However, removing the latent load of air by liquid desiccant rather than by cooling is an alternative way of reducing energy consumption. Therefore, IAQ can be improved by increasing the volume of fresh air introduced into an air-conditioning system. In this paper, a liquid desiccant based air-conditioning system is studied, with the system performance under various fresh air ratios analyzed using simulation tests. In addition, the proposed system and a conventional system are compared. In the proposed system, with the increase in fresh air ratio, the heating load for solution regeneration rises, the dehumidification efficiency increases and the regeneration efficiency drops. The coefficient of performance (COP) of the liquid desiccant based system decreases sharply when the fresh air ratio exceeds 60%. The results also show that the proposed system can save power notably. The maximum power saving ratio is 58.9% when the fresh air ratio is 20%; however, the ratio drops when the fresh air ratio increases. These findings will be beneficial in the selection of fresh air ventilation strategies for liquid desiccant based air-conditioning systems. [ABSTRACT FROM AUTHOR]

The shading effects of light shelves in indoor thermal environments have not been investigated to date. Thus, this study aims to identify the effectiveness and appropriate parameters required for a light shelf by evaluating its performance in the presence of lighting and air conditioning. A full-scale testbed was established in this study for evaluating the performance of the light shelf. Moreover, the performance evaluation was conducted by calculating the energy consumed for lighting and air conditioning to maintain proper temperature and illuminance. This study found the following: (1) During summer, the use of a light shelf would reduce the energy consumption for lighting and air conditioning by 0%–10.5% and 6.9%–9.3%, respectively. (2) During winter, the use of a light shelf would increase the energy consumption for lighting and air conditioning by 0%–25.3% and 0.2%–3.2%, respectively, which is undesirable. (3) Increasing the angle of the light shelf would increase the amount of light penetrating to indoors, thus would reduce the energy required for lighting. Based on these findings, we recommend the installation of a detachable light shelf that is 0.6-m wide with a 30° angle for buildings in Korea; and during winter, the light shelf should be removed to save energy. [ABSTRACT FROM AUTHOR]