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• A comparison method between energy-only and energy and reserve model. • Higher revenue for flexible technologies was achieved for joint model. • The down reserve proved to be more required in high RES systems. • The study showed significant difference in operation between two models. The requirements for ancillary services in energy systems are growing as the amount of renewable energy sources such as solar and wind increases. On the other hand, the system can benefit from extra sources of flexibility thanks to the increased digitalization that enables successful integration of demand response and energy storage. The majority of recent energy system analysis research did not consider the regulation markets. As a result, these investigations preclude the ability to fully evaluate the advantages of energy storage and flexible cooling loads. With the method outlined in this paper, it is possible to compare the two strategies and assess the advantages of energy storage and flexible cooling loads for each strategy. In addition to the energy storage systems, the case study in this paper focuses on flexible cooling loads as a significant consumer in the system. According to the findings, the system's operating costs increased by 19.4% when reserve limitations were placed. Furthermore, the findings demonstrated that when flexible assets were permitted to participate in the reserve market, they generated significantly higher incomes. According to the findings, mechanisms that will allow energy storage and demand response to provide reserve capacities as well as the growth of reserve markets are both necessary. [ABSTRACT FROM AUTHOR]

Abstract: Building cooling load prediction is one of the key factors in the success of energy-saving measures. Many computational models available in the industry today have been developed from either forward or inverse modeling approaches. However, most of these models require extensive computer resources and involve lengthy computation. This paper discusses the use of data-driven intelligent approaches, a probabilistic entropy-based neural (PENN) model to predict the cooling load of a building. Although it is common knowledge that the presence and activity of building occupants have a significant impact on the required cooling load of buildings, practices currently adopted in modeling the presence and activity of people in buildings do not reflect the complexity of the impact occupants have on building cooling load. In contrast to previous artificial neural network (ANN) models, most of which employ a fixed schedule or historic load data to represent building occupancy in simulating building cooling load, this paper introduces two input parameters, dynamic occupancy area and rate and uses it to mimic building cooling load. The training samples used include weather data obtained from the Hong Kong Observatory and building-related data acquired from an existing grade A mega office buildings in Hong Kong with tenants including many multi-national financial companies that require 24-h air conditioning seven days a week. The dynamic changes that occur in the occupancy of these buildings therefore make it very difficult to forecast building cooling load by means of a fixed time schedule. The performance of simulation results demonstrate that building occupancy data play a critical role in building cooling load prediction and that their use significantly improves the predictive accuracy of cooling load models. [Copyright &y& Elsevier]

Highlights • A two-stage ejector-based multi-evaporator refrigeration system was presented. • Effects of key geometries on two-stage ejector performances were investigated. • Optimum values of the key geometric parameters were obtained. Abstract A three-evaporator and dual-ejector refrigeration system was presented in this paper. By combining two single ejectors as a whole, the authors attempted to discuss the effects of key geometric dimensions of each stage on both stage performances with two-dimensional CFD simulation method. First, the CFD models were validated by experimental data. Then, the primary nozzle diameters of both stages were determined by the cooling load demands of the refrigerating and air-conditioning chambers. Next, the detailed effects of key geometric parameters such as the length of constant-pressure mixing section, the length of constant-area mixing section and area ratio of each stage on two-stage performances were identified with simulations. Finally, the optimum values of the key geometric parameters were obtained, and the results showed that the area ratio had the most significant influences on the entrainment ratio of both stages as compared to other parameters. [ABSTRACT FROM AUTHOR]

• Detailed configuration of a CO 2 heat pump with parallel compression is described. • A complete CO 2 system layout for simultaneous heating and cooling is presented. • A validated mathematical model with FSD and VSD CO 2 compressors has been developed. • System performance of actual CO 2 system is evaluated over three months of operation. Carbon dioxide (CO 2) is a natural substance and an environmentally benign, safe and economical refrigerant that can be used for cooling and heating systems. Unlike a traditional reversible heat pump system that only works either in heating or cooling, the air-to-air transcritical CO 2 heat pump system reported in this paper is capable of providing simultaneous space heating and cooling through an Air Handling Unit (AHU) at any time. The system with cooling and heating capacities of 210 kW and 110 kW, respectively, was installed in a cinema complex in South Australia, and continuously operated from September to November in 2020. In this paper, the detailed configuration of the CO 2 heat pump system with parallel compression is described. A complete system layout, comprising of cooling, heating and shared circuits, is revealed for the first time. A mathematical model based on highly efficient Bitzer compressors has also been developed in this study. The experimental data recorded in an entire heating period of approximately one hour has been utilised for model validation and analysis. Through the validation, the simulated power consumption for the compressors with Variable Speed Drive (VSD) and Fixed Speed Drive (FSD) has been compared to the experimental data with acceptable agreements. The simulated discharge temperatures agree with the actual temperatures measured within 10%. Moreover, the latest system performance from September to November has been evaluated based on the heating and cooling loads and combined COPs. It was found that the combined COP was relatively stable at around 3 regardless of climate conditions. [ABSTRACT FROM AUTHOR]

Abstract: This paper considers how to apply optimum condensing temperature control and variable chilled water flow to increase the coefficient of performance (COP) of air cooled centrifugal chillers. A thermodynamic model for the chillers was developed and validated using a wide range of operating data and specifications. The model considers real process phenomena, including capacity control by the inlet guide vanes of the compressor and an algorithm to determine the number and speed of condenser fans staged based on a set point of condensing temperature. Based on the validated model, it was found that optimizing the control of condensing temperature and varying the evaporator’s chilled water flow rate enable the COP to increase by 0.8–191.7%, depending on the load and ambient conditions. A cooling load profile of an office building in a subtropical climate was considered to assess the potential electricity savings resulting from the increased chiller COP and optimum staging of chillers and pumps. There is 16.3–21.0% reduction in the annual electricity consumption of the building’s chiller plant. The results of this paper provide useful information on how to implement a low energy chiller plant. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

• Micro heat pipe array-based BIPVT module enables efficient heat utilization. • A novel model of the BIPVT module and energy supply system was established. • Highly efficient combination of BIPVT and heat pump utilization is achieved. • Summarized the energy-saving features of BIPVT building in different seasons. • The novel BIPVT buildings achieve nearly zero energy standards. Building integrated photovoltaic–thermal (BIPVT) technology is an efficient form of solar energy utilization, which realizes self-energy supply and holds good development prospects. In this paper, a novel BIPVT module based on micro heat pipe array and BIPVT near-zero energy building are proposed. A matching multi-energy complementary energy supply system is also proposed for this building. The building and energy supply system models were built using TRNSYS. The load characteristics of BIPVT buildings were studied by analyzing the heat transfer process of BIPVT components. The energy-saving rate of the building was also calculated using the method of near-zero energy building evaluation index. The accumulated cooling load and heating load of the buildings throughout the year show that those of the BIPVT buildings are 8.6% higher than those of the benchmark building. Comparison of the energy consumption results shows that the annual cumulative energy consumption of the BIPVT building is 32.3% lower compared to the benchmark building's. In addition, 61.2% of the energy required for year-round refrigeration, heating, and electricity can be supplied by this system. The energy consumption index of the BIPVT building is 70.26 kWh / (m2 • a). Compared with the benchmark building, the BIPVT building energy saving rate is 76.6% and the building energy efficiency improvement rate is 32.3%. [ABSTRACT FROM AUTHOR]

• Cooling load characteristics are used to construct multi-cooling scenarios. • A collaborative optimization method is proposed for district cooling systems. • A compatible multi-objective optimization model is established. • The impacts of the chiller configuration on the scheduling potential are discussed. • The impacts of cooling load characteristics on economic benefits are investigated. District cooling systems have been widely used for their high economic and energy performance. However, insufficient consideration of chiller configuration selection and multi-cooling scenarios causes excessive equipment installed capacity and low energy efficiency. This paper proposes a collaborative optimization method and a compatible multi-objective optimization model to address the design and operation issues affecting the economic and energy benefits of district cooling systems. Firstly, the cooling period is divided into different cooling scenarios constructed by cooling load characteristics. Subsequently, the ε-constraint-Sequential Quadratic Programming method is used to solve the multi-objective optimization models under different chiller configurations and various cooling scenarios. Finally, the Analytic Hierarchy Process-Technique for Order Preference by Similarity to Ideal Solution method is used to get the installation scheme with optimal chiller configuration and the operation strategies under various cooling scenarios. The proposed method is applied to design and optimize a district cooling system with ice thermal storage. The optimal scheme is equipped with double-duty chillers (6 × 1800 RT, 1 × 500 RT) and water-cooled chillers (1 × 1800 RT, 1 × 900 RT), considering chiller configuration selection and multi-cooling scenarios. Compared with the conventional scheme using double-duty chillers (8 × 1800 RT) and water-cooled chillers (2 × 1800 RT), the annual costs and the annual electricity consumption are reduced by 11.03% and 11.78%, respectively. The results verify the effectiveness and advantages of the optimization method. [ABSTRACT FROM AUTHOR]

In this paper, the simulation is carried out to investigate the performance of ejector used in a parallel hybrid ejector-based refrigerator-freezer cooling cycle. The geometric parameters such as primary nozzle diameter, area ratio and constant-pressure mixing chamber length are studied firstly to achieve a good performance of the fixed area ratio ejector under a certain condition. Based on the obtained ejector geometry, an adjustable ejector with a spindle is used in the system to meet the requirements of variable cooling loads. The results show that the effect of blocking percentage of primary nozzle with a spindle on the ejector performance is considerable. Moreover, the adjustable ejector works well with relatively high entrainment ratio when the back pressure increment percentage as compared to the secondary flow pressure is no less than 16.15%. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on cooling characteristics of a realistic thermoelectric module (TEM) that operates under single and continuous square current pulse. The experimental system is built and the related study is performed. A cooling temperature enhancement of 3.0 °C relative to steady current operation on a realistic TEM is demonstrated. Further experimental data reveal that there exists an optimum initial steady current which provides the maximum cooling temperature enhancement in the current pulse operation. In addition, the value of the supercooling and the temperature overshoot always stay close. Moreover, continuous temperature enhancement in each current pulse is achieved on a realistic TEM operated with continuous current pulses. Cooling temperature in each current pulse shows an increasing trend similar to that of a first order step response. The cooling characteristics under different cooling loads are quite similar, except for the different initial temperatures. [ABSTRACT FROM AUTHOR]

• A PV assisted ground source heat pump and air source heat pump (PVGSHP-ASHP) system was proposed. • Performance for three GSHP systems were simulated and compared in depth. • Economic optimization of the integrated operation of the PVGSHP-ASHP system was carried out. • The proposed system can solve the load imbalance problem in hot summer and cold winter zones while improving the COP of GSHP and reducing the system cost. The ground source heat pump (GSHP) system is widely recognized as an efficient, clean and economical renewable energy technology for buildings, and can be utilized for building cooling, heating and hot water supply. In the hot summer and cold winter zones of China, however, the total thermal load (heating load and hot water load) of GSHP systems is greater than the cooling load, which may cause a significant soil temperature drop and GSHP performance deterioration. To solve the above problems, a photovoltaic (PV) assisted GSHP and air source heat pump system (PVGSHP-ASHP) was proposed. This paper investigated the performance and feasibility of the PVGSHP-ASHP system, using a case campus building in Changsha city, China. The PVGSHP-ASHP system was firstly established by TRNSYS, and then, its operational performance was evaluated and compared with the PV assisted GSHP (PVGSHP) system and the PV assisted GSHP and electric heater (PVGSHP-EH) system. Finally, the economic optimization of the integrated operation of the PVGSHP-ASHP system was carried out with the combined simulation of TRNSYS and GenOpt. The results showed that for the PVGSHP system, the soil temperature reduced from 18.1 °C to 11.8 °C after 15 years of operation, which caused a decrease in the annual coefficient of performance of the GSHP (COP GSHP) and an increase in the annual electricity consumption. Although the PVGSHP-EH system can solve the load imbalance problem, its annual lifecycle cost (ALCC) increased by 39.3 % due to the low efficiency of the EH. The PVGSHP-ASHP system can solve the appeal problem with high annual COP GSHP and COP sys values of 3.49 kW/kW and 4.69 kW/kW, respectively, and only 71,700 kWh of the annual electricity consumption, while its ALCC was the lowest at 99,223 CNY, which was 8.1 % lower than the PVGSHP system. After optimization, the ALCC of the PVGSHP-ASHP system reached the minimized value of 91,158 CNY, with a reduction of 8.1 %. These findings can provide new ways to solve the load mismatch problem of GSHP systems while enhancing the system efficiency in the hot summer and cold winter zones of China. [ABSTRACT FROM AUTHOR]

Multiple-chiller plant is commonly employed in the heating, ventilating and air-conditioning system to increase operational feasibility and energy-efficiency under part load condition. In a multiple-chiller plant, chiller sequencing control plays a key role in achieving overall energy efficiency while not sacrifices the cooling sufficiency for indoor thermal comfort. Various sequencing control strategies have been developed and implemented in practice. Based on the observation that ( i ) uncertainty, which cannot be avoided in chiller sequencing control, has a significant impact on the control performance and may cause the control fail to achieve the expected control and/or energy performance; and (ii) in current literature few studies have systematically addressed this issue, this paper therefore presents a study on robustness analysis of chiller sequencing control in order to understand the robustness of various chiller sequencing control strategies under different types of uncertainty. Based on the robustness analysis, a simple and applicable method is developed to select the most robust control strategy for a given chiller plant in the presence of uncertainties, which will be verified using case studies. [ABSTRACT FROM AUTHOR]

Abstract: The thermal effectiveness of a building’s roof with phase change material (PCM) is presented in this paper. The considered model consists of a concrete slab with vertical cone frustum holes filled with PCM. The objective of incorporating the PCM into the roof structure is to utilize its high latent heat of fusion to reduce the heat gain during the energy demanded peak hours, by absorbing the incoming energy through the melting process in the roof before it reaches the indoor space. The thermal effectiveness of the proposed roof-PCM system is determined by comparing the heat flux at the indoor surface to a roof without the PCM during typical working hours. A parametric study is conducted to assess the effects of the cone frustum geometry, and the kind of PCM used. The n-Eicosane shows the best performance among the examined PCMs, and the conical geometry of the PCM container is the best in term of thermal effectiveness. The results indicate that the heat flux at the indoor surface of the roof can be reduced up to 39% for a certain type of PCM and geometry of PCM cone frustum holes. [Copyright &y& Elsevier]

In this paper a comparative study between single effect and double effect absorption refrigeration systems with identical cold output is carried out. Simulation results were used to study the influence of the various operating parameters on the performance coefficient, the thermal loads of the components, exergetic efficiency (rational efficiency) and the total change in exergy of the two systems. It is concluded that the COP of double effect system is approximately twice the COP of single effect system but the exergetic efficiency of double effect system increase slightly compared to the exergetic efficiency of single effect system. It is found that for each condenser and evaporator temperature, there is an optimum generator temperature where the total change in exergy of the single effect and double effect absorption refrigeration systems is minimum. At this point the COP and exergetic efficiency of the systems become maximum. In this study and when the evaporation temperature is varied from 4°C to 10°C, condenser and absorber temperatures are varied from 33°C to 39°C and generator (HPG) temperature is varied from 60°C to 190°C the maximum COP values of the single effect refrigeration systems are in the range of 0.73–0.79 and for double effect refrigeration systems are in the range of 1.22–1.42. The maximum exergetic efficiency values of the single effect refrigeration systems are in the range of 12.5–23.2% and for double effect refrigeration systems are in the range of 14.3–25.1%. [Copyright &y& Elsevier]

Abstract: Microencapsulated phase change material (MPCM) slurry is advantageous for thermal storage systems to use as a heat transfer and storage medium. In this paper, a new design of air-conditioning system is proposed, which is a combination of CC and a MPCM slurry storage tank. The mathematical model of the combined system is provided and used to predict the system performance of an office room under Hong Kong weather condition using hour-by-hour calculations. A feasibility analysis for the combined system was also made with computer calculations. The results indicate that a small MPCM slurry storage tank is able to shift the part of cooling load from the daytime to nighttime. It is also revealed that the proposed combined system is an energy saving and economy-favorable air-conditioning system. [Copyright &y& Elsevier]

Abstract: The thermal comfort control of a room must consider not only the thermal comfort level but also energy saving. This paper proposes an enthalpy estimation that is conducive for thermal comfort control and energy saving. The least enthalpy estimator (LEE) combines the concept of human thermal comfort with the theory of enthalpy to predict the load for a suitable setting pair in order to maintain more precisely the thermal comfort level and save energy in the air conditioning system. [Copyright &y& Elsevier]

The availability of more comprehensive solar irradiance data is invaluable for the reduction of cooling load in buildings and for the evaluation of the performance of photovoltaic plants. In many parts of the world, however, the basic solar irradiance data are not always readily available. This paper presents an approach to calculate the solar irradiance on sloped planes by integrating the sky radiance distribution. Sky radiance data recorded from January 1999 to December 2001 in Hong Kong were used to estimate the solar irradiance for the horizontal and four principal vertical surfaces (N, E, S and W). The performance of this approach was assessed against data measured in the same period. Statistical results showed that using sky radiance distributions to predict solar irradiance can give reasonably good agreement with measured data for both horizontal and vertical planes. The prediction approach was also employed to compute the solar irradiance of a 22.3° (latitude angle of Hong Kong) inclined south oriented surface. The findings indicated that the method can provide an accurate alternative to determine the amount of solar irradiance on inclined surfaces facing various orientations when sky radiance data are available. [Copyright &y& Elsevier]

The prevailing local climatic conditions affect the building loads and the heating, ventilating and air conditioning equipment sizing and performance. This paper presents work on the determination of outdoor design conditions for cooling load calculation. The computer package DOE-2.1E was used to simulate the hourly cooling load of a generic commercial office building in Hong Kong. Totally, 22 weather data sets, from 1979 to 2000, were used for the analysis. The findings indicate that the outdoor climatic conditions developed for cooling load estimation via the simulations are less stringent than the current outdoor design data and approaches adopted by local architectural and engineering practices. Building designers should select and evaluate critically the outdoor design conditions in order to achieve optimum air conditioning equipment sizing. [Copyright &y& Elsevier]

• A novel CCHP-ORC system and corresponding improved FEL strategy were proposed. • Several operation and configuration parameters were synergistically optimized. • System performance was compared and analyzed based on different objectives. • The optimal ATCS, PECS, CDER and U indexes reached 38.11%, 21.05%, 47.61% and 35.38% respectively. In this paper, a novel combined cooling, heating and power-organic Rankine cycle system is proposed. The purpose of the system is to enrich the approach of energy cascade utilization by using different grades of waste heat flexibly. In addition, an improved following electric load strategy for the system is introduced, which could control the prime mover and organic Rankine cycle to share electric demand. To explore the optimization potential of the system under the new strategy, several configuration parameters and operation parameters are synergistically optimized by using enumeration method. Herein, the optimization variables are rated capacity of prime mover, exhaust smoke temperature, exhaust smoke distribution coefficient and cooling load distribution coefficient. The optimization objectives are annual total cost saving, primary energy consumption saving, carbon dioxide emission reduction and comprehensive benefit. The results indicate that the optimal values of above objectives are 38.11%, 21.05%, 47.61% and 35.38%, respectively. Moreover, the variable characteristics, the system performance indexes and the energy dispatch for different objectives are compared and analyzed. To enhance the system flexibility, the variables are further optimized according to the load characteristics of different seasons by using genetic algorithm. The results show that the optimal values of above objectives are further increased by 4.8%, 10.7%, 3.7% and 5.9% respectively. The change of exhaust smoke temperature is conducive to improve the heat utilization efficiency in winter. These findings could promote the sustainable development of the integrated system. [ABSTRACT FROM AUTHOR]

• Water adsorption characteristics on novel UiO-66 (Zr) metal-organic frameworks. • Modelling and simulation of advanced AAHT systems using functional UiO-66 (Zr) MOFs. • Models are demonstrated by isotherms and kinetics data with energy recovery. • The specific cooling and heating power with daily water production are enhanced. • The coefficient of performance (COP) improves from 0.1 to 0.8. This article presents a comprehensive study of UiO-66 (Zr) based metal-organic frameworks (MOFs) plus water systems for various adsorption assisted heat transformation (AAHT) applications such as cooling, heat pump and desalination. The paper at first deals with the evaluation of water adsorption characteristics on the parent and pyridine, amino, and hydroxyl functional groups based UiO-66 (Zr) MOFs. The experiments are carried on for temperatures varying from 25 to 80 °C and pressures up to the saturated conditions. Based on experimentally confirmed isotherms and kinetics data, the adsorption assisted heat transformation systems are modelled and simulated. Hence the thermal storage system is also modelled with the addition of both heat and mass recoveries. Finally, the performances of adsorption cooling/heat pump/desalination are calculated with respect to various cycle time, heating source and cooling load temperatures. Hence, hydroxyl (–OH) and amino (–NH 2) functional group UiO-66 MOFs improves water transfer from 0.05 kg/kg to 0.32 kg/kg. On the other hand, OH-UiO-66 (Zr) + water system shows the faster kinetics and –NH 2 group also provides relatively higher Δ q (uptake-offtake difference) per adsorption-desorption cycle. The functional groups enhance the hydrophilic behavior of the parent UiO-66 MOFs in the low pressure zone, which improves overall efficiency. The SCP (specific cooling power) enhances from to 0.36 kW/kg to 0.84 kW/kg and the SHP (specific heating power) increases from 0.9 kW/kg to 1.48 kW/kg. In addition, the SDWP (specific daily water production) improves from 24 to 40 m3 of purified water per tonne of MOFs-adsorbent per day. These results confirm that functionalized UiO-66 (Zr) MOFs are competent candidates for adsorption cooling, heat pump and desalination applications. [ABSTRACT FROM AUTHOR]