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Predicting the energy performance of household variable refrigerant flow (VRF) systems in the hot summer and cold winter (HSCW) region in China accurately is particularly challenging due to the frequent defrost operations of the VRF systems during winter. Hence, an improved energy model was developed to determine the energy performance of household VRF systems, taking into account the defrost operations. The energy model was validated by experiments and the energy performance of the VRF system for typical residential buildings in Chongqing, Changsha, Nanjing, and Shanghai was determined based on representative operation modes (full-time-full-space and part-time-part-space modes). The results indicate that the efficiency of the VRF system increases as the outdoor temperature decreases. However, the efficiency of the VRF system decreases as the part-load ratio decreases, which leads to variations in the cooling seasonal performance factor for the representative operation modes and cities. The heating seasonal performance factor is not only influenced by the outdoor temperature and part-load ratio distribution, but also defrost operations. Compared with the part-time-part-space mode of C1 and C2, the annual energy consumption for the C4 mode performs lower from 26.3% to 51.7% for typical residential buildings in the four representative cities. [ABSTRACT FROM AUTHOR]

The absorption heat pump (AHP) heating system is an efficient alternative to the conventional fuel-based heating systems, with energy saving rate reaching 20–50%. However, the coefficient of performance (COP) and heating capacity of normal AHP decreased obviously as the available driving source temperature dropped. Compression-assisted AHP (CAHP) could operate efficiently under lower driving sources, and an experimental prototype was constructed for performance investigation. At an evaporator inlet of −10 °C, as the generator inlet decreases from 130 °C to 115 °C, the COP changes from 1.442 to 1.271, while the heating capacity drops from 68.21 kW to 31.28 kW. At an increased evaporator inlet of −5 °C, as the generator inlet decreases from 130 °C to 110 °C, the COP changes from 1.511 to 1.103, while the heating capacity drops from 78.72 kW to 21.71 kW. Comparisons between CAHP and normal AHP indicated that CAHP can extend the lower limit of generator inlet temperature from 125–130 °C to 110–115 °C. Besides, CAHP can enhance the heating capacity by 96.4% even when AHP can operate normally at a generator inlet of 130 °C. Moreover, performance improvement contributed by CAHP is greater under lower-temperature driving sources. [ABSTRACT FROM AUTHOR]

Seasonal cold storage using natural cold sources for cooling is a sustainable cooling technique. However, this technique suffers from limitations such as large storage space and poor reliability. Combining seasonal storage with short-term storage might be a promising solution while it is not explored sufficiently. This paper presents a compound cold storage system that combines a heat pipe-based seasonal ice storage system with a chilled water storage system. The seasonal ice storage system automatically charges winter cold energy in the form of ice. In summer, the stored ice is extracted for cooling, and then the melting ice is used as a chilling medium for chilled water storage. Design optimization of the seasonal ice storage system and the compound storage system is addressed, including the sizes of heat pipes, the configuration and volume of the cold storage tank and the chiller capacity. A case study is conducted to demonstrate the design and the application of the proposed system in a real building in Beijing. Results show that the appropriate combination of the two types of cold storage can greatly improve the applicability of the seasonal cold storage and reduce the life-cycle cost of a building cooling system by 40%. [ABSTRACT FROM AUTHOR]

Seasonal cold storage is a high-efficient and environmental-friendly technique that uses the stored natural cold energy in winter (e.g., snow, ice or cold ambient air) for free-cooling in summer. This paper presents a seasonal cold storage system that uses separate type heat pipes to charge the cold energy from ambient air in winter automatically, without consuming any energy. The charged cold energy is stored in the form of ice in an insulated tank and is extracted as chilled water for cooling supply in summer, which help to reduce the chiller running time and reduce the associated electricity consumption and greenhouse gas emission significantly. A quasi-steady two-dimensional mathematical model of the system is developed for characterizing the dynamic performance of ice growth (i.e., cold charging). The model is validated using the field measurement data from an ice charging experiment conducted in Beijing. The impacts of various affecting factors, including the weather data and the key parameters of heat pipes, on the charging performance of the cold storage system are analyzed. The effectiveness and sustainability of the proposed system for cooling are demonstrated through a case study of a kindergarten building in Beijing. [ABSTRACT FROM AUTHOR]

A ground-coupled heat pump (GCHP) is a clean and energy-saving approach to providing air conditioning and domestic hot water. For buildings with a dominant heating load, more heat is extracted from the soil and thermal imbalance becomes a crucial problem, in turn reducing efficiency and impeding the wide application of GCHP. Due to the disadvantages of the existing solutions, a multi-mode air-source heat compensator (AHC) integrated with a GCHP system to make a hybrid AHC-GCHP system is proposed in this paper. The principles and operating strategy of AHC-GCHP are illustrated in detail and its performance is simulated in the transient system simulation tool TRNSYS. AHC can not only compensate heat into the ground but also supply heat for space heating and domestic hot water in different modes through full use of the energy in the air with the average coefficient of performance (COP) ranging from 4.49 to 15.09. The AHC-GCHP system effectively keeps the soil thermal balance, and saves 23.86% energy compared with a traditional “boiler + split air conditioner” system, and costs less than half as much as a “hybrid GCHP assisted with solar collector” system. Consequently, the AHC-GCHP system is a potentially efficient and economic approach for buildings in cold regions. [ABSTRACT FROM AUTHOR]

The compression-assisted air source absorption heat pump (CASAHP) is a promising alternative heating system in severe operating conditions. In this research, parameter studies on the annual performance under various compression ratios (CRs) and source temperatures are performed to achieve the maximum energy saving rates (ESRs). Economic analyses of the CASAHP under different CRs and partial-design ratios are conducted to obtain an optimal design that considers both energy savings and economy improvements. The results show that the optimal CR becomes higher in colder regions and with lower heat source temperatures. For a source temperature of 130 °C, the optimal CR values in all of the cities are within 2.0. For source temperatures from 100 to 130 °C, the maximum ESR is in the range of 17.7–29.2% in the studied cities. The efficiency improvement rate (EIR) caused by compression in a severe source condition can reach 10.0–20.0%. From the viewpoint of economy, the relative investment of CASAHP is reduced to 30–60% with a CR of 2.0–3.0. With a 2–6% sacrifice in ESR, the payback period can be reduced from 12–32 to 5–9 years using compression. Partial-design of the CASAHP can further reduce the payback period to 3–6 years with a partial-design ratio of 50% and a CR of 2.8. Additionally, CRs and partial-design ratios are designed comprehensively by seeking the maximum ESR for a given acceptable payback period. [ABSTRACT FROM AUTHOR]

The low-temperature district heating system based on the air source absorption heat pump (ASAHP) was assessed to have great energy saving potential. However, this system may require smaller temperature drop leading to higher pump consumption for long-distance distribution. Therefore, the applicability of ASAHP-based district heating system is analyzed for different primary return temperatures, pipeline distances, pipeline resistances, supplied water temperatures, application regions, and working fluids. The energy saving rate (ESR) under different conditions are calculated, considering both the ASAHP efficiency and the distribution consumption. Results show that ASAHP system is more suitable for short-distance district heating, while for longer-distance heating, lower supplied hot water temperature is preferred. In addition, the advantages of NH 3 /H 2 O are inferior to those of NH 3 /LiNO 3 , and the advantages for warmer regions and lower pipeline resistance are more obvious. The primary return temperatures are optimized to obtain maximum ESRs, after which the suitable distances under different acceptable ESRs are summarized. To improve the applicability of ASAHP, the integration of cascaded heat exchanger (CHX) and compression-assisted ASAHP (CASAHP) are proposed, which can reduce the primary return temperature. The integration of CHX can effectively improve the applicability of ASAHP under higher supplied water temperatures. As for the utilization of CASAHP, higher compression ratio (CR) is better in longer distance, while lower CR is more advantageous in shorter distance. For a distance of 50 km, the maximum ESR is improved from 13.6% to 20.4–25.6% under different CRs. [ABSTRACT FROM AUTHOR]

Abstract: Data centers and mobile phone base stations (MBS) are consuming more and more energy due to the development of the information communication technology (ICT) industry. The integrated air conditioner with thermosyphon (IACT) was proposed as an efficient cooling device for these spaces, combining vapor compression (VC) refrigeration with a thermosyphon (TS). In this paper, a model to simulate the annual energy consumption of IACT is built and compared with the traditional air conditioner (TAC) in four standard MBSs located in the typical climate zones of China. The results show that the IACT saves 19.1%–28.2% more energy than the TAC, and in hotter regions has a larger energy saving amount but a smaller energy saving rate (ESR). The TS mode works effectively when the mean monthly temperature is 5.4 °C–24.5 °C. The monthly ESR of IACT in the MBSs of Beijing and Guangzhou is 12.2%–48.6% and 12.1%–45.2% respectively. [Copyright &y& Elsevier]

Highlights: [•] We propose a new concept, heat adaptor, to optimize thermal system performance. [•] It is a combination of heat engine, heat pump and conventional heat exchangers. [•] The most suitable device and process can easily be identified using the concept. [•] A typical problem is used to demonstrate the advantages of applying the concept. [Copyright &y& Elsevier]

Highlights: [•] A double-stage coupled air source absorption heat pump (ASAHP) is proposed. [•] The coupled ASAHP exhibits stable and high performance in very cold regions. [•] Energy-saving rate of the coupled ASAHP in all the typical cities is above 20%. [ABSTRACT FROM AUTHOR]

Abstract: We propose a scheme to generate multipartite continuous variable atom-field entanglement via two-fold phase-dependent electromagnetically induced transparency in a five-level atomic system. Due to quantum interference, the six fields act as two collection modes to interact with the atomic ensemble. Under proper conditions, it is shown that the genuine tripartite entanglement arises between the atomic ensemble and the two collection modes. Moreover, the seven-partite Greenberger–Horne–Zeilinger entangled state included six individual field modes and the atomic ensemble is achievable. Physically, the intrinsic nonlinear interactions are responsible for the quantum correlation. The hybrid multipartite entangled state may be useful for the progress of quantum network between different objects. [Copyright &y& Elsevier]

Abstract: Spaces with high heat density such as mobile phone base station (MBS) and data center increase fast recently. Huge energy is consumed for the air conditioning because of large indoor heat rejection and year round cooling in these spaces. The integrated air conditioner with thermosyphon (IACT) combines the vapor compression (VC) refrigeration and thermosyphon (TS) in one body, which can save energy and space for these spaces. After analyzing the problems in the existing IACT, a new IACT is proposed by using the novel heat exchangers and the self-operated three-way valve (STV), which works well in both VC and TS modes. The 3HP air cooled IACT is developed and tested in laboratory. The COP of TS mode reaches 9.43 when outdoor temperature is 20 °C lower than indoor, and the COP of VC mode reaches 2.94 under standard condition. This IACT has been applied in MBSs of different cities in China and the energy consumption is tested on-site and compared with the traditional air conditioners (TAC). It is shown that the IACT can save more than 30% energy compared with TAC. [Copyright &y& Elsevier]

Abstract: We present a scheme to obtain continuous-variable multimode entanglement via multi-wave mixing. For a four-level atomic system in a diamond configuration, four strong coherence fields are applied to the four dipole-allowed transitions to amplify eight sidebands as cavity fields, respectively. Due to the atomic coherence, the eight side modes constitute a pair of double quantum-beats and combine into two quantum-beat collective modes, which are in a four-wave mixing parametric interaction. As a result, the entanglement occurs between these two collective modes. Correspondingly, any two individual modes from two different collective modes are entangled with each other. This gives rise to continuous-variable eight-mode entanglement with different frequencies, which has extensively application in quantum communication and quantum network. [Copyright &y& Elsevier]

Abstract: Gas refrigerant injection has been proven as an effective method to improve the performance of the scroll compressor and its refrigeration system under high compression ratio working conditions. Much research on the injected scroll compressor and its system has been conducted, but the universal control and design method is still lacking. A model of the refrigeration system with a gas-injected scroll compressor is developed in this paper. With this model, the effects of gas injection on the system and component parameters are investigated. Based on the identified evaporator characteristics and thermodynamic analysis, a set of general principles for the design and operation of the refrigeration or heat pump system with a gas-injected scroll compressor is proposed. [Copyright &y& Elsevier]

Abstract: A simulation model of complex refrigeration system based on two-phase fluid network is developed in part I of the paper [Shao, S.Q., Shi, W.X., Li, X.T., Yan, Q.S., 2008. Simulation model for complex heat pump systems based on two-phase fluid network – part I: model development. International Journal of Refrigeration 31 (3), 490–499.]. One same fluid network is used in the model to describe the refrigeration system in different operating modes with the method of the factual and fictitious branches. When there are many heat exchangers with concurrent cooling and heating, the traditional models are not able to define the flowing directions. The developed model, however, whether the initial flowing direction of the connecting branches is right or not, is able to predict the flow and heat transfer. Three typical complex refrigeration systems such as the multi-unit inverter air conditioner, heat pump with domestic hot water and multi-unit heat pump dehumidifier are simulated with the developed model as demonstrations on how to use it. The model can evaluate the influences of one or more parameters on the system performance, which can be used for the optimization of the system by all-condition performance analysis. It is shown that the two-phase fluid network model is effective and convenient for the simulation of different complex refrigeration system, especially for performance analysis, system evaluation, and optimization based on the performance prediction. [Copyright &y& Elsevier]

Abstract: Some complex refrigeration and heat pump systems with several condensers and evaporators have been developed for different kinds of application. Traditional simulation models were developed for systems in certain operating modes and they failed in modeling the complex refrigeration systems with uncertainties of heat exchangers function and refrigerant flowing direction. In order to predict the performance of complex refrigeration systems, a simulation model is presented based on the two-phase fluid network. The model is consisted of distributed-parameter model of heat exchangers and connecting tubes, map-based model of inverter compressor and electronic expansion valve (EEV). Based on the characteristic of refrigeration system and fluid network, the three conservation equations, i.e. energy, momentum and mass equations, are solved iteratively. This model can deal with the uncertainty of refrigerant flow direction by separating the solving process of the components and the fluid network model, and therefore can simulate different kinds of complex refrigeration systems in different operating modes and conditions. The model is validated by the experimental data of an inverter air conditioner in heating/cooling operating modes and it shows the error of the model is mainly determined by the error of submodels of components in calculating heat transfer and pressure loss. The model is applied for performance analysis of three kinds of complex refrigeration systems in the accompanying article [Shi W.X., Shao, S.Q., Li, X.T., Yan, Q.S., 2008. Simulation model for complex heat pump systems based on two-phase fluid network: part II – model applications, International Journal of Refrigeration 31 (3), 500–509.]. [Copyright &y& Elsevier]

Variable speed control of compressors is one of the best methods to regulate the capacity of heat pumps and air conditioners. An analysis is conducted for modeling the variable speed compressor for simulation of inverter air conditioner and heat pump. Having scattered the real operation performance of inverter compressor into infinite operation performance of constant speed compressor, the map-based method is utilized to fit the performance curves of inverter compressor. The model is built at the basic frequency and the map condition as the second-order function of condensation temperature and evaporation temperature. Then it is corrected by the compressor frequency as the second-order function of frequency and by the actual operating condition as the actual specific volume of the suction gas. This method is used to set up simulation models of three different compressors. Compared with the data provided by the compressor manufacturers, the average relative errors are less than 2, 3 and 4% for refrigerant mass flow rate, compressor power input and coefficient of performance (COP), respectively. This model of variable speed compressor is suitable for the simulation of inverter air conditioner and heat pump systems. Based on the experimental data and simulation model, the frequency at zero mass flow rate and power input at zero frequency are discussed and the relation between COP and compressor frequency is analyzed. [Copyright &y& Elsevier]

This paper presents a new scheme of an inverter air cooling heat pump system with domestic hot water. A water reheater is placed between the compressor outlet and the four way valve inlet to utilize the sensible heat of the superheated gas exhausted from the compressor, and a water preheater is placed between the condenser and the throttling device to use the sensible heat of the subcooled liquid flowing out of the condenser. With these two parts of heat, the domestic hot water can be heated to a temperature high enough for domestic use. In order to maintain the system efficiency in the period of part load, an inverter compressor is adopted as the substitute for the constant speed one used in the conventional heat pump system. A hot water storage tank with a circulation pump is placed in the system to reduce the peak load of the system. Compared with the traditional system, this new design is able to reduce energy consumption by 31.1% and decrease thermal pollution to the environment. [Copyright &y& Elsevier]

This paper presents an experimental study of a novel household ventilator with exhaust air heat pump enhanced by indirect evaporative cooling. In this study, a prototype was made according to this theory and tested on the test rig. The test was carried out to evaluate the energy performance of the system during the cooling season. During the test, the thermal performances of the prototype under four different operating modes were comprehensively studied. In the typical summer conditions, the prototype operating as an indirect evaporative cooler followed by an evaporative condenser heat pump shows the highest cooling capacity at 4.27 kW and energy efficiency ratio (EER) at 5.12, which is a great performance improvement compared with that of conventional operating methods. The results of variable conditions tests show that this system can operate efficiently under different summer ambient conditions with the EER varying from 4.16 to 5.65. Besides, a comparison with other prototypes found in existing literature was also made in this study. Give consideration to compact and energy efficiency, the novel ventilation system shows a good academic value and application prospect in energy saving air-conditioning domain. [ABSTRACT FROM AUTHOR]

Recovering waste heat can improve the energy efficiency of a combined heat and power plant. The pinch method is widely used in heat recovery systems; however, the minimum energy grade of the remaining heat demand cannot be determined using this method. In this study, a method for discretizing thermal energy for the heat sources and demands is proposed and illustrated with a detailed description. The proposed method can maximize heat recovery and minimize energy grade requirements. Different heat transfer temperature differences could be considered in the proposed method. Two different optimized heat recovery systems for a combined heat and power plant are developed based on the novel and pinch methods. The amount of heat recovered using the optimized systems are the same, with values 2.08% higher than that of the conventional heat recovery systems. Compared with the pinch method based optimized system, the energy grade of the remaining heat demand could be reduced from 61.9 °C to 58.2 °C using the proposed method. • Method of discretizing thermal energy for heat sources and demands is proposed. • An optimization method to match heat sources and demands is established. • Two heat recorvery systems are developed based on the proposed method. • The proposed method has the same heat recorvery with pinch method. • Energy grade of remaining heat demand is lower than that with pinch method. [ABSTRACT FROM AUTHOR]

Compared with conventional fuel-direct-burning heating systems, heat-driven absorption heat pump has high efficiency. To further improve the heating performance, generator-absorber heat exchange (GAX) absorption heat pump was developed, but its experimental research was not enough. The parameters tested were usually just COP and heating capacity in the existing literature, the variation of some internal parameters were rarely measured and analyzed. Besides, the latent heat exchange between the generator and the absorber could not continue normally under high thermal lift (T CON - T EVA) and low thermal thrust (T GEN - T ABS), instead, more sensible heat is transferred, the temperature overlap decreases or even disappears, and the circulation process of GAX cycle approaches to that of single-effect cycle. This phenomenon is named "cycle degradation", and is crucial to understand the working principle of GAX for optimal design and control. The cycle degradation was only simulated under low evaporation temperature, but has not been analyzed with experimental data, the influence rules of other external operational parameters on the phenomenon are also not clear. Therefore, a prototype of GAX absorption heat pump is built up, many internal and external parameters are measured and used to investigate the cycle degradation and overall performance under different testing conditions. During the experiment, the COP is in the range of 1.185–1.506, the cycle degradation occurs when the "lifting factor (Eq [18])" is lower than 2.3. Moreover, the performance improves with the increase of driving temperature or low-grade heat source temperature, and deteriorates due to the rise of supply water temperature. • A prototype of NH 3 –H 2 O GAX absorption heat pump is constructed. • Many internal and external parameters are measured in detail. • The overall performance and the phenomenon of "cycle degradation" are analyzed. • The COP is in the range of 1.185–1.506. • The cycle degradation occurs when the lifting factor is lower than 2.3. [ABSTRACT FROM AUTHOR]

Air conditioning systems using liquid desiccants are efficient in dehumidification, but their performance can be further improved under both design and different partial load conditions. In this study, a humidity grade-matched system with adjustable treatment stages is designed based on the use of appropriate humidity sinks to handle loads. The method to determine reasonable treatment stage numbers and packing tower areas is given by optimizing the total system energy consumption and economic performance under different working conditions, based on validated numerical system performance models and device prices from the market or literature. The performance of the proposed system is compared with traditional systems in a case office building in Nanjing. The results are as follows: 1. By optimizing the total system power consumption and economic performance under different conditions, the humidity difference for one-stage and mass transfer humidity difference should be set at 3–5 and 2–3 g/kg to determine the stage number and packing tower area, respectively. 2. The proposed fresh air dehumidification system as applied to an office building without exhaust air in Nanjing reduces 16.6% and 13.5% of the seasonal energy consumption for the entire system relative to single-stage and three-stage systems, respectively. 3. When the system selectively uses exhaust air or outdoor air, 11.0% of additional seasonal energy consumption can be saved for the entire system relative to a system using only outdoor air. • A humidity grade-matched system with adjustable treating stages is proposed. • Treatment stage numbers and packing tower areas are reasonable in different cases. • System is designed by grade-matching for dehumidification loads and humidity sinks. • The proposed system operates more energy-efficiently both for compressors and fans. • 11.0% additional energy consumption is saved by selectively using humidity sinks. [ABSTRACT FROM AUTHOR]

Abstract A heating tower is a key component of a heating tower heat pump. To figure out the heat and mass transfer characteristics of a cross-flow closed-type heating tower (CCHT) using a glycerol solution, an experimental investigation was conducted. The effects of fluids' parameters on the performance of the CCHT were studied, which indicated that its performance could be improved by increasing the air flow rate, the solution flow rate, the secondary refrigerant flow rate, the inlet air temperature, and the inlet air humidity ratio, while decreased with the increase in the inlet temperature of the secondary refrigerant and remained constant with the variation of the inlet solution concentration. Based on the results, correlations of heat and mass transfer coefficients for the CCHT were developed. In addition, a quantitative performance comparison between the glycerol solution and the CaCl 2 solution was also conducted, which indicated that compared with the performance of the CCHT when using the CaCl 2 solution, the total heat transfer capacity when using the glycerol solution was 1.3–1.7 times higher, while the latent heat ratio was 1.9–3.3 times larger. [ABSTRACT FROM AUTHOR]

Highlights • Optimal volume ratio of two-stage compressor using zeotropic refrigerant is investigated. • Optimal volume ratio firstly decrease and then increase with the increase of the R32 component. • Optimal volume ratio of 26 potential refrigerants are investigated and compared. • A modified arithmetic mean temperature method fitting for zeotropic refrigerant is proposed. Abstract Refrigerant mixtures are commonly regarded as a potential substitute in heat pumps. Two-stage compression is widely applied for improving the performance of heat pumps. The suction volume ratio is a critical design parameter for two-stage heat pumps. In this work, the optimal volume ratio of R32/R1234ze(E) mixture and 26 refrigerants named by ASHRAE Standard 34-2013 are estimated. The obtained result indicates that, for R32/R1234ze(E) mixtures, the optimal volume ratio first decreases and then increases as the R32 component increases, and the optimal volume ratio of flash tank system is lower than the intermediate heat exchanger system owing to component shifting in the flash tank. For estimated 26 refrigerants, the optimal volume ratio of the majority of zeotropic refrigerants is smaller than pure refrigerants and azeotropic refrigerants. In addition, a modified arithmetic mean temperature method is proposed to predict the optimal intermediate refrigerant states. [ABSTRACT FROM AUTHOR]

Abstract Rotary compressors encounter severe performance degradation under low-temperature ambient conditions, and the vapor refrigerant-injection technology is one of the methods to solve this problem. Traditional vapor injection technologies provide a limited improvement in performance for rotary compressors. A novel end-plate injection structure was put forward in previous research. In this paper, a rotary compressor prototype with this novel end-plate injection structure was introduced. The performance of the vapor-injected rotary compressor was tested experimentally and compared with the regular one without vapor injection. The results indicated that, compared to a single-stage rotary compressor, a rotary compressor with the novel end-plate injection structure can enhance the heating capacity and COP by 16.2–31.6% and 5.1–12.0%, respectively. [ABSTRACT FROM AUTHOR]

• An efficient CO 2 two-stage compression system is comprehensively simulated. • The main factors affecting the optimal discharge pressure are analyzed. • The correlation formula of optimal discharge pressure is proposed. • The correlation formula of optimal intermediate pressure is proposed. The CO 2 two-stage compression refrigeration system is a feasible alternative to conventional refrigeration systems for logistics cold storage cooling that provides high efficiency and environmental protection. In a previous study, we proposed a two-stage compression refrigeration cycle with an external intercooler and performed a thermodynamic analysis. Based on that, a more comprehensive simulation analysis is performed herein using the validated models. The performance, optimal discharge pressure, and intermediate pressure are investigated using a high-pressure compressor with both fixed and variable speeds. The results show that the cooling-water temperature has a significant positive linear correlation with the optimal discharge pressure, whereas the evaporator-inlet air temperature has little effect at a fixed high- pressure compressor speed. When the high-pressure speed is adjusted to achieve the optimal intermediate pressure and discharge pressure simultaneously, the coefficient of performance increases by 4.5% compared with that of the fixed-speed system, while the cooling capacity decreases by 8.4%. The correlation of optimal discharge pressure and optimal intermediate pressure is given. [ABSTRACT FROM AUTHOR]

R32/R1234ze(E) mixtures are potentially low-GWP alternative refrigerants for air conditioning and heat pumps while the rare pure refrigerants can totally meet the requirements of new international protocols on environmental conservation, thermodynamic performance, and safety. The system performance under different concentrations is important for selection of working concentration for the new R32/R1234ze(E) refrigeration or heat pump. In this paper, the thermodynamic model of an ASHP with R32/R1234ze(E) mixtures is built and used to investigate the influence of the refrigerant composition on the performance of the system. The results show that when the mass fraction of R1234ze(E) changes from 0% to 100%, the heating capacity of the ASHP decreases by 67.2%, while the COP continuously increases by 70.3%, which means the changing tendency of system COP is quite different from previous research under fixed evaporating and condensing temperature. Adjusting the refrigerant concentration will be a good system modulation method for ASHPs with R32/R1234ze(E) to meet both the heating capacity and energy efficiency requirements. Furthermore, temperature matching degree is an important factor that affects the energy efficiency of ASHPs with non-azeotropes, which can guide the circuitry optimization of evaporator and condenser in ASHPs with non-azeotropes. [ABSTRACT FROM AUTHOR]

Gas injection has been a crucial technology to avoid the serious degradation of air source heat pumps in low ambient temperature. A novel injection structure on the blade for rotary compressors has been put forward in previous research to overcome the drawback of traditional injection structures. Based on a verified numerical model, the thermodynamic performance of an air source heat pump with the new gas-injected rotary compressor is investigated. The results indicate that, compared to the air source heat pump with the regular single-stage rotary compressor, the proposed injection structure can enhance heating capacity and COP of the air source heat pump by 23.1–28.2% and 4.5–8.1%, respectively. [ABSTRACT FROM AUTHOR]

Heat supply systems based on absorption heat pump were assessed to have great potentials on energy savings and emissions reduction. A prototype of NH 3 -H 2 O water source absorption heat pump (WSAHP) designed for low temperature heating was experimentally investigated under different working conditions. The effects of driving source, hot water and source fluid temperature on the heating performance were studied. As driving source increases from 110 °C to 140 °C with 15 °C evaporator inlet and 45 °C hot water, COP increases from 1.429 to 1.552 and then decreases to 1.495, while the heating capacity increases from 32.23 kW to 88.35 kW. As hot water increases from 30 °C to 45 °C with 130 °C generator inlet and 15 °C evaporator inlet, COP decreases from 1.653 to 1.449, while the heating capacity drops from 94.55 kW to 60.37 kW. As the source fluid increases from −10 °C to 30 °C with 130 °C generator inlet and 45 °C hot water, COP increases from 1.203 to 1.609, while the heating capacity increases from 39.51 kW to 79.72 kW. Comparisons with former work indicate that the developed prototype can operate under evaporator inlet temperatures as low as −18 °C, which is significant to improve heating applicability in colder conditions. [ABSTRACT FROM AUTHOR]

Ground-coupled heat pumps are widely applied in cold regions, but soil thermal imbalances in some projects greatly deteriorate the systems’ practical performances and heavily inhibit the systems’ reasonable applications. This paper presents a comprehensive overview of the main problems caused by soil thermal imbalance and the existing solutions targeting on them. The caused problems mainly present in the following aspects: soil temperature decrease, heating performance deterioration, heating reliability decline, and even system failure. Three kinds of existing solutions can be classified. Ground heat exchanger-modified solutions including increasing borehole space, increasing borehole length, modifying borehole layout, and improving thermal properties, can retard the thermal imbalance to some extent, suitable to projects with slight imbalance. System-modified solutions integrating auxiliary energy sources like fossil fuel, solar energy, ambient air and waste heat with ground-coupled heat pumps or using ground-coupled absorption heat pumps, can eliminate serious thermal imbalance essentially by increasing soil thermal injection and decreasing the extraction. Thus, they are dominant in the applications and attract more attention along with the utilization of renewable energies. Apart from the modifications of system design, operation-modified solutions, like seasonal and intermittent operations, are also helpful to maintain better soil thermal balance. Based on the overview, the current application situations and economic performance of different solutions are discussed. Finally, some suggestions for the applications of ground source heat pumps in cold regions are proposed to make the overview helpful for the system research and applications. [ABSTRACT FROM AUTHOR]

The cooling performance of exhaust air heat pumps is limited by the high condensing temperatures owing to insufficient exhaust air volume. In this study, a high-efficiency solution for an exhaust air heat pump was developed and numerically studied. In this novel system, the exhaust air is stepped energy recovered by an indirect evaporative cooler and a heat pump with an evaporative condenser. It is considered that the combination of these two heat transfer components can provide a system with a significantly high cooling efficiency. To explore the application potential of this system further, a detailed mathematical model was established. Meanwhile, a prototype based on this design was developed, and its performance in four operating modes was tested for model validation. When the test results are compared with those of a conventional system of the same size, they show that the cooling capacity and energy efficiency ratio of the novel system increased by 53% and 135%, respectively. Subsequently, to clarify the principles underlying the design of this system, parameter sensitivity analysis and system matching optimization were conducted numerically. • IEC and ECHP is combined into a novel ventilation treatment method. • The improvements of the novel system in cooling capacity and EER are 53% and 135%. • Key design parameters of the novel IEC–ECHP was investigated. • The novel system is especially recommended for hot and humid areas. [ABSTRACT FROM AUTHOR]

Two-phase thermosyphon loops (TPTLs) are beginning to be extensively used in the field of air conditioning and heat recovery, where they have quite different flow characteristics compared with the traditional TPTLs used in cooling of electronics. However, in the existing studies, the flow features in the downcomer were ignored, and most researchers simply thought the downcomer was always full of liquid. In this study, a visual experimental setup was established, the flow features in the downcomer were observed and measured. And the influencing factors including temperature difference, liquid charge, height difference, and circulation flow resistance on the liquid head have been identified and investigated experimentally. The results show that, different from the conventional understandings, the downcomer can be partially liquid filled. At this time, the upper part of downcomer is a static saturation gas blockage, surrounded by a layer of liquid film, which does not provide the driving force. The liquid head in the downcomer, which provides the driving force, shows great self-regulation ability with different working conditions. Increasing the refrigerant charge, temperature difference, circulation flow resistance, and decreasing the height difference drives the liquid head to rise, and the downcomer tends to be fully liquid filled. [ABSTRACT FROM AUTHOR]

Two-phase thermosyphon loops (TPTLs) are extensively used in industries. Numerical simulation is always applied for their configuration design and performance rating. The conventional models are usually developed under large temperature difference, and the fully liquid-filled downcomer are taken for granted. In this study, a generalized model for TPTL is developed, in which the downcomer can be partially liquid filled or fully liquid filled under different conditions. The model is verified by experiments on an air-to-air finned-tube TPTL. Then, it is used to analyze the flow and heat transfer features of a TPTL, under different refrigerant charge and temperature difference. The results show that the downcomer is partially liquid filled in the case of small temperature difference and refrigerant charge. Additionally, the heat transfer rate first increases then decreases with the increase of refrigerant charge, and first increases linearly then increases relatively slowly with the increase of temperature difference. [ABSTRACT FROM AUTHOR]

• Efficient operating range of the original district heating substation is below 1℃. • Proposed system formed by original components operates efficiently in whole winter. • Control strategies are based on the lowest primary return water temperature. • The proposed system has advantages in energy and economic performance. With the rapid development of heating technology, heating terminals are developing toward low temperatures and diversification, resulting in the simultaneous presence of different temperature demands in district heating systems. To reduce the primary return water temperature and satisfy the temperatures of different terminals, a dual-temperature district heating substation supplying dual temperatures of hot water with two absorption heat pumps and two heat exchangers has been proposed based on the design conditions. However, whether the dual-temperature district heating substation can operate and how to control this system during the entire heating period have not been explored. In this paper, the models for the substation with two absorption heat pumps and two heat exchangers and its subsystems were established to analyze and compare the operational conditions for the substation and its subsystems at different outdoor temperatures. By comparing the primary return water temperatures of all subsystems, control strategies and a combined system for efficient operation during the heating season were determined. Then a case study and analysis of the combined system were conducted under the proposed control strategies and compared with two other systems – two heat exchangers and two absorption heat exchangers – used in dual-temperature heating stations. Results show that 1) The original system with two absorption heat pumps and two heat exchangers could only operate when the outdoor temperature was −8–1℃. 2) The subsystem with a high-temperature absorption heat pump and two heat exchangers and the subsystem with two heat exchangers which could achieve efficient operation under outdoor temperature ranges of 1–7 °C and 7–11 °C respectively were considered in the combined system to broaden the operating range of the original system. 3) The combined system had the lowest return water temperature (23.8℃) and the highest coefficient of performance (6.60) during the entire heating season. The payback period of the combined system was 1.54 years. This study provides a reference for the efficient operation of dual-temperature district heating substations at different ambient temperatures during the heating season. [ABSTRACT FROM AUTHOR]

• A high fidelity scroll compressor model with numerically efficient equations is developed for performance prediction. • The governing equations are generic for both single-phase compression and two-phase compression. • A detailed scroll wrap temperature distribution calculation method is proposed. • Validation shows predicted cooling capacity error within 3.5% and predicted power error within 2.8%. • Simulation speed is 7.9–23.7 s per case and convergence rate is 100% for various conditions. A general scroll compressor model with high accuracy, fast simulation speed and good numerical robustness is proposed in this study. The governing ordinary differential equations derived from mass and energy conservation use pressure and specific enthalpy as state variables, which can be applied to both single-phase compression and two-phase compression. Both the governing equations for inner compression and the nonlinear equations for internal leakages are explicit in pressure and specific enthalpy to avoid severe numerical stiff problems. In addition, the detailed scroll wrap temperature distribution is calculated based on the proposed second order differential equation considering heat conduction and periodic heat convection. Validation against experimental data shows that cooling capacity errors are less than 3.5% and power consumption errors are less than 2.8% in non-injection and liquid injection conditions. Evaluation of model speed and robustness shows that the model has a convergence rate of 100% and an average calculation speed of 12.4 s per case in various conditions. [ABSTRACT FROM AUTHOR]

The heat supply system combining a conventional boiler with an air source absorption heat pump (ASAHP) has been evaluated as having great potential in energy saving and emission reduction. However, an economic analysis needs to be performed before its wide applications. To improve the economy of ASAHP from a design perspective, a year-round simulation and techno-economic analysis are conducted. Results show that the energy saving rate (ESR) does not decrease much when the relative design capacity of ASAHP is within 50–100%. At a relative design capacity of 75% in Harbin, 35% in Shenyang, 50% in Beijing, and 50% in Zhengzhou, ESR can reach 21.6%, 24.3%, 26.2% and 26.3%. Given an ASAHP price of 1.5 CNY/W and a gas price of 4.0 CNY/Nm 3 , the payback period is 6.8, 6.6, 4.1 and 4.6 years in these four cities, at a 50% relative design capacity. There is a conflict between ESR and the payback period, but a small sacrifice (1.5–6.0%) in ESR can contribute a great reduction (38–48%) in the payback period. The heating period and energy price in the local area, as well as the expected ESR and acceptable payback period should be comprehensively considered for a better energy efficiency and economy. [ABSTRACT FROM AUTHOR]

Because of high thermal storage density and little heat loss, absorption thermal energy storage (ATES) is known as a potential thermal energy storage (TES) technology. To investigate the performance of the ATES system with LiBr-H2O, a prototype with 10kWh cooling storage capacity was designed and built. The experiments demonstrated that charging and discharging processes are successful in producing 7°C chilled water, 65°C domestic hot water, or 43°C heating water to meet the user's requirements. Characteristics such as temperature, concentration and power variation of the ATES system during charging and discharging processes were investigated. The performance of the ATES system for supplying cooling, heating or domestic hot water was analyzed and compared. The results indicate that the energy storage efficiencies (ESE) for cooling, domestic hot water and heating are 0.51, 0.97, 1.03, respectively, and the energy storage densities (ESD) for cooling, domestic hot water and heating reach 42, 88, 110kWh/m3, respectively. The performance is better than those of previous TES systems, which proves that the ATES system using LiBr-H2O may be a good option for thermal energy storage. [ABSTRACT FROM AUTHOR]

The use of ammonia-based working fluids for absorption prevails in a wide range of applications due to the low freezing temperature of the refrigerant and the absence of crystallization as well as the lack of problems under vacuum conditions. This paper presents a comprehensive overview on the use of ammonia-based absorption chillers and heat pumps. The thermodynamic and physical properties of pure ammonia and binary and ternary ammonia mixtures are presented in correlation formulas. Developments and applications in subfreezing refrigeration, heating/domestic hot water, renewable energy utilization, waste heat recovery, thermal energy storage and miniaturization of absorption systems are presented and summarized. In subfreezing refrigeration, the evaporation temperatures for single-stage absorption lie mainly between −30°C and −5°C, and they can reach as low as −70°C in advanced absorption systems. Air-source and ground-source absorption heat pumps are suggested for heating/domestic hot water applications in cold regions. For renewable energy uses, ammonia-based solar absorption applications with various working fluids are quite popular, whereas geothermal and biomass energy systems are less studied. In thermal energy storage, ammonia-based working fluids are not advantageous for storage capacity or cycle efficiency, but they prevail for subfreezing energy storage. Additionally, ammonia-based fluids are also attractive options for the miniaturization of absorption systems due to the absence of crystallization. [ABSTRACT FROM AUTHOR]

Indirect evaporative cooler (IEC) applied as an exhaust air heat recovery component for fresh air pre-cooling in air-conditioned zone, which successfully extends its application range to hot and humid areas. To explore more effective application method of the heat recovery IEC, an energy and exergy transfer model for IEC operating as a heat recovery devices was proposed in this study. The thermal performance and exergy transfer characteristics of three basic types of IECs: cross-flow, counter-flow, and parallel-flow IECs were numerically investigated. The results show that the irreversible heat transfer in the primary air channels and the irreversible mass transfer in the secondary air channels are the main causes of exergy loss. These two factors account for more than 90% of the total exergy destruction in all the three types of IECs. To alleviate this situation and improve the energy efficiency of the IEC, two two-stage modified heat recovery systems which combine IEC with sensible heat exchanger and energy recovery exchanger were proposed and numerical analyzed. The simulation results show that, for the modified systems, the exergy transfer efficiency is increased by 104.6% and 131.7%, while the heat transfer capacity is increased by 47.6% and 48.5%, respectively. • The performance improvement of IEC by changing the airflow direction is limited. • The irreversible loss mainly occurs at the entrance of heat recovery IEC. • Cooling capacity of two modified systems increases by 47.6% and 48.5%. • Multi-level processing for the heat recovery IEC systems is the way forward. [ABSTRACT FROM AUTHOR]

• Principles for determining the standard rating conditions of heat pumps are proposed. • Standard rating conditions for different ASHP systems in China are established. • Technical characters, energy savings and economic benefits of ASHPs are analyzed. Air source heat pumps (ASHPs) are widely used in various types of buildings in different regions of China. Considering the significant differences in the characteristics in heat source side and user side, providing different products for different zones is an effective strategy to promote the systematic development of the ASHP technology. To realize the goal of energy conservation, standard rating conditions are extremely important. The principles for determining the standard rating conditions based on a two-side (heat source/user side) multi-grade (different conditions) method were proposed along with the development of related standards. Therefore, the establishment of standard rating condition is introduced and summarized systematically. For heat source side, the standard rating conditions for heating were classified into four types according to the lowest ambient temperature (−25, −12, −2, 7 °C), while for cooling they were constant (35 °C). For user side, the conditions for supply air (20/27 °C for heating/ cooling), floor heating (35 °C), radiator (50 °C), fan coil unit (41/7 °C for heating/cooling), domestic hot water (55 °C), and industrial use were also determined. This study introduced the implications on ASHP by different standard rating conditions, especially the technical requirements, which indicated the necessity of providing different system cycles and compressors. The energy savings and economic benefits were also evaluated. The primary energy saving rate reached 15.3% and 41.6% compared with coal heating and conventional ASHP respectively by using low ambient temperature ASHP. The results showed that these standards have been satisfactorily developed. [ABSTRACT FROM AUTHOR]

Abstract: Experiments on the inner compression process of scroll compressor with refrigerant injection can reveal the essence of refrigerant injection. The difficulty of the experiment is the design of location of measuring ports, measuring system of dynamic pressure and design of the injection system. Focusing on the dynamic pressure measurement of inner compression process during refrigerant injection, an integrated bench design method for refrigerant injection research in scroll compressor is presented in this paper. The location design of injection ports and measuring ports, frequency spectrum analysis of pressure signal, selection of the sensor type and configuration, and design of the pressure-leading system are expressed, respectively. Finally, a test bench is set up. Based on it, several elementary experiments were carried out. The results show that: this design method solves most problems in the experimental research of scroll compressor with refrigerant injection and works reliably; the refrigerant injection effects the majority of the inner compression process and should not be considered as a transient process; gas injection can increase the system performance greatly and there is an optimal injection pressure for a certain scroll compressor. [Copyright &y& Elsevier]

Abstract: Based on discretional initial angles of involute of scroll compressors, a general mathematical representation of scroll wraps, working chamber volume and leakage areas is presented. The scroll wraps'' geometrical expressions, including interaction arc, of the involute angle with discretional initial angles of involute are developed. By using it, a new calculation formula of working chamber volume without restriction to special involute initial angles is set up and the expression of the volume during all the suction, compression and discharge processes in a general subsection function style is given. A geometrical model of leakage areas, including flank in, flank out, radial in and radial out, is also developed based on the discretional initial angles condition. Finally, this geometrical model is applied in a thermodynamic model and the simulation results are compared with some former experimental results. It is found that this model has a satisfactory accuracy and is easy to be used in thermodynamic simulation. [Copyright &y& Elsevier]

[Display omitted] • A direct expansion air handling unit assisted by liquid desiccant is proposed. • Temperature and concentration of solution are adjusted by heat pump and water addition. • The air handling unit can work for various sensible and latent heat ratios. • The system COP increases 37% in summer and 11% in winter compared with normal system. • The system shows better economic performance than conventional systems. Reheating is needed in the traditional cooling and dehumidification system, which results in the offset of cooling and heating. There is no reheating in the liquid desiccant system, but equipment for latent heat and sensible heat are both necessary. This paper proposes a direct expansion air handling unit assisted by liquid desiccant (LDAHU) for adapting to various sensible and latent heat ratios using only one set of equipment. Numerical models were developed for calculating the system performance under various load demands of an office building in Nanjing, China. A comparison of the energy performance and economy between the LDAHU system and two conventional systems, i.e., an electric chiller and boiler (ECB) system and an air source heat pump (ASHP) system, was performed. The results indicated that the LDAHU system can treat the mixed air for achieving the required state of the supply air directly by controlling the temperature and concentration of the sprayed solution and can operate efficiently in both summer and winter. Compared with the ECB system and the ASHP system, the coefficient of performance of the LDAHU system is 13.2% and 30.4% larger, respectively, in summer, and 37.0% and 6.2% larger, respectively, in winter. The total cost savings for the LDAHU system over 15 years of life-cycle operation are 11.6% and 6.8%, respectively, although the initial costs are 5.1% and 31.2% higher, respectively, resulting in the dynamic payback periods as 0.9 and 5.3 years, respectively. [ABSTRACT FROM AUTHOR]

• Design and optimisation on refrigerants, crucial components and innovative systems of VRFS are reviewed. • Control strategies of VRFS including energy efficiency, improved humidity, and defrosting operation are summarized. • Investigations on inherent energy performance, energy use prediction, and energy saving potential of VRFS are presented. • Advances in the fault detect and diagnosis of VRFS are reported. • Overlooks on VRFS are recommended for the future research works. Variable refrigerant flow systems (VRFS) are gradually gaining popularity in commercial and residential buildings owing to their satisfactory part-load performance, flexible control, and ease of installation and maintenance. However, the characteristic complex system structure of VRFS makes it difficult to understand their performance. This study presents a comprehensive review of VRFS concerning their design and optimisation, control strategies, modelling and simulation, and fault detection and diagnosis (FDD). This review begins with the developments in design and optimisation of VRFS in terms of alternative refrigerants, crucial components, and innovative systems. Subsequently, the control strategies of VRFS including energy efficiency, improved humidity, and defrosting operation are reviewed. Meanwhile, the research objectives on modelling and simulation of VRFS could be divided into three aspects: investigation of the inherent energy performance, prediction of energy consumption in buildings, and comparisons of energy saving potential. In addition, the advances in FDD for VRFS, based on the rapid development of data mining technologies, are presented. The main conclusions drawn from this detailed review provide a comprehensive overview of VRFS and inspire new insights and feasible solutions for relevant researchers, product developers, practitioners, and policymakers in this field. [ABSTRACT FROM AUTHOR]

As heating requirements continue to evolve and heating technology advances, radiators and radiant floor heating devices, which require different supply-water temperatures, have gradually become the two main heating terminals in district heating systems. However, the primary return-water temperature of current solutions based on heat exchangers and heat pumps is relatively high and fails to recover waste heat from the combined heat and power plants, owing to improper use of heat sources. To address this issue, a heat exchanger network optimisation method—the thermal energy discretisation and matching method—was used to design a dual-temperature water district heating system consisting of two absorption heat pumps and two heat exchangers. The primary supply water flows through the two generators, two heat exchangers, and two evaporators of the absorption heat pumps. The radiator and floor heating return water was divided into two parts and heated by the heat exchanger and the absorber and condenser of the absorption heat pump, respectively. The performance of the designed heating station was evaluated using the coefficient of performance and the primary return-water temperature and compared with that of other district heating systems. The changes in the district heating system's configuration when the boundary conditions changed were investigated. Results showed that (1) the designed system based on thermal energy discretisation and matching method -had the lowest primary return-water temperature of 18.8 °C and the highest coefficient of performance of 5.62. (2) When the low-temperature load ratio changed from 0% to 100% while maintaining a constant total load, the system's form changed regularly. (3) When the primary supply-water temperature increased, the heating station's form remained unchanged and the capacity of the heat exchange equipment changed regularly. (4) When the secondary supply and return-water temperatures increased, the evaporation temperature of the absorption heat pump increased, resulting in a change in the system's form. This study provides valuable insight into the design of district heating systems that supply dual-temperature water under various design conditions. • A dual-temperature DH system including two AHPs and HXs is designed by TEDM method. • Thermal energy of primary hot water can be used more reasonable in designed system. • Energy performance of designed system is better than that of other DH heating system. • The changes in DH system's form with different conditions are investigated. [ABSTRACT FROM AUTHOR]

• To reflect the impact of indoor units on system performance, a novel index and model were proposed. • Simulation and experimental results validated the proposed performance model. • Proposed index was applied in a field test in an office and a residential building. In the context of a large market share, enhancing the actual performance of variable refrigerant flow (VRF) air-conditioning systems is of considerable importance. The operating states of indoor units (IUs) significantly influence the energy efficiency of a VRF system with multiple indoor terminals. Therefore, it is challenging to address accurate and concise representation of the operational characteristics of IUs for analyzing their impact on system performance. This study explored a novel performance index called capacity utilization rate (CUR) to illustrate the effect of IUs on system performance and developed a performance model based on this index. Simulation and experimental results demonstrated that energy efficiency and evaporating temperature decrease with a reduction in CUR under specific ambient temperatures and part-load rates. The proposed performance model was applied to real buildings in field tests to examine the operational characteristics of the VRF system. This research offers valuable insights for system design, performance simulation, and performance evaluation of VRF systems. [ABSTRACT FROM AUTHOR]

The pipe-embedded double-skin façade (PDSF) is a superior approach to decrease building cooling and heating load by using natural energy. With pipes embedded in the shading, the overheating problem in the conventional double-skin façade (DSF) can be eliminated. Unlike the traditional DSF or glass windows, the thermal performance of PDSF depends on the ambient environment and water temperature in the embedded pipes. Although the complicated heat transfer process of PDSF can be numerically solved, it is difficult for engineers to obtain the whole picture of the PDSF at first glance. To easily understand the thermal property of the PDSF, the overall heat transfer coefficient (U value), solar heat gain coefficient (SHGC) and equivalent ambient temperature of the PDSF are derived based on the thermal network. The heat transfer characteristic of the PDSF at different cooling water temperatures is compared with that of the conventional DSF. The results show that the three proposed indices can clearly reflect the thermal property of the PDSF: U value and SHGC reflects the influence of insulation and the transparency respectively, and the equivalent temperature reflects the integrated influence of water temperature and outdoor temperature. The typical PDSF has a higher U value than the DSF in the same structure. However, the SHGC of the PDSF is only 60% of that of the DSF. Although the equivalent ambient temperature depends on the outdoor temperature and water temperature, the weighting of the water temperature is 0.8, which indicates that the equivalent ambient temperature for the PDSF can reach a better level with the appropriate water temperature. Moreover, relatively warm water is suggested on sunny days to reduce the solar heat gain, since the solar heat gain is dominant in the total heat gain. Correspondingly, cool water is recommended for cloudy days to decrease the conductive heat gain. [ABSTRACT FROM AUTHOR]

Highlights • A novel heat recovery solution regeneration system is proposed for heating tower. • Regeneration performance of internally heated regenerator is experimentally studied. • Correlations of heat and mass transfer coefficients are developed based on results. • A low-grade heat source can be used for heating tower solution regeneration. Abstract Owing to their high cooling efficiency in summer and frost-free characteristics in winter, heating tower heat pumps are becoming increasingly popular. However, the solution will be diluted during heating due to absorbing moisture from the air, and should be properly regenerated for continuous operation. In this study, a novel heat recovery solution regeneration system using an internally heated regenerator is proposed for antifreeze solution regeneration. A test bench is fabricated to investigate the regeneration performance of the internally heated regenerator. Correlations of the heat and mass transfer coefficients are proposed, and agree well with the experimental data. The influences of inlet parameters on the moisture removal rate, latent heat ratio, and humidity effectiveness are evaluated and compared to those for internally heated liquid desiccant regeneration. The results indicate that: the regeneration performance of the internally heated regenerator is affected mainly by the air flow rate, heating water flow rate, and inlet temperature of heating water. The moisture removal rate increases remarkably with increasing the heating water flow rate and inlet temperature of heating water. The latent heat ratio decreases significantly with increasing the inlet temperature of heating water. The humidity effectiveness decreases remarkably with increasing the air flow rate. The influences of the above inlet parameters on performance indices in the present study exhibit the same trends as those reported for internally heated liquid desiccant regeneration. However, compared with internally heated liquid desiccant regeneration, the regeneration temperature for internally heated antifreeze solution regeneration is much lower. This suggests that a low-grade heat source can be used to meet the antifreeze solution regeneration demands. [ABSTRACT FROM AUTHOR]

Abstract To reduce the energy consumption for fresh air handling, a novel fresh air pre-handling system that fully exploits the shallow energy to precool and preheat fresh air is proposed in this study. The model of a typical all-air system with a pre-handling system is built on the TRNSYS platform. The energy saving potential of this fresh air pre-handling system is simulated based on the diverse climate of China. The results show that the ratios of the cumulated heat transfer capacity of the fresh air pre-handling system to the annual total of cooling and heating load range from 35% to 45% in the temperate zone and the subtropical zone, such as Shenyang, Beijing, and Shanghai, while the ratio in the tropical zone is approximately 10%. The energy saving rates are approximately 30% in most climate zones, but less than 5% in Guangzhou, the tropical climate zone. Moreover, the payback periods are within 4 years in the temperate and subtropical zones. However, the system is not economical in the tropical zone. All these results indicate that the fresh air pre-handling system with shallow geothermal energy is quite promising in most climate zones except in the hot summer and warm winter region with a tropical climate. [ABSTRACT FROM AUTHOR]

To overcome the shortcomings of the conventional working fluids, ammonia/ionic liquids were analyzed for the compression-assisted absorption heat pump. The property models of different ammonia/ionic liquid mixtures and the thermodynamic model of the proposed cycle were established with verified accuracy. The primary energy efficiency and exergy coefficient of performance under various conditions were compared. N, N-dimethylethanolammonium acetate performed the best under favorable working conditions, while 1,3-dimethylimidazolium dimethylphosphate and 1-ethyl-3-methylimidazolium tetrafluoroborate performed better under other conditions. 1,3-dimethylimidazolium dimethylphosphate can operate under the lowest generation/evaporation temperatures. Compared to ammonia/water, ammonia/N, N-dimethylethanolammonium acetate showed quite similar or slightly higher efficiencies under favorable conditions, ranging in 1.026–1.491. The exergy efficiency generally increased first and decreased later with the increase of the generation/condensation/evaporation temperature and the compression ratio. With optimal compression ratios of 1.8–2.1, the maximum primary energy efficiencies were 1.339–1.382 for different ammonia/ionic liquids. The primary energy efficiencies of the compression-assisted absorption heating were improved by 36–69% compared to gas boilers, by 0.2–54% compared to the conventional absorption cycles. [ABSTRACT FROM AUTHOR]