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Solution regeneration of the heat-source tower is significant to guarantee the normal operation of the heat-source tower. Mechanical vapor recompression system is an efficient system for evaporation of solution. In this paper, mechanical vapor recompression system is applied to regenerate solution of heat-source tower. To clarify the merits of mechanical vapor recompression solution regeneration system, several typical solution regeneration systems are modelled. As a result, mechanical vapor recompression shows 35.7%, 73.5% and 91.2% energy saving compared to air-driven heat pump, three-effect evaporating system, and single effect evaporating system, respectively. Furthermore, a heat-source tower heat pump with solution generation system is installed in a typical building in Yangtze river region. The whole heating season performance is simulated to find the effects of different solution regeneration system on the whole heat pump system. As a conclusion, the seasonal coefficient of performance of heat pump is decreased 1.6% by mechanical vapor recompression regeneration system. Comparatively, the seasonal coefficient of performance of heat pump is decreased 2.6%, 4.2% and 10.0% by air-driven heat pump, three-effect evaporating system, and single effect evaporating system, respectively.Practical application: Solution regeneration systems for heat-source tower heat pump systems have been applied in building projects especially in hot summer and cold winter zone in China based on previous investigation. A heat-source tower heat pump system combined with heat pump solution regeneration system has been applied in an office building in Changsha, Hunan Province in China. And its practical operation energy consumption has been reduced obviously compared with traditional single effect evaporation system. Therefore, it is of vital importance to demonstrate the operating performance of different solution regeneration systems applied in heat-source tower heat pump systems in building. [ABSTRACT FROM AUTHOR]

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]

Recent years have seen a significant increase in study on the thermal comfort offered by room air conditioners (RACs) when utilized as heaters, especially in the steady stage. Research indicates that convective terminals can form a comfortable environment using optimized control settings and strategies. Nevertheless, complaints about the thermal comfort experienced when using RACs persist, which is probably related to cognitive bias in psychology. The final seconds of an experience are given a lot of weight by the peak-end rule, which is typically characterized as the positive/negative peak. They were used to analyze how different heating experiences rated in terms of thermal comfort. Therefore, dynamic indoor temperature variations with six different terminals and control strategies were analyzed. Furthermore, an experiment with a thermal sensation, thermal comfort, thermal preference, and thermal adaptability vote (TSV, TCV, TPV and TAV) with different dynamic controlling characteristics was conducted in an artificial chamber. Three control methods with different peak moments were determined: slow start, interval downtime operation, and continuous heating. The comprehensive experience TCVs were 2.72, 2.28, and 1.12, and average-weighted TCVs were 1.94, 1.60, and 1.14, respectively. This exhibited a significant difference in terms of the heating process evaluation. In contrast, the TCVs based on the peak-end rule were 2.52, 2.31, and 1.11, respectively, which is more consistent with field evaluation. There is strong evidence that peak-end rule applies to TCV for air-conditioning systems. Other cognitive biases were also analyzed to evaluate the heating experience. Reasons for the thermal discomfort of RACs are also summarized. [Display omitted] • Cognitive bias existed in the comprehensive evaluation of the heating experience. • Peak-end rule was used to analyze experience thermal comfort of air conditioner. • Reasons for the thermal discomfort of RACs are summarized. [ABSTRACT FROM AUTHOR]

The flue gas of boiler contains large amount of waste latent heat, and traditional heat recovery device is difficult to recover the latent heat due to the limitation of the specific heat of supply air. A deep heat recovery device between flue gas and supply air of gas-fired boiler is proposed in the paper, and the thermodynamic model is established to calculate its performance. The energy efficiency of gas-fired boiler with the device is compared with other systems. The result shows that the boiler efficiency with new heat recovery device is 5% and 13% higher than that of condensing boiler and boiler without heat recovery system, respectively. When the ambient temperature is higher, the energy efficiency is closer to the boiler with absorption heat pump for heat recovery, and the initial investment is lower. Therefore, both the energy efficiency and economy of this system is acceptable. [ABSTRACT FROM AUTHOR]

In recent years, it has been observed that room air conditioners require considerable amounts of electricity. In this study, the annual performance and applicability of a hybrid air conditioner combining a fresh air ventilator and direct evaporative cooling water spray system were evaluated. The direct ventilation temperature degree-hour (TDH), evaporative cooling enthalpy degree-hour (IDH), and hybrid temperature degree-hour (TIDH) were defined to represent the applicability of natural energy. Meteorological data in China was used to determine the natural source utilization potential for direct ventilation and evaporative cooling. An applicability analysis was conducted in 334 cities in China. To further analyze the energy-saving potential, a simulation model was established and verified for the hybrid air conditioner based on laboratory tests. The operation periods with different work modes, energy-saving rates, and energy efficiency values were considered for three typical cities, i.e., Nanjing, Beijing, and Lanzhou, representing wet, semi-wet, dry, and semi-dry zones, respectively. Considering the extra energy consumption of the ventilator, the total energy consumption was reduced in these cities by 6.4%, 22.6%, and 50.2%, respectively, and the system seasonal energy efficiency ratios (SEERs) improved by 6.9%, 29.3%, and 98.9%, respectively. Finally, the energy-saving potential, operation ratios, and absolute energy-saving values were calculated and analyzed for 31 provinces in different working zones. The results indicate that the proposed system has the best applicability and energy-saving potential in northern China. • A simulation model was established for a hybrid air conditioner. • An applicability analysis was conducted in 334 Chinese cities. • Energy consumption was reduced by 6.4, 22.6, and 50.2% in three typical cities. • The energy-saving potential in 31 provinces was calculated and analyzed. [ABSTRACT FROM AUTHOR]

With the widespread use of variable refrigerant flow (VRF) systems in various commercial and residential buildings, the performance and efficiency of VRF systems have attracted considerable attention in recent years. Although the compressor set energy conservation (CSEC) method exhibits a high accuracy in most cases of VRF performance measurement, several problems limit its accuracy. To improve the accuracy of the CSEC method for performance measurement, two methods are proposed to resolve the measurement difficulty of two-phase suction. The accuracies of the proposed methods are experimentally validated using three VRF configurations. In the experiments, the relative errors for the compressor isentropic efficiency-based method range from ±15%, ±17%, and ±18% for the three configurations. For the compressor volumetric efficiency-based method, the relative errors of the three configurations range from ±15%, ±16%, and ±16%, respectively. The capacity distribution and heat loss of the VRF system are measured and analyzed in the experiment. Heat losses from closed indoor units range from 0% to 21.5% in different cases in the cooling mode and from 0% to 31.1% in the heating mode. Additionally, an estimation method for the temperature measurement deviation is proposed to improve the precision of performance measurement. • Two methods are proposed to resolve the measurement difficulty of two-phase suction. • The accuracies of the proposed methods are experimentally validated within 18% and 16%. • The heat losses of VRF are measured and analyzed. [ABSTRACT FROM AUTHOR]

The main factors affecting field thermal comfort of convective terminals during the heating season have been widely studied in recent years. Since previous studies were conducted separately, this investigation aimed to analyze the thermal comfort under typical settings and integrated control strategies. A questionnaire, based on a field operation, was conducted to compare and find the main characteristics of different terminals. The contradiction of draft and vertical temperature difference and the continuous/intermittent feature control were the key factors investigated. The indoor environment distribution under different conditions was measured in laboratory cabins based on the different settings and control strategies of convective terminals. The thermal sensation vote (TSV) and thermal comfort vote (TCV) were conducted in an artificial chamber to show the characteristics of an indoor environment under different conditions. The results showed that people were more tolerant of drafting than vertical temperature differences (the TCV score decreased from 0.44 to 1.42 with different temperature non-uniformity and airspeed). In particular, the subjects' perceived control significantly reduced the risk of discomfort. In addition, there was no significant difference between the different control strategies, including continuous operation and intermittent operation, except for a long-term control shutdown. The TCV result was 0.48 in the on-off control with a 5-min shutdown, showing statistical significance in paired-sample t -tests (p < 0.05). • Terminals are compared by questionnaire, field test, and artificial chamber. • People are more tolerant to draft than to vertical temperature differences. • There is no significant difference in environment by various control strategies. [ABSTRACT FROM AUTHOR]

In this study, a hybrid air conditioner was proposed and investigated, based on combining a fresh air ventilator and direct evaporative cooling water spray system. Relative to a previously developed air conditioner using fresh air, the proposed air conditioner could be controlled more efficiently controlled through control strategies based on the outdoor environment. In this study, four zones with different operation strategies were considered, including direct ventilation (Zone 1), evaporative cooling ventilation (Zone 2), high efficiency direct ventilation (Zone 3), and off ventilation (Zone 4). A 1.5-HP room air conditioner was integrated with a ventilator, and the design principle and ventilator selection was illustrated. To compare the performances of conventional and hybrid air conditioners, a laboratory was used to simulate a typical day with an ambient environment and indoor cooling loads. One day at the beginning of the cooling season in three typical cities (Nanjing, Beijing, and Lanzhou, representing wet, semi-wet, and semi-dry/dry zones, respectively) were selected to conduct the field tests. The results show that the hybrid air conditioner exhibits high energy efficiency and energy-saving potential. Compared with conventional air conditioners, the total cooling capacity shows decreases ranging from 27.9% to 69.1% for the three cities. And the seasonal energy efficiency ratio test shows improvements of 12.3%, 38.5% and 221.9% in Nanjing, Beijing, and Lanzhou, respectively, indicating high operation efficiency in the cooling season. • A hybrid air conditioner combining ventilator and evaporative cooling is proposed. • Typical day and SEER tests were carried out under three typical conditions. • Operation period of mechanical refrigeration decreased from 32.5% to 56.1%. • Total cooling capacity of mechanical refrigeration decreased from 27.9% to 69.1%. • SEER improved by 12.3%, 38.5% and 221.9% respectively. [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]