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The occupant-centric Part-Time-Local-Space heating mode holds paramount significance for the carbon neutralization of buildings in China. It ensures a harmonious match between heat supply and personal demand in both temporal and spatial dimensions, effectively reducing space heating consumption. However, current studies predominantly focus on the temporal-spatial heating demands of occupants at the room scale, but the zonal scale heating demands remain inadequately explored. Thus, we developed a temporal-spatial combined quantification method to analyze residents' indoor movement characteristics. It aims to identify the localized subzones in a room where residents have prolonged stays, with spatial boundaries of subzones entirely defined based on high-resolution positioning data. Using this approach, we analyzed the temporal-spatial heating demands of four households under single- and multiple-resident scenarios in typical rooms. Furthermore, we discussed the differences in demand between different heating modes. Results revealed distinctive "local space" demand features in living room and "part time" demand features in dining room. The areas of sofa subzones generally occupied less than 15 % of a room (within 4 m2), and stay durations in dining-table subzones ranged from 0.3 h to 1.2 h. Considering the entire monitored rooms, residents occupied only 4.1–12.1 % in space with 10.7–47.9 % in time per day, highlighting the significant energy-saving potential of the occupant-centric Part-Time-Local-Space heating mode. This evaluation provides a reference for the design and implementation of personalized environmental control system. • A quantification method on personal temporal-spatial heating demand was proposed. • High-resolution indoor positioning data of four households was monitored. • Temporal-spatial heating demand of residents in typical days and rooms were analyzed. • Differences in heating demand of single and multiple resident scenarios were compared. • Ideal energy-saving effects of Part-Time-Local-Space heating mode was analyzed. [ABSTRACT FROM AUTHOR]

Chiller consumes a significant power ratio in HVAC system. In order to minimize the power consumption of chiller, many efforts have been made on load predictions and optimal control strategies. The performance of chiller (e.g., COP) and dedicated devices (e.g., operation variables) play very important roles in chiller power consumption. However, it is difficult to find proper model to predict accurate chiller COP chiller in practice. Moreover, how the operating variables of the chiller system affects the over power consumption need to be identified. This paper therefore aims to find out a simple and accurate COP prediction model for chiller and investigates the optimal values of operating variables related to the chiller system. By com-paring kinds of models (e.g., SL, BQ, MP, GNU, QHP and BP-ANN), BP-ANN is considered as the proper model in predicting COP of chiller accurately. By adopting GA-based operating variables identification, optimal values of the variables can be found in specified ranges as well. This study evaluates the performance of different COP prediction models by using actual operation data of chiller plant in a commercial building. Furthermore, optimal settings for operating variables have also been identified in resulting of minimum power consumption of chiller plant. [ABSTRACT FROM AUTHOR]

To prevent frosting of air source heat pump used for space heating in winter, heat-source tower heat pump has been developed for its advantages such as frost-free, stable and reliable. Due to the mass transfer process between air and solution, however, the solution can continue to absorb the moisture of air, which results in the decrease of solution concentration and the increase of freezing point. It’s very essential to regenerate the dilute solution to ensure the stability and reliability of the operation of heat-source tower heat pump. Therefore, in this paper, the experimental test of closed-type heat-source tower is built to study the effect of inlet parameters of three fluids on heat and mass transfer performance under low temperature condition. According to the experimental results, with the increase of air volume, flow rate of internally heating water, so does the solution regeneration performance of closed-type heat-source tower. [ABSTRACT FROM AUTHOR]

Conventional absorption refrigeration systems (ARSs), which are mainly driven by heat, have a competitive primary energy efficiency ( PEE ) compared with chillers driven by electricity. In the typical ARS, a large quantity of high-temperature heat is supplied into the generator, while a substantial amount of low-temperature heat is rejected to the environment from the condenser, it’s a huge waste. In order to decrease the input heat for generator and enhance the performance of conventional ARS, a kind of absorption-compression hybrid refrigeration system recovering condensation heat for generation (RCHG-ARS) was ever proposed. In the present study, the models of both RCHG-ARS and double-effect absorption refrigeration system (DEARS) are established, and the effects of different parameters on them are simulated and compared with each other. As a conclusion, the PEE of RCHG-ARS can be 29.0% higher than that of DEARS, and RCHG-ARS has a wider working conditions than DEARS due to the existence of the compressor. [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]

Building energy systems consume increasing amounts of energy and emit many pollutants (e.g., NO x , PM 2.5 ) and CO 2 into the atmosphere. The problems of air pollution are very serious in China due to the very rapid urbanization and economic development over the past few decades and the fact that most of the primary energy comes from coal in China. In addition, China is facing serious indoor air quality problems caused by various pollutants with both indoor and outdoor origins. These pollutants have been found to be associated with certain diseases. The questions of increasing the energy efficiency of building energy systems and of how to effectively control temperature, humidity and pollutant concentrations in indoor air in an energy efficient way are two great challenges in the field of building energy and environment in China. Although engineering thermodynamics and heat and mass transfer are fundamental concepts for addressing building energy and environment problems, there are still some limitations in both theories: (1) the former can be used to optimize heat and work conversion processes, but it fails when used to optimize various heat and mass transfer processes and the processes of simultaneous control of indoor temperature, humidity and various pollutants; (2) the latter (including the entransy-based theory) can only be used for analysing or optimizing pure transfer processes. Based upon the inverse problem and variation method, a new approach is put forward for solving building energy and environment problems. Through illustrative examples we show that this new approach can overcome the limitations outlined above when addressing some building energy and environment problems. [ABSTRACT FROM AUTHOR]

Urban heating energy consumption in northern China accounts for 40% of total building energy consumption. In traditional central heating system, heat transfers from primary network (130°C/70°C) to secondary network (60°C/45°C) through heat exchangers in substations. In this paper, by introducing heat engine, heat pump and considering obtaining heat from environment, a new heat adaptor is built and the best system can be deduced out after thermodynamic optimization through extremum principle. The preliminary results indicate that when the return water temperature of primary network equals the ambient temperature, the heating capacity reaches the maximal value, which increases by 40% compared to absorption heat exchange system. Thus the thermal performance of existing heating systems can be evaluated. [ABSTRACT FROM AUTHOR]

Urban heating energy consumption in northern China accounts for 40% of total building energy consumption. In traditional central heating system, heat transfers from primary network (130°C/70°C) to secondary network (60°C/45°C) through heat exchangers in substations. In this paper, by introducing heat engine, heat pump and considering obtaining heat from environment, a new heat adaptor is built and the best system can be deduced out after thermodynamic optimization through extremum principle. The preliminary results indicate that when the return water temperature of primary network equals the ambient temperature, the heating capacity reaches the maximal value, which increases by 40% compared to absorption heat exchange system. Thus the thermal performance of existing heating systems can be evaluated. [ABSTRACT FROM AUTHOR]

Carnot cycle and theorem are major contributions of classical thermodynamics since proposed in 1824, while Carnot failed to prove it because of the influence of Caloric theory of heat. Then in 1850, Clausius confirmed Carnot theorem via reduction to absurdity and put forward the second law of thermodynamics. From then on, the theory that Carnot cycle is the one with the highest efficiency is generally accepted by scholars and regarded as the key premise or basis of thermodynamic analysis. However, few researchers care about how Carnot proposed the theory with the absence of the second law of thermodynamics. Can we get and prove Carnot theorem without the help of the second law of thermodynamics? In this paper, based on the polytropic process equations and p-v diagram, an analytical method of thermodynamics is developed and the cycle with the highest efficiency is deduced out only through extremum principle, instead of the second law of thermodynamics. The preliminary results indicate that Carnot cycle just serves as one form of the best cycles and only if the polytropic exponents ( n ) of the expansion and compression processes equal to each other, the efficiency of that cycle reaches the highest value, just that of Carnot cycle. This work gives a new insight into Carnot theorem and classical thermodynamics, which is of great importance in enlightenment for applying the new analysis method to address the complicated problems which are very difficult to address by using the second law of thermodynamics. [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]