Wenxing Shi

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 di...

With the rapid development of radiant floor heating in residential buildings, high‐temperature water for radiators and low‐temperature water for radiant floor heating are needed simultaneously. As a renewable energy solution, the geothermal district heating system(GDHS) is used. In this paper, a GDHS supplying dual‐temperature hot water for radiato...

Heating, ventilation, and air conditioning (HVAC) systems account for almost half of the energy used in buildings due to the rising demand for better thermal comfort in indoor environments. Building energy metering and management have received a lot of attention recently as a means of achieving the Paris Agreement’s objectives of energy conservatio...

Refrigeration and heat pump systems consume approximately 20 % of global electricity. The (quasi) two-stage compression and auto-cascade cycle configuration are effective approaches to save energy for vapor compression refrigeration and heat pumps because the former can reduce throttling irreversibility and the latter takes advantage of the concent...

With increasingly serious environmental and energy issues, efficient and environmentally friendly electric vehicles have received more attention. However, the high heating and dehumidification energy consumption of their air conditioning system reduces their driving range in winter, giving passengers and drivers range anxiety. In this study, a dual...

Refrigeration and air conditioning systems consume 20% of the overall global electricity. Developing refrigeration systems using zeotropic refrigerants is an effective approach to save energy in air conditioning systems, because the temperature glide of zeotropic mixtures can improve the temperature matching between the refrigerant and airflow. How...

With the increasingly stringent energy consumption and carbon emission policies enforced in China, the run-around heat recovery system has demonstrated significant potential for the energy retrofitting of existing ventilation systems. To explore the applicable regions of such projects and their optimal design schemes, a novel thermo-economic couple...

Energy efficiency and thermal comfort are the main factors reflecting the performance of air-conditioning units, but these characteristics have been evaluated separately in previous studies. Considering that the goal of an air-conditioning device is to provide thermal comfort, energy efficiency should be simultaneously evaluated with thermal comfor...

Two types of air-conditioning systems, named as room air conditioners (RAC) and multi-connected air-conditioners (variable refrigerant flow (VRF) systems) have become popular heating and cooling facilities for residential buildings featured with ‘part-time-part-space’ operation characteristics in the Yangtze River region. However, the research on t...

The indoor environment and energy performances of convective terminals have been widely studied under the strong heating demands in cold regions. As different operative conditions affect the performances of heating devices, investigating these factors under different conditions can help improve the performances. In this study, the thermal performan...

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 compre...

Going by current usage trends, the use of room air conditioners will increase by three times by 2050. Therefore, it is necessary to investigate an ultra-efficient air conditioner with extremely low operating energy consumption to realize the goal of climate change, especially in the (sub) tropical area. In this paper, an ultra-efficient air conditi...

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), eva...

With the increasing demand for winter indoor thermal comfort, increasingly many residents in the hot summer and cold winter zones in China have begun to take various intermittent heating measures. Different heating terminals show dissimilar intermittent heating performances, including heating capacity and thermal response speed, which further influ...

Performance evaluations of heat pumps play an important role in regulating energy markets and promoting energy conservation technologies. The development of air source heat pumps (ASHP) standards, especially seasonal performance factors including the annual performance factor (APF) method and integrated part-load value (IPLV) method, are reviewed f...

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,...

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,...

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 o...

Biopharmaceutical cleanrooms have high cleanliness requirements to supervise and manage processes and ensure the quality of production. However, on-site data, including real-time particle concentrations and differential pressure in biopharmaceutical cleanrooms, are scarce for both operational and at-rest conditions. In this study, a field experimen...

To locate the major imperfections and determine the optimization directions for developing high-efficiency vapor compression systems, a modified exergy analysis method is proposed in this study. In contrast to previous exergy analysis methods, the proposed method can split the exergy destruction of the refrigerant and simultaneously exhibit exergy...

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 realiz...

Utilizing natural energy directly for building cooling and heating can reduce the energy use of the HVAC systems significantly. There are various utilization forms of natural energies for building cooling and heating. The applicability of natural ventilation was evaluated in the previous studies by degree hours method which cannot be used for the e...

Room air conditioners are widely used to improve indoor thermal environments. However, the key factors that affect the performance have not been investigated systematically, which greatly influence the application of room air conditioners. Therefore, a subjective questionnaire and objective field test were conducted in this research. In the subject...

In variable refrigerant flow (VRF) systems with multiple indoor units, individual energy metering (IEM) not only contributes to a fair charge for the tenants, thus avoiding their complaints on the charging fee, but also shows the actual allocation of capacity for IUs. However, it is extremely challenging to measure the accurate capacity of each IU...

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 ad...

The heat-source tower heat pump, a frost-free heat pump with superior energy efficiency, has been used for heating in cold regions. Because the solution in the heat-source tower absorbs moisture continuously from the outdoor air and becomes diluted during heating, solution regeneration is necessary. However, existing regeneration technologies have...

Both quasi two-stage and two-stage compressions are important ways for improving the energy efficiency of the vapor compression heat pump system, especially for high compression ratio conditions. Many experiments and simulations have been conducted to investigate the performance improvement of two-stage or quasi two-stage systems. In most occasions...

The field performance of room air conditioners (RACs) directly affects energy consumption. In this study, a long-term field test was conducted in six residential rooms in the Yangtze River Region, China. Using specially developed test equipment, the occupancy pattern, control level, and energy performance factors for constant frequency and inverter...

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 propo...

Room air conditioners (RACs) are used worldwide and have become one of the major energy consumers in buildings. Because the actual field performance directly affects the energy consumption, the actual performance of an RAC must be determined. The compressor energy conservation (CEC) method exhibits better adaptability to the existing field test met...

The gas-fired boiler for heating is an important way for space heating in China due to low pollutant emission. Meanwhile, because the flue gas temperature is much higher than the ambient, there is a great amount of waste heat in the flue gas. To effectively recover waste heat, a novel heat recovery system that integrated gas engine driven heat pump...

The room air conditioner (RAC) is considered the most suitable space heating method for residential buildings without domestic heating in the mild climate zone. The heating performance of RACs has been well researched in laboratories. However, the field performance of RACs is far from the laboratory experimental results owing to their installation...

In residential buildings of the Yangtze River region in China, convective heating terminals operate intermittently, whereas radiant heating terminals function continuously. Different convective heating terminals include wall-mounted air conditioners (WMAC) and floor-standing air conditioners (FSAC). Previous thermal comfort studies comparing these...

Pipe-embedded external wall using low-grade energy has been shown to significantly reduce the cooling or heating load of buildings. However, previous studies have generally focused on the heat transfer between water pipes and pipe-embedded wall and paid less attention on the energy use of water distribution. In this paper, a numerical model of seri...

Influenced by the international environmental situation, refrigerant mixtures are regarded as potential alternatives in the field of air conditioning and heat pumps. Meanwhile, as an effective means, two-stage system is widely applied to improve the system performance of heat pump under large compression ratio. While according to the previous study...

Heat pumps have been widely applied owing to their high energy efficiency. Two-stage and quasi-two-stage systems are effective in enhancing the performance of heat pumps under large pressure ratio. Meanwhile, refrigerant mixtures are commonly regarded as potential substitutes for heat pumps because they can provide more flexibility in searching for...

Traditional single source heat pump systems, e.g., air source heat pump (ASHP) and ground source heat pump (GSHP), cannot work efficiently in the whole year. To develop an energy-efficient heat pump system for year-round operation, temperature grades of common natural energies are compared with each other. Based on the comparison, the combination p...

The traditional coal-fired boiler used for heating has a low efficiency and emits large amounts of pollutants. Thus, the use of natural-gas-fired boilers has become a popular method for heating all over the world owing to their cleanliness and high efficiency. Condensing domestic gas boilers have higher thermal efficiency than traditional boilers....

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...

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 p...

A two-phase natural loop (TPNL) has been widely used in air-conditioning systems for energy conservation. Under some extreme conditions, a liquid pump is usually added to be a two-phase liquid-side mechanically-driven loop (TPLMDL), but it is not always satisfactory because it enlarges the pressure drop along the gas line. Then, gas-side driving be...

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...

In recent years, variable refrigerant flow (VRF) systems have gained popularity in commercial and residential buildings. It is extremely significant to obtain the real performance of VRF systems in order to improve design. However, the measurement of the field cooling or heating capacity of air-cooled VRF systems has not yet been thoroughly address...

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 mech...

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 per...

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 ASHRA...

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...

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...

The gas injection technology had been developed to enhance the performance of the single cylinder rotary compressor at high compression ratio. However, the improvement of current designs was unsatisfactory because of the limited effective mass injected. A novel end-plate injection structure with check valve for rotary compressor was proposed and it...

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 solutio...

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 en...

The gas-injected single-cylinder rotary compressor has potential in better seasonal performance than the twin-cylinder rotary compressor for air conditioning application. However, the gas-injected single-cylinder rotary compressor with traditional injection structure could not improve the thermodynamic performance as expected. Analysis shows that b...

For energy conservation, two-phase thermosyphon loops (TPTLs) have been widely used in air conditioning systems. Unfortunately, the evaluation index and design criterion of the TPTL is currently lacking, and causes for poor performance are inconclusive. In this study, an “ideal cycle” (optimal state) of the TPTL was proposed, and an approaching deg...

The heat compensation unit with thermosyphon has been developed to eliminate the annual soil thermal imbalance of ground-coupled heat pump in heating-dominant buildings. But the issues on heating capacity deficiency at peak heating loads and on the high borehole investment are still unsolved in this non-coupled system. In this paper, a coupled oper...

Recovering heat from the flue gas of a gas-fired boiler can both improve boiler efficiency and decrease pollutant emissions. To improve the efficiency of the gas-fired boiler in a more cost effective and higher efficient way, a non-contact total heat recovery (NCHR) system is proposed for recovering heat from flue gas for use in heating and humidif...

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 se...

A gas engine-driven heat pump (GEHP) is traditionally applied for both heating and cooling; however, the cooling performance may be worse than that of an electric heat pump (EHP) because of the waste heat rejection of the gas engine. To improve the system performance of the air source heat pump for the entire year running, a hybrid power-driven hea...

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...

In order to effectively utilize the outdoor units and minimize material waste and reinvestment in the replacement of split-type air conditioners by a new household multi-split variable refrigerant flow (VRF) system, a recombined household multi-split VRF system with the original split-type air conditioners has been introduced in residential buildin...

The traditional refrigerants such as CFCs or HCFCs has been phased out for ODP and many HFCs is being phased down for their relatively high GWP. Among all the substitutions, the mixture has become much attractive because it can reach a balance between thermodynamic performance and environmental effects. R32/R1234ze(E) is one of them. At the same ti...

The coupled HCUT-GCHP system (integrating the GCHP with the efficient heat compensation unit (HCUT)) can operate in heat compensation mode and coupled heating mode to effectively eliminate the soil thermal imbalance and increase the heating supply at peak heating load. The coupled heating strategy directly influences the soil heat extraction not on...