Radiant Air Conditioning Research Articles

Experimental study on cooling feasibility and indoor thermal comfort of multi-connected dry capillary radiant air conditioning system

Abstract The traditional capillary radiant air conditioning system with water as heat exchange medium in the indoor unit may have defects of water leakage, pipeline freezing in winter and time delay of cooling and heating effect. It can only achieve good cooling or heating comfort, which is related to the installation of radiant capillary or panel in the floor or ceiling. In view of these defects, this work proposes a multi-connected dry capillary radiant (MDCR) air conditioning system with refrigerant as heat exchange medium. For the cooling operation, the fan coil assisted capillary radiant cooling (FCR) is developed. The fan coil bears part of the sensible cooling load to improve cooling effect and undertakes the entire latent cooling load to dehumidify the air to avoid the condensation. Two operation modes including the capillary radiant cooling (CR) and the FCR were comparatively tested. The test results show that the FCR can maintain the indoor temperature at 19–22°C, a comfortable temperature range, and can dehumidify the air to prevent the condensation. The experimental results demonstrate the application feasibility of MDCR for radiant cooling. In addition, the FCR can maintain the comfort relative humidity at 74–80% during the whole process of the refrigeration operation. The thermal comfort indices of predicted mean vote (PMV) and predicted percentage dissatisfied (PPD) can be kept at −0.5 ~ 0.5 and 0–10% at different heights of the indoor room. It can be concluded that FCR can achieve good thermal comfort and the indices of PMV and PPD can reach Class I standard.

Research on thermodynamic performance of a novel building cooling system integrating dew point evaporative cooling, air-carrying energy radiant air conditioning and vacuum membrane-based dehumidification (DAV-cooling system)

In this work, a novel building cooling system is proposed, namely DAV-cooling system, which integrates dew point evaporative cooling, air-carrying energy radiant air conditioning and vacuum membrane-based dehumidification. The DAV-cooling system does not use any organic refrigerants, and can naturally provide fresh air indoors to prevent managers from arbitrarily reducing fresh air, and can be flexibly adjusted to meet different cooling requirements. In addition, the thermodynamic model of the DAV-cooling system is established, and some systematical analysis of parameters of the DAV-cooling system is carried out. The results indicate that there is an optimal ratio of fresh air to primary air for the DAV-cooling system, and the optimal value of this ratio should be in the range of 0.2–0.4. When the DAV-cooling system operates under the condition of a higher flow of primary air, the requirements for the dehumidification efficiency of the vacuum membrane-based dehumidification device can be reduced. Moreover, the relationship between COP and cooling capacity ratio is revealed, and it is found that COP decreases as the cooling capacity ratio increases, but they are not in an absolutely one-to-one relationship. Outdoor temperature and humidity also have a greater impact on the performance of the DAV-cooling system. For Singapore and Changsha in the period from June to August, the COP of the DAV-cooling system is about 5–7 and 4.5–9 respectively when the permeate side pressure is 20 kPa. Finally, the engineering design methods of the DAV-cooling system are discussed, and it is found that the DAV-cooling system can be designed as a temperature and humidity independent control air conditioning system through the proposed design method and the established model. This work can provide a complete solution reference and some new insights for the application of next-generation HVAC systems.

Indian Oil lets contracts for new units at Barauni, Haldia refineries

In this work, a novel building cooling system is proposed, namely DAV-cooling system, which integrates dew point evaporative cooling, air-carrying energy radiant air conditioning and vacuum membrane-based dehumidification. The DAV-cooling system does not use any organic refrigerants, and can naturally provide fresh air indoors to prevent managers from arbitrarily reducing fresh air, and can be flexibly adjusted to meet different cooling requirements. In addition, the thermodynamic model of the DAV-cooling system is established, and some systematical analysis of parameters of the DAV-cooling system is carried out. The results indicate that there is an optimal ratio of fresh air to primary air for the DAV-cooling system, and the optimal value of this ratio should be in the range of 0.2–0.4. When the DAV-cooling system operates under the condition of a higher flow of primary air, the requirements for the dehumidification efficiency of the vacuum membrane-based dehumidification device can be reduced. Moreover, the relationship between COP and cooling capacity ratio is revealed, and it is found that COP decreases as the cooling capacity ratio increases, but they are not in an absolutely one-to-one relationship. Outdoor temperature and humidity also have a greater impact on the performance of the DAV-cooling system. For Singapore and Changsha in the period from June to August, the COP of the DAV-cooling system is about 5–7 and 4.5–9 respectively when the permeate side pressure is 20 kPa. Finally, the engineering design methods of the DAV-cooling system are discussed, and it is found that the DAV-cooling system can be designed as a temperature and humidity independent control air conditioning system through the proposed design method and the established model. This work can provide a complete solution reference and some new insights for the application of next-generation HVAC systems.

Comfort design and optimization of direct expansion multi-connected radiant air conditioning based on 3D flow field simulation

The air conditioning method based on radiation heat exchange has the characteristics of small vertical temperature gradient, high thermal comfort and energy saving, and has become a hot spot of attention. The Fluent numerical simulation, the experiment in this paper studies the direct expansion multi-line radiant air conditioner under the artificially simulated climate environment in winter heating, summer cooling and dehumidification. The temperature difference of the radiation + fresh air mode at the same time indoors under heating conditions is less than 2.5 °C, and the time to reach the indoor set temperature of 24 °C is about 2–3 h. Under cooling conditions, the temperature difference of the radiation + fresh air mode at the same time in the room is about 0.5–2 °C, and the time to reach the indoor set temperature of 26 °C is about 1–3 h. In the fresh air mode, the indoor temperature difference and response time at the same time are slightly larger than the radiation + fresh air mode. The freezing and dehumidification effect of fresh air is obvious, the moisture content of dehumidifying fresh air is between 6.3 and 10.5 g/kg, and the dehumidification efficiency can reach 50%. Under the same artificial simulated climate environment, the consumption of the three modes is not much different. When the outdoor temperature in heating conditions is higher than 9 °C, the fresh air mode can get better, and the radiation + fresh air mode can achieve better comfort when running indoors under various conditions.

Inverse design of indoor radiant terminal using the particle swarm optimization method with topology concept

Radiant air conditioning system could create thermal comfortable and energy saving indoor environment. However, previous studies indicated that the design scheme, such as the area, geometry, and installation position, of the radiant terminals have significant effects on indoor thermal environment. That is because the current radiant terminal design method is a trial-and-errors process, and this time-consuming method is very difficult to achieve the optimal design. To fix that problem, this study tried to develop an efficient inverse design method, the particle swarm optimization (PSO) method combined with the topology optimization, which can inversely identify the area, geometry, and installation position of the modularity radiant terminal based on the requirements. This investigation also explored the impact of some key factors on the inverse design results and finally the proposed method was used to design modularity radiant terminals for a multi-occupant's office. The results indicated that the proposed PSO method with the topology optimization could help with the design of high energy-efficiency radiant air conditioning system and the inversely identified modularity radiant terminal could create thermally comfort indoor environment.

Application of Capillary Network Air Conditioning System Based on Three-constant Technology in Gymnasium

With the advancement of social development, the continuous improvement of the level of science and technology puts higher requirements on the environmental quality of modern large-scale venues, which requires innovative concepts and high-tech to meet the requirements. In the paper, the capillary radiant air conditioning system based on three-constant technology is taken as the research object, and the steady heat transfer mathematical model of heat transfer from the cold water in the capillary network to the room is established. The structural parameters and operating parameters of the capillary radiant air conditioner are simulated and analyzed for the influence of its thermal performance, the environmental quality detection and control method based on bilinear model was established, and the algorithm of each index parameter was optimized to improve the high consistency between the model prediction parameters and the control tracking parameters. After verifying and testing the model parameters, it proves that the research content of the paper is real and effective, which its effect has reached the value of practical application. Through the research on the capillary network air conditioning system based on three-constant technology, it proves that the application in the construction of large venues has the effect of energy saving and environmental protection, and provides an innovative reference for the construction and development of the stadium.

Study on Radiation Air-Conditioning System as a Renovation Technology to Realize ZEB for Middle and Small Type Office Buildings

Study on Radiation Air-Conditioning System as a Renovation Technology to Realize ZEB for Middle and Small Type Office Buildings

Effect of air supply mode on airflow distribution in winter train sleeper compartments

Few of existing literatures on the airflow distribution of compartments have studied combined applications of radiant heating and air conditioning in winter. Simulation of airflow distribution in 25 T soft sleeper compartments under different heating and ventilation schemes is provided in this paper. Firstly, reliability of the numerical simulation model has been verified by the experimental data in the literature, and the appropriate turbulence model has been selected. Afterwards, numerical simulations are carried out on airflow distribution in those compartments with four ventilation modes under radiant heating conditions in winter. Research results show that as for thermal comfort, task air supply can provide the smallest temperature difference between head and foot positions as well as the best thermal comfort. As for effectiveness of air supply, the ventilation efficiency of louver side air supply is the highest among others. As for effectiveness of pollutant removal, the ventilation efficiency of task air supply is higher than the other three options. These four heating and ventilation schemes are evaluated comprehensively with fuzzy comprehensive evaluation method. Results reveal that task air supply is the mode with best comprehensive performance indices. It is followed, respectively, by louver side air supply, perforated ceiling air supply and louver top air supply.

Evaluation of membrane-based air pre-dehumidification for a capillary radiant air conditioning system

The polyvinylidene fluoride hollow fibre membrane air dehumidification tests were carried out between the liquid desiccant solutions and the wet air. Three liquid desiccant solutions of LiBr solution (50%), LiCl solution (35%) and CaCl2 solution (40%) were tested under different wet air conditions. The results showed that all the membrane dehumidification processes were stable. The air moisture content in the outlet of the membrane was maintained as 6.5 g/kg (da)–8.2 g/kg (da) when the air moisture content in the inlet of the membrane was operated from 17.1 g/kg (da) to 32.4 g/kg (da). The dehumidification amount of LiBr solution (50%) and LiCl solution (35%) was more productive. On this basis, a membrane-based air pre-dehumidification process for the capillary radiant air conditioning system was built. Since the ideal dew point temperature range of the indoor air is below 14–17°C according to the cold supply water, all the air moisture content at the membrane outlet is much lower than that of the ideal dew point temperature range, which means non-condensing occurs in the capillary tube surface. The membrane-based air pre-dehumidification process can easily form an adaptive regulation process of humidity with the capillary radiant air conditioning system under different environmental parameters.

Optimization of floor radiant air conditioning heating system in building heating design

Abstract For areas with hot summer and cold winter, air conditioning is an essential tool to improve the living environment, but the traditional air conditioning needs to consume a lot of energy in cooling and heating, the fan operation noise is large and the sense of blowing will be uncomfortable. This paper briefly introduced the basic structure of a ground-source heat pump-floor radiant air conditioning system and the control strategy which was used for regulating the operation of the air conditioning system. Then, in order to ensure the appropriate comfort and reduce energy consumption, the control strategy was optimized. An experimental room in Xining, Qinghai province, was taken as an example for analysis. The results showed that the thermal comfort under the control strategy proposed in this study was more stable at the moderate degree and the temperature was slightly higher under the traditional control strategy, although the indoor temperature fluctuation under the optimal control strategy was large and the temperature was slightly lower than that under the traditional control strategy; under the control strategy proposed in this study, the air conditioning system had shorter operation time and less power consumption.

Optimization of carbon dioxide refrigerant charge in capillary radiation air conditioning system based on genetic algorithm

AbstractThe traditional capillary radiant air conditioning system based on back propagation (BP) neural network optimization model of carbon dioxide refrigerant filling, using neural network algorithm to optimize the carbon dioxide refrigerant filling, there is a big error. Aiming at this problem, a carbon dioxide refrigerant charging and filling optimization model in capillary radiant air conditioning system based on genetic algorithm (GA) is constructed. Based on the idea of solving multiobjective optimization problem with genetic algorithm, an adiabatic capillary steady‐state distribution model is constructed to analyze the change of refrigerant flow rate and critical temperature in capillary tube. Corresponding data samples, the GA‐BP neural network model is calculated based on the sample data, and the optimization of carbon dioxide refrigerant filling capacity is realized through the interpolation and extrapolation test model of condenser heat transfer and refrigerant outlet temperature. The experimental results show that the model has a significant application in optimizing the charging capacity of carbon dioxide refrigerant. The error of optimizing the charging capacity of carbon dioxide is small, and the error range is between (−0.03, 0.03).

The performance of a closed cavity radiation system with built-in heat exchanger

Radiant ceiling systems have good comfort levels and energy savings. However, traditional radiant air conditioning systems have many problems, such as condensation forming on the cooling surface, insufficient cooling capacity, and complex structure and control. In this paper, a closed cavity radiation system with a built-in finned heat exchanger is proposed and the heat transfer mechanism, heat transfer performance, and operation characteristics of the system are analysed. The results show that the direct-expansion large-temperature-difference heat transfer method, with refrigerant as the working medium, realises the required cold supply through the low-temperature working medium and the required heat supply through the high-temperature working medium. Heat is transferred to or from the ceiling through a multi-stage strength buffer and direction conversion so that the ceiling respectively forms a hot or cold radiant plate with uniform temperature for indoor heat exchange. The heat transfer efficiency is more than 90%, which greatly improves the cooling or heating potential of the heat exchanger, reduces the required heat exchanger area, and simplifies the installation structure. In this study, the installation area of the finned heat exchanger only accounted for 14% of the ceiling. In practical application, the number of finned heat exchanger plates can be determined according to the cooling and heating load demand, providing a reference for new radiant air conditioning system design.

Simulation and experimental study of phase change cooling and heating wall radiation air conditioning system

This paper presents a case study of phase change cooling and heating wall radiant (PC-CHWR) air conditioning system application in an energy-saving renovation project in a laboratory in Wuhan, Hubei province in China. To test the thermal performance of the system, the PHOENICS software was utilized to simulate and analyse the indoor thermal environment in the laboratory under both winter and summer operating conditions. In addition, field experiments were also conducted under winter operation condition. By comparing the results between numerical simulation and field experiment, it is found that thermal performance of the PC-CHWR air conditioning system evaluated by these two evaluation methods are quite match. Moreover, the results also show that the PC-CHWR system can meet the cooling and heating load of the building within the acceptable range.

Study on the heat transfer performance of the ceiling radiant panel

The purpose of this study is to acquire data to examine the design method of radiant air conditioning in Japan. The radiant panels were installed in the population weather chamber, and the convective heat transfer coefficient and the radiant heat transfer coefficient on the upper side and the lower side of the radiant panel were experimentally calculated. As a result of this experiment, the radiant heat transfer coefficient was larger than the convective heat transfer coefficient during cooling and heating. In addition, CFD simulation of the thermal environment and airflow in the environmental control chamber was conducted. From the simulation results, it found that there was almost no temperature unevenness in the environmental control chamber, and the air flow was very small. There were differences in the comparison between the experimental values and the analysis values of the vertical temperature distribution.

Influence of asymmetric radiation on heat exchange of planar radiant air conditioning and its correction

In this paper, the influence of radiation asymmetry on radiant heat transfer in the room of plane radiant air-conditioning system is analyzed. The radiation heat transfer model used in the Fanger thermal comfort equation is introduced. Using Airpak simulation analysis, it is concluded that external Windows and external walls should be taken as separate enclosure structures to calculate the PMV value. A new radiation heat transfer model was established, and the radiation heat transfer was solved under the new radiation heat transfer model. As the radiation heat transfer in the PMV equation, the thermal comfort equation was modified.

Cooling performance of Ceiling Radiant Textile Air Conditioning System with Ceiling Cassette Unit of Packaged Air Conditioner

The authors developed a new radiant air conditioning system named ceiling radiant textile air conditioning system with ceiling cassette unit of packaged air conditioner (PAC). The nonflammable textile is stretched under the ceiling with ceiling cassette units of PAC with a distance of around 30 cm. The aim of this study is to investigate the cooling performance of this new radiant system, so the experiments with full scale model were conducted for three system. The first system is “textile only”, the second system is “textile with guide for air return grille” and the third system is “textile with guide and opening for air return grille”. Airflow rate through textile is measured by tracer gas method. In all cases, the vertical temperature distribution is almost uniform, and the cooling effect of “textile with guide and opening for air return grille” is the largest. As for the radiant effect, two systems of “only textile” and “textile with guide for air return grille” are superior to “textile with guide and opening for air return grille”. The airflow rate trough textile is doubled when using guide, and increased by five times if the opening was provided under the guide.

Thermal performance of a suspended ceiling fin heat transfer panel with drain pan

Radiant air conditioning systems provide better comfort and energy efficiency than air conditioning systems based on forced convection. In order to prevent condensation, the surface temperature of the radiant heat transfer component in conventional radiant air conditioning must be maintained above the dew point temperature, resulting in insufficient cooling capacity. In this paper, a new type of suspended ceiling fin heat transfer panel with a drain pan is proposed to achieve a large temperature difference for the cooling/heating supply. This panel has the characteristics of large heat flux per unit area, sufficient cooling capacity, and simplified heat exchange system. The research results show that the heat flux of the fin heat transfer panel accounts for 90%. In a comparison of the suspended ceiling radiant panels of different structures, the suspended ceiling fin heat transfer panel may be used with a refrigerant with a lower temperature relative to the other two structures and has great potential to improve heat flux, which can reduce the installation area of indoor radiant panels. Finally, the structure of the fin heat transfer panel was optimised. When the fin spacing of the fin heat transfer panel was 5.2 mm, the cooling/heating capacity of the fins was improved by a factor of 1.5 compared to the panel with the original spacing of 1.8 mm, and the metal material required was reduced to approximately 33% of the total. These results serve as a theoretical and practical reference for the study of such air conditioning systems.

A simulation study for evaluating the performances of different types of house-hold radiant air conditioning systems

As one potential solution of independent temperature and humidity control in small-to-medium scaled residential buildings, systems of outdoor air dehumidifier with radiant terminals attracted lots of researchers’ interests. In this paper, three types of house-hold radiant air conditioning (A/C) systems, a conventional air source heat pump (ASHP) based, a high-temperature ASHP based and a novel variable refrigerant flow rate (VRF) based radiant A/C system, were proposed. Simulation models for three systems were established using Energy Plus. A prototype of the VRF based radiant A/C system was built and tested in an existed psychometric room. Testing results were compared with the simulated results showing that the average relative errors between them were less than 8%. Therefore, simulation studies were carried out to evaluate the energy performances of the three types of house-hold radiant A/C systems. Compared to the conventional ASHP based system, the high-temperature ASHP based system achieved 14.99% annual energy saving and the VRF based system 19.34%. Therefore, the VRF based system achieved the best energy efficiency, providing a promising solution for the house-hold radiant A/C system to realize the independent control of temperature and humidity in small-to-medium scaled residential buildings.

躯体蓄熱併用型輻射空調システムを導入した次世代テナントオフィスビル （第2報）計測計画および実測計画について

躯体蓄熱併用型輻射空調システムを導入した次世代テナントオフィスビル （第2報）計測計画および実測計画について

躯体蓄熱併用型輻射空調システムを導入した次世代テナントオフィスビル （第1報）施設・設備概要について

躯体蓄熱併用型輻射空調システムを導入した次世代テナントオフィスビル （第1報）施設・設備概要について