Radiant Air Conditioning System Research Articles

Thermodynamic performance assessment of vacuum membrane-based dehumidification and air carrying energy radiant air-conditioning system (VMD-ACERS)

Temperature and humidity independent control (THIC) air-conditioning system is a promising technology. In this work, a novel temperature and humidity independent control (THIC) system is proposed, namely VMD-ACERS, which integrates vacuum membrane-based dehumidification and air carrying energy radiant air-conditioning system. This work establishes a novel coefficient of performance (COP) model of VMD-ACERS. The main parameters affecting the COP of conventional fan coil unit cooling system (FCUCS) and VMD-ACERS are investigated. The performance of FCUCS and VMD-ACERS are compared, and the energy-saving potential of VMD-ACERS is proved. Results indicate that, for FCUCS, the importance ranking of parameters is basically stable. However, for VMD-ACERS, the importance ranking will be affected by FCU and refrigerant. The most important parameters of VMD-ACERS are condensation temperature and permeate side pressure. On the contrary, superheating, subcooling are relatively less important parameters. For VMD-ACERS, it is not necessary to pursue the membrane with very high selectivity, because the selectivity of membrane would also be a less important parameter when it reaches 500. The COP of VMD-ACERS is higher than that of FCUCS when the permeate side pressure is higher than 8 kPa. The VMD-ACERS solves two technical problems about power-saving and thermal comfort of conventional THIC, and can extend the application of THIC air-conditioning system.

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.

Field study and numerical investigation on heating performance of air carrying energy radiant air-conditioning system in an office

A ceiling-sidewall composite air carrying energy radiant air-conditioning system (ACERS) is presented, and the heating performance of the ceiling-sidewall composite ACERS combined with air source heat pump is investigated by field experiment. The results show that the combined system can meet the heating requirement for office buildings in south-central China, and also have the energy-saving potential. Moreover, the indoor thermal environment under three different installation types, namely the ceiling, the sidewall, and the ceiling-sidewall composite type, is analyzed by using computational fluid dynamic (CFD) simulation. The comparisons of three types indicate that all of them can meet the temperature requirement, but the temperature is more uniform and higher in the composite ACERS. Meanwhile, the temperature gradient in the ceiling ACERS is smaller than that of the sidewall ACERS due to the further heat transfer caused by air penetration. Both the experimental and CFD simulated temperature distribution demonstrates that the shelter of furniture has an impact on the indoor thermal environment, and it should not be ignored in practical engineering. This research shows the feasibility of winter heating by using the ACERS in office buildings, and is helpful for HVAC engineers to design and apply different ACERS types and realize the integration of air conditioning in winter and summer in this area.

Study of an integrated radiant heating/cooling system with fresh air supply for household utilization

With the increasing demand for indoor thermal comfort in recent years, radiant heating & cooling systems have been very popular in China. However, for the household air-conditioning in hot-summer and cold-winter regions, an effective solution of heating and cooling source supply for radiant air-conditioning system remains to be developed. In this paper, an energy-efficient radiant heating/cooling system with fresh air supply is proposed and investigated for household utilization numerically. Under summer conditions, dehumidified fresh air supply is a tough problem in radiant cooling since the chilling water temperature for radiant cooling is much higher than traditional air-conditioning systems. In the proposed system, the fresh air handling unit is composed of both pre-cooling dehumidification coil and liquid desiccant dehumidifier, where high-temperature chilling water is used for cooling source and small part of condensing heat is used for liquid desiccant regeneration. The results indicated that the fresh air can be steadily supplied and sufficiently dehumidified for indoor air quality and humidity control. The chilling water flow rate in pre-cooling coil (mw,coil) and the solution flow rate from regenerator to dehumidifier (ms,SS) can be recognized as control parameters to reliably regulate the indoor air humidity. The load ratio of sensible heat to latent heat had no significant impact on COPsys, which means the system can operate with a steady energy efficiency despite of the indoor heat load. Satisfactory energy-saving potential was revealed in the proposed system with a COP improvement of 25.8%–30.1% compared to the conventional system under typical summer conditions in Nanjing.

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.

Human-Oriented Design of an Indoor Thermal Environment

In this study, an initial survey of clothing insulation and changes in the metabolic rate of individuals in office spaces was performed to establish the distribution of room temperatures at which individuals perceived a neutral thermal sensation. Subsequently, the indoor thermal environment in four offices was surveyed during the summer with different air-conditioning systems to determine the thermal environment stability in each case. The results revealed that for the required temperature, there was a noticeable difference between the average and most frequent values. Moreover, it was determined that the required temperature distribution is not normal, but rather, it is skewed to the low-temperature side. In addition, the radiant air-conditioning system was found to generate a narrow distribution of the equivalent temperature and hence, facilitated a more uniform thermal environment compared to a convective (multi-unit) air-conditioning system. Therefore, in buildings with convective air-conditioning systems, even if the planar average thermal environment is categorized as comfortable, it may be possible that workers who are sensitive to the cold or heat will complain of discomfort more frequently than those in buildings with radiant air-conditioning systems because the probability of workers sitting in cold- or hot-spot areas is higher in the former case.

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.

Evaluation of Thermal Behavior of the Skeleton in a Green Building with the Aid of TABS

In this study, an office building in Japan that incorporates energy-saving features and environmental technologies was investigated. This office building features a green façade, natural ventilation, a concrete slab with no suspended ceilings, and thermo-active building systems. Two airconditioning systems were installed in this building—a ceiling radiation air-conditioning system and a whole floor-blow off air conditioning system. In addition, a natural ventilation system was installed. We surveyed the heat flux of the ceiling surface and indoor thermal environment of this building from 2015 through 2016. The ceiling using the heat storage amount of concrete maintains a constant temperature in the workplace during as well as after office hours. We also performed detailed measurements of the heat flux of the ceiling surface and indoor thermal environment in the summer of 2017. The results showed that the ceiling radiation air-conditioning system provided a stable thermal environment. Furthermore, we report that making use of the thermal behavior of the skeleton improved the operation of the ceiling radiation airconditioning system.

Investigation on thermal comfort of air carrying energy radiant air-conditioning system in south-central China

A field study of thermal environment and thermal comfort under air carrying energy radiant air-conditioning system (ACERS) and split air conditioner was conducted in south-central China. The results reveals that the ACERS can create a comfortable thermal environment with small vertical temperature gradient. Based on the regression equation of thermal sensation vote and operative temperature, it is found that the neutral temperature in ACERS is about 28 °C in summer and 18 °C in winter, while in split air conditioner, the temperature is about 26.1 °C and 19.3 °C. Besides, the comfortable temperature range for 80% acceptability in ACERS is 25.5–30.7 °C in summer and 13.8–22.2 °C in winter, and the corresponding range of split air conditioner is 23.9–28.3 °C and 16.7–21.8 °C. The results show that the ACERS has a larger temperature adjustment range compared to the split air conditioner and the thermal comfort stability of ACERS is better. The actual comfortable temperature range is wider than the theoretical value calculated by PMV-PPD equation, and the reason may be that people in their long-term life have been adaptable to the environment. This research is helpful for the design and operation of air-conditioning system in future and provides the theoretical basis for indoor temperature setting in this area.

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.

Investigation of operation performance of air carrying energy radiant air-conditioning system based on CFD and thermodynamic model

This study aims to investigate the operation performance of a new terminal form of radiant air-conditioning system called the air carrying energy radiant air-conditioning system (ACERS). Three summer operation conditions, namely steady condition (without opening door and window), open-door condition and open-window condition, are researched in a residential apartment using experimental, computational fluid dynamics (CFD) simulation and thermodynamic methods. The concept of dynamic synergistic operation of mechanical ventilation driven by the air-conditioning system and natural ventilation driven by the open door or window is proposed. A thermodynamic model formulated by the dynamic enthalpy equation, dynamic temperature equation and dynamic moisture equation is developed to analyze the heat and mass transfer process of the test room under the synergistic operation of mixing ventilation. Moreover, the CFD simulation results are used to analyze the synergistic operation and thermodynamic energy transfer of the test room under the mixing ventilation of ACERS and open door/window. It is indicated that ACERS is an important technology with a low temperature gradient of less than 0.1 °C between the head (1.5 m) and ankle level (0.1 m) and low velocity of approximately 0.1 m/s in the occupied zone under the steady condition. The thickness of the boundary zone under the orifice plate of ACERS under the steady, open-door and open-window conditions is 12, 6, and 8 cm, respectively, which can effectively prevent condensation. This study proves that ACERS is a promising technology for air conditioning in residential buildings in regions with hot and humid summers.

Study on radiant heat amount and room comfort of air-type radiant air-conditioning system

Study on radiant heat amount and room comfort of air-type radiant air-conditioning system

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.

空調用冷温水のカスケード利用による放射式空調に関する研究 （第2報）放射冷房を施した事務所ビルの室内温熱環境シミュレーション

空調用冷温水のカスケード利用による放射式空調に関する研究 （第2報）放射冷房を施した事務所ビルの室内温熱環境シミュレーション

パッシブチルドビームを用いた天井内冷却式放射空調の基礎検討 （第3報）CFDを用いた圧力損失特性と天井パネル表裏間移流量予測手法の検討

パッシブチルドビームを用いた天井内冷却式放射空調の基礎検討 （第3報）CFDを用いた圧力損失特性と天井パネル表裏間移流量予測手法の検討

パッシブチルドビームを用いた天井内冷却式放射空調の基礎検討 （第2報）実大オフィスモデルにおける冷房実験

パッシブチルドビームを用いた天井内冷却式放射空調の基礎検討 （第2報）実大オフィスモデルにおける冷房実験