Radiant Air Conditioning System Research Articles

Comparative analysis of radiant air-conditioning systems combined with two different types of solar-powered dehumidification methods

Abstract This paper proposes a solar liquid desiccant radiation air-conditioning system(SLDRS) and a solar desiccant wheel radiant air-conditioning system(SDWRS) that combine with a phase change energy storage radiation terminal, solar energy, and heat pump system. The models of the two systems are simulated with the transient system tool (TRNSYS) to compare the refrigeration and dehumidification effects and energy saving of the two systems. The results show that the total refrigeration capacity of the SLDRS is reduced by 20.45% compared with the solar desiccant wheel radiation air-conditioning system, the monthly average dehumidification capacity is increased by 37.09%, and the total energy consumption is reduced by 712.9 KW·h. It is evident that the cooling and dehumidifying effect and energy efficiency of the SLDRS are superior to those of the SDWRS.

Study on infection risk in a negative pressure ward under different fresh airflow patterns based on a radiation air conditioning system.

COVID-19 and other respiratory infectious viruses are highly contagious, and patients need to be treated in negative pressure wards. At present, many negative pressure wards use independent air conditioning equipment, but independent air conditioning equipment has problems such as indoor air circulation flow, condensate water accumulation, and improper filter maintenance, which increase the risk of infection for healthcare workers and patients. The radiation air conditioning system relies on the radiation ceiling to control the indoor temperature and uses new air to control the indoor humidity and air quality. The problems caused by the use of independent air conditioning equipment should be avoided. This paper studies the thermal comfort, contaminant distribution characteristics, contaminant removal efficiency, and accessibility of supply air in a negative pressure ward with a radiation air conditioning system under three airflow patterns. In addition, the negative pressure ward was divided into 12 areas, and the infection probability of healthcare workers in different areas was analyzed. The results show that the application of radiation air conditioning systems in negative pressure wards can ensure the thermal comfort of patients. Stratum ventilation and ceiling-attached jets have similar effects in protecting healthcare workers; both can effectively reduce the contaminant concentrations and the risk of infection of healthcare workers. Ceiling-attached jets decreases the contaminant concentrations by 10.73%, increases the contaminant removal efficiency by 12.50%, and decreases the infection probability of healthcare workers staying indoors for 10min by 23.18%, compared with downward ventilation.

Optimization of Air Supply Conditions for Large Space Radiant Air Conditioning Based on Response Surface Analysis

In large spaces, the comfort control of radiant air conditioning systems still has deficiencies. Mainly reliant on traditional parameter control methods, the interaction effects of diverse operating conditions are not taken into account, and the control results are still in need of optimization. To improve indoor air conditioning comfort control and address gaps in existing research, the response surface analysis method combined with numerical simulation is applied to determine the optimal air supply conditions for large-space radiant air conditioning. With the real model as a reference, simulations are carried out in Airpak, selecting four factors: supply air temperature, supply air humidity, air supply volume, and air supply angle for the response surface design. Discussions on interaction effects are carried out based on the simulated results of various scheme designs, determining eight groups of air supply schemes with the highest comfort. The research concludes that the response surface analysis method, considering the interactive effects of impacting factors, can lead to the strategy of high comfort and reasonable air supply conditions. Additionally, a set of recommendations are proposed for future practical application and promotion.

A simulation study on the heating characteristics of residential buildings using intermittent heating in Hot-Summer/Cold-Winter areas of China

Radiant air conditioning system is an important heating method with better thermal comfort, less noise and greater energy-saving potential. However, different intermittent heating modes may significantly impact both the heating efficiency and indoor thermal comfort, which has been neglected in existing studies. Therefore, to obtain optimal intermittent heating modes for achieving higher energy efficiency and better indoor thermal comfort for the residential buildings in Hot Summer and Cold Winter areas, a TRNSYS model of the radiant air conditioning system was developed and validated. The indoor thermal comfort and energy consumption characteristics during the coldest day and entire heating season were simulated and analyzed based on four different intermittent heating modes. The results demonstrated that the supply water temperature of the air source heat pump unit and the radiant terminals stabilized at the set temperature in about 1 h during the start-up stage, and the indoor air temperature stabilized at 24.0 °C after 7.5 h during the shutdown stage. The proportion of time that meets first-level thermal comfort under the four intermittent heating modes was above 90.1% and even higher at over 96.1% when considering the sleeping period. Compared to the continuous heating mode, the four intermittent heating modes saved 22.3%, 25.8%, 40.4% and 48.4% of energy. Overall, the preferred intermittent heating mode for residential buildings with the radiant air conditioning system in Hot Summer and Cold Winter areas was identified as switching on from 7:00 to 15:00 and 19:00 to 3:00, while switching off from 15:00 to 19:00 and 3:00 to 7:00. This model not only considered the immediate benefits of improved indoor thermal comfort and energy efficiency, but also showed great advantages in developing sustainable construction.

A Comparative Analysis of a Radiation-Cooling-Plate-Coupled Adhesion-Jet Air Conditioning System in Different Positions

Compared with the traditional radiant cooling combined with a displacement ventilation air conditioning system, an air conditioning system of radiant cooling combined with an attached jet can not only effectively prevent dew on the surface of the radiant cooling plate, but also further improve the cooling capacity of the radiant air conditioning system; however, most scholars have installed the radiant cooling plate on the radiant roof and the ground, and there are fewer studies on installing the radiant cooling plate on the two sides of the wall. Based on this, this paper builds an experimental system of radiant air conditioning and conducts experiments on summer working conditions in June–October to experimentally study the indoor thermal and humid environments and thermal comfort under different water supply temperatures when radiant cold panels are installed in single-side-wall, symmetrical-wall, and top-panel positions. The experimental results show that the optimal water supply temperatures of single-side-wall radiation combined with an attached-jet air conditioning system, symmetrical-wall radiation combined with an attached-jet air conditioning system, and roof radiation combined with an attached-jet air conditioning system are 18 °C, 22 °C, and 16 °C, respectively, and at the same time, the temperatures of the human body’s working area under the above water supply temperatures are 26 °C, 26.3 °C, and 26.4 °C, respectively. The average humidities in the working area are 58%, 53%, and 57%, which can meet the requirements of our country’s level II comfort when the indoor heat and humidity environment is stable, the energy consumption amounts of the radiant end are 5.71 kW·h, 3.99 kW·h, and 10.81 kW·h, respectively, and the highest efficiency of cooling and dehumidification is achieved with the symmetric-wall radiation combined with the adherent-jet air conditioning system.

Field studies on indoor thermal environment and start-stop characteristics of the radiant air conditioning system during intermittent heating

With the improvement of social economy, the heating demand of residents in Hot Summer and Cold Winter (HSCW) areas in China is increasing. The radiant air conditioning (A/C) system, is popular as a heating way due to its high comfort, low noise and high energy saving potential. There is still a lack of field research on the system under the intermittent heating mode in the HSCW area. To provide a guide for the operation mode of the radiant A/C system during intermittent heating in HSCW areas, this paper focused on the radiant A/C system with the fresh air system, and then studied system's practical operational parameters and dynamic characteristics in winter. The indoor and outdoor air temperatures and relative humidity, the water temperatures of inlet and outlet of the air source heat pump (ASHP) unit, the supply and return water temperatures of radiant terminals, as well as supply air temperature were analyzed in three stages, i.e., the initial start-up stage, the intermittent shutdown stage and the intermittent start-up stage. The results show that, it took 7 h and 50 min for the indoor air temperature to reach the set indoor temperature during the initial start-up stage. Compared to the initial start-up stage, the intermittent start-up stage reduced the time for the indoor air temperature to reach the set indoor temperature by 4 h and increased the indoor air temperature rise rate by 97%. The indoor air temperature rise rate was 0.46 oC/h and 0.91 oC/h, during the initial start-up and the intermittent start-up stage, respectively. The indoor air temperature decrease rate was 0.23 oC/h during the shutdown period. During the entire winter season, the ASHP unit switched on and off intermittently 10 times. The longest shutdown lasted for 111 h, and the indoor air temperature dropped to 17.2oC.

STUDIES ON WINTER OPERATION EFFICIENCY OF TABS AND FLOOR BLOW AIR CONDITIONING SYSTEM USING GROUNDWATER AS A HEAT SOURCE/SINK

With the promotion of zero energy in buildings,the use of TABS (Thermo Active Building System), a form of radiant air-conditioning systems, is increasing. A survey on the actual conditions of operation in winter was conducted for the TABS adopted in the S Company’s Hokuriku Branch Office. Data on temperature and flow rate of hot water, as well as power consumption of heat pumps and pumps were obtained every one minute. The purpose of this study is to clarify the application effect to buildings by analyzing the energy consumption efficiency of TABS and floor blow air conditioning system.

Experimental study on heating performance of micro-holes radiant plate under different installation types in severe cold regions

In order to alleviate energy shortage and maintain comfortable indoor environment, radiant air conditioning system is widely used. This paper designs and produces a miniaturized micro-holes radiant plate, which has the characteristics of orifice plate air supply and radiant heat transfer. The micro-holes radiant plate can be installation on the ceiling or sidewall without adding dynamics system and piping system. In order to explore the heating performance of the micro-holes radiant plate under different installation types, an experimental bench of air source heat pump micro-holes radiant plate heating system was built in Harbin, China, for laboratory heating. The experimental results showed that the indoor average temperature under various installation types could basically meet the set requirements, and the deviation was within 1 °C. The indoor horizontal temperature distribution was relatively uniform, and the temperature difference of each measuring point was less than 2 °C. The indoor vertical temperature difference was the smallest under the installation type with sidewall 50 mm from the ground at only 2.68 °C in the sitting position and 3.14 °C in the standing position, which meet China and ASHRAE standards. The ratio of the radiant heat transfer quantity under the sidewall heating was about 60 %, while the ratio under the ceiling heating was only about 30 %. The maximum ratio of the radiant heat transfer quantity was close to 70 % under the installation type with sidewall 50 mm from the ground. The experimental results provide theoretical support for the design and operation of air conditioning systems in severe cold regions.

Improved Thermal Performance of Combined Convection and Radiation Using Room Air Conditioner

This study aims to evaluate the indoor thermal environment within a detached residence in summer by applying combined convection and radiation air conditioning system using the refrigerant gas of room air conditioners (RACs). First, field measurements were performed in a detached residence at Hiroshima, Japan, in July and August 2021. Consequently, PMV values were generally maintained within the comfortable range during air-conditioning operation. The amount of heat generated by convection (via the RAC indoor unit) Qc and that by radiation (via the radiation panel) Qr were determined as 426 and 259 W, respectively, and the overall heat generated Qtotal was determined as 685 W. Applying the CFD model, thermal environment was compared varying the ratio between Qc and Qr with a constant Qtotal of 685 W. Results showed that the synergistic operation of a RAC and a radiant panel presented more comfortable PMV values than that of a single RAC application. Furthermore, the airflow from the RAC decreased with an increase in Qr ratio, and the chilled radiant panel provided a cooling effect around the dining area, where the airflow of the RAC was inadequate, thereby improving the thermal comfort.

A model predictive control regulation model for radiant air conditioning system based on delay time

Radiant air conditioning (RAC) systems are widely used because of the advantage of higher thermal comfort compared to convection systems. However, RAC systems exhibit considerable hysteresis and significant time delays in heat transmission from the terminal to the interior environment. Traditional feedback control methods do not adequately account for the system's delay impact while implementing dynamic control, resulting in a mismatch between supply and demand loads in time series, an inefficient impact of interior temperature control, and energy waste. According to this study, the time-delay characteristics of the RAC system are quantified by the startup-process delay time (SPDT) and operating-phase integrated delay time (IDT). The system startup time is set by the SPDT. Based on the IDT, the prediction interval of the model predictive control (MPC) and the step time of rolling optimization are determined. On this basis, a short-term forecasting model of air conditioning operating load and the regulation model of the system using MPC are established and verified by comparing with the conventional rule-based control of constant water temperature (CRBC) and proportionally-integral-differential (PID) control. The results for the RAC system with a large time delay indicate that the stability of indoor temperature under MPC controlling is 18.8% higher than the PID control and 63.5% higher than the CRBC method. Also, the indoor temperature controlled by the MPC is closest to the set value and shows the minimum fluctuation. Furthermore, the overall energy consumption of the system is estimated for reducing by 14.89% in comparison with the CRBC and by 8.51% in comparison with the PID.

Experimental study of condensation characteristics and operation strategies of induction radiant air-conditioning system

To study the operation and condensation characteristics of an induction radiant air-conditioning system as a novel system that combines induction ventilation and radiant air conditioning, the characteristics of convection and condensation of an indoor terminal device radiant induction unit were studied. The mass transfer coefficient, condensation temperature, and condensation rate were analyzed experimentally. The time required to achieve a steady state indoor thermal environment was collected. The results indicated that the primary airflow rate and temperature mainly affected the mass transfer coefficient, condensation temperature, and condensation rate. When the indoor thermal environment reached a steady state, the heat transfer performance of the radiant induction unit was mainly affected by the primary air temperature. When condensation occurred, the primary airflow rate had a greater influence on the condensation rate. The start-up and response performances of the system were better than those of a traditional radiant air-conditioning system. In the condensation condition, reasonable control strategies maintain the primary air temperature and adjust the primary air flow rate, which can ensure sufficient heat transfer and stabilize the indoor thermal environment faster.

A New Type of Air Conditioning System Based on Finned Ceiling Radiant Coupled with Independent Fresh Air and Its Thermal Comfort Experimental Study.

The traditional radiation air conditioning system has some problems, such as easy condensation, insufficient refrigeration capacity, complex structure, and control system. Therefore, this study proposes a new type of finned metal radiant plate with large heat flow per unit area, sufficient cooling capacity, and simplified heat exchange system, in order to realize large temperature difference between cooling and heating. The temperature field uniformity and thermal comfort test of a novel type of finned ceiling radiant panel and independent fresh air linked air conditioning system under summer cooling and winter heating circumstances are accomplished through artificially generated climate environments. The study's findings demonstrate that in the radiation and fresh air modes, the maximum interior temperature differential under cooling conditions does not rise over 2.1°C. The maximum temperature differential in the space at any one moment in the radiation and fresh air modes cannot be greater than 3°C when heating conditions are present. The fresh air's cooling and dehumidifying effects are clear. The dehumidification efficiency may reach 50%, and the moisture content ranges from 5.48 to 9.63 g/kg. With PMV ranging from −0.34 to 0.54, the enhanced air conditioning system in this research provides exceptionally good thermal comfort. Additionally, the finned radiant panel's installation area occupies just 14% of the ceiling, which is sufficient to fulfill the room's cooling and heating load needs as well as provide high thermal comfort and consistent indoor temperature. The theoretical investigation and practical implementation of the direct expansion radiant air conditioning system are both strongly supported by this research.

Research on the Influence of Ventilation Mode on the Condensation Risk at the Wall Radiant Terminal

The separate control of indoor heat and humidity in radiant air conditioning has more energy-saving advantages than convection air conditioning that use the same cold source to handle heat and humidity loads, which is in line with the international trend of carbon reduction and emission reduction. However, the surface of the radiation terminal is prone to condensation, which poses a health and safety hazard. In order to reduce the risk of condensation at the wall radiant terminal, this paper uses CFD to study the effect of ventilation mode on the risk of condensation at the wall radiant terminal, and evaluates the risk of condensation by using the term of the minimum supercooling condensation temperature. The simulation results show that the thermal boundary layer on the surface of the radiant terminal under different ventilation velocity is different, which affects the minimum supercooling condensation temperature, and makes the condensation risk of the radiant air conditioning system different. When the wind speed of the attached jet is 1.07 m/s, the thickness of the thermal boundary layer is 0.045 m, and the minimum supercooling condensation temperature at the radiation terminal is 1.79 K. By further increasing the wind speed and reducing the thickness of the thermal boundary layer, the minimum supercooling condensation temperature can be further increased to 2.2 K, reducing the risk of condensation.

Numerical simulation study on thermal performance of sub-tropical double-layer energy storage floor combined with ceiling energy storage radiant air conditioning

In view of the high energy consumption of heating and air conditioning in buildings, the study takes the unit radiation plate filled with Phase Change Material (PCM) as the research object, and proposes an energy storage scheme combining double-layer energy storage floor with ceiling-mounted energy storage radiant panel air conditioning to improve the utilization rate of valley electricity. Numerical simulation method is used to simulate the phase change heat transfer process, and the heat transfer characteristics of the phase change energy storage radiant air conditioning system under different ambient temperatures and indoor heat fluxes are studied. The results show that the floor surface can maintain a warm surface of 24–18 °C in the heat storage environment of 19 °C and the heat release environment of 12 °C in winter. And the floor surface can maintain a cool surface of 19–24 °C, and the radiant panel surface can maintain a cool surface of 18–23 °C in the cold storage environment of 26 °C and the cold release environment of 32 °C in summer. The system can not only meet the requirements of indoor heating and ventilation, but also alleviate the uncomfortable problem of rapid temperature change of radiant panel, and effectively solve the dewing problem of radiant panel.

Investigation of physiological and subjective responses under composite air carrying energy radiant air-conditioning system

Air carrying energy radiant air-conditioning system (ACERS) as a new radiant air conditioning system has shown its important alternative technology to achieve current sustainable cooling/heating requirements. This study aims to further investigate the occupants’ physiological and subjective responses under the ceiling-sidewall composite ACERS. An experiment of the climate chamber installed with the composite ACERS was conducted under different thermal conditions. The results show that the composite ACERS can create a comfortable thermal environment , when the operative temperature varies between 23 °C and 30 °C. Physiological parameters , including blood oxygen saturation (SpO 2 ), pulse rate and skin temperature (local and overall) are measured to explore their relationship with operative temperature and thermal sensation. Statistical analysis demonstrates that SpO 2 and pulse rate are not sensitive to the operative temperature, while the skin temperature is linearly related to the operative temperature. Also, these three physiological parameters both show significant difference in gender. Besides, it is found that the lowest temperature body part is the lower arm, but the hand is the most sensitive segment to the operative temperature, followed by the anterior calf and lower arm. Besides, the calculated comfortable temperature range for 80% acceptability is about 23.74 °C–30.40 °C from TSV and 23.57 °C–27.67 °C from PMV, demonstrating the environmental adaptability of people in their long-term life and the energy-saving potential of the composite ACERS as well. The findings of the study can help HVAC engineers to better apply the composite ACERS and further recognize the human physiological responses to the environment. • Thermal environment of composite air carrying energy radiant system was measured. • Human subjective and physiological responses were considered. • Correlations of physiological parameters with operative temperature were analyzed. • Physiological responses of different body parts were compared.

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.

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.

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

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.

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.