Radiant Air Conditioning Research Articles

The Impact of Radiant Air-conditioning on Sleep Quality: A Mini-Review

Sleep is a vital aspect of human health, influencing both physical and mental well-being. Environmental factors, particularly indoor temperature, play a crucial role in determining sleep quality. Traditional cooling systems, while effective in temperature control, often create uneven cooling and noise, which can disrupt sleep. Radiant air-conditioning systems, which cool rooms through radiation without the use of fans, have emerged as a promising alternative for improving sleep quality. This mini-review discusses the effects of radiant air-conditioning on sleep quality, comparing it with traditional air-conditioning systems. The review highlights research findings that suggest radiant cooling promotes sleep by regulating body temperature, reducing stress, and minimizing noise disturbances. Studies indicate that individuals sleeping in rooms cooled by radiant systems experience better sleep quality, longer sleep duration, and fewer insomnia symptoms. The mechanisms underlying these benefits include the activation of the parasympathetic nervous system, improved thermoregulation, and a more stable thermal environment. Despite these advantages, most studies have been conducted in controlled environments, raising concerns about the applicability of these findings in real-world settings. Furthermore, research has largely focused on adults, leaving gaps in understanding how radiant air-conditioning affects other populations. Future studies should address these limitations by evaluating the performance of radiant cooling in various residential settings and across different age groups. Expanding research in this area could pave the way for more energy-efficient and sleep-promoting indoor climate solutions.

Earth's Long-Wave Infrared: Review and Study of Scalable Applications

The Earth's infrared energy storage is substantial, and its large-scale utilization could effectively ameliorate the greenhouse effect on Earth. Several applications of utilizing Earth's infrared radiation for cooling and power generation are summarized based on existing literature. Building upon this foundation, the use of water as an excellent energy storage medium is proposed, and a long-wave energy storage system is designed. This system can harness the immense energy density of long-wave infrared radiation with fixed bandwidth or wavelength. A comprehensive study on large-scale application is outlined in four aspects, leveraging the energy storage and radiation advantages of the system: (a) Long-wave infrared is efficiently transported using hollow glass infrared fibers for room cooling and heating. This addresses the issues of separate terminals for capillary radiation air conditioning, high costs, and maintenance challenges. (b) Building on existing literature, taking Hainan as an example, the utilization of a temperature difference of approximately 15 °C between the lowest and highest temperatures in a day for power generation is suggested. (c) The composition and structure of planar antennas are derived, and parameter selection for rectifying diodes is proposed based on radiation fluctuation theory and antenna theory. This lays a theoretical and practical foundation for converting long-wave radiation waves using rectifying antennas. (d) The long-wave radiation quantum theory is utilized to propose the concept of manufacturing components that can directly convert energy from long-wave radiation. In each of these four aspects of large-scale utilization, the emphasis is on water's excellent insulation, storage, and radiation properties, presenting new perspectives for the widespread utilization of Earth's infrared and offering a quick pathway for humanity to explore new energy sources and mitigate the greenhouse effect on Earth, facilitating a harmonious coexistence between humans and nature.

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.

Energy simulation and CFD coupled analysis for the optimal operation of combined convection and radiant air conditioning considering dehumidification

The use of radiant panels in homes has increased recently because they do not cause a drafty feeling, unlike air conditioners. However, air conditioners are more power-efficient than radiant panels and have a higher coefficient of performance (COP). Therefore, combining radiant panels and air conditioning can provide an optimal solution for thermal control in residences. Energy simulation (ES) and computational fluid dynamics (CFD) can be used to simulate such environments. ES is suitable for non-steady state calculations, and combined with appropriate modeling, enables an accurate estimation of power consumption. Effective dehumidification becomes necessary, during summer as the relative humidity in a room increases. Both air conditioners and radiant panels can achieve this. This study developed a simulation tool that incorporates the effects of dehumidification. Based on a relative evaluation, a case was proposed where both energy efficiency and comfort were satisfied by jointly using air conditioners and radiant panels. The study found that a small number of panels could achieve the most balanced operation. The results of this study can serve as a reference for general housing, and the developed simulation tool can be applied to product development and building material design.

Cooling performance of radiant air conditioning with an infrared-transparent membrane

Cooling performance of radiant air conditioning with an infrared-transparent membrane

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.

Operation characteristics of radiant air conditioning with an infrared-transparent membrane

A model for radiant air conditioning with an infrared-transparent membrane has been developed to address the problems of the risk of condensation on the surface of the radiant cooling plate and the limitation of the cooling capacity by the indoor dew point temperature. The condensation and cooling characteristics of two types of radiant air conditioning were compared and analyzed by numerical simulation. The effects of different water supply temperatures, water supply velocities, and indoor relative humidities on the cooling and condensation characteristics of radiant air conditioning with an infrared-transparent membrane were investigated. For every 1 °C decrease in the water supply temperature, the cooling capacity increased by 8.92 W/m2 and the surface temperature of the infrared-transparent membrane decreased by 0.47 °C, and the water supply velocity was optimal. In addition, under indoor relative humidity conditions of less than 70 %, there was no condensation risk for radiant air conditioning.

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.

Сольовий плав як визначальний чинник розвитку системи кондиціонування рідких радіоактивних відходів

The dynamics of annual generation of liquid and solid radioactive waste at Ukrainian nuclear power plants (NPPs) with WWER reactors standardized for electricity production is considered. It is established that in the last ten years the indicators of specific generation of radioactive waste do not show significant variations. The conclusion is made that the possibilities of implementing organizational and technical measures at the NPP in order to minimize the generation of radioactive waste have been exhausted. Further operation of WWER reactors will lead to a fairly stable level of radwaste generation, which provides grounds for forecasting the volume of their accumulation, planning and implementation of appropriate measures for their conditioning with subsequent transfer to landfill. Thus, the main goal of solid radioactive waste management at existing NPPs of Ukraine should be to create efficient solid radiant air conditioning lines using reference technologies. It is noted that the amendments to national regulations on the classification of radioactive waste and the assignment of salt melt to solid radioactive waste mean the abolition of the requirements for additional conditioning for the transfer of salt melt for disposal. In turn, this gives grounds for creating a simple, reliable and cost-effective technology for processing the bulk of liquid radioactive waste from nuclear power plants with WWER reactors in a safe form suitable for disposal. This technology involves the maximum use of waste processing equipment, which is already available at NPP sites, by processing all already accumulated and formed in the future evaporator bottoms to the state of salt melt. As a result, a package for radwaste disposal will be formed as a part of a protective container, four KRO-200 containers with salt melt with void-filled geopolymer, which is quite acceptable in terms of radiation protection properties.

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.

Development of a non-stationary thermal environment analysis method for combined convection and radiation air conditioning

Advanced thermal environment simulation technology has been developing rapidly in recent years. The thermal environment simulation tools used in thermal engineering can be broadly classified into energy simulations and computational fluid dynamics programs. The combination of these approaches allows the high-accuracy prediction of a non-stationary thermal environment in a continuous space. The main feature of the coupled analysis method is that the radiation is calculated using energy simulation, which reduces the analysis load and makes transient analysis possible. Here, a method was devised for predicting the thermal environment of air conditioners and radiant panels, and its accuracy was verified. By coupling the convective heat transfer coefficient, the maximum mean absolute error of the proposed method was calculated to be 0.674 [-], which is acceptable considering the variable environmental conditions. Although in the acceptable range, this error is attributable to computational fluid dynamics, which is a steady-state analysis and does not fully track the non-stationarity of the radiant panel because of its stop–start nature. The results of this analysis are comprehensive, with the convective heat transfer coefficient calculated using the input conditions for each wall. Regarding the energy simulation, when temperature stratification occurred near a surface, such as the ceiling, a small error was induced because the reference temperature was set to the bulk temperature. However, as the overall trend was captured by the analysis method, these minor errors were deemed acceptable. These results show that the proposed method can be applied to a range of applications, including office spaces.

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.