Radiant Panel System Research Articles

Classification of radiant and convection time series for cooling load calculation of radiant cooling systems

Radiant cooling systems have the potential for energy saving, better thermal comfort, and space-saving. The lack of cooling load calculation methods limits the engineering application of radiant cooling systems. A universal radiant and convection time series (RCTS) set is indispensable in radiant cooling system design. In this study, an RCTS dataset with 100,000 sample rooms is generated based on the combinations of 9 room characteristic parameters. Extreme gradient boosting (XGBoost) is used to grade the room characteristic parameters and classify RCTSs. Gaussian mixture model (GMM) is used to extract the representative RCTSs for each category. The RMSE is used to measure the accuracy of the representative RCTS. The results indicate that XGBoost and GMM perform very well. Non-solar radiant time series (RTS), convection time series (CTS), solar RTS for radiant ceiling panel systems and solar RTS for radiant floor cooling systems are classified into 12, 8 and 1 categories, respectively. The representative RCTSs of all categories constitute a universal RCTS set. Fifteen room characteristic parameters are taken into account to construct sample rooms for Changsha. The accuracy of the representative RCTS was compared with the self-RCTS and heat balance method. The relative deviations of the design cooling load calculated using the representative RCTS and self-RCTSs were within ±3 % for 90 % cases of the sample rooms. The relative deviations between the design cooling load calculated using the representative RCTS, self-RCTSs, and theoretical design cooling load are within ±7 % for 90 % cases. The universal RCTSs set is applied for radiant cooling systems design.

Exploring the potential to mitigate airborne transmission risks with convective and radiant cooling systems in an office

Based on the recognized airborne infection risk, there is a raised demand to develop innovative ventilation systems to mitigate the airborne transmission risk indoors. This paper focused on two micro-environment ventilation systems, namely personalized ventilation combined with radiant panel system (PVRP) and a local low velocity unit combined with radiant panel system (LVRP) and studied the potential to minimize the airborne infection risk. The performance was compared with a typical mixing ventilation system, where supply air is released from a perforated duct. The droplet nuclei of an infected person were simulated with tracer gas (SF6) released by a thermal breathing manikin. The effect of the heat gain (38 W/m2 and 73 W/m2), breathing pattern of the infector (exhaled via the nose or mouth), desk partition wall, and air distribution methods on the infection risk were studied. The results show the infection risk of the exposed person is around 0.5 % with micro-environment systems (42 l/s) and 0.7% (61 l/s) with the perforated duct system when the occupants remain for 102 min in the space. The higher heat gain slightly increased the infection risk (from 0.71 % to 0.81 %) with the LVRP system, but it did not have an effect with the PVRP system. The desk partition wall could reduce the infection risk only to an extent. The breathing patterns of the infector do not have any influence on the infection risk for the three studied air distribution methods.

A novel cooling capacity prediction model for open-type cooling radiant ceiling

Open-type cooling radiant ceiling panel systems (O-CRCP) have a higher cooling capacity, but their cooling capacity can only be calculated roughly according to the model of the closed-type cooling radiant ceiling panel systems (C-CRCP), which may cause economic and energy waste. This study aims to develop a novel cooling capacity prediction model for O-CRCP considering the impact of panel size, layout, and installation position. The experimental results revealed that the heat flux of the O-CRCP was 49%–64% greater than that of the C-CRCP. A detailed analysis of the simulation results shows that the natural convective heat transfer is the main factor for the cooling capacity enhancement which basically determines the trend of the total heat flux varying with various factors. Based on the simulation results, a novel cooling capacity prediction model for O-CRCP was developed using a multi-regression method. It was evaluated in an actual room with O-CRCP, and the predicted cooling capacity curve showed good agreement with the measured values, the relative error ranged from 5.78% to 9.72% with an average of 7.47%, which is acceptable for engineering applications. The proposed model can provide support and guidance for designers and engineers in selecting and arranging O-CRCP in real applications.

The design of solar power thermoelectric radiant panel as cooling system in small buildings under tropical climate

The usage of an air–conditioning (AC) system in any building is necessary to maintain its indoor thermal comfort and health. However, this system consumes a lot of energy, while the usage of refrigerant causes irreversible damage to the ozone layer. To solve this problem, a solar thermoelectric radiant panel (PV-TERP) system has a high potential in replacing conventional AC system because it requires no refrigerant and easier to be controlled due to the absence of moving and mechanical parts such as water pumps, compressors, including auxiliary and hydronic pipes. Meanwhile, the usage of solar energy in the PV-TERP system can also help reduce fossil energy consumption and carbon emissions. The main objective of this work is to design a new PV-TERP system for replacing conventional AC systems in buildings located in tropical climate countries, like Malaysia. It is found that the designed PV-TERP system can provide up to 4.84 kW of cooling power, which is about 0.6% higher than the cooling load of targeted rooms. Here, the targeted rooms operate under indoor parameters within the acceptable range of ASHRAE standard-55. The obtained results clearly show that the new design is applicable to be used as a cooling system for the targeted building. In the future, it is then essential to understand the thermal properties and mechanism of the design via simulation process, followed by experimental validation to support the design feasibility. In conclusion, this new design of PV-TERP will lead the path toward expanding renewable energy applications for cooling purposes in sustaining and preserving the environment. HIGHLIGHTS Alternative cooling system in replacing air-conditioning (AC) system for maintaining indoor thermal comfort without harming the environment. Designation of the PV-TERP system as a cooling system for building in a tropical country (Malaysia) under indoor parameters within the acceptable range of ASHRAE Standard-55. The designed PV-TERP is refrigerant-free and operates using renewable energy, which can sustain and preserve the environment for a better future. GRAPHICAL ABSTRACT

All-air vs. Radiant Cooling Systems: Analysis of Design and Operation Factors that Impact Building Cooling Loads (ASHRAE RP 1729)

ABSTRACT When compared to all-air systems, radiant cooling systems can improve chiller efficiency by using a higher refrigerant evaporation temperature. However, the details on differences in heat transfer and building cooling load between all-air and radiant systems are not well defined. This study uses experimental data and numerical modeling to examine the dynamics of cooling load and overall heat transfer for both radiant panel and all-air systems under various operating conditions. This study investigates the effect of: (a) heat gains (transmitted solar, internal radiative, convective), (b) set-point temperature control (air vs operative), (c) building thermal mass, (d) air circulation and surface convection, (e) panel surface area, (f) radiant system configuration (ceiling vs floor panels), and (g) intermittent system operation on the space cooling load of radiant cooling panels. Results show that for the same set-point air temperature radiant systems have slightly larger peak load than an all-air system regardless of dominant heat gain type. When considering set-point, control by operative temperature provides better performance for radiant systems. When air mixing and convection are enhanced, radiant panels allow for operational cost savings for space cooling as well as shifting building peak load to off-peak hours.

Exploring the potentials of micro-environment ventilation in mitigating airborne transmission risk

In the background of COVID-19, new requirements are occurring in the novel ventilation systems to mitigate airborne transmission risk in indoor environments. In this study, two micro-environment ventilation systems: personalized ventilation combined with radiant panel system (PVRP) and low velocity unit combined with radiant panel system (LVRP) were studied to explore the potential of reducing the airborne infection risk. In a simulated double layout office, the droplets generated by a thermal breathing manikin were used to simulate the breathing process of an infected person. Opposite the manikin, a heated dummy was as an exposed person. During the 102-minute measurement, the results show that the infection risk at the inhaled air with micro-environment systems is lowest. The heat gain levels do have much effect on infection risk with the PVRP system, but higher heat gain will increase the risk slightly with the LVRP system.

Comparative Modelling Analysis of Air Pollutants, PM2.5 and Energy Efficiency Using Three Ventilation Strategies in a High-Rise Building: A Case Study in Suzhou, China

This study investigated the ventilation efficiency and energy performance of three ventilation strategies—an all-air system (AAS), a radiant panel system with a displacement ventilation system (DPS), and a radiant panel system with a decentralized ventilation system (DVS). The research analyzed the indoor air quality (IAQ) in a high-rise building based on the building’s height, the air handling unit (AHU) location, air infiltration rate, outdoor air pollution rate, seasonal change, and air filter efficiency. The results indicated that the AAS had the best performance in terms of IAQ in the high-rise building in winter; however, the AAS also had the highest annual energy demand. For the same conditions, the DVS consumed less energy but had the worst performance in maintaining a satisfactory IAQ. Considering energy consumption, it is worth developing the DVS further to improve ventilation performance. By applying a double-filter system on the lower floors in a high-rise building, the DVS’s ventilation performance was dramatically improved while at the same time consuming less energy than the original DPS and AAS. The application of DVS can also minimize the negative effect of the infiltration rate on indoor air quality (IAQ) in a building, which means that the DVS can better maintain IAQ within a healthy range for a more extended period. Moreover, it was found that the DVS still had a substantial potential for saving energy during the season when the outdoor air was relatively clean. Hence, it is highly recommended that the DVS is used in high-rise buildings.

Human response to thermal environment and perceived air quality in an office with individually controlled convective and radiant cooling systems

The purpose of this study is to analyze the human response to the indoor climate with two individually controlled convective and radiant cooling systems: a low velocity unit combined with radiant panel system (LVRP) and a personalized ventilation system combined with a radiant panel system (PVRP). As a reference system without individual control, diffuse ceiling ventilation combined with a radiant panel system (DCV-RP) was also studied. In laboratory conditions, 10 males and 10 females gave subjective response to the indoor climate during various office activities. The indoor parameters and CO2 concentrations were measured. The results show that with the reference DCV-RP system, the indoor conditions were worse than with the LVRP and PVRP systems. The thermal sensation and perceived air quality with the PVRP system was better than the LVRP system. After a medium activity task, the thermal acceptability reverts faster with the PVRP than LVRP system. Both the LVRP and PVRP systems were able to create a micro-environment around the workstations and the CO2 concentrations near the workstation were slightly lower than at the exhaust grille. Compared with the PVRP system, the subjects preferred the higher airflow rate at the workstation with the LVRP system. Males preferred a higher airflow rate than females under the same conditions with both micro-environment systems. This research found that there was significant variation in the control preferences of the human subjects concerning the micro-environment, and this emphasizes the need for personalized control to ensure that all occupants are satisfied with the indoor conditions.

Human response to thermal environment and perceived air quality in an office room with individually controlled convective and radiant cooling systems

The purpose of this study is to analyse the human response to the indoor climate with two individually controlled convective and radiant cooling systems: a low velocity unit combined with radiant panel system (LVRP) and a personalized ventilation system combined with a radiant panel system (PVRP). As a reference system without individual control, diffuse ceiling ventilation combined with a radiant panel system (DCV-RP) was also studied. In laboratory conditions, 10 males and 10 females gave subjective response to the indoor climate during various office activities. The results show that with the reference DCV-RP system, the indoor conditions were worse than with the LVRP and PVRP systems. The thermal sensation and perceived air quality with the PVRP system was better than the LVRP system. After a medium activity task, the thermal acceptability reverts faster with the PVRP than LVRP system. Compared with the PVRP system, the subjects preferred the higher airflow rate at the workstation with the LVRP system. Males preferred a higher airflow rate than females under the same conditions with both micro-environment systems. This research found that there was significant variation in the control preferences of the human subjects concerning the micro-environment, and this emphasizes the need for personalized control to ensure that all occupants are satisfied with the indoor conditions.

CFD Analysis of the Effect of Emissivity Change on Indoor Thermal Comfort

Not only air temperature and humidity, but also radiant temperature affects indoor thermal comfort. Therefore, radiant heat transfer should be considered in computational fluid dynamic (CFD) simulation. In this paper, thermal environment in a room equipped with cooling radiant ceiling panel (CRCP) system was estimated by radiation-coupled CFD. In order to introduce radiant heat transfer into CFD, the distribution factor was used. Two calculation cases with different emissivity were evaluated using the predicted mean vote (PMV), a measure of thermal comfort. Case of this paper, the value of PMV increases by 1.19 in the case of emissivity of 1.0 compared to the case of emissivity of 0.9. Therefore, it is important to properly consider the effect of emissivity when evaluating thermal comfort by CFD simulation.

Analytical modeling of a radiant cooling system for thermal performance analysis

The aim of this paper is to investigate the energetic and exergic performance of the close loop radiant cooling panel system using mathematical modeling. In this study, efforts have been made to determine the COP, cooling capacity and second law efficiency of radiant panel at different operating parameters. Based on results, it is found that mass flow rate of heat carrying fluid plays a major role as compared to plate thickness and pipe thermal conductivity in the thermal performance radiant panel system. The increase in mass flow rate of circulating fluid from 0.01 kg/s to 0.04 kg/s leads to increase the cooling capacity of the radiant panel around 20.9%. Whereas the reduction in inlet temperature of 22% increases the rate of heat transfer to around 62% and the maximum COP is observed as 2.26 at 0.01 kg/s. Further, COP of the panel is found to increase with the increase in plate thickness and with the increase in inlet fluid temperature the exergy of the panel reduces.

Experimental Data and Simulations of Performance and Thermal Comfort in a Patient Room Equipped with Radiant Ceiling Panels

Hospitals require the highest energy demands in non-residential buildings. They provide healthcare 24/7/365 and, at the same time, they ensure indoor air quality, thermal comfort and sterility. However, several studies reveal that high indoor temperatures and low relative humidity (RH) are often perceived in patient rooms during the heating season, suggesting an important energy saving potential. Against this background, radiant ceiling panel (RCP) systems result to be one of the most appropriate solutions as they allow to achieve significant energy savings while providing the highest level of thermal and acoustic comfort, as well as of infection control. In the present study the microclimatic survey of a patient room at Maggiore Hospital in Bologna, Italy, equipped with an air conditioning system integrated with RCP, has reported occupant thermal discomfort. Experimental data were used to calibrate a building model and dynamic building energy simulations were carried out to analyse indoor air temperature, relative humidity, predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD) indexes under different inlet air temperatures, to identify the best design conditions for energy efficiency and thermal comfort improvement. It was found that the highest advantages can be obtained when neutral air is supplied.

A radiant and convective time series method for cooling load calculation of radiant ceiling panel system

Traditional cooling load calculation theory and methods are based on the assumption that the room heat gains were only removed through convection by all-air systems. Studies have shown that they were not suitable for radiant systems that remove room heat gains through both radiation and convection. This study defined radiant and convective time series (RTS and CTS) factors to quantify the cooling load conversion process for radiant ceiling panel (RCP) system. The RTS and CTS factors were verified to follow the linear superposition principle, and on this basis, a radiant and convective time series (RCTS) method was proposed. To evaluate its accuracy, a parametric simulation of 34992 cases for rooms with only RCP was firstly performed, we found the relative errors of the peak cooling load for all the cases are within 10% compared to heat balance method, and more than 90% of the cases have no peak load occurring time difference. In addition, the RCTS method was also found to have good accuracy for integrated operation of RCP and dedicated outdoor air system (DOAS). Finally, a new cooling load calculation procedure based on RCTS method was proposed.

Study on dynamic thermal characteristics of thermoelectric radiant cooling panel system through a hybrid method

Thermoelectric radiant panel system (TERP), requires no hydronic pipes, pumps and chillers and the size is compact in solid form. In this study, the main results include a new system model of TERP and some new findings on the system dynamic characteristics. The new model integrates finite difference method and state-space matrix, which is an integration of great simulation accuracy, high speed, and easy implementation. The thermal response time (TRT) and its asynchronism are confirmed and a new concept of AM (Asynchronism Magnitude) is defined to measure the degree of TRT asynchronism. Some new observations are obtained: (1) Under a certain environment, AM becomes a constant even when different step changes of current are imposed; (2) The TRT asynchronism disappeared at the second stage when environmental condition is step changed. Three new definitions of TRT are proposed and compared. Finally, in order to realize the fast and accurate prediction of TRT for the use of system on-line control or fast evaluation under dynamic state, an artificial neural network-based model is proved to be effective. The dynamic analysis can offer a new paradigm to the evaluation, control and optimization of radiant cooling and other dynamic systems.

Experimental comparison of local low velocity unit combined with radiant panel and diffuse ceiling ventilation systems

In this study, the performance of a micro-environment system was analysed and compared with diffused ceiling ventilation. In the analysed micro-environment low velocity radiant panel system, two low velocity units and radiant panels were installed above workstations to supply directly clean air to occupants and to cover the cooling power required. With diffused ceiling ventilation, all cooling demand is covered with air and thus, the airflow rate required is higher than with low velocity radiant panel system. The varied heat gain from 40 to 80 W/m2 consists of two seated dummies, laptops, monitors and simulated solar gain. The results show that with perimeter exhaust and local supply air, 8–13% reduction of the total cooling load required is possible, in comparison to the standard mixing systems. The average exhaust temperature was 0.7–1.9°C higher than average room air temperature at the workstation. Moreover, the mean air temperature with the low velocity radiant panel system at the occupied zone was 0.6°C lower than with diffused ceiling ventilation. With low velocity radiant panel system, the air velocity was less than 0.12 m/s in the occupied zone. Also, the draught rate was less than 10%. Furthermore, the air change efficiency with the low velocity radiant panel system was over 70% which is better than 44–49% efficiency with diffused ceiling ventilation.

A computational model of an improved cooling radiant ceiling panel system for optimization and design

Radiant cooling system comes to the foreground recently due to its improved thermal comfort and energy saving potential. However, surface condensation is still an unsolved problem and hinders the application of radiant cooling systems especially in hot and humid areas. An inside air layer was introduced to the improved cooling radiant ceiling panel (CRCP) system to achieve uniform temperature distribution on panel surface and reduce water condensation risk. A computational model for heat transfer analysis of the improved CRCP system was established and verified with experiment. The effects of the thickness of aluminum sheets, cooling panels and air layer, as well as the diameter and spacing of copper pipes on cooling capacity of the new system are studied. It is shown that the cooling capacity increases with thicker aluminum sheet and thicker radiant panel but thinner air layer. A thickness of 4.0–5.0 mm for the cooling panels is recommended to achieve a uniform surface temperature distribution according to numerical simulations. Besides, copper pipes with small diameter and thin plastic join are both beneficial to system performance. This study also provides a method to evaluate the maximum temperature difference and lowest surface temperature of the whole cooling panel, as well as a simple design chart for the improved CRCP system. Moreover, it is feasible to enhance the flow disturbance in air layer to improve heat transfer between the aluminum sheets and cooling panels, which can contribute to the savings of initial investment by using less pipe materials in CRCP.

Enhancement of cooling capacity through open-type installation of cooling radiant ceiling panel systems

Cooling radiant ceiling panel (CRCP) systems have been increasingly applied to modern buildings, owing to high thermal comfort, energy-saving potential, and integration with building design. Currently, the cooling capacity of CRCP is generally evaluated for the closed-type CRCP, wherein the overall ceiling surface is covered with ceiling panels. However, there have been few previous studies on the evaluation of the cooling capacity for open-type CRCP, which are installed with openings (void areas) between adjacent ceiling panels. This study was conducted to verify the hypothesis that the open-type CRCP can enhance cooling capacity by utilizing the cooled plenum air moving through the opening. If the plenum air is cooled by the upper surface of ceiling panels and descends to the conditioned space, it can contribute to increasing the convective heat transfer and cooling capacity. A simulation model for open-type CRCP was developed and validated against the mock-up experiment. Using the simulation model, the cooling capacity of the open-type CRCP was evaluated with respect to the opening area and panel layout. The results showed that the open-type CRCP could provide 54–80% (average 64%) higher nominal cooling capacity than conventional closed-type CRCP. The enhanced cooling capacity may lead to reduction in construction costs and energy consumption, because panel installation area could be reduced and the water temperature can be increased to provide the required cooling capacity. The results of this study would be able to offer fundamental data about cooling capacity of open-type CRCP.

Response of stone wool–insulated building barriers under severe heating exposures

This article presents the experimental results of stone wool–layered sandwich constructions, with either steel or gypsum claddings, tested under four different heating exposures: 7 kW/m2 incident radiant heat flux exposure, 60 kW/m2 incident radiant heat flux exposure, parametric time–temperature curve exposure and ISO 834 standard time–temperature exposure. The test apparatus used were a movable radiant panel system, a mid-scale furnace (1.5 m3) and a large-scale furnace (15 m3). The results show that reduced-scale tests are capable of reproducing the heat transferred through the construction at large scale provided there is limited mechanical degradation. The results indicate that the availability of oxygen is fundamental to the fire behaviour of the sandwich composites tested. Reactions occurring in stone wool micro-scale testing, such as oxidative combustion of the binder or crystallisation of the fibres, have a limited effect on the temperature increase when wool is protected from air entrainment.

Energy analysis of a hybrid radiant cooling system under hot and humid climates: A case study at Shanghai in China

A conventional radiant panel system offers advantages in terms of energy savings; however, compared with an all-air system, it has limitations such as moisture condensation risk, slow air movement, difficult space zoning, slow air pollutants removal from a highly polluted room, and time delay in start-up of the radiant panel system. This research performs an energy consumption analysis of a hybrid radiant cooling system for buildings in summer. The hybrid radiant cooling system combines a typical radiant panel with a decentralized air convector connected in series. The hybrid radiant panel system generates additional cooling output through its air convector, dehumidifies indoor air, increases indoor air movements, and reduces the time delay in start-up and a filter in the air convector removes air pollutants. This study exhibits the energy performance of the hybrid radiant cooling system compared with an all air system and a typical radiant panel system via numerical modeling using experimental data. This hybrid radiant panel system is effective for energy-saving, because it has a higher cooling impact ratio, and larger coefficient of performance of the chiller, and because the air movement increases the offset effect of the operation indoor temperature rise by an enhanced mixed convection effect. Thus it can reduce cooling energy consumption. The hybrid radiant cooling system can be used very effectively for saving energy in the summer season.

Experimentally-determined characteristics of radiant systems for office buildings

Radiant heating and cooling systems have significant energy-saving potential and are gaining popularity in commercial buildings. The main aim of the experimental study reported here was to characterize the behavior of radiant cooling systems in a typical office environment, including the effect of ceiling fans on stratification, the variation in comfort conditions from perimeter to core, control on operative temperature vs. air temperature and the effect of carpet on cooling capacity. The goal was to limit both the first cost and the perceived risk associated with such systems. Two types of radiant systems, the radiant ceiling panel (RCP) system and the radiant slab (RS) system, were investigated. The experiments were carried out in one of the test cells that constitute the FLEXLAB test facility at the Lawrence Berkeley National Laboratory in March and April 2016. In total, ten test cases (five for RCP and five for RS) were performed, covering a range of operational conditions. In cooling mode, the air temperature stratification is relatively small in the RCP, with a maximum value of 1.6 K. The observed stratification effect was significantly greater in the RS, twice as much as that in the RCP. The maximum increase in dry bulb temperature in the perimeter zone due to solar radiation was 1.2 K for RCP and 0.9 K for RS – too small to have a significant impact on thermal comfort. The use of ceiling fans was able to reduce any excess stratification and provide better indoor comfort, if required. The use of thin carpet requires a 1 K lower supply chilled water temperature to compensate for the added thermal resistance, somewhat reducing the opportunities for water-side free cooling and increasing the risk of condensation. In both systems, the difference between the room operative temperature and the room air temperature is small when the cooling loads are met by the radiant systems. This makes it possible to use the air temperature to control the radiant systems in lieu of the operative temperature, reducing both first cost and maintenance costs.