Radiant Panel Research Articles

An experimental and numerical investigation on thermal performance of a new modified baseboard radiator

In this investigation the performance of a new modified skirting board heating system is analyzed. Two important aims have been pursued in this work. At the first in order to enhance thermal efficiency a new modified geometry of the baseboard radiator is designed and presented. Using of waving fins and change the cross-section of the fluid transfer are among the innovations of the new design. Experimental method based on the EN-442 is employed to measure the thermal efficiency of the new system. Also based on the obtained experimental data an equation for output heat rate is created by curve fitting. The proposed function can be used in heating calculations. In the next step thermal comfort conditions is studied. Fanger comfort model in the Design Builder software is used to predict the level of thermal comfort and also temperature distribution inside the building. Experimental results showed that thermal efficiency of the new modified baseboard radiator increased about 32% compared with the conventional model. Baseboard radiators due to the uniform distribution of heat in the space compared to the panel radiator, in addition to energy saving, also provides more thermal comfort conditions.

Study on the heat transfer performance of the ceiling radiant panel

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

Investigation the effectiveness of using heat pipe on the temperature uniformity distribution over the SC equipment panel

The heat pipe is a thermal device which allows an efficient transport of thermal energy. In this paper parametric study has been achieved to investigate the importance of using heat pipes about the uniformity of the temperature distribution over the equipment panel of the spacecraft (SC), which is a part of a real thermal control subsystem. Heat pipe analytical solution is used as a guide for design and geometrical parameters selection. The design of SC equipment panel radiator and a parametric study of the heat pipe are obtained numerically using Thermal desk top program (TDT). The space environment and the spacecraft operational conditions have been simulated by TDT program. Heat pipe prevents the hot spots which can be occurred due to the different equipment heat dissipation. The selected heat pipe design approach incorporates a conservative reliability philosophy and provides maximum operational flexibility.

Development of empirical models to predict cooling performance of a thermoelectric radiant panel

Performance simulations of thermoelectric radiant panels (TERPs) provide valuable information for the use of TERPs as alternatives to conventional hydraulic radiant panels, which require refrigerants based on the vapor compression cycle. Several existing models are appropriate for the design of the TERP; however, there are limitations to the building simulation with respect to the evaluation of the annual energy performance because existing models for TERP are based on the numerical method, therefore it is very complex to integrate with the building model. To overcome these limitations, simplified empirical models should be developed based on experimental data and then verified.This study aims to develop two simplified prediction models for the cooling capacity and energy consumption of TERPs. Using the 2k factorial experiment design method, a total of 16 experiment sets were designed according to the four main operation parameters: room temperature, outdoor air temperature, face velocity of air in duct, and combined heat transfer coefficient between room and panel surface. The developed models were designed in dimensionless forms to ensure broad applicability. The developed models yielded good R2 values exceeding 0.99 and were validated under additional operation conditions. Finally, the guidance of using the developed models and the performance tables of the TERPs was confirmed with respect to the use of TERPs in the construction of heating, ventilation, and air conditioning (HVAC) systems.

Dynamic variation of surface temperatures on the radiant ceiling cooling panel based on the different supply water temperature adjustments

Radiant ceiling cooling panels has been easily integrated with air system to reduce the building energy consumption, yet their surface is prone to condensation, restricting the application of such systems in hot and humid climate. In order to prevent surface condensation of the radiant ceiling panels, the dynamic temperature changes of radiant ceiling panel surface must be fully understood. In this paper, experiments are used to investigate radiant ceiling panel surface temperature changes. Experimental results are used to perform numerical simulations and a SAS (Statistical Analysis System) program via linear regression method, in order to study the effect of supply water temperature adjustments on the dynamic temperature changes of radiant ceiling panel surface. Results show that radiant ceiling panel surface temperatures change exponentially with water supply temperature changes when there is a danger of condensation on the radiant panel surface. When the water supply temperature rises, the surface temperature of the radiant ceiling panel increases, effectively preventing surface condensation occurrence and the variation of the supply water temperature has the greatest influence on the surface temperature of the radiant ceiling panel. When the supply water temperature is lowered, the indoor temperature has the greatest influence on the surface temperature of the radiant ceiling panel.

Constructal design of flow channels for radiant cooling panels

The main thrust of this study is to bring insight into the influence of the flow channels layouts on the global performance of suspended radiant cooling panels. The flow passages, set on the upper side of a metal plate, represent the crucial part of the panel. Water is conveyed to the panel via these channels to extract the heat flux absorbed by the underneath plate. Therefore, the distribution of the flow over the surface of panel is the key toward efficient panels design. Applying a Constructal approach, the objective of the present work, is to explore the thermal and hydraulic performances of radiant panels equipped with different flow architectures. Including the standard serpentine configuration, branching flow designs are investigated. The flow architectures are categorized into two groups according to the location of the inlet and outlet of the working fluid and further sub-categorized based on the flow arrangements. The influence of the Reynolds number is reported. It is concluded that the proposed Constructal flow structures have the potential of improving the overall efficiency of radiant panels in terms of temperature distribution, cooling capacity, and pumping power demand.

The dynamic effect of supply water flow regulation on surface temperature changes of radiant ceiling panel for cooling operation

Radiant ceiling cooling panels are limited in applications due to surface condensation. Surface temperature is a key factor affecting condensation problems, and supply water flow regulation is closely related to surface temperature fluctuation. In this paper, the dynamic change of surface temperature in regulating the supply water flow is investigated. It is found that when the chilled water supply is closed, the condensation on the radiant ceiling panel surface can be effectively prevented. Using simulation results and statistical analysis, the three main factors affecting the surface temperature for fixed supply water flow are determined as the average temperature of the non-cooling surface, the indoor air temperature, and the internal surface temperature of the outer window. The contribution rates of these factors are 47.6%, 39.2% and 10.1%, respectively. On the basis of this research, the dynamic changes of surface temperature of radiant ceilings for the closed water supply are simulated and verified, and the results are in agreement with the experimental results.

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.

Conditioning using ceramic floor panels with capillary tube mats and solar thermal panels on the Mediterranean coast: Energy savings and investment amortisation

Radiant floor conditioning installations that distribute water through PPR capillary tube mats bring about significant energy savings and high standards of comfort. Their design usually includes air-water heat pumps and fan-coil dehumidification. They also allow incorporating solar thermal panel energy. In summer mode, they can also be combined with absorption systems with lithium bromide, or solar cold based on lithium chloride. In this way, annual energy demand is further reduced by low water channel transport and reduced heat flows through the enclosures. This study focused on the application of large-format radiant floor thermal ceramic panels (TCP), with capillary tube mats, in the Museum of the University of Alicante (MUA). The water distribution system was made of two heat pumps combined with a solar thermal panel rooftop installation. Using thermal simulation tools, the MUA's annual energy demand was quantified over various scenarios. An energy saving of 24.91% was obtained compared to conventional all-air systems, and a 60.79% saving was obtained with the use of solar panels. User comfort levels and the energy consumptions of the various elements of the installation were also comparatively quantified. To finish, we calculated the investment amortisation periods for the TCP panels and solar panels.

Modal reduction for a problem of heat transfer with radiation in an enclosure

We propose an original method to reduce a radiation dominated heat transfer problem. To that end, the Amalgam Reduced Order Modal Model (AROMM) method, which preserves the integrity of the geometry, is coupled to the classical radiosity method. The treated application is a complex titanium piece heated by two radiant panels placed in a furnace. The AROMM method reduces by a factor 100 the computation time needed to obtain the solution, while keeping an average error below 0.1%. These very good performances open the way for control or identification procedure in a reasonable time for these kind of applications.

Parametric evaluation of a heat pipe-radiator assembly for nuclear space power systems

The research and technological development towards compact energy conversion systems for space applications allow the emergence of new mission possibilities, especially those directed for deep space explorations. Besides the final efficiency, the most crucial factor of an energy conversion system for nuclear propulsion purposes is the total mass and size of the system. Considering the Closed Brayton Cycle (CBC) as the energy conversion system for a nuclear power system, a numerical analysis was carried out in order to predict the thermal performance of cold side of the system (i.e., heat pipes and radiator) for initial design purposes. The complete space heat pipe-radiator array was discretized in control volumes where a variation of geometrical parameters was included, resulting in a stepped trapezoidal-shaped radiator (RAD) as output. The heat capacity was limited by the geometry of each panel section, being its heat pipe modeled to fit the given geometry and verified against operational limits. The proposed design-based model considered a physical and thermal coupling with temperature drops along the heat pipe (HP) axial direction, the radiator panel surface, and the cold heat exchanger duct, providing reasonable global parameters to aid the design considering mass and size optimization of a heat pipe-radiator assembly. The number of heat pipes and the total heat pipe-radiator assembly mass and length were evaluated for different heat pipe spacing, heat transfer rate, cold heat exchanger (CHE) inlet temperatures, and radiation shield shadow angles. It was observed a point of minimum HP-RAD mass and length when the heat pipe spacing and CHE inlet temperature are varied, for a given heat transfer rate and shadow angle.

Displacement ventilation with radiant panel for hospital wards: Measurement and prediction of the temperature and contaminant concentration profiles

Displacement ventilation (DV) is known to provide high air quality and ventilation efficiency. With DV, a contaminant interface is formed in a room, and the air quality in the occupant zone below the contaminant interface height can be kept clean. This paper proposes a DV system to solve the serious odor problem in hospital wards. A vertical radiant panel that can be controlled individually is suggested as a complementary heating system. In order to study the influence of the panel on the displacement ventilated room, the temperature and contaminant concentration profiles were examined under different panel conditions: the distance between the panel and bed, height of the panel, surface temperature of the panel, and supply airflow rate. When the radiant panel was heated, it created a stronger plume than the human body, which produced contaminated air. When there was space between the radiant panel and bed, the contaminated air was locked up before reaching the ceiling. Personal exposure of a standing person was also investigated because the contaminated interface is generally lower than the breathing zone of a standing person with DV. The zonal model and improved zonal model were validated by a comparison of their results with the measured contaminant concentrations.

Applicability and energy saving potential of thermoelectric radiant panels in high-speed train cabins

This paper proposes a dedicated outdoor air system (DOAS) with thermoelectric radiant panels (TERPs) for high-speed train cabins that prevents air quality problems and reduces operation energy consumption. The DOAS supplies cooled and dehumidified outdoor air for ventilation and the removal of latent loads. The cooling and heating loads can be accommodated using TERPs, which are suitable for use in train cabins owing to their simple structure. Moreover, the air flow at the exterior surface during train running can be used to remove rejected heat from the TERP. In this study, detailed energy simulations were conducted to evaluate the energy saving potential of the proposed system compared to the conventional variable air volume system. The results indicated that the proposed system can save 32.6% of the annual operation energy. In addition, the TERP system showed an annual COP exceeding 2.2 during 75% of its operational time.

Enhanced solar still condensation by using a radiative cooling system and phase change material

In this study, an experimental investigation of using the radiative cooling potential in a solar still was studied. Instead of using an auxiliary radiative panel, an integrated collector was utilized for both processes of absorption of solar radiations and emission of infrared radiations for radiative cooling. At night-time, the coldness was stored in the PCM inside the PCM-condenser. While during the day, the water was evaporated in an evaporation tank, the produced vapor was directed to the PCM-condenser and the air cooled-condenser. Different condenser configurations were tested to evaluate the effect of radiative cooling on daily yield and solar still efficiency. The lower temperature of PCM compared to the ambient air caused the condensation to start sooner. Therefore, the radiative cooling enhanced the condensation in the solar still and increased its daily yield by about 31.2%. The daily yield of the system was 2.139 kg/m2 without radiative cooling with an efficiency of 23.9%. Using the radiative cooling at night to store coldness in the PCM-condenser increased the daily yield and efficiency to 2.805 kg/m2 day and 30.7%, respectively. Because of the limited cooling capacity of radiative cooling, utilizing an air-condenser beside the PCM-condenser was necessary to condense all produced vapor.

Experimental investigation of flammability and numerical study of combustion of shrub of rockrose under severe drought conditions

Structure of vegetation significantly influences its flammability and resulting fire spread. Despite considerable amount of laboratory studies, experimental works carried out with full plant specimens, representative of field conditions, are still limited. Present study aims to collect meaningful experimental data on structure and flammability of shrub of rockrose and evaluate the predictions of a fire model (WFDS) against this dataset. Spatial distribution of fuel elements, sorted according to their characteristic thickness, was established from destructive measurements. 28 fire tests were conducted with full plants under a calorimeter. Foliar moisture content was in the range of 4–18% on dry basis. Radiant panels were used as source of ignition. Flammability was investigated using ignitability, sustainability, combustibility and consumability. Comparison to previous studies highlighted the necessity of standardization among test procedures. Principal component analysis revealed four flammability regimes depending on proportion of thin fuel elements within the crown, position of ignition and duration of preheating. Finally, combustion dynamics of a shrub was numerically investigated with WFDS. A bulk density model was developed from the characterization study and used as input data for the numerical code. Predicted HRR was in good agreement with experiments, although simulation results need improvement in initiation phase of burning.

Optimization of Distance Rings in Panel Radiators

The aim of this paper is to introduce the issue of distance rings in panel heating radiators, which are an integral part of their construction and which influence the flow of water in the radiators. A new way of meshing the simulation model in Ansys Meshing, including the boundary layer modelling, is described. In the simulation model it is possible to turn the distance ring and observe the effect in changes to the velocity and temperature fields. In addition, research into my own shape of the distance ring is described and whether there is a greater influence from a change in the geometry on the temperature field than just turning it. In the end of the contribution the results of a mathematical simulation of the heating radiator at low operating temperatures are discussed.

Thermoelectric Air-Conditioning System: Building Applications and Enhancement Techniques

The high reliability, the absence of working fluid and auxiliary pipes in the thermoelectric cooling application have attracted the attention of researchers in the last two decades. However, the use of thermoelectric air-conditioning system for building application has not been entirely explored due to its low coefficient of performance (COP) compared to the conventional air conditioning system. To overcome this primary limitation, different COP enhancement techniques of thermoelectric for air conditioning system building application are made available. This paper provides the recent development of thermoelectric air conditioning system in building applications, such as thermoelectric radiant panel ceiling, thermoelectric air duct system and thermoelectric cooling facades. It also provides the different strategies to enhance its performance in order to fit this technology in real building applications such as the integration of water-cooling system, phase change materials, evaporator cooling system and nanofluid micro-channel heat sinks. Lastly, the challenges of thermoelectric air-conditioning systems and future research directions are discussed.

Experimental investigation on the cooling performance of a novel grooved radiant panel filled with heat transfer liquid

Radiant ceiling cooling system is considered as a promising technique, which has huge potential to energy saving and suits for independent control of temperature and humidity. In this paper, a novel radiant panel was developed for cooling, which consists of top flat plate, bottom groove plate, and heat transfer liquid filling in the gap of two plates. A series of tests were conducted and results suggested that the cooling capacity of this radiant panel could reach at 93.5 W/m2 to 153.3 W/m2 in test condition, which was higher 18%～25% than that of traditional metal radiant panels. Besides, the maximum temperature difference on the surface of the novel radiant panel was <2.9 ℃ which is smaller than traditional one that is designed as cold-water tubes touching radiant plate directly without filled liquid. These advantages indicate that the radiant panel is suitable for hot and humid environment. The vertical temperature gradient of indoor air within staff activity area was 2.31–2.89 ℃ /m, meeting the requirements of ISO 7730. Moreover, the cooling performance of radiant panel can be changed when filled with different kinds of liquids, so that the radiant panel can be applied in different occasions and suitable for using in series.

Assessing the onset of swelling for thin intumescent coatings under a range of heating conditions

In the past decades, the steel industry has experienced a rapid growth in the use of intumescent coatings for protecting load-bearing steel structures in the event of a fire. The onset of swelling is key for assuring the effectiveness of thin intumescent coatings for providing thermal insulation to the steel substrate during fire. The study presented herein investigates the onset of swelling for a commercially available thin intumescent coating applied on steel plates and exposed to a wide range of heating conditions. Experiments were performed using an array of radiant panels for controlling incident radiant heat flux at the exposed surface of coated steel samples. Within the scope of this research study, the onset of swelling was defined based on two conditions: (1) visual observation of swelling during heating or (2) time-history of the steel temperature. Research outcomes derived from this work defined a threshold for the onset of swelling in terms of steel and coating temperatures and it concluded that the onset of swelling is directly influenced by the heating conditions at the exposed surface and the original applied dry film thickness.

A combined analytical model for increasing the accuracy of heat emission predictions in rooms heated by radiators

The efficiency of heat emitters plays an important role in the improvement of building energy performance, especially in the context of system and product comparison. In particular, it can be directly related to thermal comfort via the operative temperature that is effectively sensed by the users.For the first time in the literature, in this paper we develop a combined analytical model for room and radiator that computes directly the heat output required to maintain a specific operative temperature. The total heat balance of the enclosure is used to accurately quantify and compare the heat emission losses of different radiator types via an analytical calculation of the operative temperature. This determines the efficiency of a selection of panel radiators with different surface temperature, radiation fraction and number of panels, which were tested in a chamber conforming to the EN 442-2 standard.Additionally, we assess the related annual energy consumption in different climates by carrying out annual simulations in old (without heat recovery) and new (with heat recovery) building types located in Tallinn, Estonia and Strasbourg, France. In the new building we find a similar performance for all the radiators. In the old building however, one radiator outperforms the other two with up to 1.38% lower annual energy consumption, due to smaller rear losses and higher thermal comfort provided by the larger front panel surface.