Radiant Ceiling Research Articles

Physics-consistent input convex neural network-driven reinforcement learning control for multi-zone radiant ceiling heating and cooling systems: An experimental study

Radiant ceiling heating and cooling system is a technology used for space heating and cooling. Owing to the variable weather conditions, occupant behavior, and thermal lag of the system, it is challenging to design a control strategy to reduce air-conditioning energy consumption while maintaining the thermal environment. This study is the first pilot implementation of a physics-consistent input convex neural network (PCICNN)-driven reinforcement learning (RL) approach for real-world multi-zone radiant ceiling heating and cooling systems. A multi-zone PCICNN based on a graph neural network (GNN) was developed to simulate the zone temperature. The radiant panel load was simulated using the physics-based ε-NTU method. The PCICNN-driven RL agent was based on the soft actor-critic algorithm and trained in an environment model comprising the PCICNN and ε-NTU models. The proposed controller was deployed in real-time on one floor of an office building for one month. The real-world implementation showed that the proposed PCICNN-driven RL control can reduce the radiant panel cooling load by up to 33% compared with the inherited baseline control strategy under similar weather conditions. This study provides a comprehensive demonstration of real-world data-driven building controls and leverages future research on advanced building control.

Calculating the local and overall view factors of a multi-segment human model

In non-uniform environments, such as spaces with radiant ceilings or floors, or with hot or cold windows, view factors (VFs) of a person towards these surfaces are needed for calculating the heat exchanges between the person and the surroundings. Multi-body segmented human models can simulate the heat exchanges of individual body parts with the environment. Simulating heat transfer at the local body parts is important for assessing comfort in non-uniform environments. These models require VFs for each individual body part. Accurately determining these VFs is time-consuming, often requiring methods such as ray-tracing techniques. A fast calculation method to accurately determine the view factor (VF) for each segment has yet to be investigated. This study employed a 16-segment human model into various architectural radiation scenarios. The surface-to-surface model in computational fluid dynamics was utilized to simulate VFs for the 16 body segments in relation to radiant surfaces at different locations. Through a series of simulations, comprehensive formulas for VFs were derived for each individual at various positions within a room, encompassing 16 body segments and computing parameters for 24 building surfaces. The accuracy of these general formulas was validated by comparing the whole-body VF with results from several available studies. Additionally, this study developed a visualization tool for calculating VF and mean radiant temperatures with different room space dimension and embedded radiant surfaces. The users can use this online tool to easily calculate VFs and mean radiant temperatures for each body parts, and for the whole-body. The tool offers valuable insights for predicting thermal comfort in asymmetric radiant environments and facilitating control over building environments.

Allowable surface temperature of ceiling heating based on radiant temperature asymmetry

Radiant temperature asymmetry as one of the criteria for local thermal discomfort has an influence on the practical design of the heating system, as people are most sensitive to the radiant heating of the top of the head. The paper presents the determination of the allowable surface temperature of the heated ceiling based on the theoretical calculation using the angle factors and taking into account the allowable the radiant temperature asymmetry according to the standard values of 5 and 7 K. In practice, the radiation temperature asymmetry is determined by measuring two radiant temperatures. In this paper, the measurement of radiant temperature asymmetry is measured in an experimental room with a heated ceiling and the results are compared with the theoretical calculation procedure. The paper points out the differences between the measured and calculated values of the radiant temperature asymmetry. Based on the analyses, the allowable ceiling temperatures for radiant heating have been determined for different room geometries so that the radiant temperature asymmetry for thermal comfort categories A, B is actually observed. A new correlation has been established to determine the allowable surface temperature of the radiant ceiling as a function of the angle factor between the small plane element and the ceiling. For practical use, the correlation has been adjusted for typical geometric cases without the need for calculation of angle factors. Maximum ceiling surface temperatures are graphically displayed without causing thermal discomfort. Conversely, in large rooms with a heated ceiling, the ceiling surface temperature is severely limited, precisely because of the potential for thermal discomfort due to radiant temperature asymmetry.

Thermal performance study of PCM embedded radiant cooling ceiling assisted by infrared-transparent silicon wafers

Phase change materials embedded radiant chilled ceiling (PCM-RCC) systems are great for cutting peak power demand and boosting energy efficiency, but they might not work as well in really humid areas due to condensation issues. Infrared-transparent silicon wafer-assisted PCM-RCC (ISW-assisted PCM-RCC) is proposed to improve the cooling capacity in this study. A heat transfer model of ISW-assisted PCM-RCC is established and its reliability is verified. Effects of thermal conductivity, phase change temperature, and control strategy on the thermal performance of ISW-assisted PCM-RCC are discussed by using the model. The simulation results show that the thermal conductivity of PCM is recommended to be above 0.6 W/(m·K), and the temperature difference between the lower limit of the selected PCM phase transition temperature range and the chilled water temperature should not be less than 1℃. The maximum cooling power of the system is more than 80 W/m2, 46 % higher than the non-condensing cooling capacity of traditional RCC at 70 % relative humidity conditions. Interestingly, the prolonged cold energy storage strategy at night should be avoided which is not friendly to the energy efficiency of the system. In short, the combination with ISW is an effective means to increase the cooling capacity of the PCM-RCC.

Operational performance of PCM embedded radiant chilled ceiling using a rule-based control strategy

The increasing energy demand for space cooling, projected to triple by mid-century and surpassing a quarter of today's global electricity usage, underscores the urgent need for innovative, more energy-efficient air-conditioning technologies. The research introduces phase change material (PCM) embedded radiant cooling (PCM-RCC) as a promising solution, offering enhanced energy efficiency and indoor environmental quality. Despite its potential, PCM-RCC remains in the developmental stage, requiring further research to fully unlock its benefits. This work aims to analyse the operational performance of PCM-RCC and develop an advanced rule-based control strategy to enhance its efficiency further. The analysis was conducted using a validated PCM-RCC transient system simulation model. To quantify the advantages of PCM-RCC over typical radiant cooling and evaluate the effectiveness of the proposed control strategy, two reference cases are defined: (1) basic-controlled PCM-RCC, and (2) radiant cooling without PCM. Results reveal that PCM-RCC with advanced control demonstrates higher load flexibility (∼93% off-peak time operation), 12% less electricity usage, a 5% coefficient of performance improvement, and a 30% decrease in operational costs compared to radiant cooling. Furthermore, the proposed system shows 9% lower energy usage with a 20% improvement in thermal comfort compared to basic-controlled PCM-RCC.

Solar-Powered Smart Buildings: Integrated Energy Management Solution for IoT-Enabled Sustainability

The increasing demand for energy-efficient and sustainable solutions in the building sector has driven the need for innovative approaches that integrate renewable energy sources and advanced control systems. This paper presents an integrated energy management solution for solar-powered smart buildings, combining a multifaceted physical system with advanced IoT- and cloud-based control systems. The physical system includes a heat pump, photovoltaics, solar thermal panels, and an innovative low-enthalpy radiant wall and ceiling, providing self-sufficient heating and cooling. The control system makes use of advanced IoT and communication engineering technologies, using Modbus, HTTP, and MQTT protocols for seamless interconnectivity, monitoring, and remote management. The successful implementation of this solution in an average-sized model house in Paris and a deep energy retrofit of a semidetached single-family house in Oviedo, northern Spain, demonstrates increased energy efficiency, improved thermal comfort, and reduced environmental impact compared with conventional alternatives. This study illustrates the potential of integrating solar energy, IoT, and communication technologies into smart buildings, contributing to the global effort to reduce the environmental impact of the building sector.

Design and control of radiant heating and cooling systems in Japan: Results from expert interviews

AbstractThis research conducted investigations of buildings equipped with radiant systems and expert interviews in 2021–2022 with manufacturers and mechanical, electrical, and plumbing (MEP) engineers in Japan who had experience designing radiant heating and cooling systems for non‐residential buildings. In total, interviews were conducted with 56 respondents from 16 companies. Results from the building investigation showed that 69% of the identified buildings had radiant ceilings, and 30% had radiant floors. In terms of working fluid, 56% were water‐based, and 43% were air‐based. For the expert interview, 79% of all respondents answered that the use of radiant systems will continue to increase in the future. In total, 54% of all respondents answered that it has become easier to design radiant systems at present compared to the 2010s. Based on the results, knowledge gaps and challenges in the design of radiant systems were summarized in terms of design method, room temperature control, auxiliary systems, and their relevance to building decarbonization.

Development of design calculations for radiant ceiling panels incorporating phase change materials (PCMs)

Thermally active building systems (TABS) show significant benefits such as providing peak load shifting, peak load reductions, and energy savings. Phase change material (PCM) applications with water circulation have benefits similar to TABS, but PCMs can store more heat per unit volume than concrete due to the latent heat exchange. Radiant panels with PCM can be applied in building retrofit, which gives this application a significant advantage compared to TABS. A design methodology for determining heat flux does not exist though for dimensioning a radiant ceiling system that incorporates PCM. Design methods according to standards for TABS – ISO 11855-2 and for radiant panels – ISO 18566-3 were investigated. Five radiant ceiling panels incorporating PCM were selected from Denmark, Canada, Germany, the Czech Republic and Latvia. The resulting heat flux between the panel and conditioned space, i.e. the room, following methods represented in the standards, were compared with the measured or simulated values reported in the literature. The comparison showed that the calculation for TABS (ISO 11855-2) led to similar results to the measured or simulated values.

Experimental study to understand the thermal environment of an office cooled by radiant ceiling panels and dedicated outdoor air system

This research aims to better understand the radiant environment of an interior space located in the tropical climate that is cooled by Radiant Ceiling Panels (RCPs). To do so, we have designed a highly instrumented 177m2 office testbed in Singapore installed with RCPs, Dedicated Outdoor Air System (DOAS) and Fan Coil Units (FCUs). An 11-day experiment is designed to monitor the radiant environment when being cooled by 1) RCPs + DOAS and 2) FCUs + DOAS with a fixed internal load of 2kW and humidity load of 8g/hr. We alternate between these two cooling modes, with variations in panels’ water supply temperature and window blinds. We expect to see a separation of Mean Radiant Temperature (MRT) and air temperature in mode 1 with the use of improved radiant sensors. However, results showed only minor differences in the radiant environment between the two modes of cooling. There was no significant MRT and air temperature separation (<1°C). These insights provide a better understanding of our radiant environment, which can potentially improve the way we control radiant systems. With better understanding, we can support high thermal comfort performance of a radiant systems as compared to a more common air-based system.

Experimentally investigating and numerically simulating the performances of various low-temperature hydronic heating/cooling systems connected to a vertical closed-loop ground-coupled heat pump

The method used in this study consists of evaluating different terminal heating/cooling systems in an experimental office at the Polytechnic University of Timișoara, Romania, through experimentation and numerical simulation. This paper is focused on the energy efficiency exploratory research of various low- and very low-temperature hydronic radiant heating/cooling systems (floor, wall, ceiling, combined floor-ceiling) and of the medium-temperature radiator heating system, connected to a vertical ground-coupled heat pump (GCHP) in double U-tube borehole heat exchanger (BHE) configuration. The main performance parameters are obtained for five weeks of operation in heating mode and three weeks in cooling mode, and a comparative analysis of these parameters together with indoor thermal comfort is carried out. The four simple heating systems (radiator, floor, wall, ceiling) have relatively small differences (maximum 7.4 %) in their coefficient of performance (COP) values, but the number of starts/stops in the case of radiator heating is twice that of floor heating, which leads to greater wear and tear on the heat pump equipment. Under the same operating conditions, the CO2 emission of the radiator heating system are 0.7–16 % higher than those of the heating system with radiant panels (floor, wall, and ceiling). The floor-ceiling combined radiant heating system has the highest COPsyst of 5.45 as well as the lowest CO2 emission value of 2.15 kg. The predicted mean vote (PMV) index (pair 1.1 met-0.29 clo) has values approximately equal to 0 only in the case of the floor-ceiling heating, when the percent of likely dissatisfied with the thermal comfort is 5 %. The three cooling radiant systems show differences in their energy performance, namely the radiant ceiling cooling system has the best COPsyst, 39.8 % higher than that of the radiant floor and only 5.9 % higher than that of the radiant wall. The values of the PMV index (pair 1 met-0.9 clo) for the radiant wall cooling system are 31–41 % lower than those of the radiant floor and 10.4–14.2 % lower than those of the radiant ceiling. Finally, numerical simulations of the useful thermal energy and the system COP in heating and cooling modes are performed with TRNSYS software for a duration of 8760 h and then analysed and compared with the experimental tests to validate the simulation models.

Numerical simulation of cooling performance of radiant ceiling system interacting with a ceiling fan

Numerical simulation of cooling performance of radiant ceiling system interacting with a ceiling fan

Experimental Investigation of Mean Radiant Temperature Trends for a Ground Source Heat Pump-Integrated Radiant Wall and Ceiling Heating System

Mean radiant temperature (MRT) is one of the six primary factors that determine thermal comfort in a given thermal environment. In this study, the average radiant temperature was determined using a calculation method based on the surrounding surface temperatures and view factors. The present study specifically investigated the use of calculated radiant temperature, compared to measured radiant temperature, for predicting the mean vote (PMV) and percentage of dissatisfied (PPD) comfort parameters. The method was validated by the experimental measurements via the black sphere thermometer at five different reference points in a test room, including radiant panels on the ceiling and walls. By using global thermometer measurements, the proposed approach achieved a high degree of compatibility and an accuracy of 0.17 °C, which was the difference between calculated and measured values. The results demonstrated the reliability of the procedure using view factors and surrounding surface temperatures to calculate the radiant temperature in the designated test room; here, a straightforward method for evaluating the thermal conditions of an office room and determining the optimal location of an air temperature sensor in PMV-controlled radiant systems was also proposed. This study contributes to the increasing field of research on thermal comfort and offers knowledge that is beneficial for the design and optimization of indoor environments.

Indoor Temperature Control of Radiant Ceiling Cooling System Based on Deep Reinforcement Learning Method

The radiant ceiling cooling system is widely adopted in modern office buildings as it improves cooling source efficiency and reduces fossil fuel usage and carbon dioxide emissions by utilizing low-grade natural energy. However, the nonlinear behavior and significant inertia of the radiant ceiling cooling system pose challenges for control systems. With advancements in computer technology and artificial intelligence, the deep reinforcement learning (DRL) method shows promise in the operation and control of radiant cooling systems with large inertia. This paper compares the DRL control method with traditional control methods for radiant ceiling cooling systems in two typical office rooms across three different regions. Simulation results demonstrate that with an indoor target temperature of 26 °C and an allowable fluctuation range of ±1 °C, the DRL on–off or varied water temperature control satisfies the indoor temperature fluctuation requirements for 80% or 93–99% of the operating time, respectively. In contrast, the traditional on–off or PID variable water temperature control only meets these requirements for approximately 70% or 90–93% of the operating time. Furthermore, compared to traditional on–off control, the DRL control can save energy consumption in the radiant ceiling cooling system by 3.19% to 6.30%, and up to 10.48% compared to PID variable water temperature control. Consequently, the DRL control method exhibits superior performance in terms of minimizing indoor temperature fluctuations and reducing energy consumption in radiant ceiling cooling systems.

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.

Experimental study on the performance of a stepped phase-change radiation terminal integrated with a building used in summer and winter

The rapid growth of world energy consumption and massive carbon dioxide emissions have exacerbated energy shortages and environmental pollution. It is important to put forward effective means to reduce energy consumption. In this study, paraffin was adsorbed on expanded graphite (EG) to prepare composite phase change material (CPCM), and microencapsulated phase change materials (MPCMs) were used to perform secondary apparent adsorption on the surface of CPCMs to further improve the stability and latent heat. Two kinds of composite micro-phase change materials (C-MPCM1 and C-MPCM2) with thermal conductivity of 3.78 W/(m·K) and 3.45 W/(m·K), respectively, were prepared. The C-MPCM was pressed into phase-change energy storage bricks and embedded into heating/cooling-medium coils to form a phase-change radiant floor and ceiling. The scaled-down experiments and the real-size outdoor experiments were used to verify each other and proved that the optimal water supply temperature is 17 °C in summer and 40 °C in winter. The energy consumption of the room with dual-active cascade phase change radiant terminal in the flow mode of “heating medium-floor-ceiling; refrigerant medium-ceiling-floor” is 44.79 W/m2 for cooling load in summer and 47.08 W/m2 for heat load in winter, with significant energy efficiency and comfort. The energy utilization efficiency was improved.

A Study on Establishing Thermal Output Conditions of Radiant Ceiling Heating Panels for Improving Thermal Comfort of Perimeter Zone in Buildings

Amid concerns over airflow-induced transmission of the COVID-19 virus in buildings frequented by large numbers of people, such as offices, the necessity for radiant ceiling heating panels has increased. This is due to the concern that the airflows emitted from the convection heating systems installed near the ceiling or windows for winter heating may be a major cause of COVID-19 transmission. In this study, we aim to evaluate thermal comfort under various indoor and outdoor environmental conditions of a building and present the thermal output conditions of the radiant ceiling heating panel that can replace the convection heating system while ensuring comfort in the perimeter zone and handling the heating load. As a result, we were able to present, in a chart format, the thermal output conditions that can secure thermal comfort by analyzing the indoor airflow distribution depending on the surface temperature of the radiant ceiling heating panel, the interior surface temperature of the window, and the influence of internal heat generation. Moreover, through derived empirical formulas, we were able to determine the heating conditions of the panel that can secure the necessary heat dissipation while minimizing discomfort, such as downdrafts, even for indoor and outdoor conditions that were not evaluated in this study.

Experimental study of a low-cost ceiling cooling system in the north Algerian climate

This experimental study aimed to characterize the performance of a new type of radiant ceiling heating/cooling system in terms of thermal comfort and energy savings in a room of a building located in northeastern Algeria. Good insulation was applied to the room located on the ground floor after studying its heat losses and gains. Tests were conducted during the summer period, more precisely in June, to evaluate the thermal conditions of the room during the intermittent periods of operation of the radiant ceiling system. Results showed that the room's ambient temperature decreased by 1.1 °C after 15 min of operating the cooling system during the first day of the experiment and remained below 27.2 °C throughout all the experimental days regardless of the outdoor temperature. The system was highly efficient, did not require daily use, and reduced cooling energy consumption by 89%. Despite the primitive and simple materials and tools used to manufacture the radiant panels (diffusers), the system produced satisfactory results at 38 EU/m2.

Thermal and energy performance evaluation of a full-scale test cabin equipped with PCM embedded radiant chilled ceiling

The escalating global demand for space cooling has led to the emergence of new cooling technologies, including the phase change material embedded radiant chilled ceiling (PCM-RCC) system. This technology improves energy efficiency and indoor environmental quality, while also offering demand-side flexibility. The present study experimentally evaluates the thermal efficiency and energy performance of a PCM-RCC system in a full-scale test cabin equipped with PCM panels. Here, the transient thermal behaviour of PCM ceiling panels besides the cooling energy delivered during charging-discharging cycles are examined. The indoor thermal comfort and peak electricity demand reduction enabled by the present PCM-RCC are also discussed. The results reveal that chilled water circulation for 4–5 h overnight was sufficient to fully recharge the PCM panels. Over 80% of the occupancy time was classified as “Class B″ thermal comfort according to ISO 7730. The system's daily electricity usage was mostly concentrated during off-peak hours, accounting for ∼70% of the total usage. While the controlling schedule used in this study responded to the transient thermal behaviour of the indoor space and PCM ceiling panels, a more dynamic, predictive schedule is necessary to improve the system's overall efficiency and further enhance indoor thermal comfort in response to the changing environmental conditions.

Novel radiant heating and cooling panel with a monolithic aluminium structure and U-groove surface – Experimental investigation and numerical model

Thermally activated panels with monolithic structure and complex shape are not known well. Additionally, studies of radiant heating–cooling panels described in the literature mainly focus on either cooling or heating as well as either ceiling or wall option. In this paper, a novel heating and cooling panel with a U-groove surface and aluminium monolithic structure that increases heat exchange between the heating–cooling medium and the panel was studied. The performance of a new panel for the wall and ceiling options was investigated experimentally. For this analysis, an extended study was carried out that included both heating and cooling modes to develop a universal solution. A numerical model to predict the temperature in a room with the cooling and heating panels installed was developed and compared with experimental results. The specific thermal capacity of the panels observed in the experiments ranged from 82 to 158 W/m2, sufficient to maintain thermal comfort in modern buildings that meet low-energy or passive building standards. The specific cooling capacity of the studied panels ranged from 47 to 59 W/m2, similar to high-temperature radiant cooling systems used in modern buildings. The investigated panels are compatible with mechanical ventilation systems equipped with a cooling function. The simulation results were in agreement with the experimental measurements. Thus, the numerical model can be used to design heating and cooling radiant ceilings as well as to assess thermal conditions in a room.

Development and validation of a transient simulation model of a full-scale PCM embedded radiant chilled ceiling

The recent significant rise in space cooling energy demand due to the massive use of air-conditioning systems has adversely changed buildings’ energy use patterns globally. The updated energy technology perspectives highlight the need for innovative cooling systems to address this growing cooling demand. Phase change material embedded radiant chilled ceiling (PCM-RCC) has lately acquired popularity as they offer more efficient space cooling together with further demand-side flexibility. Recent advancements in PCM-RCC applications have increased the necessity for reliable simulation models to assist professionals in identifying improved designs and operating settings. In this study, a transient simulation model of PCM-RCC has been developed and validated using measured data in a full-scale test cabin equipped with newly developed PCM ceiling panels. This model, developed in the TRNSYS simulation studio, includes Type 399 that uses the Crank-Nicolson algorithm coupled with the enthalpy function to solve transient heat transfer in PCM ceiling panels. The developed model is validated in both free-running and active operation modes, and its quality is then evaluated using several validation metrics. The results obtained in multiple operating scenarios confirm that the model simulates the transient behaviour of the PCM-RCC system with an accuracy within ±10%. Aided by this validated model, which offers the user detailed flexibilities in the system design and its associated operating schemas, PCM-RCC’s potentials regarding peak load shifting, energy savings, and enhanced thermal comfort can be investigated more reliably.