## 1 Introduction  
Radiant heating and cooling systems have been present inside buildings for a very long time [1]. In the last 50 years, the advances in materials science and design process led to an increase of applications of this technology. The two main families of radiant systems are electrical and water-based. These systems can be installed on every surface of a room but the most common applications are on floor and ceiling. Heating systems have been constituted for many years by a boiler and by the terminals, the classical cast iron radiators first and the other types of metal or alloys later, and by all the other components necessary for the whole system to work. In recent times, the use of heating systems made by radiant panels is growing. These systems promise valid air-heating, a feeling of better comfort thanks to the absence of air motions that cause movement and suspension of dust and mites, and a very high thermal performance. The piping (for water systems) or the electrical cables or mats (for electrical systems) could be integrated with or embedded into different materials. An example is the integration of an under-floor electric heating system with shape-stabilized phase change material (PCM) plates. Differently from conventional PCM, shape-stabilized PCM can keep the shape unchanged during the phase change process, thus avoiding dangerous leakage. This system can store heat by transformation of cheap nighttime electricity and take advantage of the stored heat during daytime. [PERSON] et al. [2] analyzed the thermophysical properties of shape-stabilized PCM developed by the research group itself. A prototype room with this electric heating system was set up in Beijing to test the thermal performance and the feasibility of this heating mode. The results showed that the temperature of the PCM plates' upper surface could be kept near the phase transition temperature during the whole day, and that a lot of off-peak period electricity could be used for space heating instead of using peak period electricity, which would obviously lower the operational costs. To assess the performance of radiant systems, several authors have proposed different modeling and testing methodologies, mainly using water as thermal carrier [3; 4; 5; 6; 7]. [PERSON] et al. [8] analyzed transient conduction, convection, and radiation heat transfer mechanisms for radiant floor heating using the finite element method with particular attention to the type and thickness of the floor cover, which are the most important parameters in the design of radiant heating systems. The obtained results confirm that radiation is the dominant mechanism of heat transfer in a floor heating system. Computer simulations are also utilized to analyze the energy demand and the comfort conditions both for residential and commercial buildings using radiant systems [9; 10; 11]. Even if the embedded water heating panels are the most used both in new buildings and for retrofits, literature shows interesting experimental works in the field of electric radiant heating, [PERSON] et al. [12] analyzed in steady state the temperature profiles of a radiant floor formed by several layers: the insulation layer, the electric heating element, the plastic substrate, and the floor tile. The same work develops an experimental study on the performance of these heating systems. A prototype reproducing the different layers of a radiant floor was designed. Temperature sensors were placed on each of the layers and, finally, an on/off switch allowed the control of the surface temperature of the device. With the help of this assembly, the dynamic performance and the energy consumption of the system were analyzed. Different configurations were studied, changing the type of floor tiles, the nature of the substrate, the insulation thickness, the type of deck on which it was installed, and the location of the temperature control sensor.