Reflecting panels for radiators in residential buildings: theoretical analysis of energy performance

The paper deals with the analytical evaluation of energy advantages that could be obtained by inserting a panel made of reflecting material between the wall and radiators used for central heating. As a consequence of the panel installation, a higher percentage of the heat emitted by the radiator remains inside the room to be warmed, diminishing the heat loss through the external wall, thus improving the global efficiency of the entire heating system. The analysis is based on equations that describe the heat exchange by irradiation between the three surfaces: radiator, reflecting panel and inner surface of the external wall; the natural convection with interior room air flow is also taken into account. The study covers three different wall types, with the aim of investigating the influence of the enclosure on the panel performance, and three different climatic zones in Italy (North, Centre and South), to take into account the variation with the external temperature. Results show how the performance of the reflecting panel depends strictly on the insulation level of the external wall facing the radiator; more specifically, efficiency increases when the thermal resistance decreases, reaching energy savings of up to 8.8% in worst insulation conditions. The variability with external temperature conditions is negligible, showing similar values for all the investigated zones.