Energy Benefit of Parallel Operation of Radiant Floor Heating with Convective Heat Pump Heating in Residential Buildings

Abstract

Heat pump system, recognized worldwide as a high-efficiency energy system, can greatly benefit in reducing heating energy when applied as a building installation system. Meanwhile, floor radiant heating system heats the room through the heated floor and improves the thermal comfort of indoor residents because the temperature difference with indoor air is relatively low. Since the two systems, which clearly have their complementary advantages, are applied together to the recently constructed apartment houses, the optimal operation conditions for radiant and convective heating are deduced. Therefore, in this study, the energy performance of the system considering the thermal comfort of occupants as residential heating systems was investigated by combining the floor radiation heating system (RFH) and the air heat source heat pump heating system (EHP). In order to figure out the appropriate optimal operating ratio of integrated heating taking advantage of the two systems, floor temperature in floor heating was set with minimal discomfort and the remaining loads were handled by electric heat pump system. With changes in floor temperature, how much energy is saved compared to the use of floor heating alone was calculated. The heat pump was designed in an electric heat pump system using the theoretical calculation of thermodynamics with the efficiencies of each component. The floor surface temperatures that occupants have less local discomfort of foot were determined considering the international standards and literatures of thermal comfort in the radiant floor heating system. Then, the energy consumed by all components consisting of two heating systems were calculated through Engineering Equation Solver (EES). Consequently, in a well-insulated building when the floor temperature was 25°C, all heating loads were removed only by floor radiant heating. When handling all heating loads with heat pump convection heating, 59.2% less energy was used compared to floor radiant heating. Considering the local discomfort of the soles of the feet, the floor temperature is expected to be applicable at 22–23°C, and 31.5– 37.6% energy savings compared to floor radiant heating were confirmed. In addition, prediction formula was derived from a virtual test using TRNSYS so that the heating capacity and floor surface temperature of the floor radiant heating can be simply calculated.