Simulated thermal performance of a solar heated floor

A low cost, simple solar heating system consisting of an active collector with an In-Floor Heat Distribution and Storage (IFHDS) system was developed in response to the energy crisis of the 1970s. A two-dimensional finite difference model was developed and used to simulate the performance of IFHDS system cross-sections. Simulation runs were conducted with a steady-periodic model for the temperature of the solar-heated air in the IFHDS system crosssection. The steady periodic simulation results indicated IFHDS system energy efficiency increases with decreasing air temperature in the room above the IFHDS system, peak temperature of the solar-heated air in the IFHDS system crosssection, and required temperature of the IFHDS system floor surface. The results also indicated that energy efficiency increases as thermal storage mass thickness decreases. The thermal storage mass thickness should be the minimum necessary to meet the requirements for maximum permissible daily floor surface temperature fluctuation, or time lag between time of peak, solar-heated air temperature in the IFHDS system cross-section and time of peak floor surface temperature. Keywords, Alternate energy, Solar heat. Heat distribution. Swine housing. The energy crisis of the 1970s generated a great deal of interest in alternate energy sources including use of solar energy. A portion of the research effort was aimed at the development and evaluation of practical and economically viable solar heating systems. One of the active solar heating systems developed uses natural convection heat transfer to move the heat from the thermal storage to the living space. A portion of the thermal storage mass is placed directly underneath the living space floor with the floor itself making up the balance of the thermal storage mass. Heated air from the collector passes through passageways in the thermal storage mass transferring heat to it by convection. Heat is conducted through the thermal storage mass to the floor surface and transferred to the space above by natural convection and radiation. This In-Floor Heat Distribution and Storage (IFHDS) system physically integrates the thermal storage system in the same unit with the heat distribution system. The IFHDS systems have been used in residential buildings (Mitchell and Giansante, 1978) and swine housing (Bodman et al., 1980, 1987, 1989; DeShazer et al., 1980). This type of heating system has gained popularity as a primary heating system for non-mechanically ventilated swine nursery and farrowing facilities (Bodman et al., 1987, 1989). Article has been approved and reviewed for publication by the Structures and Environment Div. of ASAE. Published as Paper No. 9644, Journal Series Nebraska Agricultural Experiment Station. Supported in part by USDA's Solar Demonstration Project, Hybrid Solar System for Young Pigs and Energy Integrated Farm Project. The authors are Michael F. Kocher, Associate Professor, James A. DeShazer, former Professor, and Gerald R. Bodman, Associate Professor and Extension Agricultural Engineer, Biological Systems Engineering Dept., University of Nebraska, Lincoln. Design of IFHDS systems is hindered by lack of a method for predicting floor surface temperatures and heat output. Without this prediction capability, design of IFHDS systems is dependent on experience and engineering judgement to select thermal storage mass and insulation levels. Heat storage in, and heat loss from, the thermal mass of the IFHDS system, and variation of the solarheated air temperature with time, are factors that complicate the analysis of IFHDS system performance. These time dependent factors prevent use of steady-state heat transfer analysis methods for designing IFHDS systems.