An experimental and theoretical study of a hydronic radiant ceiling panel heating system

Abstract

The objective of this study is to improve the design of hydronic radiant panel systems through the understanding of the thermal performance of panel systems. The scope of this study includes performing experiments using testing facilities and the radiant panel ceiling in the Energy Research House, and developing a theoretical model that can predict heat transfer from a radiant ceiling panel. In the experimental part of this study, a solar-radiant heating system was field tested to examine the feasibility of using a radiant system coupled to a solar heating system to provide space heating. Through experimental testing a system energy flow chart was made which showed how solar energy is utilized by the system through its various components. It was also found that room temperatures could be maintained at comfort levels using hot water from a solar storage tank at only about 32°C. This verified the concept that a radiant panel ceiling, due to its extended heat transfer surface, can effectively utilize low temperature heat sources such as solar energy. By operating the solar collector at a low temperature, the collector efficiency was also improved; an average efficiency of 40% was maintained in the test. A monthly averaged analysis showed that about 50% of the heating load was met by solar energy when using these combined systems in March, 1985. A study on the transient thermal response of the radiant ceiling and room enclosure was also performed. This study provided a data pool for checking the theoretical model to be developed in the later part of this study. Another experimental study performed at the Energy Research House was a comparison of radiant heating and forced-air heating. Its major objective was to determine if radiant heating saves energy compared to forced-air heating. The experiment was carried out by alternatively operating the two systems and recording all relevant data during a tenweek testing period. It was concluded that the radiant heating was 15 to 20% more energy efficient than forced-air heating in normal winter conditions. Theoretical modeling of the radiant panel heating system was performed in three steps. First, a panel unit was isolated from whole panel in order to to set up a domain. Numerical methods were used to solve heat transfer in this domain. Then a semi-analytical correlation was developed. Finally, a complete model was built by integrating heat output per panel unit along the entire tubeline, thus establishing an interrelationship between various system parameters. The model predicted the thermal behavior of the radiant panel to a reasonable accuracy.