Both theoretical and experimental studies have been made on the subject of solar heat gain through single and composite barriers. (1-4) But because of the complexity of the solution, these studies are restricted to the steady-state response. For systems with negligible heat storage and with a relatively constant source, these solutions serve as acceptable engineering approximations. However, in practical applications it is often desirable or necessary to know the error involved in ignoring the transient response. Thus the author (5) used a lumped analysis to find the transient solution for heating a fluid through a single semi-transparent barrier which compared well with experimental results.

The object of the present paper is to extend the solution to the case of the more commonly encountered composite barrier by introducing more parameters in order to broaden the usefulness of the solution. A simple criterion to determine when the transient response may be considered negligible is included, together with numerous examples which illustrate the wide variety of problems where the solution carr be applied.