Thermal penalty of an immersed heat exchanger in integral collector storage systems

The use of a heat exchanger in solar water heating systems reduces the over all system? efficiency. In this paper, we derive a simple "penalty factor" that gives the fractional reduction in thermal efficiency imposed by a heat exchanger immersed in an isothermal integral collector storage (ICS) syste m. The penalty factor depends only on the effectiveness of the heat exchang er, the capacitance of the hot water delivered, and the product of the loss coefficient and aperture area of the ICS. This factor allows the designer to select an appropriate heat exchanger without extensive simulation or exp eriments. Application of the penalty factor for a load-side (or on-demand) heat exchanger, which Operates intermittently at varying flow rates, is dis cussed and illustrated through example.