Inexpensive solar-wood water heating combinations

A promising batch heater recently built and now being tested consists of lengths of eight-inch galvanized culvert pipe painted with semiselective black coating, hooked in series and tied in as part of a passive closed loop, unpressurized solar-wood water heating combination. One 10-foot length of eight-inch culvert contains 14.6 gallons of water. Eight-inch culvert provides a near optimum surface area per unit volume ratio, resulting in quicker, more efficient solar water heating. Moreover, the proposed arrangement minimizes the mixing of hot with cold water as warm water is used, often a problem with many types of batch heaters. Details for constructing this type of batch heater are provided. The system is an unpressurized, closed loop set-up, which means that the same liquid circulates continually from solar heater to wood heater to storage tank heat exchanger. The collector design is a variation on the inverted batch heater which takes its inspiration from a number of solar designers of similar units and introduces several additional measures to take advantage of the wood heating connection and to improve the design based on operating experience.