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Variations on residential solar water heating: learn about closed loop/antifreeze-based systems.

Article Excerpt
Current interest in solar thermal technology is--to say the least--hot! Every month, more vendors enter the North American market with new hardware. Training programs for implementing this hardware are usually filled to capacity. At our office, inquiries about use of solar thermal technology come in almost every day. If you plan to work in the HVAC field over the next decade, chances are you will deal with solar thermal technology in some capacity.

Of all the potential loads that can be served by a solar thermal system, domestic water heating ranks No. 1. The primary reason is that domestic water heating is a year-round load. It takes advantage of the high solar availability in warmer months to boost the total amount of energy harvested per square foot of collector per year. This allows solar water heating systems to provide better returns on investment relative to solar systems designed for space heating.

A Little History: Before there was electricity, there was solar water heating. In the late 1800s, Clarence Kemp of Baltimore patented the Climax solar water heater. His device consisted of multiple cylindrical tanks that were blackened and mounted in a glass covered box. This was the predecessor of what is now known as a passive "batch heater." By the turn of the century, several companies had entered the solar water heating market with variants of this design. However, these devices had an "Achilles heal"--they lost much of the heat collected during a sunny day through subsequent nighttime cooling.

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In 1909, an engineer named William Bailey put forth a new design concept that separated the solar collector and storage tank and, thus, greatly reduced nighttime heat loss. It was appropriately named the Day and Night Solar Water Heater. It operated on the principle...

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