There can be times when there is no way to use the excess heat produced, like in a pool or hot tub, but it still needs to be dissipated with an automatically controlled heat dump. These systems usually use copper fin-tube to shed heat to the atmosphere. The method is simple, economical, and effective. The recommended fin-tube is the core of baseboard heaters—a readily available product from hydronic-heating suppliers. There are commercial water-to-air heat dumps available as well.
The fin-tube is installed behind the solar collectors and the solar fluid is diverted through the fin-tube before it enters the collectors. One way to divert hot solar fluid through the fin-tube is to use the same control method mentioned above with a dual-relay controller. When the storage tank reaches a preset temperature, the main circulator stays on and the second relay also turns on. In this case, the relay energizes a motorized valve to divert the solar fluid to the fin-tube before it flows back to the collector array.
Another way to control the fluid flow is to use an additional set-point thermostat or an aquastat to operate a motorized valve that diverts the flow of the solar fluid. If the solar fluid reaches a preset temperature as it travels to the collectors, the flow is diverted through the fin-tube, where it cools. This fluid does not need to be cooled to ambient temperature; it only needs to be kept below 200°F.
There are several strategies you can use to keep your SHW fluid from overheating, and the best solution will depend on the climate and system specifics. A pool or hot tub can be an excellent choice and add to the enjoyment of living with solar. If properly designed and installed, SHW systems can provide decades of service—and hot-tubbing or pool heating.
Bob Ramlow has been active in the solar thermal industry for more than 40 years as an installer, consultant, manufacturer, and teacher. He is an ISPQ-certified solar thermal independent master trainer and a NABCEP-certified solar thermal installer. He is the co-author of Solar Water Heating: A Comprehensive Guide to Solar Water and Space Heating Systems. He teaches about solar heating and is a consultant to the industry (see arthaonline.com).
IMC Instruments • solar.imcinstruments.com • Solar thermal controllers