Rheem SolPak Use and Care Manual - Page 8

Section 2: System Decription and Operational Principle The key components in the solar water heating system include the solar collector, solar storage tank with integral heat exchanger, circulation pump, differential thermostat, expansion tank, pressure gauge, mixing valve and the non-toxic propylene glycol heat transfer fluid (HTF). The solar collector is the heart of the system. Simply stated, when the sun is shinning, heat energy is absorbed by the solar collector's all copper absorber plate and tranferred to the HTF circulating through the solar collector. The system pump efficiently circulates this heated fluid through the collector piping and integral tank heat exchanger. As the HTF passes through the heat exchanger the heat in the fluid is transferred by conduction to the potable water in your solar storage tank. As this process is continuously repeated during the average sunny day the temperature in your solar storage tank rises. When the solar collector absorber plate is approximately sixteen degrees hotter than the temperature in the bottom of your solar storage tank, the controller will turn the circulating pump on. When the temperature difference has been reduced to eight degrees, the controller automatically turns the pump off. Both single and double tank systems are designed to provide three separate modes of system operation. The system will, (1) accommodate 100% solar operation, (2) serve as a preheater to your solar storage tank or back-up water heater, or (3) bypass the solar collector and run 100% on utility power. Section Six provides instructions for setting the system for automatic operation in each of these three modes. The Dowfrost HD HTF protects your solar system against freezing. Dowfrost HD can provide reliable freeze protection at temperatures as low as minus 60° Fahrenheit if properly applied and maintained. Use of uninhibited propylene glycol, plain water or a concentration of these two fluids as the HTF in this system is strictly prohibited. Propylene glycol can degrade over time. The process of degradation is accelerated in presence of oxygen and/or heat. We strongly encourage you to establish a preventative maintenance schedule with your installation contractor. The HTF pH level must be maintained between 8 and 10 in order to prevent glycol oxidation and corrosion of the collector piping. Manufacturer's collector warranty specifically excludes freeze damage for any reason and absorber plate damage resulting from the oxidation of the propylene glycol HTF. In order to completely protect the integrity of the solar collector and piping, the system is designed to be drained manually if subject to extended periods of disuse or persistent hard freeze conditions below minus 60° Fahrenheit. (See Sections 8.1 and 8.2). 8