The sun’s raw energy can be absorbed in two ways, either the conversion of sunlight into electricity or the utilization of the sun’s energy as a direct source of heat. The latter (solar thermal) has been in use since 1891 and has recently become mainstream again due to various incentives and pressures to utilize renewable energy sources. The solar industry now must serve a seemingly insatiable demand. It was only natural that this movement toward renewable energy would become prevalent in all hot water applications, including those such as heating pools. With various benefits, including efficiency, and simple design and installation, solar pool heating systems have become a more eco-conscious way for providing a means of human comfort. The Uniform Solar, Hydronics & Geothermal Code® (USHGC®) is a key component to properly installing such systems. The USHGC can be utilized for proper installation of solar pool heating systems, as it lists provisions for materials, installation and prevention of corrosion and heat loss.
Solar pool heating systems primarily consist of a solar collector, a filter, a pump, and a flow control valve. The solar collector acts as the device through which pool water is circulated and heated using the sun’s energy. Typically, unglazed collectors are installed for such use due to their simple design, which consists of a heavy-duty rubber or plastic treated with an ultraviolet inhibitor to extend the life of the collector. To protect the solar collector from debris, Section 505.3 of the USHGC lists provisions for filters and their required location within the system. Furthermore, sizing of the pump that is used to direct water to the solar collector must also be completed using the manufacturer’s pump performance graphs.
Since these systems utilize a pump and operate with high flow rates, they are considered to be active low temperature systems. This allows for the installation of piping and fittings that are meant for low temperature applications. Table 408.1, as provided in the USHGC, lists applicable material standards for piping, tubing and fittings, and has proven to be an excellent source of material standards for all types of solar thermal systems. As previously stated, high flow rates are desirable for these systems, but excessively high flow rates must be avoided, as they cause erosion of interior pipe and fitting surfaces. This can be achieved by installing appropriately sized piping based on pipe flow charts pertaining to flowrate and correlating pressure drops.
The USHGC also addresses corrosion prevention of solar pool heating systems. Section 505.4 of the USHGC prohibits the use of glazed solar collectors made of copper, as this material may lead to excessive concentrations of copper ions within the pool water. This excessive concentration of copper causes the pool water to become acidic, as it drops the pH of the water. This also commonly leads to the formation of colored precipitates along the pool wall. The acceptable pH range for pool water falls between 7.2 and 7.8, and this range — along with various other acceptable water chemistry parameters — can be found in Table 505.2 of USHGC. As an added measure, the provisions in the USPSHTC can be also be considered as this code includes provisions for maintaining water quality not only for bather safety but also safety of swimming pool system components.
Solar pool heating systems also experience a vast amount of energy loss due to evaporation of heated water. Evaporation rates are dependent upon a variety of factors, such as air temperature, relative humidity, wind velocity and water agitation. In order to raise 1 pound of water 1 degree Fahrenheit, 1 BTU of energy is required; but losing 1 pound of water at 82 degrees Fahrenheit due to evaporation causes a loss of 1047 BTUs of energy from the pool. In addition to installing active type solar systems as depicted previously, passive methods may also be used to decrease the amount of heat lost due to evaporation and increase the efficiency of the overall system. Installing vapor retardant covers when the pool is not in use can drastically improve the system’s ability to meet the desired pool water temperature.
With the increasing demand for alternative energy, a movement has been started to harness and convert solar energy as an environmentally friendly alternative. The USHGC provides a means of utilizing this free and renewable energy, and through its use, public health and safety — as well as proper installation of solar pool heating systems — can be assured. Overall, the USHGC is an excellent source for solar pool heating system provisions as they address water quality, installation, material standards, corrosion prevention, and various other aspects of such systems.
Taylor Costea
Taylor Costea is a technical code administrator for IAPMO. In her role, she works on the development of the Uniform Solar, Hydronics and Geothermal Code (USHGC) as well as the Uniform Swimming Pool, Spa and Hot Tub Code (USPSHTC). Costea has a bachelor’s degree in Mechanical Engineering from California State University Los Angeles and is an Engineer in Training (E.I.T.) for the State of California.
Last modified: April 5, 2023