SRCC Best Practices Design and Operation Tips

Professionals Should Design to Avoid System Overheating

Solar Water Heating Systems (SWHS) can be designed to minimize, or avoid altogether, overheating problems.

SWHS overheating problems typically occur during warmer months, and frequently are the result of lowered hot water demand occurring during family vacations or similar events where hot water usage is reduced, leading to elevated temperatures in solar heat storage tanks.

• This condition can lead to a variety of system operational problems, which can include:
• · Excessive discharge of pressure relief or pressure/temperature relief valves installed at the solar collector location, on the system piping, or in the solar storage tank location;

• · High temperature discharge of safety valves into whatever location they are so directed;

  · Elevated solar storage tank or conventional water heater temperatures, which can lead to significantly reduced tank operating life;

• · Elevated solar collector temperatures, which can also lead to reduced system operating life;

• · Premature degradation of pipe insulation, and wiring, if any.

• SWHS designs can address these issues up-front considering the following when designing systems or directing new owners in their commissioning:

• · Avoid installing more solar collector surface area than is necessary for a given water heating application. For systems which include a separate solar storage tank in addition to the conventional electric, gas, oil or propane-fired water heater, a good rule of thumb is to install no more than 1-1/2 square feet of solar collector surface area for each gallon of solar storage in colder climates, and no more than ¾ square feet per gallon in warmer climates.

• · Don't assume that the higher the temperature a system is able to achieve, the better. A greater volume of slightly cooler water is more advantageous than a lesser volume of hotter water for the reasons discussed above.

• · By all means, do not forget to install a pressure reduction or pressure relief valve, as directed by the manufacturer's Installation Manual, in any section of piping which can be mechanically isolated, including the supply/return piping from and to the collector loop.

• · Consider instructing customers to cover the solar collectors during periods when they will not be using hot water. Options for doing so include a canvas-type tarpaulin which can be secured around the solar panel(s), and which is non-transparent;

• · Know that Incentive Programs designed to encourage the purchase of solar water heating systems may sometimes lead to over sizing of systems in order to maximize incentives that are based on energy production of the system. Keep in mind that your customers will be calling you for service if their systems are overheating.

SRCC offers this information to help avoid issues related to system design and operation leading to problematic experiences by purchasers. We believe that identification and avoidance of known system operating issues will help increase the acceptance of solar water heating equipment, and lead to increased utilization.