An air vent is a valve that expels any air that may pass into the system. This way, it stops air locks from forming which would impair the circulating fluid’s flow. Air vents are normally placed vertically and at the top region of the solar hot water system.
Temperature-pressure relief valves, as the name suggests, safeguards the system from extremes in pressure and temperatures. They are usually located in the storage tank. A pressure relief valve protects the system against extremes in pressure that may accumulate within the system itself.
A pressure gauge checks the pressure within the solar hot water system’s solar fluid loop, in indirect systems. In any solar hot water system, its job is to detect a drop in pressure within the system.
A vacuum breaker allows atmospheric pressure to entering the piping of the system, which facilitates drainage of the system.
Vacuum breakers are located at the collector outlet pipes or anywhere on the return line of the collector, where it enables the collector loop to be properly drained. There are some valves that can come with both air vent and vacuum breaker properties.
Drain valves, check valves, mixing valves & freeze-protection valves
Drain valves drain the solar hot water system’s primary components, including the collector loop and storage tank. Depending on what system is used, this may also include the heat exchange or drain-back reservoir of the system. Indirect systems also use drain valves as fill valves.
Check valves ensure that the water or fluid travels in only one direction. This prevents the thermosiphoning action of water in active systems, which involves the effect of gravity and the natural tendency of water to move when it is heated. There are different types of check valves. A motorised check valve is connected by wire to the pump, so that when the pump is on, the check valve opens, and vice versa. A vertical check valve is one that opens with photovoltaic-powered pumps. A horizontal swing check valve is placed horizontally, and it closes with the flapper’s weight and gravity.
A mixing valve mixes cold water with hot water in the tank to increase the hot water supply at a given temperature. It serves to conserve water. An anti-scald valve acts as a mixing valve too. It is also is a safety device that closes off the flow to the water supply that is used, when the cold and hot water mixing is not working.
Freeze-protection valves open at temperatures at near freezing levels. They are typically located on the return passage to the collector, and when they open they release hot water to prevent the collector and components from freezing. The valve may be controlled by a spring-loaded thermostat or a bimetallic switch. A check valve is used in conjunction with freeze-protection valves. It stops tank water from passing straight from the storage tank to the freeze-protection valve in which case it would bypass the collector.
Temperature gauges & flow meters
Temperature gauges detect the temperatures of the fluid in the system. Those that are located at the top of the storage tank detect the hottest temperature of the available water. A single gauge can be facilitated by several temperature wells installed at various points in the system, in order to monitor operation of the whole system.
Flow meters monitor the operation and flow rate of the pump. They are usually placed near the collector, above the pump.