Keeping the pressure on
The speed that a hot-water system can deliver water to the hot taps is mainly dependent on the pressure at which the system operates. Low pressure hot-water systems that were once very prevalent and some forms of electric instantaneous systems that are still used today often cannot effectively deliver hot-water to more than one tap at once. High pressure hot-water systems avoid these constraints but they must be protected with appropriate pressure control valves to ensure safety and longevity. Envirosun solar hot water systems are fitted with three levels of pressure control. First, the inlet pressure is reduced to 450kPa. This represents the minimum pressure at which the tank will deliver hot-water. Second, there is a cold-water relief valve that operates at 600kPa – this represents the normal operating pressure of the tank. The purpose of the cold-water relief valve is to relieve excessive pressure that will otherwise build up in the tank due to thermal expansion of the water. Because the relief is connected to the bottom of the tank, no hot water is lost in this process. Third, there is a hot-water relief valve that operates at 700kPa or when the tank temperature reaches 99oC. This valve is provided as a secondary level of safety and will only operate as a pressure control valve if there is a problem with the cold-water relief valve.