What type of backflow protection is required for a chemically charged solar heating system with an expansion tank?

In a chemically charged solar heating system with an expansion tank, the requirement for backflow protection is particularly stringent due to the potential hazards associated with the chemicals used. The most appropriate protection method in this situation is a Reduced Pressure Zone (RPZ) assembly.

RPZ assemblies are designed to protect potable water supplies from contamination due to backflow. They are especially suitable for high-hazard applications, like chemically charged systems, where there is a risk of harmful substances entering the drinking water supply. The design of an RPZ includes two check valves and a pressure differential relief valve, which ensures that if the pressure in the system drops below a certain level, any backflow that may occur is safely released into a designated drainage area, preventing contamination of the drinking water.

Additionally, the RPZ provides a higher level of reassurance against backflow than other options such as single check valves or double check valves. While those options may be acceptable in lower-risk situations, they do not provide the same level of protection as RPZ assemblies when dealing with potentially hazardous substances.

Overall, the requirement for an RPZ in chemically charged solar heating systems reflects the necessity for robust safety measures in protecting public health and the integrity of the water supply.