Insulating ring mains to a very high standard is essential. Any ring main is a fixed operating cost for a building. Where occupancy is low (think hotels during Covid), the heat loss from the ring main can be a significant proportion of the hot water energy use. Remember in systems not incorporating UV sterilisers, return water temperature must be greater than 55°C (AS/NZS3500.4) or 60°C (G12/AS1). For applications where temperature is limited to 45°C, an even higher standard of insulation is required to ensure water at the last fixture is sufficiently hot. Temperature gauges should be fitted to the storage vessel (or heat source) outlet, return water connection, and after the mixing valve of temperature-controlled systems. It is important that the sensing elements of gauges are inserted into pockets that sit well into the flow stream of a pipe. We have seen many temperature gauges which don’t sense the actual water flow temperatures. This makes it difficult to demonstrate compliance.
A well-operating ring-main system ensures near-instant hot water at the customer’s tap. Rinnai has advice on implementing a successful ring-main project.
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uidance on ring main design and installation can be found in Section 1 of AS/NZS 3500.4:2021 and scattered throughout G12/AS1. Ring mains (or circulatory heated water reticulation if you’re a fan of AS/NZS 3500.4) can be divided into two basic types: temperature-controlled and tank-temperature. Temperature controlled ring mains are normally below 55°C in residential buildings to meet the safe water temperature limits of G12/AS1. They may also be controlled below 45°C for retirement homes (and other buildings defined by G12/AS1 6.14.1 b). They can be controlled at greater than 60°C where: tank temperatures may be higher than the pipe system rating; or there is a poorly controlled temperature source; or the hydraulic designer prefers to have a known temperature circulating.
1 Tank-temperature systems
Tank-temperature systems have the advantage of simplicity. They are lower cost to install where there are a small number of outlets. Hot water can be provided at a variety of temperatures to different fixtures. Challenges with tank temperature systems include: excess temperature degrading polymer pipe access to point-of-use mixing valves for maintenance sticking non-return valves causing cross-connection through mixing valves (which results in low temperature water and high running costs) cost of valves in large installations.
Ring mains can be divided into two basic types: temperature-controlled and tank-temperature.
2 Temperature-controlled systems
Temperature-controlled systems are commonly set to 55°C in medium to large accommodation buildings, which allows simpler connections to each unit without mixing valves. The possibility of future cross-connections through partially open non-return valves is eliminated. The most common issue found with installation of mixing valves in temperature-controlled systems is the failure to include a short circuit path from the ring main return to the cold port of the mixing valve (see Figure 1, Point 1).
Figure 1: Temperature-controlled ring main. 1. Return connection to mixing valve. 2. Cold connection to mixing valve. 3. Ring main return non-return.
Two ring main return loops, each with active/standby pumps.
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This is required to supply the mixing valve with a source of water at a temperature below the set temperature at times of no draw. Without this connection supplying the cold port, the mixing valve will have flow only into the hot connection, which will then close
