water system designs

Firstly, there are many Codes, Australian Standards and Water Heater Manufacturers requirements to be considered and provided for, when a System is required to produce warm water (not exceeding 45°C at the outlet).

It is a requirement that all storage water heating systems must be heated and kept at temperatures above 60°C.

It is recommended that a water heating system that can provide for warm water in Hospitals, Aged Care, Childcare centres and the like should be designed by a Licenced Hydraulic Services Consultant.

By engaging a professional to provide the design of the system, the technical aspects in regard to the type of building, number of outlets to be served, layout of amenities and size of the system can be catered for. Other important factors would be water supply source and quality as well as pressure.

When all the system requirements and constraints are known, then the system designer would determine which design is best suited for the application.

The building might be best suited to either several remote water heating plants or maybe a single central plant to serve the building.

The determination of whether a system or systems is to be a “deemed to satisfy” or a system that may need to be approved as an “alternate solution” is something the building owner, Consultant and Architect would need to determine at the early design stage of the building’s design so that provision for the system can be catered for in terms of space and location. There are a number of ways that warm water can be supplied to the points of use and these are systems that are currently in use in various buildings throughout Australia. One system is where the water is heated and stored above 60°C and delivered throughout the building in a pump circulated “Ring Main” at 60°C with a thermostatic mixing valve being installed at the points of use, for example, at ensuites, amenities for persons with disabilities, childcare amenities and the like.

Other systems are where the water is heated and stored above 60°C and has a thermostatic mixing valve or valves located at the water heater and pump circulated at 45°C to 50°C throughout the building to ensure temperature at the points of use is at 42°C to 45°C maximum.

All system designs should consider that the pipe materials used are fit for purpose and that “Dead Legs” in the pipe system are kept to a minimum. “Dead Legs” can be the pipe from the ring main to the mixing valve and
similarly for a warm water circulated system being the branch from the main to the outlets. These branches are typically where bacteria and in particular Legionella can multiply. Other “Dead Legs” are branches to isolated basins that are not used frequently.

One issue is designing a system that has no “Dead Legs”, which is near impossible and an ensuite to a room that is not occupied and therefore is not used for some time could also be considered a “Dead Leg”. While these issues like isolated fixtures or unoccupied ensuites are not a design problem, the building operator must ensure these points are regularly flushed. Other “Dead Legs” occur where fixtures have been deleted and pipes capped
at the point of use. It is of utmost importance, that any redesign when pipework is no longer required, the pipework should be taken out and capped at the main line, thus eliminating any branch at all from the main line.

While we can take into account good design parameters, it should be noted that Legionella is in the cold supply, not in the hot water that has been heated to 60°C+.

However, it is very difficult to eliminate Legionella in cold water without first heating the water to temperatures above 60°C. Therefore, it is imperative the cold water design considers the use of filters, Ultra Violet Light and
Chlorination. These system design items, along with Thermostatic mixing valves should be maintained and monitored regularly in accordance with a Water Management Plan suited to the system selected. 

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