Thermostatic mixing valves and water safety

Whether a homeowner or land-lord or a local council, building owners have a duty of care for those living, working, or using their facilities, which is why thermostatic mixing valves (TMV) play a crucial role in all plumbing systems. It is imperative that some form of TMV be specified for every hot water system. The main benefit of a TMV is keeping water at a safe temperature, which therefore prevents scalding and helps stop the build-up of harmful Legionella bacteria. This is achieved by mixing hot and cold-water streams together to ensure a safe temperature at the outlet.

The type of TMV required for an individual application will vary greatly on what kind of building the specification is taking place in, as domestic and commercial buildings have a different requirement to buildings in the healthcare sector.

It is recommended that in domestic and commercial environments, a TMV2 approved valve is specified, and safely installed, tested and maintained to current standards. These valves are designed to reduce the risk of scalding at outlets, while minimising the potential build-up of Legionella bacteria in the pipework that is fed from the outlet side of the valve to the tap. They are typically found under sinks and basins, and never more than 2m away from the outlet they are serving. For buildings occupied by the healthcare sector, such as hospitals, a TMV3 needs to be specified, which functions the same way as a TMV2, but undergoes more rigorous testing, both at the point of installation, as well as every six months after initial sign- off. This is to ensure the safety of the end users, who are likely to be more vulnerable to both scalding and the potential harmful infection from Legionella bacteria.

Where a TMV2 can typically only work with water pressures of 5 bar or below, a TMV3 is safe to work with 10 bars of water pressure.

Water safety in buildings, published by the World Health Organization in 2011, defines thermostatic mixing valves as: ‘Tempering valves that are typically temperature-activated. Used to mix hot and cold water to achieve a predetermined outlet temperature, and that are fitted between the water heater and the point of use to control the distribution temperature. Slightly different temperature ranges are used in some countries.’

Legionnaires' Disease - Operation and Maintenance Log Book (BG 58/2015), written by Reginald Brown and Salim Deramchi, and published by BSRIA in May 2015, defines a thermostatic mixing valve as a: ‘Mixing valve in which the temperature of the water at the outlet is pre-selected and automatically controlled by the valve.’

The above article includes an extract of "Do not get your ABCs confused – all you need to know about TMVs, PRVs and the Tenant Valve" published in the AT journal, issue 144, Winter and written by Richard Bateman, Product Marketing Manager, RWC

--CIAT

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