The system includes the electrical control box, face plate, tap operation counter, keyswitch, solenoid valve and fittings. Includes automatic purge for avoiding stagnation when not in use and keyswitch thermal decontamination.

Thermal Purging

Thermal purging offers an effective way of disinfecting the thermostatic mixing valve, solenoid valve, tap outlet and interconnecting pipe work.

It is however important to understand the effectiveness of temperature in disinfection. There does not appear to be any absolute guidelines however considering the disinfection effects at different temperature ranges some tolerance should be made to ensure effectiveness.

You cannot just pass normal circulating hot water (often around 55ºc to 63ºc) through the system for a short period for effective disinfection.

The following table gives some indication of the effectiveness of different temperatures for killing Legionella:

Legionella

An optimum design for the plumbing

For Thermal Purging to be really effective the temperature needs to be raised to above 70ºc. To provide some tolerance the target temperature should be 75ºc.

There are 2 possible considerations to ensure water temperature is high enough to achieve disinfection.

The optimum solution would be to have local water heaters allocated to the areas where thermal disinfection is beneficial and these could then be set at say 75ºc.

A second option is for the circulating water to be increased to 75ºc to 80ºc during the maintenance period for disinfection purposes.

It is important that all the outlets from this heating source have suitable thermostatic mixing valves to safeguard against the risk of scalding.

Minimum Deadlegs

For healthcare applications we recommend pipe work to be copper, stainless steel, PE such as LLDPE or PEX or with Flexibles lined with PE.

It is important to have very short legs from the circulating water to the thermostatic mixing valve.

The thermostatic mixing valve and solenoid valve should be mounted above the tap and as close as practicable thus most water is drained after operation and there is very little warm water retained in the system.

Cold Water Risks

Sometimes risks in the cold water supply is underestimated, and is an area that needs further research. Whilst Legionella is dormant below 20ºc, Pseudomonas Aeruginosa can grow from 11ºc.

Using refrigerated water at 4ºc is best, but as a minimum it should be ensured that the cold water supply remains below 20ºc. Other water treatments such as Chlorine Dioxide may be a consideration.

Many factors contribute to biofilm and bacteria growth in water systems but provided the plumbing is to good standards then stagnation is one of the most important contributors to guard against.

Automatic purging can help eliminate this potential problem. All hospitals should have some procedure to ensure water cannot stagnate in dead legs. Any device that has a water pipe feeding to it where the water is not constantly circulating can become a dead leg if the device is not used for a period of time. This could apply to taps, WC’s, showers etc.

For high risk areas where patients are highly vulnerable with low immune systems extra care is require to avoid against bacteria from water.

This system allows hot water to be passed through the thermostatic mixing valve to disinfect the thermostatic mixing valve, solenoid valve, tap and interconnecting pipe work. We must however remember the importance of getting the water temperature to above 70ºc to be effective.