WATER SYSTEM HYGIENE & SAFETY DELABIE THERMOSTATIC TECHNOLOGY SHW
Temperature control No non-return valves Mixed water Mixed opening control Mixing chamber
SMW By closing the control , the SHW is closed.
The thermostatic cell therfore closes the SCW. There is no risk of cross-flow between the SHW and SCW.
SCW
Temperature control Non-return valves Mixed water Mixed opening control Mixing chamber
SMW
Sooner or later, the non-return valves are obstructed by impurities, causing cross-flow between the SHW and the SCW, responsible for bacterial development.
Figure 1: Delabie has developed a new dual control thermostatic shower mixer with an anti-scalding failsafe that it says meets TMV3 standards without the need for NRVs.
infection. Current healthcare guidance recommends thermostatic mixing valves (TMVs) approved to the D 08 performance specification to provide anti-scalding safety wherever there are vulnerable people, defined as: ‘children; older people; people with reduced mental capacity, mobility, or temperature sensitivity; people who cannot react appropriately, or quickly enough, to prevent injury’.3
TMVs with anti-scalding features To protect these vulnerable users, point- of-use TMVs typically incorporate several anti-scalding features, including: n Thermostatic control to deliver a stable and safe mixed water temperature regardless of pressure and flow rate variations in the system;
n A ‘cool-touch’ body and connectors to prevent burns;
n A maximum temperature limiter set at 41 °C that cannot be overridden by the user;
n And, critically, a hot water and cold water failsafe to shut off the outlet in case of sudden supply failure.
However, more recently, Estates & Facilities teams have begun to remove TMVs which are perceived to present a high risk of infection due, in particular, to their integrated filters and non-return valves (NRVs). NRVs are routinely installed on the hot and cold water inlets to prevent interconnection or cross-flow. They allow the incoming water to flow in one direction only, operating as a check valve or backflow prevention device. However, they must be regularly checked and serviced to ensure that they continue to function correctly and safely. In a patient room with a basin and shower, this means four NRVs, multiplied by the number of rooms… which potentially equates to an overstretched maintenance team. Sometimes, the expedient solution is to switch TMVs for mixers without NRVs, and manage the risk of scalding by alternative means. Non-return valves require regular
maintenance to ensure that they are functioning correctly. Any failure due to the build-up of scale or debris can lead to interconnection, also known as cross- flow. Cross-flow occurs if there is a sudden drop in the cold water supply pressure to the mixer; for example when several toilet cisterns are refilling simultaneously. This creates an imbalance in the system, and the higher pressure on the hot water side
causes hot water to flow back into the cold water system. This inevitably changes the conditions in the cold water supply pipe, heating the water above 20 °C to the point where Legionella bacteria are no longer dormant.
Six resident deaths in French retirement home An investigation into the cause of death of six residents in a French retirement home found that NRV failure caused heat transfer from the hot water to the cold water upstream of the thermostatic mixer, resulting in bacterial proliferation. This reinforces the ECDC advice: ensure regular maintenance to prevent component failure, which will then ensure that cold water supply temperatures remain below 20 °C. So, the challenge is to not only
balance the risk of scalding versus the risk of infection, but also to consider the maintenance burden. However, removing TMV technology is a short-sighted response, which increases the risk of scalding for the most vulnerable users. Not all TMVs rely on NRVs to prevent cross-flow. Delabie has developed a new dual control thermostatic shower mixer with an anti-scalding failsafe that meets TMV3 standards without the need for NRVs. The left-hand control (4) opens and closes only the hot water, allowing the hot water to flow into the mixing chamber (See Figure 1). The thermostatic cell blends the mixed water to the desired temperature set by the right-hand
Delabie says that ‘thermostatic anti- scalding technology reduces the maintenance burden’.
76 Health Estate Journal October 2023 CLOSED
Full flow COLD WATER
Full flow MIXED WATER
Figure 2: With Delabie’s thermostatic single control sequential basin mixers, the single lever controls both flow and temperature. The mixer opens with only cold water, and the hot water begins flowing once the lever passes the perpendicular, allowing the thermostatic cell to start blending the hot and cold water while taking into account pressure and temperature variations.
CONVENTIONAL THERMOSTATIC TECHNOLOGY SHW SCW
© Delabie
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