The problem
Legionella, responsible for legionnaire's disease, is a bacterium naturally present
in water and is found in water pipes.
Its spread represents a very serious danger for public health.
Contamination occurs by inhaling contaminated air.
The most frequent reasons for a dangerous spread of the bacterium are :
- hot water temperature too low,
- stagnation of this water in the systems,
- sedimentation and scaling in pipes.
Destroying the bacteria requires raising the temperature at 60°C - 140°F
(Legionella will die in +/- 30 minutes).
On the other hand, the increased temperature of hot sanitary water systems
multiplies the risks of serious scalding of users at a point of use.
The analysis and know-how of WATTS INDUSTRIES
The worldwide expertise and know-how of WATTS Industries
leads to better prevention with a complete solution for temperature control
in hot sanitary water systems : from the ULTRAMIX
constant temperature mixed water loop through to MINIMIXing
point of use protection, the "multi-level" approach guarantees
the right water temperature for each type of use.
This involves controlling water temperature in facilities from production and
distribution through to the point of use. Hot water production should provide
water at a constant 65°C, or even higher to carry out thermal disinfecting.
The principle of the loop is essential.
The first distribution loop, for washbasins and kitchens, is kept constant with
a return to production at 50/55°C minimum.
With ULTRAMIX, the thermostatic
mixing valve for multi-point applications, the loop ensures that all points
of the loop are supplied with water mixed to a temperature that is constant
to within one degree, regardless of the flow rate, pressure and temperature
variations of the installation.
When the temperature has been raised as a preventive or curative measure, the
mixer allows the temperature in the loop to be re-established immediately so
that operation can quickly resume.
A second "level" of the loop, intended for high-risk areas such as
showers, is fitted with a mixer calibrated to 39°C.
This shorter system, with a lower
volume of water (≤ 3 litres), avoids any risks due to stagnation.
The thermostatic mixer, in addition to providing protection against
scalding, also reduces scaling on equipment and pipes, extending the operating
life of the complete system and minimising a bacterium development factor.
The principle of automatic fluid control ensures good management of hot water : no wastage of water and heat through trial and error adjustment of the temperature, reduction of heat loss along the line, turning the warm water on and off as often as required.
In multi-point applications, it is essential to combine usefulness, robustness
and ease of use with cost savings.
Distribution of hot sanitary water
imposes obligations on operators who must reduce their control costs but also
provide systems that are very reliable for users. Comfort and safety
of users must also be guaranteed.
The " multi-level " approach is a perfect response
to these specific requirements.
The wide possibilities of use, easy maintenance and compatibility with sanitary
requirements make it an ideal solution.
Both ULTRAMIX, and the new MINIMIXing
mixing valve, are available with temperature ranges from 30 to 70°C,
they are fitted with approved check valves withstanding temperatures higher
than 90°C and the mechanisms can be easily removed for replacement or descaling
and disinfecting.
They allow preventive and curative operations against legionnaire's disease
to be carried out : thermal and/or chemical shocks essential for killing the
bacterium. But their most important quality is their minimum flow rate guaranteeing
perfect operation even with only one shower in use, this is not the
case with all multi-point mixing valves, which often require a higher flow rate
to operate correctly.
This safety aspects must not be overlooked : imagine the risks for the late-arriving child who is last in the shower after the match !
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The "multi-levels" approach
The right temperature
for each application
Key points of the regulation :
 - Increased hot temperature from the heater (use water
heaters with minimal or no storage) 
- Use of recirculation systems : circulating loop and balancing valves 
- Ensure that the target temperature is achieved throughout all levels of
the loop 
- Circulating loop should be designed to return the mixed water to the storage
not less than 55°C*.
- Mixing valves must be as close as possible to the point of use.
- Mixing valves must have integrated check-valves.
- Mixing valves must allow easy cleaning and disinfection operation.- Dismantle and clean hoses, tap, showerheads and mixing valves minimum once a year. - Hot and cold water distribution pipes must be insulated sufficiently (never together). * according to National Regulation Flow diagram for a "multi-levels" complete mixed water circuit VM : micrometer valves to stabilize circuit temperature. VM1 A : Open between 70 and 90%. Remark : If there is a connection point on the boiler (R) the return circuit should be connected here (A). Recycling of the loop : with a minimum of six times the mixed water's volume per hour. Delivery of the pump : total manometric height, minimum 4 meters + head loss of the loop. * according to National Regulation |
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| At the Interclima 2004 trade show WATTS Industries
presented MINIMIXing : a
thermostatic mixing valve for point of uses. MINIMIXing plays its role in the complete "multi-level" solution deploying the ULTRAMIX multi-point mixing valve, by providing safe point of uses at the first temperature level of the distribution loop (temperature above 55°C) : - prevention of legionella - temperature control of the hot sanitary water system (up to the point of use) - removing the risks of scalding by excessively hot water. The MINIMIXing is a very compact, modern-design (polished, chromium-plated body) thermostatic mixing valve that is easily installed on a wall-mounted isolating valve or on the wall-mounted plate supplied. The protected temperature setting is preset by the installer and the mechanism is remarkably fast-acting. MINIMIXing complies with European standard EN 1111. MINIMIXing's features for preventing the spread of legionella include : - Easy removal of the thermostatic cartridge for descaling and disinfecting without dismantling the mixing valve. This is an annual operation (subjet to survey of water conditions). - 2 check valves and stainless steel filters to prevent any contact between hot and cold water (allowing the bacterium to move from one system to the other : from the hot water to the cold for example), Product solutions - Possibility of carrying out a thermal shock : By opening the cover of the MINIMIXing and turning the cartridge to the maximum hot position (killing the bacterium from 60°C). This operation is carried out annually or after each period of inactivity (easily achieved on the MINIMIXing by means of its thermostatic cartridge allowing temperatures up to 70°C). Note : During thermal shocks, raising the temperature can break the seal on the check valves and counteract the required effect since the bacteria in the hot water will be in the cold water (or vice versa) and will contaminate both parts of the system. On MINIMIXing and ULTRAMIX, the approved check valves withstand thermal shocks because they are able to resist temperatures higher than 90°C. - Possibility of carrying out a chemical shock : Using the rinsing kit supplied, it is very easy to carry out a flush with a disinfecting solution. “No-scald” guarantee
with MINIMIXing : |
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Table 1 Development of legionella according to water temperature
<20°C / 69°F lethargic state
20-46°C / 68-115°F growth
50°C / 122°F 90% of bacteria will die in a period of 2 hours
60°C / 140°F 90% of bacteria will die in 2 minutes
80°C / 178°F 90% of bacteria will die in less of 1 minute
