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Legionella madness

On a recent training course, he was informed that, to conform to G3, you must heat your hot water cylinder to 60 deg C or more every day to prevent legionella. I'm not belittling this advice; legionella prevention is very important, but every day? Really?

In the past we have always done this once a week.

In almost all cases where a heat pump is used, this means heating the water from the normal operating storage temperature of 50 deg C to 60 deg C with an electric immersion heater. This is very inefficient and unnecessarily costly.

Here's the maths - to heat 300 litres of water by 10 degr C electrically takes 3.5kWhr of electricity which costs 50p using full price electricity. To do this every day would cost £180 a year.

Is this advice really true or has my customer been sold a pup?

Our units, much like most others, have the facility to heat the water every day for legionella if required, but is it really a good idea?
Posted by Graham Hendra 26 March 2013 10:11:23 Categories: Graham's Gossip


By Tim Jones
26 March 2013 10:19:23
I wish the cold water side in my gaff was routinely between 20 and 50! It would save me a fortune in heating bills.
By Dane Madsen
26 March 2013 10:18:23
1) The problem with this plan is that water will scald to 2nd degree burns at this temperature in only 2 seconds, 2) this does not remove the colonies in the distribution system. 50 degrees C will inhibit growth but one the water cools, legionella will continue to propagate, and 3) it does not address the cold water side where water is routinely in the 20 to 50 C range and is the prime temperature for growth. This water is mixed in showers and taps so the super heated water is significantly lower thant the heat levels to kill therefore the cold side legionella will survive.
By steve austin
26 March 2013 10:17:23
as Graham said, if it's in L8 you should do it, but if you don't you have to prove in a court of law the you have followed the provisons of the code or have something better, remember legionella is now covered under corporate manslaughter so prepare you bed in a cell.
By Graham
26 March 2013 10:16:23
158 In a hot water system, cold water enters at the base of the calorifier with hot water being drawn off from the top for distribution to user points throughout the building. A control thermostat to regulate the supply of heat to the calorifier should be fitted to the calorifier near the top and adjusted so that the outlet water temperature is constant. The water temperature at the base of the calorifier (ie under the heating coil) will usually be much cooler than the water temperature at the top. Arrangements should therefore be made to heat the whole water content of the calorifier, including that at the base, to a temperature of 60 C for one hour each day. This period needs to coincide with the operation of boiler plant (or other calorifier heat source) and is usually arranged during a period of low demand eg during the early hours of the morning. A shunt pump to move hot water from the top of the calorifier to the base is one way of achieving this, however, it should not be used continuously except for about one hour each day (see above). In all cases the operation of the pump should be controlled by a time clock.
By Malcolm Kennard
26 March 2013 10:15:23
Copper/Silver Ionisation - can facts be checked before comments are made please?
I thought this blog might have some specialists input, given it will be read by the original author looking for facts.
This is exactly what is meant by the use of inappropriate or incorrect advice or comments being made when it comes to water hygiene. The FACTS ARE:
An EU Directive called the Biocidal Products Directive with the Biocide Products Regulations 2001 gave notice that, as from 1st February 2013, it became illegal to market, sell or use copper/silver ionisation systems that produce copper ions that are displaced into the water system for the control of Legionella. It is an EU-wide ruling applicable to the UK. If in doubt, please refer to the HSE website.
The HSE has, however, submitted an essential use derogation notice to the EU Commission requesting the UK be allowed the continued use of the systems, but the decision to allow their use will be made by the EU Commission after completion of a 60 days commenting period that ends on 20th April 2013. Whatever the EU Commissions decides will be final. If they decide the systems cannot be used in the UK, that will be the end of the such system in the country.
By Vee Namli
26 March 2013 10:14:23
Install a Tarn Pure Copper/Silver ionisation system and store hot water at whatever temperature you deem suitable. CuAg technology is an alternative to thermal control and is recognised in the ACoP L8.
By Malcolm Kennard
26 March 2013 10:13:23
Unfortunately there are too many individuals and organisations offering erroneous legionella advice. Even advice correctly given is often misunderstood.
In this case, the description of water temperature requirements given to the customer is partially correct. To explain:
The Building Regs Part G, edition 3, has no reference to either 50degC or 60degC in connection with legionella prevention, although it makes reference to water being distributed from hot water generating plant at temperatures no higher than 60degC. However, the G3 Guidance Note 3.6 refers the reader to a publication issued by the HSE entitled HSC ACoP.
Temperature control is contained within Section 151 (Hot Water, Section B)of HSC ACoP L8 wherein it describes that hot water generating equipment (cylinders/calorifiers, direct fired water heaters etc) should deliver water to the hWS distribution pipework at a temperature no less than 60degC and with return temperatures (if applicable) at no less that 50degC. Branches from all HWS pipework must be designed to deliver water to outlets at no less than 50degC after one minute of opening the tap. Some establishments such as schools, care centres, hospitals etc are governed by regulations dictating the installation of Thermostatic Mixing Valves set to 43 or 45degC (dependant on the application and building), but the hot water entering the TMV must still be at 50degC.
Therefore heating plant thermoststas must be set to 60degC, not just once a day, not just once a week, but constantly.
Systems that have been idle for a week or more must have the temperature of the heater raised to at least 60degC for one hour immediately prior to use and the water circulated through the HWS pipework with the return pumps operational.
Hoping this helps.
By Christopher D. English, PE
26 March 2013 10:12:23
I recommend you review the Draft ASHRAE 188P Standard on Prevention of Legionellosis.
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