Legionella

[MikeHolm]

In my solar work, the European emphasis on keeping Legionella to a minimum is front and centre but in north America it seems to be a second rate concern. I can think of one report, here, that I have seen outlining the issues with legionella in water tanks.

Does anyone know of real world deaths or major sickness attributed to use of HPs or water borne (from tanks, not ducted AC issues)? This can be from anecdotal as I am not expecting anyone to come up with a report.

I am trying to determine if the likelihood of legionella is a big issue at water heated to 50C (max).

[monkey spanners]

This is something i have been wondering about, recently i have installed the fridge pipework a open top heat recovery tank which doesn't get much above 55C, and i have been meaning to phone and ask the manufacturers about the possibility of legionella in it.

What made me wonder was a friend of a friend who has a heatpump in a barn conversion who has had to fit a suplimentary electric heater because the water doesn't get hot enough to ensure no bugs are growing in it.

[Oakgreen16v]

Legionella could potentially be an issue with DHW systems hence the HSE guidelines and the inclusion of immersion heaters on a number of ASHPs to raise cylinder temperature from 55°C to 60°C. The work undertaken for the HSE came up with the following stages of legionella existance relating to temperature, however it also found that the thermal clensing process is only required every 3 - 5 weeks, therefore situations with frequently used flowing water are less at risk of infection. Weekly periodic pasturisation is more than sufficient but in theory if the cylinder is replenished and rehaeated completely every few days there is no risk storing at lower than 60°C anyway. There has never been a known case of domestic hot water systems causing legionella infection in the UK.

At 60 °C - Legionella dies instantly
At 55 °C - 95% die
50 to 55 °C - Can survive but do not multiply
35 to 46 °C - Ideal growth range
20 to 50 °C - Growth range
Below 20 °C - Can survive but are dormant

[frank]

Found this information regarding the number of cases reported in the Uk over the last few years

http://www.hpa.org.uk/web/HPAweb&HPAwebStandard/HPAweb_C/1195733748327

[stufus]

As OG16 Says +60 is the number
Did an install a few years ago and got called back to a meeting.
Went back to find someone was seriously ill in hospital and the A/C was the cause.
Seriously concerned , decided to investigate along with the local authority.
On investigation discovered the cause was a rarely used shower room that was out of bounds during the refurb,the cause being the stored water as opposed to the shower obvously.
But got me interested.
Cheers
Stu

[MikeHolm]

All good answers and I thought as much. The main outbreak was in Philly in the 70s at a convention of retired army dudes, hence the name "Legion". The cause was attributed, if memory serves, to the open cooling tower and mist type dispersal units in ducts (this isn't my area so forgive me if I don't use the right terminology).

I don't recall ever seeing a case related to mist from a shower stall but since Stu has, there must be more. In solar, the European controls will increase the max tank temp once every few days to 65 or 70C. North American controls don't do this.

Cheers

[Aper Willy]

Het grootste probleem van legionella zit hem in de koudwaterleidingen, deze liggen soms te dicht bij de warmeleidingen waardoor de temperatuur oploopt tot de legionella broeitemperatuur. Indien de douche sproeiers leeglopen na gebruik zal hier geen legionella aanwezig zijn.
Warmwater opstoken tot boven de 60°C heeft geen zin als het daarna gemengd wordt met deels verwarmdt koudwater. Als je koud drinkwater aftapt en het is eerst te warm om te drinken dan is er al een probleem.

[Aper Willy]

The biggest problem of Legionella is in the cold water pipes, which are sometimes too close to the hot lines so that the temperature rises to the legionella heating temperature. If the shower drain after use sprinklers will be no Legionella present.
Hot water heating up to above 60 ° C is useless if it is then mixed with some cold water verwarmdt. If you cold water and draining it is but too hot to drink then there is already a problem.