Thermostatic Mixing Valves

[WHPES]

I had some guy on saying that I should be fitting TMV's on cylinder outlets to reduce hot water temperatures down to 45 degrees C on leaving the cylinder. Apparently he fits his that way! Now I have been involved in legionella prevention in commercial and industrial systems for about 20 years and know that kind of thing is really risky. He mentioned G3 to me, then I quoted back word for word the requirements for blending valves on cylinder outlets heated by uncontrolled heat sources (stoves) is what that part is intended for, and the temperature must be (if I remember correctly without looking up, (correct me if I am wrong) 60 to 65 degrees C). TMVs should be located as close as possible to the taps (less than 1m). Then he tried to tell me that you couldnt fit any valves between the cylinder outlet and the taps!

It's scary what some people do! How many people are reading the Building Regualtions without actually understanding the requirements?

 

[SimonG]

Holy crap. The bloke wants his tools taking off him.

 

[Best]

On Albion Mainsflows thermal stores, they came with blending valves already fitted to their factory pre plumbed arrangement. As the Mainsflows only had a maximum heat store of about 65 degrees, the valve was intended to blend the heat to much lower temperatures.
Guess that then was wrong.

 

[Best]

As in this photo

 

[WHPES]

Building regulations state tmvs should be as close as possible to outlets to reduce areas with potential for microbial colonisation

 

[oz-plumber]

If you have a cylinder and a TMV on the outlet of the cylinder, the system is correct because if the cylinder is heated to over 60 C, then the legionella is killed before it enter the hot water line. Due to the variants of temperatures in the hot water line from 50 C down to less than 15 C, the bacteria is dormant and not able to breed - considered safe.

If you have a ring main system then you need TMV's closer to the outlet, because the ring main becomes part of the cylinder system and the ring main must be heated to over 60 C to kill off the bacteria.

If you have a system that is a warm water ring main - 45 C - then you will need another source to kill off bacteria - ie: ultra violet disinfection system.

It's all dependant on what type of system setup you have installed.

 

[WHPES]

It is also down to risk assessment. You also need to consider that the legionella may be present on the surfaces of the line after the cylinder rather than in the cylinder itself. The industrial standards for control of warm water supply and cooling systems can be mind boggling! In some cases calls for routine disinfection cycles and as you say, UV treatment.

 

[tamz]

Legionella in domestic premises must be negligible to zero. It is all a part of the HSE's nothing else better to do (now we have shut the pits and every other heavy industry except construction) game.
By the HSE's own admission it is all down to a risk assessment
Case 357 - Some Consultants and Letting Agents misinterpreting landlords responsibilities regarding legionella risks to their tenants

Btw wHPEs never doubt yourself in the face of an idiot even a confident one.