Unvented Mains Pressure Systems (AKA Heatstores)

[Philip W]

Hi

I was wondering if with these cylinders it is possible to avoid having a heat dump. Let me explain my reasoning.

Firstly I am assuming there is a themostatic mixer valve on the HW out to prevent burns from the hot tap.

With a heat store the 'bath' of heated water is vented so presumably if allowed to reach boiling point (may happen with an uncontrolled heat source like a wood burner), all that would happen is some steam and boiling water would exit via a vent pipe (3nd asssumption the pipework would be such that this would be done in a safe manner). The water level of the bath would drop only to be replaced by a cold water feed.

Am I correct in my assumptions or am I missing something here?

Many thanks

[titan]

Unvented cylinders cannot be connected to uncontrolled heat sources.

[clockmanFR]

I have noticed this last few months that the European hot cylinders are starting to make inroads into the UK.

Here in France we are direct pressure fed to the hot cylinder (no header tanks whatsoever) and there is no pressure open vent system to anywhere.
Because, on the input side is a pressure reduction valve (can be up to 10bar) and then still on the input a pressure release valve and drain. Tank gets to hot and to much pressure then the valve weeps, works great but i have to replace this £40 valve every year or so because of limescale build up and then the valve constantly weeping.

[Philip R]

Philip W

Do not assume anything. To ASSUME is to make an ASS of U and ME.

PhilipR

[JohnS]

Titan and Clockman
You have missed the point.  Phillip W is talking about a vented thermal store with a header tank and expansion overflow.

Phillip W
I don't have the answer, but I am posting to keep the thread on topic regarding vented/unvented.

John

[kennyt]

I've seen setup with thermal store and no heat dump radiator which had over heated, the plastic overflow pipe had bends in it.

Would recommend using copper expansion tank and pipe, especially if you are not connecting heat dump radiator.

[titan]

Titan and Clockman
You have missed the point.  Phillip W is talking about a vented thermal store with a header tank and expansion overflow.

Maybe, but the thread title is " Unvented Mains Pressure Systems (AKA Heatstores) not vented thermal store.

[Philip W]

Thanks for the replies, Sorry guys I did mean vented. I have seen the vids on youtube showing what happens to unvented cylinders that are deliberately allowed to overtemp with a blocked relief valve.

The thermal stores I have seen including the Navitron ones don't seem to need a header tank, unlike my current vented cylinder and header tank in loft.

So the question still remains, can a thermal store be allowed to reach boiling point, providing the steam and hot water can be safely vented off and the hot water outlet protected with a TMV?

I am not suggesting this should be allowed to happen regularily but like a stagnation event, it might stress the system but good design should mean that if it does happen, it is not dangerous or cause damage.

[clockmanFR]

As I said mine does every night. My neighbour farmer across the road super boil his, (removed electric thermostat) for steam cleaning/sterilisation in the dairy parlour. Like me he gets through valve gear every year or so, and he gets throught a tank, calcium blockage, every 5 years.

On our tanks you can not block the release valve, it works the other way round.

Try...., all these are designed to be unvented and high bar pressure, but remember fittings are different sizes until you get to your 22mm copper pipe.
http://www.bricodepot.fr/carpiquet/chauffage-production-deau-chaude/chauffe-eau/chauffe-eau-electriques

[asorton]

Clockman,

The temperature & pressure relief is a safety device and not designed to run off excess heat, doing so and allowing this to happen is both dangerous & irresponsible.

The fact that this is even happening means your thermal cut out is either not functioning or not fitted correctly (assuming french regs are as strict as ours).

Your first line of defense has failed (or not fitted/fitted correctly/not required under regs) and your abusing your final line of defense, this is a recipe for disaster

[chrisenavi]

I have seen several in france where the rayburn (or equivalent) is connected to an unvented cylinder indirect coil in 28mm on a gravity circuit. The gravity circuit is vented via an f&E tank also driving radiators via an injection tee, pipestat and pump. The tanks are around 150l as recommended by aga. The unvented mains pressure (limited to 3bar) cylinder has all the usual PRV safety valves. Surely the unvented tank will take more heat than a vented indirect. These were installed by "artisans".

Any thoughts?

[dimengineer]

The point would be that using an atmospheric pressure stove loop limits the temperature to 100C max. So it's safe (kind of) although having a cyclinder full of water at 100C does scare me a bit  - but I guess if you have a main TMV you can limit the hot water to the taps to 55C or whatever.

[clockmanFR]

asorton,

I stated the facts as they are here in France.
 
I think you need to actually see a French system, before jumping to spurious conclusions, it is nothing like the English rubbish.

I have fitted English in UK but the French stuff is something else and designed for rough and tumble. I like working with the French stuff where copper pipe is 0.5mm wall and comes annealed, all joints have to be brazed/silversolder because most water pressure is around 5 bar and soft solder is a no no.



 

[Solal]

Clockman  , do you have a  link  for  a French unvented cylinder  installation manual?
Do they fit expansion  vessels? And what does  the "valve gear" include?

Also what happens  if you fail  to replace  this  valve gear  after its concreted up  with limescale?

[dimengineer]

I have a flat in France - its got a 250/300 litre DHW tank, electrically heated. No Expansion vessel. (and of course the heating is electric).
The water pressure is high - as said, probably about 5 bar, so the pipework is tiny - 10mm feed into the flat. Its similar in my Brother in Law's flat in the Alps.
As said, the continental water systems are v. different from here.