Heating - mixing valve (vanne melangeuse)

[Nev]

Vanne melangeuse (4 voie) Can anyone explain why it's necessary to have one of these valves in the central heating pipework, in our case, just behind the boiler. We have a fioul system and I can't understand why it all looks so complicated. Back in UK we'd have hot water by gravity circulation and heating by a pump switched by thermostat. All of my system here is manually switched and looks like the engine room of QE2, with valves to switch circuits on and off and the pump is just on a standard socket !! Ideally I'd like to use a UK-type programmer to control the heating and hot water.

[Thedunnes]

Nev

Snap.  I could not believe the size of the darn thing fitted chez nous, but a year on I can offer a few tips.

I am guessing that you have a boiler with a built in hot water tank.  This means that the boiler stat needs to be set at 60 degs.  If you did not have the mixer valve you would be send water round the house at 60 dges with would result in a lot of heat.  Use the mixer valve as a way to control the max temp of the rads.  Iset mine at about  4.

My boiler has two settings, one for summer use which basically means no power to the CH pump and a winter setting that does supply power to the pump.  On inspection there was a place on the control panel to wire in a room stat which I have done which basically cuts the power to the pump when the house gets up to temperature.

I have also taken a UK type timer over and installed this onto a board and passed the power supply to the boiler through it.  This gives me control over when the whole thing fires up.  As an extra measure I have also fitted the board with the new timer with a frost stat and wired it in parallel.  This means that if the basement where the boiler is drops below 5 degs the whole system fires up to protect from frost.  I have another frost stat to take down and wire into the upstairs to do the same should the temperature in the house drop below 5 degs.

they are rather unusual bits of kit compared to what we have in the UK, but they do work if not a little noisily.  When you fit a timer, make sure you warn people to make sure that the boiler is actually on before trying to have a shower as the hot water (in mine) can run out mid shower.  The tank is not very big on mine but does re-heat very quickly when the boiler is actualy on.

Hope this helps

Stephen

www.forsac.co.uk

 

[Richardbk]

This is the standard French system. We have a brand new system in our new house, which is practically identical to that in our older house. The system of mixing water is the same as the UK (which BTW is a more efficient way of modulating the radiator water than simply adjusting the heater temperatue),  except the 4 way valve is simply a replacement for the 2 3-way valves that you have in the UK. In fact most (not all) newer french systems use 3 way valves. The reason is due to the fact that with a 4 way warm water is fed back into the base of the bolier, rather than freezing cold - some older boliders can't cope with the temperature difference. In the UK most 3 ways systems are either on or off operated by a servo, but in fact the french system allows finer control and modulation of the valve (you can also get modulated valves in the UK). You can buy control systems to automatically control the whole system, but generally it is good enough to change the position of the valve each season. 

Then because the French use a pressue system rather than gravity feed system there are a few extras to keep the pressure maintained. The advantages here are hot water at same pressure as cold - e.g no UK type dribbling showers and it doesn't need the complication of tanks in the roof space etc , which BTW many French houses do not have.

regs

Richard

[Dave&Olive]

it is to keep the water temp to 60 + in the back boiler, this is to stop rust in the back boiler and condensation forming on it, it will run without but the fire manufactures guarantee will be void

[Nev]

Thanks guys. I'm beginning to understand, although I've never seen anything like this on our UK systems. Is the condensation risk higher because the boiler is in a colder utility room outside the main house? How do you know what the mixer setting should be? Ours is graduated 1-10 and is currently set at 7. Is it necessary to adjust it from day to day depending on what heating demands there are?

We have a separate hot water tank, a tall white cylindrical thing, so it's not incorporated in the boiler.

I've tried searching the internet but I can't find any operating instructions for these valves. I can see that they can be operated by servo-motors though, in which case where do the sensors go?

Nev

[Dave&Olive]

Ask this lad         http://www.gasman.fsbusiness.co.uk/index.htm 

[Richardbk]

You can get some very complex control systems, e.g honeywell that will have sensors all over the place - on the main flow and return pipe, outside temperture and zone/room temperature.  they will control the hot water pump and also modulate the valve. They can save quite a bit of money and keep the system running efficiently, but they are generally very expensive.  There are simpler systems that can control just the pump or valve based on room temperature or a timer.

regs

Richard

[Punch]

[quote]Vanne melangeuse (4 voie) Can anyone explain why it's necessary to have one of these valves in the central heating pipework, in our case, just behind the boiler. We have a fioul system and I can't un...[/quote]

The role of the vanne melangeuse is to mix in variable proportions the flow and return water from the boiler.

For instance, in the case of underfloor heating, it is used to have the flow water at a lower temp than the boiler output water.

The more common use is to increase the temperature of the return water so as to not cause condensation and therefore corrosion in the boiler heat exchanger, which is important in steel heat exchangers.

They can also be used to control temperature and the programmable ones can be used to zone off areas for individual control.

Paul

 

 

[Michael]

Depends on how its plumbed in and what model,if it is plumbed in as a mixing valve or plumbed in as a diverting valve, its two completly separate functions.One way it bypasses back to the boiler the other it goes around the system.Not normally used or needed on small domestic systems.Happy heating.