Valve types for showers... two hot water feeds

[mayfel]

Hi!

I'm having solar panels fitted soon and to make the most of the power during the day I'll be fitting a low power immersion heater and water tank in the loft. Having a combi boiler that means I'll have two forms of hot water supply.

I'd like to have a "selector" valve wall mounted above the bath taps which will change from combi hot water to immersion hat water. This valve won't need to adjust for pressure... just be a mixer.

Then for the shower i'll need a shower mixer valve (which will be adjustable for pressure as well).

Untitled

• mayfel
• 24 Sep 2011
• 1

I just wondered what valve is necessary for the "selector" Have searched the internet and find 2-way diverter valves and 3way diverter valves but not sure of difference. Any recommendations?

Cheers,
Matthew

 

[cantaloup63]

The hot water storage vessel for the solar/immersion, will this be vented or pressurised since this will have a bearing on what sort of mixer valve you need for your shower as you are no doubt well aware.

In terms of divertor valve, would a 3-port valve do the trick, hidden and with a control switch somewhere convenient (presumably outside the bathroom, unless you use some kind of wireless version?) to toggle the valve?

 

[mayfel]

Cheers for the quick reply.

The system will be vented. In terms of valve I was actually just thinking a manual one. Kind of like a shower mixer http://www.plumbworld.co.uk/architeckt-avus-recessed-1739-384 . Then I could have it mounted just below the shower mixer but above the bath taps. Just wasn't sure of difference between 3-way / 2-way etc.

Cheers.

 

[SimonH2]

Sounds a bit complicated and you can be sure that people will forget to switch it to the solar tank - they'll switch to combi when the solar tank is cold as there'll be an incentive, but the other way round is rather doubtful. Unless you are the only person in the house that is.

Alternatively, you could wire a 3 port valve to a thermostat on the hot water tank (or program a spare relay output on the solar controller) so it will switch automatically.

There is also the issue that your combi produces main pressure hot water, your tank is vented - so there will be a noticable difference in flows between the two. And I'm not sure what the regulations situation is with connecting the two systems since a leaking valve could allow water from the tank to backflow into the mains - probably need a double check valve.

Alternatively, and I'm surprised this hasn't been suggested if you are having solar panels installed, consider a thermal store or heat bank. Rather than regurgitate all the same again, see this thread I've just posted on, but obviously ignore reference to wood burners.
//www.diynot.com/forums/plumbing/combi-boiler-with-cylinder-and-wood-burning-stove.291767/

 

[mayfel]

Hi! Sorry for not replying... I've been away for a few days.

Cheers for the reply. The thermal store deal look rather complex doesn't it? I looked into bought thermal stores like this but my combi doesn't allow pre-heated water.

Regarding the 3-port valve. Do they usually have any non-return check valve in them? I wondered if it's definitely possible to have them work so instead of the usual set up of water flowing out to A or B they could flow in from A or B (combi or immersion)?[/b]

 

[mayfel]

in fact, I still don't see why something like this http://www.ukbathroomstore.co.uk/va...h-square-backplate-p-148378.html?currency=GBP (low pressure too so can accept immersion tank HW) can't be used assuming (like the 3-port motorised valve) that it can be used in reverse as 2xInput--1xOutput rather than 1in--2out

 

[SimonH2]

The thermal store deal look rather complex doesn't it? I looked into bought thermal stores like this but my combi doesn't allow pre-heated water.

Trust me, your combi boiler makes a thermal store look as complicated as a garden hosepipe ! The only difference is that you (as the user) never see all that complexity except when it breaks down.

As for that one you link to, it's not clear what's included there. 100l is not big enough to make effective use of decent sized panels, and for 100l it's quite a bit of cash to lay out.

I would still suggest that if you want to get effective* use of your panels then you want a largish store (size depends on type and size of panels, and property size/occupancy) and ditch the combi option on the boiler. Just use the boiler to keep the store top sufficiently hot when there isn't enough solar input. Ideally, run the heating off the store as well - you can then run the heating with a modulating pump and TRVs on all rads as you don't need to worry about minimum flows through the boiler.
* Unless you only use hot water when the sun is shining, then you need sufficient storage to absorb whatever the panel produce when it's sunny, and allow you to use it when it's not. If the store is too small, then you'll end up not being able to capture all the heat, and then be using the boiler later when you run out.

In my view, a thermal store is most effective since you extract heat even from cool water at the bottom of the store - and thus you can extract the highest amount of energy from the solar panels The main downside is that the coil sets an upper limit on DHW flow rates/temperatures.
A heat bank can do the same in theory, but it needs more sophisticated controls than you get as standard - you need to throttle the primary flow to match DHW draw off rate so that the PHE can do it's job most effectively.

Regarding the 3-port valve. Do they usually have any non-return check valve in them? I wondered if it's definitely possible to have them work so instead of the usual set up of water flowing out to A or B they could flow in from A or B (combi or immersion)?[/b]

In general, a 3-port valve doesn't have check valves incorporated. You will need these in your arrangement to prevent cross flow between main and stored water as any means of backfeeding non-mains (and hence potentially non-potable) water into the mains is a big no-no.

in fact, I still don't see why something like this http://www.ukbathroomstore.co.uk/va...h-square-backplate-p-148378.html?currency=GBP (low pressure too so can accept immersion tank HW) can't be used assuming (like the 3-port motorised valve) that it can be used in reverse as 2xInput--1xOutput rather than 1in--2out

It would do (provided you add sufficient check valves) and you reduce your mains pressure. As I read it, max pressure is only 1 bar - but I'm sure there are other options. But as said before, I personally think a manual valve is a complete waste of time unless you are the only person in the house - anyone else will forget what it's for and just switch it back to the boiler the first time they get a cold shower. So you'll not get to use any of the solar heated hot water.