Combi's don't work in larger houses - still true?

[dilalio]

One step further is a second coil in a vented cylinder to provide mains pressure hot water to the shower with taps being fed at lower pressure from the water stored in the tank.

How are you dealing with expansion in this setup?

 

[bernardgreen]

The maximum volume of expansion in the mains pressure coil occurs when the whole vented tank is heated from cold to 60°C

That maximum volume of expansion is less than 2% of the volume of the dedicated pipe bringing mains water to the coil, cold supply to shower and cold water storage cistern. That dedicated pipe is an 11 metre run of 15 mm with a rise of 5 metres from kitchen to coil. Hence water expanding in the coil and moving back into that feed pipe will not travel more than a metre along the pipe and thus contamination of the supply to the kitchen tap cannot occur.

 

[John D v2.0]

Hence water expanding in the coil and moving back into that feed pipe will not travel more than a metre along the pipe and thus contamination of the supply to the kitchen tap cannot occur.

True but I thought there were also issues with water meters with built in check valves? When we had a meter fitted ii had to add a mini expansion vessel before the boiler to meet vaillants requirements.

 

[bernardgreen]

If there is a check valve then the alternative "pressure relief system" may be called into play. Ball valves in cold water tanks shut off the flow of water when the force exerted by the ball mechanism is greater than the force exerted by the small area of water pressing on the washer in the valve. Force not pressure. Force = pressure X area

Hence valves for low pressure water can have a larger aperture in contact with the washer than valves for high pressure for the same force from the ball mechanism.

The force exerted by the water on the washer in the valve will increase if the pressure in the water increases. If this increase in pressure means the force is greater than the opposing force from the ball mechanism the valve will let by. Hence excessive expansion causing a significant increase in pressure will cause the valve to open very slighty and thus release the pressure

 

[durhamplumber]

was at worcester bosch a few days ago doing a training course. There was a really knowledgable guy doing the course - focussing on the cdi... during the day he said that a new boiler range was ‘pretty much there’ and would be a ‘game changer’ (his words...). Now, i don’t know any timescales but i got the impression it was imminent as he was talking[/QUOTE

 

[John D v2.0]

@bernardgreen i think I'm going to need a diagram to understand that!

 

[Dan Robinson]

And some bench tests - after all - why bother with open vents if ball valves act just as effectively? .

 

[dilalio]

And, as for meeting regs???

 

[bernardgreen]

why bother with open vents if ball valves act just as effectively?

because with a pressure of 1 bar in the water the open vent would need to be 10 metres ( 32 feet ) above the highest part of the system. With 3 bar the height needed would be 30 metres ( 96 feet )

 

[bernardgreen]

@bernardgreen i think I'm going to need a diagram to understand that!

Really. http://www.atcmtanks.org.uk/technews.html and click on "Float valves Their ins and outs

Doesn't specifically mention pressure relief function but does relate upthrust from the floating ball to the pressure.

Further considerations are the float may be damaged and unable to provide the necessary upthrust. A ball float should be no more than half submerged when the valve closes against its rated pressure.

or http://www.upperplumbers.co.uk/plumbing/plumbing_pages.php?title=Float-operated Valves&cat=9

mentions the word "equilibrium"

Time to do some homework. ?

 

[pete50]

I'll wander it back on track. Combis don't work anywhere if you want a decent shower.

 

[John D v2.0]

I'll stick with the mini ev. Should also reduce the load on our remaining length of lead pipe that's buried in the foundations.

And back on track indeed, agreed completely with Pete if your idea of a decent shower is 45 degree water at 25+ litres a minute in midwinter.
For us around 8l a minute at 37c is fine and well within the capabilities of a 24kw Combi all year round.
IE depends entirely on the requirements of the end user.

 

[Hot&Cold]

love this thread,it just keeps giving & giving Mr

so many people will read this thread and assume everything posted is correct,got to love the internet and 's lack of obtaining any wras approval for their adhock install.

Thank you microsoft

 

[garyo]

Thanks for the responses. I think you've sold me on sticking with the idea of unvented. If I site the cylinder in the downstairs utility room then space isn't really an issue. I presume that doesn't change the complexity or performance other than meaning that that circuit would need to be pumped from the boiler rather than gravity.

 

[dilalio]

love this thread,it just keeps giving & giving Mr

so many people will read this thread and assume everything posted is correct,got to love the internet and 's lack of obtaining any wras approval for their adhock install.

Thank you microsoft

I have this vision... Bernard in full Fred Dibnah attire, complete with oily rag, sitting on a 3-legged wooden stool, by his steam-punk contraption, constantly monitoring gauges and operating levers 24/7 to keep everything in perfect working order... for the rest of mankind, with jobs, wives, kids... and a life... perhaps you should go with more conventional systems that the day-to-day tradesmen on here advocate