Upgrading Current System

[ln1234]

From responses so far, it looks like my current flow of 20l/min may not be sufficient for an unvented system to supply 5 showers (not all on at the same time). The current system is a vented hot water cylinder, with a pump to boost water to showers. Cold feed is currently provided by tanks in the loft, which need to be decomissioned to make space for a roof extension.

Here is a rough flow diagram of the current system:

This is what I am proposing (cold fed from mains)

Would this system work, bearing in mind the mains feed will be providing water to both boiler and cold taps? I appreciate there may be pressure differences.

Thanks

 

[ChrisR]

Not surprised nobody answered yet, you're in a mess mate.

Your first drawing's wrong. The mains doesn't go to the boiler, unless it's a combi, but it would still be wong. The mains probably goes to the tank in the loft, and from there cold water goes to your hot water cylinder where it it heated by the boiler. ?

From responses so far, it looks like my current flow of 20l/min may not be sufficient for an unvented system to supply 5 showers (not all on at the same time).

But you haven't a clue what your max mains flow is! You have measured the flow at one tap, yes? You need to measure the combined output of a couple at least and if you want to supply several showers, more. You're unlikely to see more than 20l/min from any single sink tap! You also have to have pressure information as pointed out before.

Your second sketch is as wrong as the first, for the same reason.

Do not try to arrange a shower where the mains feeds the cold and a pump the hot.
You can't pump the mains for this use.
You have 2 options as I see it.

1) use vented, stored cold water, (in what would be called a Break Tank)which could be anywhere, eg in a cellar.
Then pump it to unvented hot water tank(s). That gives you pressurised HW. Use the same pressure controlling valve which is used on the input to the HW cylinder in one of those systems, to give you your cold water at the same pressure.

2) Use the same system as 1) but don't use the "break" tank and pump, just use the mains direct. This demands a VERY good mains supply, which you may not get even if you increased all the pipe sizes.

Without knowing your mains pressure and flow, you/we can't decide anything. Ask your water supplier what your mains pressure range should be.

 

[ln1234]

Chris,

My apologies for my lack of knowledge. I was trying to do a bit of thinking for myself which clearly did not work!

Anyway, I will measure my mains flow 'properly' this weekend and try to get hold of a pressure tester. Your first solution with the break tank sounds quite suitable as I do have some space in an outside coal vault that can house a break tank and pump.

thanks for taking the time to get back to me.