Unvented Cylinder Query

[Lordjonnyb28]

I’ve recently moved into a property which currently has a combi boiler, two bathrooms, one power shower and one electric shower. I’m wanting to change this out for an unvented system with two showers operating from the cylinder. Both showers would run at 20 LPM. My current water supply is 15MM which is located at the back of the property. I don’t want the stress or cost of rerouting 25MM into the property. Here is my query as follows: I currently have 20 LPM and an unbelievable 8 BAR pressure I am considering putting either an accumulator or a pumped accumulator into the loft and then feeding the water supply thereafter. However, I don’t know if I require an accumulator with that amount of pressure or anywhere that would tell me what size accumulator I would require with a 300
litre unvented cylinder. Many thanks for any advice you can offer.

 

[Sharp Point]

Is that 8 bar working or standing?

 

[Lordjonnyb28]

8 BAR standing and working.

 

[Sharp Point]

You 100%, did you test? If so, how did you carry out each test?

 

[Lordjonnyb28]

Yes. I connected a pressure gage off the outside tap which is immediately after the stopcock and then turned the kitchen tap on. I was surprised also

 

[Sharp Point]

Does the outside tap have a check valve built in or inline?

 

[Sharp Point]

Does the outside tap have a check valve built in or inline?

 

[Riley]

I’d recommend you get a G3 qualified engineer in to design it for you as you will need one to install the cylinder anyway

 

[Sharp Point]

And another biggie is.... if you go down the route of an accumulator and cylinder( maybe in the loft) is the weight. I’d hazard a guess the accumulator will be nigh on the size of the cylinder. So a rough guesstimate of around 700kg of weight in the loft, so you’ll have to look at a structural engineer to design a structure/ added joists to accommodate the weight

 

[Riley]

Might be easier to mole in a new mains

 

[Millsy 82]

Does the outside tap have a check valve built in or inline?

I did that many years ago not thinking.

 

[Sharp Point]

T

I did that many years ago not thinking.

thats How we all do it, learn from our mistakes.

 

[Brambles]

I do a lot of work with accumulators in the Thames Water Area. They are excellent when the incoming pressure is below 2 bar. They are unsuited, for a number of reasons, to be located in the loft space.

The starting price, installed, is well over £2k for the simplest of systems.

If you have a working pressure of 8 bar on a 15mm incomer, in my view start to spend your money upgrading to a 22mm from the mains to the Combi.

Therafter, if required look at further modifications

 

[Welder]

I’ve recently moved into a property which currently has a combi boiler, two bathrooms, one power shower and one electric shower. I’m wanting to change this out for an unvented system with two showers operating from the cylinder. Both showers would run at 20 LPM. My current water supply is 15MM which is located at the back of the property. I don’t want the stress or cost of rerouting 25MM into the property. Here is my query as follows: I currently have 20 LPM and an unbelievable 8 BAR pressure I am considering putting either an accumulator or a pumped accumulator into the loft and then feeding the water supply thereafter. However, I don’t know if I require an accumulator with that amount of pressure or anywhere that would tell me what size accumulator I would require with a 300
litre unvented cylinder. Many thanks for any advice you can offer.

By far & away your best option is the upgrade. Simpler, cheaper no main or running costs. No brainer.

Just make sure the meter installed is NOT a 1/2" one as that will make the upgrade virtually worthless.

Time for a good G3 installer...

 

[Lordjonnyb28]

Apologies for delay but I’d thought I’d get back to you with some decisive figures as yes you’re right the outside tap does have a check valve on. I took the static pressure from the washing machine outlet at 8 bar with one tap open it drops to 7.5 bar, two taps open 4 bar and three taps open 2 bar. Flow rate added through each outlet is 35 LPM. I’m thinking I now don’t need an accumulator and just upgrading 22mm pipe from the stopcock to the cylinder. Would this work? Thanks

 

[Brambles]

That does not look like a set of results fed by a 15mm incomer.

Generally you want to limit the velocity of water travelling through a 15mm pipe to 2m /second - above that the noise of the water travelling through the pipe will get progressively louder. A 35 litre /minute (lpm) flow from a 15mm service would mean that the water has a velocity of about 4m/ second.

It may well be the case that with a pressure differential of 6 to 7 bar you are indeed getting 35 lpm from a 15mm supply, but that is a more complex calculation for a Saturday morning.

However, at the flow rates you are citing I would expect the noise from the flow of water through the 15mm incomer to be audible and annoying.

I suggest you try to undertake a detailed study of all the pipe sizes, valves et al from your incoming point (water meter - including the bore of the meter) to the first offtake to establish the correct position of exactly what is already installed.

My belief is that your incoming is a probably a 22mm supply - possibly with a short 15mm restriction, that could be removed

Once you have determined the above, then you can look at the options available to achieve what you are seeking.

I hope this helps

 

[Lordjonnyb28]

Many thanks. This sounds more plausible. The incoming is underneath tiled floor which I was hoping not to take up yet but will have to check the pipes.

 

[Welder]

That does not look like a set of results fed by a 15mm incomer.

Generally you want to limit the velocity of water travelling through a 15mm pipe to 2m /second - above that the noise of the water travelling through the pipe will get progressively louder. A 35 litre /minute (lpm) flow from a 15mm service would mean that the water has a velocity of about 4m/ second.

It may well be the case that with a pressure differential of 6 to 7 bar you are indeed getting 35 lpm from a 15mm supply, but that is a more complex calculation for a Saturday morning.

However, at the flow rates you are citing I would expect the noise from the flow of water through the 15mm incomer to be audible and annoying.

I suggest you try to undertake a detailed study of all the pipe sizes, valves et al from your incoming point (water meter - including the bore of the meter) to the first offtake to establish the correct position of exactly what is already installed.

My belief is that your incoming is a probably a 22mm supply - possibly with a short 15mm restriction, that could be removed

Once you have determined the above, then you can look at the options available to achieve what you are seeking.

I hope this helps

Great advice.

 

[Riley]

As Brambles said the key here is what your pipe up to your internal stopcock is