water flow rate and combi

[boolie]

OK so just to re-iterate - bought an old house.

Anyway I contacted the water provider to locate the stop cock.. they didnt know where it was so sent someone out. The external stop cock is located about 20 metres away from the garden. So the water supply runs beneath someone else's private land.

Whilst he was here, I asked him to measure flow rate. and he measured 2.4 bar 50 l/min at the cock and 1.1 bar 10 l/m at the property

Now, I want to install a combi boiler for convenience sake - the current vented set up isn't adequate and keeps getting air locked.. but I think this water pressure is probably too low for a combi

Am I right? Can I get the water company to relocate the water supply so it falls beside my property rather than 30 metres away? Also what could be causing the massive pressure drop between the stop cock and my house (distance to kitchen is approx. 30-40 metres)?

 

[bernardgreen]

I want to install a combi boiler for convenience sake

Convenient for the qwicky fit'n'go installer but not necessarily convenient for the people who have to depend on it for the next few years.

 

[muggles]

You could just about run a 24kW on your supply but that's it. Definitely worth speaking to your supplier about options to upgrade but they may want to charge you if it means extending the pipe in the road.

The pressure drop will be due to the size of your supply pipe and length of run creating resistance. A larger bore pipe would fix this

 

[boolie]

You could just about run a 24kW on your supply but that's it. Definitely worth speaking to your supplier about options to upgrade but they may want to charge you if it means extending the pipe in the road.

The pressure drop will be due to the size of your supply pipe and length of run creating resistance. A larger bore pipe would fix this

Thanks @muggles - just been speaking to the water board and they can give me a new water connection where the stop cock is literally just outside my garden. There's a public path that runs down the side of my house and they can use that (at a cost of course!). This process will take several months though

So, I'm thinking to future proof the boiler so it ultimately has a good shower flow rate to go with a 30KW combi? but it will need to work on the current low flow rate until the supply is upgraded. Will a 30KW combi work ok-ish with a 10l/min supply?

 

[Gasguru]

10 litres is rubbish...every time the loo is flushed/washing machine's on you'll have a significantly reduced flow so timing showers will be required.
You could however fit flow limiters to restrict them down so as to give an 8 litre/min shower to get you by for now.

 

[Harry Bloomfield]

Whilst he was here, I asked him to measure flow rate. and he measured 2.4 bar 50 l/min at the cock and 1.1 bar 10 l/m at the property

Unless there is flow, there should be no drop in pressure - was the 1.1 bar measured at the 10 L/m flow?

 

[boolie]

Unless there is flow, there should be no drop in pressure - was the 1.1 bar measured at the 10 L/m flow?

yes, if I remember correctly he did the pressure test as the kitchen tap was fully on.

 

[Agile]

Measuring the water supply needs to be done by someone who understands pressure and flow.

If you just open a kitchen tap you get the "open" flow rate but this leaves hardly any pressure in the supply pipe.

If you can only measure an open flow rate then you really need to have twice the hot water flow rate you need for the boiler.

The best way to measure is to measure the dynamic flow rate. This means the flow rate which leaves, say 0.5 bar pressure in the supply pipe. This pressure is required to overcome the flow resistance in the boiler and to lessen the effect of any other outlets in the property being turned on or toilets flushing etc.

A basic 24 kW combi delivers about 10 li/min of hot water and a higher power one about 13 li/min.

An expensive and space using solution is to fit an accumulator. Basically a tank half filled with air to supply a short term boost to the flow rate for a limited time.

Another rarely used method is a loft tank and a pressure boosting pump to supply the combi.

You have not mentioned the distance involved in a shorter supply pipe to the property. If you must use a combi then ensure the supply pipe is a minimum of 32mm to minimise the flow resistance.

A better solution is always an unvented hot water tank. These have less resistance than a combi boiler and can be heated by a boiler at off peak times such as during the night or during the afternoons. Often undersized. I use the rule of thumb of 50 litres plus 50 li per person living there. Even that can cause hot water to run out for people who like full baths.

 

[muggles]

Thanks @muggles - just been speaking to the water board and they can give me a new water connection where the stop cock is literally just outside my garden. There's a public path that runs down the side of my house and they can use that (at a cost of course!). This process will take several months though

So, I'm thinking to future proof the boiler so it ultimately has a good shower flow rate to go with a 30KW combi? but it will need to work on the current low flow rate until the supply is upgraded. Will a 30KW combi work ok-ish with a 10l/min supply?

It'll work inasmuch as it'll get your water hot, yes, but you'll find that you get a drop in preprogrammed if someone flushes a loo at the same time

 

[boolie]

Convenient for the qwicky fit'n'go installer but not necessarily convenient for the people who have to depend on it for the next few years.

Pros of combi:

• convenient for medium to large families having showers in sequence
• hot water on demand
• minimal space
• piping is simple and clean
• easier to keep system and water clean
• everything that can go wrong is in one place (easier to work on)
• If you look after it (regular servicing / clean system) then wont break for years
• Popular brands have easily available parts

Negatives of combi:

• Cant shower in parallel
• More gas usage (more expensive bills)
• single source of failure - if it breaks you could lose CH and DHW

 

[bernardgreen]

everything that can go wrong is in one place (easier to work on)

and all crammed into a single case so harder to access the faulty component.

 

[boolie]

and all crammed into a single case so harder to access the faulty component.

yep - although that's why they spend £millions on design. You'd be surprised at some of the modern internal boiler designs. A lot going on and very accessible in compact boxes. One of the reasons installers dont like WB is because they are lacking in the design department - they focus more on the cosmetic design than the practicalities

 

[boolie]

By the way, Ive been doing some research on the flow rate thing - anyone have any experience with one of these bad boys?
https://www.screwfix.com/p/salamand...ooster-mains-water-boosting-pump-1-6bar/75286

My water pressure is 10l/min and 1.1 bar.. so wondering if this will make any significant difference

 

[bernardgreen]

You'd be surprised at some of the modern internal boiler designs.

Surprised, more like appalled. Like modern cars many modern "compact" ( compacted ) boilers are not designed for easy service....

 

[Gasguru]

Most boiler manufacturers are now outsourcing much of the design and buy in combustion/hydraulic modules etc....eg. Worcester buy in hydraulics from Grundfos and Bitron (Italian).
Only a few manufacturers have their own unique primary heat exchangers and of course they are outsourced to China for greenwashing their CO2.
Very few genuine design engineers are left in boiler manufacturers now.

Mains boosting pumps only up the flowrate to 12 litres/min ...they have a flow limiter for compliance with the water regs.