Flow Rate question of the day :)

Hi all, I'll list as is scenario and target and thoughts most welcome on options

Today:
Lead pipe mains incoming (measured earlier as c.0.79" outside diameter at slight angle, by digital calipers)

Then converts post stopcock, afterwards to 15mm, two 90° turns to another 15mm stopcock and 15mm limescale filter, then two 90° turns and finally switches to 22mm pipework, a 22mm PRV (I set at 3.5 bar), then 22mm piping though spine of house.

I DIY measured from kitchen tap with nothing else in use, at 3.5 bar on prv,. (Correction it's 30l/minute)

System is Worcester Bosch 40cdi regular boiler 28mm piping by it, zoned by floor, s plan, vented 159litre gledhill tank (one with extra length coil) with 28mm piping, and two cold tanks above cylinder in loft. Two showers in house, each with salamander ct50+ connecting to them. The mains cold feeds all cold outlets bar the showers.

All works actually for a family of five for ten plus years but tabling to move to system boiler as below as we upgrade bathrooms and showers for first time in 2 decades...

Viesmann 111-w, gledhill stainless pro unvented 300l, remove that 1m of mess piping from incoming to PRV to 22mm straight, white/red expansion 24l vessels as needed, and possibly 100l accumulator.

Aim:
To run one 20mm and one 25mm shower head with over lap of say 5 mins and not have water flow and pressure collapse, and same if short term a toilet flushes. (I had thought maybe just a lot simpler to move to whole house pump/ remove old shower pumps and change nothing else)

Above changes likely to work?

Note 30l/minute currently before any pipework changed or 15mm stuff removed

1. The key variables are:
1.1 Length of each shower (minutes)
1.2 Flow rate required for each shower (litres per minute (lpm)). Probably given as lpm / bar. If cylinder upstairs, assume 3.0 bar if incoming is 3.5.
2. From the above work out the water usage. Probably safe to assume 2/3 to 3/4 of water usage is hot, remainder cold.
3. If (shower 1 at given lpm + shower 2 at given lpm) litres < 300 you'll be OK. If close, look at fast recovery cylinder (which your suggested one probably is) and recalculate.
4. Just a word of caution. Take pressure and flow rates at different times of the day. They can often be substantially less at morning and evening peak usage times.

We are top of a hill, 83m up, our local water company said not the highest bar as that record goes to a farm nearby that hit 12 bar on Affinity water database, but was why had added PRV fitted and put at 3.5 as was each winter going to c6.7 bar night time and shower pumps failing until that change made. Great for filling a summer pool though it's what 4pm, If I touch PRV and open it would happily rise to 4.8bar...

Target temps to each shower 41c
Assume cylinder is set (wiser system) to heat before usage
The rainfall showers takes what 60c (yes temps will drop over time from cylinder) with say 10c incoming from mains.

Shower 1 200mm rainfall one say 20mins
Shower 2 250mm rainfall one, say 10mins. 5 min overlap to other one
Also someone hits WC pulling water to fill it's 6l/ or washing machine draws happens worse case

finlaand said:

Lead pipe mains incoming (measured earlier as c.0.79" outside diameter at slight angle, by digital calipers)

Click to expand...

0.79" would come in around 19mm, the closest lead pipe OD that would align to would be 0.74"/18.9mm or 5lb - 3/8". In the all mains system you are proposing then that would be the bottleneck to flow.

Test the system flow with 2 or 3 outlets running at the same time for a dynamic reading, as suggested at differing times through the day.

I wouldn't waste money on an accumulator, that's just something else that needs to be looked after/serviced - use the money to upgrade the mains, results dependent, if the mains is that good. No need for pumps either.
Similarly, if the boiler isn't showing signs of distress then no real need to replace it either.

Well boiler has had new heat exchanger 6 years ago now, and WB for free replaced motherboard (that had big transformer on it).and other parts for free 2 years ago after accepting my serial number from 2008 May was a firmware with fault (as found a WB engineer told me), so overall yes boiler works well.

But Id like to get rid of the tanks, so a change is happening... Not going to dig up 25 metres driveway that was just finished last summer

Ok let me do some more stuff and come back