fezster

Simple answer is, Yes - increasing the diameter of pipe A will increase flow and reduce the pressure drop across that section of pipe, which means dynamic pressure will be higher (static pressure remains the same, as you rightly said).

Soem UVC manufacturers have 40KW+ coils (eg. Joule High Gain). With DHW priority, you could get away with a smaller cylinder which heats up rapidly to keep up with demand.

Thanks again, appreciate the expert opinion, and it's definitely made me confident to splash the cash on one now ?

That's awesome - thank you. I did consider using 2.5bar/4bar - though this would mean adding a second PRedV (one for the incoming main and another for the unvented at 3 bar). I used this formula, taken from a forum years ago, to try and calculate the usable capacity: Using Precharge = lowest dynamic pressure, Vessel volume V and Static Mains pressure M, (all pressures as measured on gauge) Stored volume is given by V(1 - (P+1)/(M+1)) which for a 450L accumulator gives a usable capacity of 135L (30%). Even at 1.5bar/3bar, usable capacity is only 37.5%. Could be the formula is wrong.

Nick, would you be able to advise on my setup as I'm unable to get a definitive answer on how / whether an accumulator would solve my issue. Static incoming main is 4-6 bar (depending on time of day). Megaflo unvented cylinder with PRV set to 3 bar. 32mm incoming MDPE with a flow rate of >40L/min off peak. I haven't measured, but I suspect this drops significantly to about 20L/min during peak time. 28mm pipework to unvented and balanced cold. This then reduces to 22mm polypipe running to both showers. 2 showers in the house: - 1 shower being used is great, with working pressure of ~2.2 bar at PRV. - 2 showers being used are either just ok or not very good (depending on time of day) - working pressure drops to ~1.4 bar at PRV. If I have a 450L accumulator installed with a pre-charge of 1.5 bar, what kind of performance gain can I expect and will it allow both showers to operate at full blast until the accumulator depletes? Am I right in thinking the accumulator will increase the working pressure to 3 bar, which will then gradually reduce to 2.2 bar as the accumulator discharges?

I missed this post. What is your shower performance like now? Any pics of the pipework / prv / pump setup?

Interesting. What kind of pressure drop do you get when running a shower? (I presume the intent is to increase shower performance?). My understanding of an accumulator is that it maintains working pressure whilst boosting flow. So - for example - if your internal pipework resulted in a pressure drop of 1.5 bar whilst running the shower (at say 10 litres/min), you'd only have 0.5 bar working pressure. The accumulator (obviously charged via a pump in your case) would initially output max flow rate at 3 bar (eg. the shower can run at 20 litres/min) , and the working pressure would slowly drop to 0.5 bar until the accumulator is depleted. During this process, the mix of water from accumulator + mains would start by being heavily weighted to accumulator -> then 50:50 -> and finally all mains (i.e. back to 10 litres/min), once the accumulator depletes. It's the amount of flow rate achievable during this process I'm trying to understand. I'm sure there must be a way to calculate it.

I've been considering an accumulator for quite a while (albeit, not pumped, as my static pressure is 4-6 bar incoming). The question I can't seem to answer, though, is whether my internal pipework is good enough to benefit and be able to run multiple showers. I'm certain there must be a way of determining this without "just trying". Who is fitting your kit? And have you found them to be knowledgeable on the product?

Yes, a pump can be used to increase the static pressure. I thought you were saying you increased the pipe size to the road and saw no increase in static pressure - you wouldn't expect to. Sorry if I misunderstood.

You can't increase static pressure, regardless of pipe size. The increased diameter will allow for more dynamic / working pressure, though, at a given flow rate.

The Pressure Reducing Valve is 3 bar though. So given the dynamic pressures measured (< 3 bar), I dont think that is a bottleneck in terms of pressure. If you meant in terms of pipe size restriction, the PRV is a 28mm reliance valve, so should easily handle in excess of 100L/min.

I've been thinking for a while now on whether a cold mains accumulator will resolve my "problem". I'll explain the setup: 1. 32mm incoming MDPE. Mains pressure > 4 bar (higher depending on time of day) and flow rate ~40-50 litres/min measured at outside tap. 2. 3 bar pressure reducing valve at the mains with an unvented cylinder for hot water. 3. I have three rain head type showers, capable of >16 litres/min according to the spec sheet. 4. Internal pipework is a short run of 28mm, then 22mm running through the house, with 22mm teed to each shower. 5. Running any one shower any time of day, the flow is great. Working pressure at the mains drops to 2.2 bar. 6. Running two showers, working pressure drops to 1.4 bar. This is where it gets confusing - depending on time of day, the performance of both showers is either adequate or pitiful (usually the latter in the peak morning time). However, the working pressure is always the same - 1.4 bar. I'd have thought with a lower incoming flow rate, the working pressure would also drop more substantially - but this isnt what I've observed (albeit, my method is not scientific, rather how I perceive the shower to be performing). I searched the forum and see a lot of posts from people about accumulators and was hoping someone might know - is it possible to determine, beyond doubt, that an accumulator close to the incoming main would enable both showers to run to full capacity? A calculation, perhaps, based on the measurements taken? I've invited Stuart Turner reps and plumbers but nobody seems to be able to say definitively whether it would work or not. The standard response I get is that my incoming flow rate is pretty amazing already, an accumulator won't help - which doesnt help if you want to run 3 x high performing showers at the same time.