How to solve our water flow issue.. pumped accumulator vs breaker tank & pump

[Jake_M]

1st post on the forum, found via google and I see the topic of accumulators has been asked a number of times prior, I'm hoping for some advice based on our situation! I've probably gone too far with the detail, so apologies for the long read!

We live in a small village where the mains water flow/pressure isn't great. We have an unvented hot water cylinder (megaflo) linked to a system boiler, therefore our hot and cold water performance is based on the mains pressure. We only have 1 bathroom currently but are planning a loft conversion to add a second bathroom (shower). We've just renovated our existing bathroom and have a Aqualisa digital shower, its nice but the flow isn't excellent (passable but not great, see below).

I'm considering 2 options currently:

- a pumped accumulators like the Accuboost (450L version) https://www.salamanderpumps.co.uk/product/accuboost-450l-pumped/59
- a breaker tank and pump like the DAB sybox / sytank https://www.anglianpumping.com/product/mains-pressure-boosting-systems/dab-e-sytank-and-e-sybox-pump

This would live in our garage, which is attached to the house and has a spare bedroom above (there is noise from the boiler / underfloor heating manifold already but we wouldn't want something super loud.

Measuring our cold water flow today I have the following readings (the kitchen sink is a mixer type tap, the bath has a standard dial for hot, dial for cold).

Outside tap on its own 14.8 l/min
Outside tap + 1 other outlet open 12.5 l/min
Outside tap + 2 other outlets open 11.11 l/min
Outside tap + 3 other outlets open 10.54 l/min

Bath cold tap on its own 9.92 l/min
Bath cold tap + 1 other outlet open 7.56 l/min
Bath cold tap + 2 other outlets open 6.06 l/min

Kitchen sink cold tap on its own 8.13 /min
Kitchen sink cold tap + 1 other outlet open 6.16 l/min
Kitchen sink cold tap + 2 other outlets open 5.3 l/min

Shower set at 40degrees on 'max flow' (which should be 12l/min) = 9.16 l/min (no other outlets open).

I've ordered a water pressure gauge to test the pressure of outside tap (that's the only tap with an accessible threaded connection) which I'll do on the weekend, not expecting it to be much above 1bar though!

Based on the above, which way should I go? I know the sytank would give me 500L of usable water vs half that in the accumulator, but I worry about the increased legionella risk, and not sure we need 500L really!

Both options are within a few hundred pounds of each other.. Would the pumped accumulator be viable? What are the cons of the sybox/sytank set up?

 

[Madrab]

The accumulator will always 'run' out of pressure after a certain time (size and mains dependent)and then it'll revert to the pumped output up to a max of 12L/Min or the mains, whatever would be higher.

A break tank and pump will always maintain the pumped pressure until it empties the tank. It would probably be more considered like an attic cistern with a whole house pumped supply. Your outlets would need to be designed for this, rather than for a mains supply so possibly not suitable for an unvented cylinder.

Both would require yearly maintenance, which would be gauged by water type etc

 

[Jake_M]

Thanks Madrab, when looking at the flow values I'm seeing, when you say the accumulator pump will revert to 12l/min (or mains if higher), would that be 12l/min at each outlet no matter how many outlets are open (i.e. providing an increase in what I am seeing now at the shower / bath) or 12 l/min through the incoming mains and therefore it wont change much vs what we're currently experiencing? Possibly a moot point as we tend to use c. 120L of water during a typical shower, and with the additional shower its highly unlikely both would be in use at the same start/finish time, so a 450L sized accumulator should cover us with a accumulator supply each morning / evening.

I hadn't though the accumulator pump would continue to work when the accumulator is empty, hence trying to establish if that serves as an additional benefit vs the beaker tank. Other benefit I see of the accumulator is that legionella risk is vastly recued as has constant flow through it and not holding stagnant water.

 

[Bodd]

My advise would be to stay well clear of DAB. I fitted one of their units two years or so back.

The customer claimed that it would go off even when there was no demand. I searched and searched for a leak or a reason other than the pump.

DABs customer support was awful. They would not come out, I had to send the unit to them at my cost.

If they found it was not their unit on inspection I would be charged for their time and postage back.

I ended up telling them to stick it up their arse and bought a Grundfoss unit.

Not as loud, works as it should and a happy customer.

 

[Madrab]

12l/min at each outlet

The way the accumulator works is that it either uses the pump or the mains to pressurise the cylinder up to a max set pressure, usually around 2 bar. Once the accumulator releases that stored pressure, then it revert to the mains flow rate or pump the mains up to 12L/min at around 2 bar'ish, if the mains is lower. That delivery will drop as any normal dynamic flow would, the more outlets that are opened. Looking at the figures the vessel can be run down within 9Mins @ max flow rate (the 450L can max out @ 36L/Min, cold water system spec dependent)

A Pumped mains will max out at 12L/Min, you cannot legally pump the mains at a higher rate than that.

A 450L accumulator will not deliver 450L of stored water, almost 50% of that volume is taken up by the pressure vessel so the accuboost system @ 453L will actually only hold 225L.

Legionella shouldn't be an issue with the break tank w/ pump, as long as it is looked after properly, temp is kept correctly, it is used daily and serviced properly.

 

[Jake_M]

Thanks for the responses so far, I'll be honest and say I'm no clearer on the best solution for us! If a typical shower uses say 120L water, and its really only the showers where we care about decent flow (i.e. when 2 showers are live at the same time and/or kitchen appliances are on whilst shower is on), then the 225L capacity of a 450L accumulator would pretty much cover it?

I've now taken pressure readings from our outside tap - does this change anything?

Static pressure - 1.8 BAR
Dynamic pressure -1 other outlet open - 1.6 BAR
Dynamic pressure - 2 other outlets open - 1.5 BAR
Dynamic pressure - 3 other outlets open- 1.4 BAR

Its worth noting that whilst I can't test the pressure of the bath tap or shower, these feel alot les powerful than our outside tap, and this is reflected in the much lower flow rates, we definitely don't have a leak so I wonder why we have such a difference?

 

[wundaboy]

Do you maybe have flexible hose connectors with reduced bore connecting these? What's the state of the pipework leading to the bath and shower? Lots of elbows rather than smooth pulled bends would have a detrimental effect on the flow rate, particularly if the pipework is 15mm.

Do your bath/shower fittings have flow restrictors fitted? I've come across these prefitted for ecological reasons, though they can be removed. Also, some fittings, especially cheaper ones, have a more restricted internal bore.

Lots of possible reasons, as a first diagnostic step I'd be inclined to remove the shower fitting and test the flow rate at the open outlet (cold only, hot turned off).

 

[Jake_M]

There's no restrictors fitted as our bathroom is recently refurbished (it was gutted) including all new pipework for the shower (right back to the hot water tank) and new pipework runs for the bath and sink going into the bathroom.

Yes the plumber has installed flexible hoses with 90 degree plastic elbows where there is a bend for all replaced pipework. The shower for example use flexible hose right from the hot water tank (hot and cold feeds), up and over via the loft and back down into the bathroom.

Given this is all newly installed and finished, I've no intention on replacing any of the pipework, so looking to make the best of what we have..

 

[Madrab]

The shower for example use flexible hose right from the hot water tank (hot and cold feeds), up and over via the loft and back down into the bathroom.

Are you talking about plastic pipe?

Flexi pipes (flexible tap connectors/hoses) are the steel braided wrapped rubber pipes that are commonly used to connect up taps, they invariably have a narrow restrictive internal bore

 

[Bodd]

Are you talking about plastic pipe?

Flexi pipes (flexible tap connectors/hoses) are the steel braided wrapped rubber pipes that are commonly used to connect up taps, they invariably have a narrow restrictive internal bore

And in time leak. Had one Saturday night rubber perished....

 

[Madrab]

And in time leak. Had one Saturday night rubber perished.

Yup the cheap crap ones from China can be a nightmare, rust out and then burst, alway make sure to buy stainless steel WRAS approved.

 

[Gary_Funwick]

@Jake_M
We have a Dab Esybox and it works very well. It's in an insulated shed fed by an insulated tank (500l, maybe in reality 400l; I think the rule of thumb is 2x the capacity of the hot water cylinder). The inflow to the tank and the outflow from the pump differ at most by 1 degree Celsius (warmer in summer, colder in winter) - I too was worried about legionella so I measured the temps. I would be less comfortable with the Dab tank which I think is single skinned plastic.

Installed for similar reasons to you - water from a water tower not much higher than us, static pressure variable (0.6bar to 2.1bar) and dynamic pressure obviously worse.

With the pump set to 3.4 bar we're limited by our water softener to about 35-40 litres/min, bypass (or replace?) the water softener and that pressure will supply about 55 litres/min.

The pump is very quiet so I doubt that your bedroom will suffer. You will however need to allow for a bypass for if/when electrical power is cut off and if/when the pump fails.