Water Flow Accumulator Question

[Dmox]

Hi all - looking for some advice on ways to get better water flow in my house. Details are:

Issue: Low flow/pressure, particularly when other appliances are in use.
Flow: Approx 9/l min downstairs and upstairs
Static Pressure: Approx 3.8 bar
Dynamic Pressure: Approx 2.2 bar
Boiler: Combi

We live in a Victorian terrace and recently did our bathroom. I'm looking to try improve the flow rate, particularly for our shower which runs direct off the combi boiler. One solution that has been suggested is to install an unpumped accumulator tank given the pressure seems to be fairly good. Is this what you would advise and if so could I install that in the bathroom cupboard so it supplies the boiler, noting that the downstairs cold water would not benefit (this isn't a massive issue)? Or is there something else that would be a better idea? I would obviously get a qualified plumber to do the work but I've received various advise on the issue.

 

[Madrab]

Static Pressure: Approx 3.8 bar
Dynamic Pressure: Approx 2.2 bar

With those pressure levels then the issue is more likely to be down to a restricted flow. I'd be looking at size of supply from the mains and through into your property first. The estimated costs of an accumulator etc could probably pay for a new mains supply pipe to the house.

Get a survey done on the mains outside and see if the figures hold true and what the dynamic flow could be, if suitable then time to look at the size/age of the mains to the house.

 

[Dmox]

Thanks Rob - we've got a new blue water main pipe coming into the property from the main that was installed prior to us moving in. I also got the water company to check and they said the pressure is above the minimum they are required to provide.

 

[Madrab]

we've got a new blue water main pipe coming into the property from the main that was installed prior to us moving in.

OK - something doesn't make a sense then.

With a dynamic pressure @ 2.2bar and a new MDPE pipe be it 25mm or 32mm then it should be delivering a lot more than you are getting. Unless the restriction is in the district mains. I'd be tempted to check the supply figures where the Blue MDPE connects to the mains stop tap in your property.

Is the outside mains fully open? Shame they didn't give the actual mains supply figures rather than the generic, 'we're supplying enough to meet our SLA's'

 

[Dmox]

Yeah, I went and checked the outside mains stop tap as well and when I measure the flow at the outside tap (where the blue pipe connects) it is also about 10 l/m. None of the neighbours have fantastic flow either. We live in Cornwall, up a very steep hill so maybe that has something to do with it?

 

[Madrab]

We live in Cornwall, up a very steep hill so maybe that has something to do with it?

It's the pressure figures that really define how the supply should perform, that being said If you are on the end of a smaller district main then flow could be restricted, it's just a bit surprising given the dynamic pressure.

OK - if that's all been investigated then yes it's down to alternatives. Accumulators have their place but their main issue is their performance isn't completely stable - They will give the supply a boost right up until the accumulator's store is exhausted and then it's back to the mains flow, how long that will take is basically down to the capacity of the tank.

If it's in a bathroom cupboard then it isn't going to be the largest store I would suggest?

 

[Dmox]

Probably not, I could build a housing for a larger one outside and insulate it to boost the incoming water I guess but I'd rather it went indoors for simplicity. One more final question - given the pressure seems good, I think I can use an unpumped accumulator, does that sound right or should I really be going for a pumped one? If it's in the cupboard there is at leas electricity available but I'd rather not have a pump noise if I don't need to.

Also, thank you so much for this - I really appreciate it.

 

[Harry Bloomfield]

Static Pressure: Approx 3.8 bar
Dynamic Pressure: Approx 2.2 bar

Does that static 3.8bar, remain fairly stable, when there is no water being used in the house?

Does it remain stable even when others, local to you, are likely to be using their water supply?

If both are true, then it suggests a restriction somewhere on your supply alone.

 

[Madrab]

Do not that with an accumulator it's actual capacity is a fair bit lower than it's stated volume and ergo actual size of the unit. The usual guide is around 60% of actual capacity - so say a 100L vessel would provide around 60L of accumulated water before the flow would return to the mains output. That would give around 5mins on a shower @12L/Min

If you have that level of static pressure then a non pumped unit would probably be ok - anything above 2.5bar is the norm.

 

[Dmox]

Does that static 3.8bar, remain fairly stable, when there is no water being used in the house?

Does it remain stable even when others, local to you, are likely to be using their water supply?

If both are true, then it suggests a restriction somewhere on your supply alone.

The static drops to around 2.2 bar when using other appliances in my house, but is otherwise stable. It seems stable at other times other times. I can't find any restrictions other than perhaps the pipework in the house being 15mm after it comes in off the new blue water main. We recently had the kitchen and bathroom done so it's all new pipework internally (I now realise I should've upgraded the diameter of the pipework, but that ship has sailed).

 

[Dmox]

Do not that with an accumulator it's actual capacity is a fair bit lower than it's stated volume and ergo actual size of the unit. The usual guide is around 60% of actual capacity - so say a 100L vessel would provide around 60L of accumulated water before the flow would return to the mains output. That would give around 5mins on a shower @12L/Min

If you have that level of static pressure then a non pumped unit would probably be ok - anything above 2.5bar is the norm.

Thanks a lot - yeah, I'd read about the size of the vessel not actually being what you get as the pressure equalizes. I'll do some research and get a plumber in to advise further on installation.

 

[Harry Bloomfield]

The static drops to around 2.2 bar when using other appliances in my house, but is otherwise stable. It seems stable at other times other times. I can't find any restrictions other than perhaps the pipework in the house being 15mm after it comes in off the new blue water main. We recently had the kitchen and bathroom done so it's all new pipework internally (I now realise I should've upgraded the diameter of the pipework, but that ship has sailed).

Then you must have a restriction on your pipework somewhere. My static pressure is only around 1.9bar, with entirely 15mm indoor, but it is adequate, despite shower stopping, when any other water is drawn in the house.

 

[Johntheo5]

25mm MDPE has a ID of 20.4mm
The friction loss of 20M at a flowrate of 20LPM should only be ~ 0.14bar so definitely appears to be a restriction somewhere if you are getting a loss of 1.6bar, (3.8/2.2), at only a flowrate of 10LPM?.

15M of 15mm copper (13.6mm ID) only has a pressure loss of 0.47bar at 15LPM.

Friction Loss Calculator

Calculate the friction loss in pipes for different materials using the Hazen-Williams equation.

www.omnicalculator.com

 

[Dmox]

Then you must have a restriction on your pipework somewhere. My static pressure is only around 1.9bar, with entirely 15mm indoor, but it is adequate, despite shower stopping, when any other water is drawn in the house.

Does this mean you have a restriction because the shower stops? I'm out of ideas for where to look for a restriction beyond taking the floor in the kitchen back up. So an accumulator it is.

 

[Harry Bloomfield]

Does this mean you have a restriction because the shower stops?

No, the shower stops, because when a tap is opened, the pressure drops below that which is acceptable to the shower. We are at a high part of the village, so we get closest to the lowest pressure in the area. There is no restriction, other than is normal, for the pipework.