New Build Water Storage

[mike2016]

Just approving drawings for the timber frame and wanted to ask about where to put the water tank. They have squeezed one into a tiny attic (warm roof), the alternative is to have a vaulted ceiling in the upstairs bedrooms. Another alternative is a tank under the stairs with a submersible pump (noise). I've 3-4bar mains pressure but I was thinking of using an accumulator as a buffer in the plant room. 

So - stupid questions:

• Can unvented hot water systems use a gravity tank in the attic? 
• Is using an accumulator as a cold water buffer a daft idea? 
• Do I just go with the attic tank with a drip tray and keep things simple? 

Much appreciated! Only 2 showers and a bath in the property, the swimming pool was cancelled....! 

[ProDave]

Why do you need a water tank?  Not mains water?

[PeterW]

What problem are you trying to fix ..?? 3-4 bar of pressure is ample 

[JohnMo]

Why unvented? Why a huge cylinder in the loft, when you have room for a plant room?

[mike2016]

The only issue I'm fixing is keeping an onsite buffer when they turn the water off for faults / maintenance. Don't like the idea of having no water reserve at all when that happens. 

[JohnMo]

Trying to fix a REAL problem - not.  Buy some bottled water.

 

Or an accumulator.  Storage tank means air gapping the supply, a super low pressure system.

[Nickfromwales]

9 hours ago, mike2016 said:

The only issue I'm fixing is keeping an onsite buffer when they turn the water off for faults / maintenance. Don't like the idea of having no water reserve at all when that happens. 

Really? The water wouldn’t be fit for human consumption! The idea is not sound, so buy a few 25L bottles of mineral water and put them somewhere cold and out of sunlight. 
 

This one is defo a very bad idea / complete waste of money imho. 

[mike2016]

So, no tank, no accumulator. Unvented hot water system. no buffer? 

[Iceverge]

+1 to the above. 

 

Stick a water butt under in the garden for watering the plants and as a emergency flush for the toilet. 

 

 

[Iceverge]

2 minutes ago, mike2016 said:

So, no tank, no accumulator. Unvented hot water system. no buffer? 

 

 

Can you describe your situation as is please @mike2016?

 

New build/refurbishment?

Heat source? Gas ASHP etc?

Regularity of water outages? 

Modifying an existing system or installing a new one?

 

 

[mike2016]

New Build

ASHP

Outages: Once or Twice per year, I'll put a filter in as they flush a lot of sludge when they turn things on again. I'm urban so outages are rare enough and usually planned. We have had water treatment pump failures with the council but they have been rounded on for single points of failure etc so hopefully less common in future

This is a new system design, just considering if I need rafters or not to hold a tank in the loft. I've never lived in a house without a gravity tank so not used to the idea, did live in an apartment once with a pumped system which was interesting & a bit noisy. 

Just curious with new builds what's the simplest solution and it sounds like a tank is old school or at least overkill. 

Thanks!

[Kelvin]

Tanks up the loft with a dead rat in have been old hat for years. 

[Iceverge]

12 minutes ago, mike2016 said:

New Build

ASHP

Outages: Once or Twice per year, I'll put a filter in as they flush a lot of sludge when they turn things on again. I'm urban so outages are rare enough and usually planned. We have had water treatment pump failures with the council but they have been rounded on for single points of failure etc so hopefully less common in future

This is a new system design, just considering if I need rafters or not to hold a tank in the loft. I've never lived in a house without a gravity tank so not used to the idea, did live in an apartment once with a pumped system which was interesting & a bit noisy. 

Just curious with new builds what's the simplest solution and it sounds like a tank is old school or at least overkill. 

Thanks!

 

Ah ok. 

 

Unvented cylinder, as large as you can comfortably fit. Aim for 300l at least. A vastly nicer system to use. Mixer taps+showers work properly, no noise etc. 

 

 

No need for any tanks in the attic.

 

A cold water accumulator may be called for if your dynamic pressure (I think) is too low. 

 

Beware high bills with an ASHP unless you have a very low flow temp heating system and a low heat loss house. 

 

 

[Dave Jones]

accumulater is essential depending on your useage. 2 showers happening and the dishwasher turns on for example will result in a dribble. 

 

 

[PeterW]

49 minutes ago, Dave Jones said:

accumulater is essential depending on your useage. 2 showers happening and the dishwasher turns on for example will result in a dribble. 

 

 

why ..?? 30 litres / min at 3 bar is a lot of water !! OP doesn’t say they have a flow issue ..?? 

[Nickfromwales]

8 hours ago, mike2016 said:

So, no tank, no accumulator. Unvented hot water system. no buffer? 

Bugger. Apologies for my hit-n-run reply. Just very busy atm with about a billion new enquires.

8 hours ago, mike2016 said:

I've never lived in a house without a gravity tank so not used to the idea, did live in an apartment once with a pumped system which was interesting & a bit noisy. 

Just curious with new builds what's the simplest solution and it sounds like a tank is old school or at least overkill. 

Thanks!

I doubt you are alone. Let me explain.

With 3-4 bar of incoming pressure, many folk would be jealous of you. Having stonking showers off an unvented hot water cylinder ( UVC ) is easily within your grasp. 

 

If you have multiple occupants then you may want / need to consider fitting a cold mains accumulator, but if you are just yourself and the better half then you can discipline yourselves to avoid this cost / space requirement ( for another cylinder the same size as the UVC ) by choosing when to shower / run the dishwasher / washing machine etc.

 

[Gus Potter]

For all.. you can do a lot to help yourself..here is some old scoool stuff that should save you money .. get it right.

 

I live in an ex council house that is in a terrace. The mains supply off the street is 3/4" (~22mm) and that one pipe serves all three houses.

 

Now the static pressure say at 3.00am in the morning is 4.0 bar just say as we are all in bed..

 

When we all get up in the morning and start turning on the taps.. we don't have anything like 4.0 bar as soon as the flow starts . Once the flow starts we have loses due to every bend in the pipe.. so this idea of having 3.0 -  4.0 bar static pressure is bollocks.. you need to know the pressure combined with the flow rate at the point of delivery.. if you don't then you could waste a lot of money.

 

To put it another way I could supply your house with 8 bar in a 10mm pipe at 3.00 am.. akin to a heavily furred old lead pipe where you have chalk soil. But try and fill a bath.... the laws of hydraulics means that as soon as the flow starts the static pressure drops.. often like a stone.. and so does the flow rate don't take my word for it do your research.

 

That is why we have accumulators for mains water if weneed them.

 

Maybe we should all go back to looking at the  basic hydraulic equations and understand what we are talking about before we splash the cash? Folk say 4.0 bar at the street.. yes fine if you have a modern 25mm alkathene pipe under say 50- 75 m run.

 

The first thing you do is ask when assessing any supply is to ask.. what type of supply do I have; is it metered and what type of restriction to flow applies in terms of pipe diameter (and bends in the pipe) and at the meter.

 

Next test the static pressure at 3.00 am and and then again at 6.00 - 8.00 am .. that is when folk bath their kids..get up in the morning.. use your judgement on where you live and how you want to live.

 

Get a bucket of known volume and test the flow rate at 3.00 am and at 6.00 - 8.00 am

 

To nail this down put a pressure tester on the line when you are filling the bucket.. now you know flow rate and pressure when the water is running.

 

Now you at least have some ball park figures on how the water supply to your house behaves..

 

Give this data on what you have measured to your heating plumbing Engineer.. otherwise.. up to you I suppose.

 

If you don't know how the water gets into your house and how it behaves when you turn on the tap how are you supposed to make an informed decision when selecting the right system for you and spending thousands of pounds?

 

Gather this information and you are on your way to getting you plumbing right at the right price.

 

I know it sounds like a bit of hassle but if you gather the basic info yourself you'll at least know if folk are trying to sell you a pup?

 

 

 

 

 

 

 

 

 

[PeterW]

5 hours ago, Gus Potter said:

To nail this down put a pressure tester on the line when you are filling the bucket.. now you know flow rate and pressure when the water is running.

 

Now you at least have some ball park figures on how the water supply to your house behaves..

 

Give this data on what you have measured to your heating plumbing Engineer.. otherwise.. up to you I suppose.

 

If you don't know how the water gets into your house and how it behaves when you turn on the tap how are you supposed to make an informed decision when selecting the right system for you and spending thousands of pounds?

 

Gather this information and you are on your way to getting you plumbing right at the right price.

Spot on !!! 30 litres / min at 3 bar is a very healthy flow - we had one currently that is coming direct off an Anglian Water 8” main and the static pressure is just over 8 bar and dynamic is around 7 - customers plumber ignored the design (PRV at the main stop valve to 4.5 bar) and just went with the control group on a tank 10m away. A failed joint in the run - thankfully before board out - and they had a 7 bar fountain in the new lounge ..! Amazing how much water that is and how difficult it is to explain that controls are put into designs for a reason.. 

 

[joe90]

With a recent application fir a water supply I was told if the mains pressure was above 6 bar it was compulsory to have a PRV.

[Marvin]

I always install a Pressure Reducing Valve on mains. It saves all the equipment from straining / wearing faster.

 

I have worked on properties where the overnight pressure is 6 bar and during the day 2.5 bar wandering to 6. 

Edited February 18, 2023 by Marvin

[SimonD]

One thing I'm going to raise here that never seems to get much of a mention is flow regulation. Many showers come with flow rates of up to 16l/min as standard but the flow can can easily be reduced down to as little as 6l/min without affecting the performance of the shower. This way you can provide satisfactory flow, often to multiple outlets without necessarily using accumulators or over-sizing the hot water storage. Definitely something helpful when dealing with comi boiler installations, but also very useful where there is water storage without the space or budget for accumulators etc. It also saves a lot of water consumption 😉

 

40 minutes ago, joe90 said:

With a recent application fir a water supply I was told if the mains pressure was above 6 bar it was compulsory to have a PRV.

 

There's actually nothing in the water regulations to support this. The water regs basically state that fittings must be able to cope with 1.5times the maximum operation pressure.

Although some fittings are only suitable for lower pressures and unvented cylinder installations typically demand max 3bar, other British and European standard fittings are designed to 10bar and tested to 15bar.