Storage combi-boiler - increasing water pressure

[RedEric]

I'm another unlucky one living in London unable to get decent pressure and flow rate from an old lead pipe water main. I'm getting 12 l/m at 4 bar - which isn't enough to supply anything other than a gravity HW system. Thames water told me it could cost £3k just for them to install the communication pipe. It could cost the same again to install my supply pipe to the house - so this option is out of the question.

All we need is enough pressure for 2 simultaneous showers with decent pressure. We have no space for a cylinder so a Megaflow wouldn't work - but we already have a large CWS tank in the attic.

If I install a Storage Combi-boiler, such as the "Vaillant ecoTEC plus 937 power store" or "Potterton Promax HE Store", can I increase the supply pressure/flow rate by pumping from an already installed CWS tank in the attic?

Tech. support at Ariston suggested the "Grundfos Home Booster cold water booster" but this is very large and heavy and I'm not sure my attic space would support it. Has anyone ever installed one of these?

Sorry for the long post, but any advice would be much appreciated.

 

[simond]

We would recommend an accumulator. Around 50% of our large combi installations incorporate one, because the water supply in South London can be variable at peak times.

The accumulator can be a number of small units linked together in areas with limited height, or can be sited outside in an insulated shed. Typically we site it where the old hot water cylinder was located though.

Grundfos home booster uses a pump which is totally unnecessary if you have 4 bar static. Do you like the noise from pumps? And the fact that you don't get any water in a power cut?

 

[RedEric]

Thanks for the reply, simond.

Could I simply replace my current CWS tank in the attic with an accumulator? How do I calculate the size of the accumulator required?
The current CWS tank is 60x50x120 (cm) which is approx 270 litres if 3/4 full.

Would the accumulator supply water to the boiler and cold water taps?

 

[simond]

Yes, but height will be an issue.

The accumulator will store approx half of its total volume with useful water. The amount you need will depend on your usage patterns rather than a hard and fast rule. If 4 people are running showers one immediately after the other then the accumulator has no time to recharge itself and thus a greater capacity is needed.

You would be best getting someone in who has experience with the equipment to advise you. If you end up telling your installer you need to be concerned. Ours is one of an increasing number of companies out there regularly specifying this equipment.

 

[RedEric]

I noticed you suggested a DualStream on another thread, would this be an option for me?

Would the DualStream fit in the attic - which isn't reinforced?

I'm based in North Ealing - could you visit us and give us an estimate?

btw. I think the 4bar pressure is dynamic pressure - not static.

 

[simond]

Can't help you in North Ealing I'm afraid, we only take on work up to the South London congestion zone.

DualStream is a brand name for a combined accumulator and unvented cylinder. You can buy the accumulator on its own, called ColdStream, which can be paired to a combi or an unvented cylinder. Other manufacturers of accumulator are available.

I suggest you email www.gah.co.uk for a local North London specialist.

PS: I doubt the 4 bar is dynamic pressure.

 

[RedEric]

Thanks, Simon.

Do you have any experience/knowledge of Altecnic accumulators? www.altecnic.co.uk They seem to be quite a bit cheaper.

I will double check the pressure, but I'm sure when the plumber turned off the tap, the pressure gauge was showing 7-8 bar.

 

[simond]

In which case you will need to protect the installation with a pressure reducing valve.

Regarding the different types of accumulators, things are a bit complex legally but not necessarily technically......but check the unit has WRAS approval. I cannot really say any more in public on this forum.

 

[RedEric]

Thanks for your advice regarding the accumulator.

Maybe you could advise me on which combi boiler to get.
All as I need is enough pressure for two showers running simultaneously.
Maybe a powerful combi (Mikrofill Ethos 54c) or a storage combi (WB Greenstar Highflow 440 CDi or Vaillant ecoTEC plus 937) for example. Or any other type you could suggest.

The boiler will be installed in a large/high kitchen cupboard so it can floor standing or wall hung.

In your experience, which combi would you recommend?

btw. Should I post this on a new thread?

 

[Agile]

Thanks for your advice regarding the accumulator.

All as I need is enough pressure for two showers running simultaneously.

btw. Should I post this on a new thread?

If you are to specify an accummulator then its essential that you measure the flow rate of each shower and decide how long you will want it to run for. If its very long then the accumulator will be very expensive and large.

I still dont understand why you cannot use your loft tank system with a vented hot water cylinder.

I hope you understand that your requirement to run two showers together is going to cost you a lot !

Stick to this thread.

Tony

 

[RedEric]

The showers aren't installed yet. I'm guessing an average shower will run at 10 l/m for and average of 10 minutes. So that's 100 l per shower. So would a 300l accumulator be suitable?

I still dont understand why you cannot use your loft tank system with a vented hot water cylinder.

The current HW cylinder is in a bedroom and needs to be removed. Currently it does not deliver enough pressure for showers or HW and I definitely don't want any noisy pumps.
We could put a MagaFlow type HW cylinder in the attic with the accumulator, but then we will need to reinforce the attic floor space.

There must be a combi out there that can supply 2 showers!

 

[Agile]

A Vaillant 937 would probably just about supply two 10 litre showers for about 10 minutes but I would not recommend it as its too close to its limits!

You must wait for an accumulator expert to reply but if you have an open pipe flow of 12 li/min and 4 bar static pressure then I would expect a 300 li accumulator to be adequate. However it will take about 40 minutes to recharge! Much longer if ANY tap or water outlet is used!

Still a very expensive cost just to be able to run two showers together when 80% of London can only manage one at a time. But its your money!

Tony

 

[RedEric]

Do you have any suggestions?

 

[EliteHeat]

Do you have any suggestions?

I still dont understand why you cannot use your loft tank system with a vented hot water cylinder.