Water pressure inadequate for Megaflo system ?

Albermarle

When we had a Megaflo system fitted many years ago, one way it was sold to us was that you could have multi showers running at the same time ( or shower and run a  bath at the same time, or washing machine would not affect the showers etc )
It has never really achieved that aim, and we have to time showers etc. Over the years we have just got used to it, as otherwise the heating/hot water system has always worked well. However reading posts on here about heating systems, has got me thinking/wondering what the problem is, and I have done some googling as well.
Would I be right to guess that our mains pressure of 1.5 bar is just enough to support the system?
Three storey house. Ground floor flow rate around 13/14 Litres a minute. First floor shower flow rate around 8L per minute. Second floor shower ( loft room ) 11 L/minute . I think the first floor shower has a longer pipe run.
I read somewhere that you need a minimum of 2 bar for an unvented system to perform well. Is that true? 

housebuyer143

It appears 1.5 is fine. I have an unvented megaflow and have no such issue with showers. We can run 2 showers, taps downstairs, Taps upstairs with no noticeable drop in pressure. The pressure in my area is silly though, as in you need to turn all taps off tight or they will drip (certainly took getting used to coming from my old house).

ThisIsWeird

Hi Albe.

"Would I be right to guess that our mains pressure of 1.5 bar is just enough to support the system?
Three storey house. Ground floor flow rate around 13/14 Litres a minute. First floor shower flow rate around 8L per minute. Second floor shower ( loft room ) 11 L/minute . I think the first floor shower has a longer pipe run.
I read somewhere that you need a minimum of 2 bar for an unvented system to perform well. Is that true?"

Given these figures, I wouldn't recommend an unvented - 'Megaflo' - to anyone. 

1.5 bar is pitiful, and this pressure will almost certainly collapse when more than one outlet is opened. 13-14lpm flow is also poor. Yes, it's above the min obliged by most WBs, but it's still not at all good.

Both the pressure and flow are borderline.

A combi boiler would almost certainly have provided a similar performance, taken up less space, and have been cheaper to install.

You can transform the situation, tho', and that's by installing a pressurised accumulator tank on the incoming mains. Is that something you'd entertain? Do you have the room - it'll be a bit like another cylinder? They can be installed in attached garages, utility rooms, places like that if it helps.

Albermarle

ThisIsWeird said:

Hi Albe.

"Would I be right to guess that our mains pressure of 1.5 bar is just enough to support the system?
Three storey house. Ground floor flow rate around 13/14 Litres a minute. First floor shower flow rate around 8L per minute. Second floor shower ( loft room ) 11 L/minute . I think the first floor shower has a longer pipe run.
I read somewhere that you need a minimum of 2 bar for an unvented system to perform well. Is that true?"

Given these figures, I wouldn't recommend an unvented - 'Megaflo' - to anyone. 

1.5 bar is pitiful, and this pressure will almost certainly collapse when more than one outlet is opened. 13-14lpm flow is also poor. Yes, it's above the min obliged by most WBs, but it's still not at all good.

Both the pressure and flow are borderline.

A combi boiler would almost certainly have provided a similar performance, taken up less space, and have been cheaper to install.

You can transform the situation, tho', and that's by installing a pressurised accumulator tank on the incoming mains. Is that something you'd entertain? Do you have the room - it'll be a bit like another cylinder? They can be installed in attached garages, utility rooms, places like that if it helps.

Thanks . The installation was done in a rush as we were having a loft extension, so the old cold water tank had to go and the hot water cylinder was in the way. The builders plumber mate never turned up and we had to bring in a new one at the last minute and they said Megaflow was the way to go for a high usage house. Which is true but with hindsight not when the local mains pressure is not great, as you have kindly confirmed. Although they did fit a new plastic mains pipe which should have helped maybe.
I have had a look at the accumulator tank but I have no room for one, and anyway they only seem to boost the flow up to around 16/18 Litres for 9 mins max, so not a perfect solution.
Looks like will just have to live with it. Not the end of the world. Thanks.
I think our water pressure is not great because the local water comes from aquifers, so no natural gravity pressure. Also they are under pressure to extract less water and encourage reduced consumption. So I guess keeping the pressure and flow down maybe be deliberate.

ThisIsWeird

If you don't have room for one, that's that. But they will boost your supply to more than you could  possibly cope with; 30+ lpm at 3 bar, anyone?!
Yes, often a deliberate ploy by WBs to reduce loss - Thames cut the pressure back in parts of London due to excessive leaks in their system....

Albermarle

ThisIsWeird said:

If you don't have room for one, that's that. But they will boost your supply to more than you could  possibly cope with; 30+ lpm at 3 bar, anyone?!
Yes, often a deliberate ploy by WBs to reduce loss - Thames cut the pressure back in parts of London due to excessive leaks in their system....

One silver lining is that I had always resisted a water meter as I thought we were an above average user . A few months ago one was 'forcibly' fitted, and I have seen the results for the first months, and we are below average and should save about £100 pa.
I am presuming now that at least part of the reason we use less water, is due to the flow not being that great .

grumbler

Static pressure is meaningless. If the supply pipe is thin or blocked, high static pressure can drop to zero at very low flow.

'Dynamic pressure' mentioned above makes no sense either without the corresponding flow rate. I guess it has to be 1bar+ at the flow high enough for the system to work.

Albermarle

grumbler said:

Static pressure is meaningless. If the supply pipe is thin or blocked, high static pressure can drop to zero at very low flow.

'Dynamic pressure' mentioned above makes no sense either without the corresponding flow rate. I guess it has to be 1bar+ at the flow high enough for the system to work.

The system works on a basic level, but not to the extent that multiple outlets can be used at the same time, which is supposed to be the advantage of Megaflo/unvented systems.
It seems pretty clear from the@ThisIsWeird post, that the pressure and flow in the area is not high enough for that to work, and probably it should never have been installed in the first place in an area with only modest water pressure.