IS THIS GOOD PRESSURE?

[bobby62]

Had a pressure test done on a school building (standing pressure was 7 bar and working pressure was 1 bar with 4 taps running) the flow rate was measured at 30 litres per minute.

Is this good pressure? the building is being extended and I am worried the school will be short of water performance when it is up and running. I would like to suggest to the plumber to put a storage tank in with a pump to boost the water.

There are a few showers and a number of sinks and basins.

Any advice would be greatly appreciated.

 

[bengasman]

that will be one big tank and one biiiiiiiig pump

 

[bobby62]

that will be one big tank and one biiiiiiiig pump

What makes you say that, what size are you thinking (it isn't a hotel) its a small community building.

 

[bengasman]

School? with showers, basins, toilets, kitchen/ lunch area. that is a lot of water potential.

why on earth a pump and tank if you got 7 bar pressure?

 

[bobby62]

School? with showers, basins, toilets, kitchen/ lunch area. that is a lot of water potential.

why on earth a pump and tank if you got 7 bar pressure?

There is 7 bar static pressure, but only 1 bar running pressure when only 4 outlets are open. It is likely there could be more than 4 open at any one time.

There are only 6 showers and probably 3 sinks and 10 hand basins. Not much more than a very large house I suppose (there are no baths).

At 30 litres per min. that seems too low dosent it. The supply pipe is probably 25mm. dia.

On one hand you say it would need a large tank and pump to meet the possible demand, and on the other you say, why does it need a tank and pump if there is 7 Bar, are you suggesting this will be ok without a pumped supply?

 

[AlanE]

7 Bar static would suggest that the street pressure is 7 Bar therefore if opening 3 or 4 taps reduces it to around 1 would suggest a major restriction somewhere.

Maybe this should be investigated first and if the supply pipe is 25mm maybe this needs to be increased somewhat.

 

[bobby62]

7 Bar static would suggest that the street pressure is 7 Bar therefore if opening 3 or 4 taps reduces it to around 1 would suggest a major restriction somewhere.

Maybe this should be investigated first and if the supply pipe is 25mm maybe this needs to be increased somewhat.

Thanks AlanE,
I have spoken to the guy that did the pressure test and he is confident there is no restriction in the pipe. Increasing the supply pipe would be alot of work as it is some distance back to the boundary meter (40m) plus there is no guarantee this would 'solve' the problem.

The new system will be a pressurised hot water system and I thought by putting a tank and pump set in, this would at least guarantee the the correct pressure and flow will be available whatever the demand ?

Based on this info, what would you advise.

 

[mickyg]

You don't state what hot water system is in place and what the flow rate is of the hot water outlet. So its impossible to give any advice in regards to hot water. You might get away with what you already have, but you should be looking to fit flow limiters to all the outlets. 3-4 l/min at small basins and so on....
All in all I would say its right on the verge of being too low. But with the right balance you could get away with it.

 

[bengasman]

we can go through all sorts of what-if scenarios, but as the work will be done by a plumber, why don't you leave it to him to sort it out?
That is what plumbers do.

 

[bobby62]

we can go through all sorts of what-if scenarios, but as the work will be done by a plumber, why don't you leave it to him to sort it out?
That is what plumbers do.

Because, I have learnt that not all plumbers know what they are doing. I want to find out from you guys what you think before he fits the system.

The new hot water system will be a 600 litre mains pressure cylinder feeding the showers, sinks and basins.

Its the 30 litres per minute flow rate on the mains water supply that I am concerned about, even if outlets have restriction valves fitted to reduce the flow, there would still be little available if numerous outlets were being used at the same time (i.e. if all 6 showers were being used)

For example:
6 showers x 8 litres = 48litres / min req'd

 

[bengasman]

be that as it may, doing it this way has several downsides.

quality engineers/plumbers tend to get annoyed when others outside the trade tell them how to do their job, not in the least because it is rarely correct design.

personally, i take a list of the client's wishes and design accordingly, if he starts to tell me what pipe to use or how to run it, i am finished there and then, and walk away.

your example of 8 litre per shower would give the most miserable shower i have ever seen. i don't know if that is enough for you, but certainly would not satisfy me.

biggest problem from your point of view; if you order to put in item x, it is your problem if it is not up to the job, and you will have no come back

 

[Biggles..]

If youve got a 600litre DHW store your cold store for the pumpset will be quite large and heavy.

If your looking for pumpsets try BOSS or DAB amd look at the ones with active driver controls.

An accumulator might be a better solution.

As well as all that the distribution pipes have then got to be sized to deliver that amount of water.

Lee

 

[BigBurner]

Fit flow regulators on basins and sink taps and toilet cisterns.
BES Part number: 17527 flow cartridges less than £1.
http://www.bes.co.uk
This "regulates" flow, not pressure and balances the system.

Fit an accumulator - 600 litres that can take 7 bar static- then no pump sets needed. After the accumulator (stored at 7 bar) you can drop the pressure using a pressure reducer to 1.5 to 2 bar.

6 showers at 10 litres/min = 60 litres/min.

The cylinder needs rapid re-heat. This is achieved by using a bronze pump and plate heat exchanger on a direct cylinder. Using coils is old hat. It can then take all the boilers heat if need be to get a rapid re-heat and to re-heat while water is being drawn off to ensure a larger cylinder than a 600 litre is not needed. Operation is like this Plateflow:
http://www.mcdonald-engineers.com/plateflowspec.html

Lay down your specs:

• 600 litre Accumulator
• Pressure dropped after accumulator to 1.5 to 2 bar
• 600 litre cylinder heated via a plate heat exchanger
• "flow" regulators on all water outlets.

 

[simond]

You'll be best advised not to run the accumulator at 7bar, best fit a PRV in front of it. Other than that a plateflow Hex is a good idea, or an ACV.

Just completed one of these set ups in a house in Dulwich.

 

[jon26]

Fit flow regulators on basins and sink taps and toilet cisterns.
BES Part number: 17527 flow cartridges less than £1.
http://www.bes.co.uk
This "regulates" flow, not pressure and balances the system.

Fit an accumulator - 600 litres that can take 7 bar static- then no pump sets needed. After the accumulator (stored at 7 bar) you can drop the pressure using a pressure reducer to 1.5 to 2 bar.

6 showers at 10 litres/min = 60 litres/min.

The cylinder needs rapid re-heat. This is achieved by using a bronze pump and plate heat exchanger on a direct cylinder. Using coils is old hat. It can then take all the boilers heat if need be to get a rapid re-heat and to re-heat while water is being drawn off to ensure a larger cylinder than a 600 litre is not needed. Operation is like this Plateflow:
http://www.mcdonald-engineers.com/plateflowspec.html

Lay down your specs:

• 600 litre Accumulator
• Pressure dropped after accumulator to 1.5 to 2 bar
• 600 litre cylinder heated via a plate heat exchanger
• "flow" regulators on all water outlets.

Where can you get the 600 litre accumulators from?