Unvented - how many showers/performance?

[fezster]

I have a megaflo unvented cylinder which feeds 3 bathrooms. In particular, it feeds 3 showers which have pura thermostatic valves:

http://www.purabathrooms.co.uk/catalog/index.php?route=product/product/datasheet&product_id=24158

The MI state the valve uses 32 litres/min at 3 bar. Two of my showers have 200mm heads and the other has a 250mm head.

Individually, these showers perform wonderfully. Pressure and flow is great. However, the first of these showers (closest to the cylinder, with the larger 250mm head) definitely has a noticeable drop in performance if either of the others are turned on. It's still adequate, but given my incoming mains is 32mm MDPE and over 60 litres/min flow, I'm surprised they don't all work without a drop in performance together.

All the showers are fed using a mixture of 22mm polyplumb and copper.

Are my expectations too high? Is it the pipe route which is the problem? Trying to get my head around what (if any) solution there could be in the future if I ever undertake any work.

Thanks.

 

[townfanjon]

60 litres a min , people would kill for that lol
Initial thought is the nearest head scaled up / ready for a clean maybe

 

[fezster]

I should add this has been the same since it was fitted (about 3 years ago). And the first shower is fine on it's own, only reduced when another is switched on.

 

[Stanios]

Every elbow, every meter of pipe, every valve reduces your flow. There is another issue I see with having two showers at 30l/m running simultaneously is your megaflo will fill will cold water in about 10 minutes. Thats assuming a 400 litre cylinder.

One thing I can say is 32l/m at 3 bar must mean the shower head is very large. Typical hand helds push out 9l/m at 3 bar. You can see how no matter what your mains is if the hole is large enough you will always lose pressure and flow the more you open up.

 

[fezster]

What is the solution (lets pretend cost was no issue). If you were designing a system from scratch that needed to run 2 rain type showers simultaneously, what would you spec?

 

[Ch4 plumbing]

Have a look into accumulators, TWS GAH and plenty more manufacturers make them but be warned it would have to be massive to be any real help!

Might be a good idea to get a G3 qualified plumber round to give you a better idea about what's achievable with your set up and demands.

 

[fezster]

Am I right in saying that if I have adequate pressure and flow from the mains, an accumulator would not be required?

I have had G3 qualified plumbers round. The advice seems to vary from upgrading the internal pipework to 28mm, but this will result in more heat loss and wasted water, to changing the PRV to >3 bar (which I know is against the regulations!). I'm trying to gauge if others with unvented setups and multiple large showers get great performance, and if so, compare setups.

I've bought a pressure gauge today, so will measure this at various outlets to see if maybe my PRV is faulty or has debris.

 

[Ch4 plumbing]

if you have around 60ltr a min incoming on the mains and you have 3 showers each at 32ltr a min even with just 2 running your over your max incoming ltr a min, what's your dynamic water pressure?

 

[Ch4 plumbing]

An accumulator can help even out and reduce any drop in flow and pressure when multiple outlets are open.

 

[fezster]

Just used the pressure gauge. So on outside taps, which bypass the PRV, I am getting a solid 4 bar.

On an outside tap after the PRV, I am getting 2.2 bar. Also tried on the bath taps and on all 3 shower outlets, all giving 2.2 bar.

PRV strainer need cleaning? Faulty PRV? Or something else.

 

[ShaunCorbs]

That's static pressure put on outside tap and run an the kitchen sink will give you the working pressure

and could be something simple get your G3 Eng to investigate

 

[fezster]

Would you expect the gauge to read exactly 3 bar, or would pressure be lost in the pipework? For the outside tap, we're talking 2m of 22mm and then 3m of 15mm to outside. I would have thought it should be pretty close to 3 bar.

I did try the dynamic pressure test. It drops by 0.5 bar. So bypassing the PRV, I have 4 bar static, and 3.5 bar dynamic.

G3 engineer is coming tomorrow. Would still like to understand what should be expected from the setup and what typical real world scenarios achieve. Haven't ruled out the gauge itself may be inaccurate (monument gauge from amazon).

 

[ShaunCorbs]

Would you expect the gauge to read exactly 3 bar, or would pressure be lost in the pipework? For the outside tap, we're talking 2m of 22mm and then 3m of 15mm to outside. I would have thought it should be pretty close to 3 bar.

I did try the dynamic pressure test. It drops by 0.5 bar. So bypassing the PRV, I have 4 bar static, and 3.5 bar dynamic.

G3 engineer is coming tomorrow. Would still like to understand what should be expected from the setup and what typical real world scenarios achieve. Haven't ruled out the gauge itself may be inaccurate (monument gauge from amazon).

its unlikely for the pipework to cause a drop of more than 1 bar, sorry we cant give any more info out just incase you decided to have a go (you have said you wont but we cant guarantee that and you could damage something/ mess with a safety device)

hope you understand

 

[Scott_D]

Pictures are always helpfull

 

[macackau]

60 litres a minute?!!! A litre a second? Where do you live? That's amazing, I've never seen a domestic premises with that sort of flow rate

 

[Howsie]

It's also over the water regulations guidelines!

 

[CP1111]

Scubatank would probably sort this

 

[fezster]

This is what I was told by the guy who put the new mains in for me and tested it.

Regardless, what I would say is that if I try to fill a bucket using the outside tap, it's almost impossible to do so at full flow. The water just bounces straight out there's so much of it. So I'm assuming flow is going to be as good as it gets in London.

 

[Howsie]

You can have better flow if you want it, many ways to skin this cat. Many of my customers have six plus bathrooms and have no issues to usage concurrency.

 

[fezster]

Could you tell me specifically about the PRV and the reading I am getting of 2.2 bar on the first outside tap after this PRV? Cleaning the strainer will be the first thing the plumber does, but is there anything else I could try or suggest in case that does not work?

 

[Howsie]

Get a decent plumber that know what he's doing and you'll be fine. I'm not going to offer an suggestions about working on an UV cylinder and it's associated controls and safety devices.

 

[fezster]

Fair enough. I have a G3 plumber coming later today.

Whilst I can understand why a lot of members who are RGIs default to not giving advice in case somebody decides to have a go themselves, there are many of us who want advice only so we can use that to help a qualified professional arrive at an answer. I've had a lot of plumbers/RGIs during building works a few years ago and they varied massively in how competent or capable they were. To be fair, even the good one's when sometimes prompted would arrive at an answer quicker or look at something they may otherwise have not of.

 

[ShaunCorbs]

Fair enough. I have a G3 plumber coming later today.

Whilst I can understand why a lot of members who are RGIs default to not giving advice in case somebody decides to have a go themselves, there are many of us who want advice only so we can use that to help a qualified professional arrive at an answer. I've had a lot of plumbers/RGIs during building works a few years ago and they varied massively in how competent or capable they were. To be fair, even the good one's when sometimes prompted would arrive at an answer quicker or look at something they may otherwise have not of.

Once he's told you what's wrong you can ask us if it sounds about right

 

[fezster]

Ok, thanks.

 

[Howsie]

It can be difficult finding a decent one, just like in any business I guess.

 

[fezster]

So the reducing valve was pretty clean.

When he did the pressure test on the outside tap (he had the same gauge as me), initally he got the same 2 bar reading. He noticed when the thread on the gauge's connector was fully tightened onto the tap, the bit inside the connector wasnt snug against the tap (if that makes sense). So he wrapped some PTFE tape around it to get a snug connection. Then the pressure read 2.5 bar, and slowly crept up after about a minute to just under 3 bar. So I guess it's ok.

Is the gauge quite sensitive in that way to being tightly up against the tap (even though no water is escaping). Never used one before so didn't realise it made a difference.

 

[mutley racers]

If the gauge is creeping up and it is an outside tap then there will be a double check valve in it so you won't be getting the correct dynamic pressure I believe

 

[mutley racers]

It is really best to do the pressure test from a washing machine connection and open the kitchen tap

 

[Staffy85]

whats the pressure before the PRV with nothing running? and then what does this pressure drop down to with the shower running?

 

[fezster]

Thanks mutley, I think you are right about the double check valve (I read that elsewhere also).

Staffy85 - pressure on outside tap before the PRV is 4 bar, and drops 0.5 bar if the kitchen tap (also before the PRV) is switched on.

 

[PhoenixServices]

You want readings from outlets after the prv

 

[Howsie]

You have standing and dynamic pressure.

 

[fezster]

Done some measurements. It's not as easy as it looks. Ended up getting drenched!

Measured 3 outlets at a time, and repeated the test twice. By far the highest output is from the outside tap. This is also the hardest to measure using a 1.5 litre jug!

Results:

First test:
Outside tap - 1.2 litres in 2.9s.
Utility - 1 litre in 9s.
Ensuite shower - 1 litre in 13s.

I make this to be 30 litres/min.

Second test:
Outside tap - 1.4 litres in 3s.
Utility - 1 litre in 13s.
Kitchen - 1 litre in 10s.

which gives 38 litres/min.

I then measured just the outside tap in a bucket, and got 9.4 litres in 18s, which is 31 l/m.

I think overall it's probably about 40 - 42 l/m.

This points to my overall flow not being enough to drive 2 showers according to the shower spec. However, I also measured just the shower on it's own, and got 3.8 litres in 18s which is only 13 l/m. Nowhere near the 32 l/m the instructions state.

With the outside tap running, the shower gives me 1.4 litres in 11.5s which is 7.3 l/m. This felt similar to when I have a second shower running.

Not sure what to make of all of this. Is the pipesize to the showers the restriction? Or is the mains the restriction?

Not sure if I mentioned before, and Im wondering whether it's pressure rather than flow which is the problem - but I measured pressure at 4 bar static at outside tap, and drops to 3.5 bar dynamic with another outlet open. This is bypassing my 3 bar PRV. I tried to measure pressure on shower, but Im not sure it's entirely accurate because of the attachment I had to use. It read less than 3 bar static. There's approximately 15m of 22mm pipework to the first shower.

I have a thread on diynot on this also, in case anyone experiences deja vu.

 

[rpm]

I have a thread on diynot on this also, in case anyone experiences deja vu.

Go wash your mouth out with soap!

 

[fezster]

Go wash your mouth out with soap!

Sorry if that offends! Getting desperate with frustration. Want to work out what is going on here.