7kw electric shower - 4mm2 too risky?

[Yonny24]

Something else has come to my attention - can an electric shower be fed from a large storage tank on the roof? The tank is fed by the mains and has a booster pump underneath it which triggers whenever a tap is turned on.

Similar scenario to this

How to convert current mixer valve tap to a cold water supply inlet.

Any plumbers can advise the best way to convert the current mixer valve tap to cold water supply inlet for electric shower. I have mixer valve tap , I would need to install a new electric shower on shower area wall .Currently is the mixer valve tap. I want to know how to do before I ask the...

www.plumbersforums.net

Been thinking of getting rid of the tank sometimes and relying on the mains only (seems to have a good pressure as the front garden tap is fed directly).

The tank was originally installed to provide a supply to a solar collector and tank next to it - we are in the process of removing this as the structure has corroded and is in bad shape.

It's a semi-detached house and the neighbour just has the entire house supplied by mains with no tanks on the roof.

This is the solar tank/panel which is now half dismantled. Not in view is a massive plastic tank that the mains fills up next to it. (solar tank being dismantled as the concrete bases have penetrated the roof membrane and the inner hot storage tank has started leaking.

 

[marconi]

I will discuss with my brother-in-law and his friend tomorrow at breakfast. They are/were both plumbers. What floor will shower be on or how many metres above the outside pavement?

 

[Yonny24]

I will discuss with my brother-in-law and his friend tomorrow at breakfast. They are/were both plumbers. What floor will shower be on or how many metres above the outside pavement?

upper floor (2 storey house) - probably about 3-3.5 metres at a guess
The booster pump gives a decent pressure.
Pump specs: Hiser HS-120
Datos Técnicos:
-Potencia: 275w
-Caudal: 3.2 m3/h
-Altura: 12m
-Diametro 3/4

I could perform a rudimentary test with a pipe from the front garden tap up to the balcony.
Can ask the neighbour also what her pressure is like from the shower she has that is fed by the mains via a hot water immersion style tank as shown below (these are located at the same height of the upper floor shower/bathroom taps.



Storage tank with pump underneath:



We have talked about removing this tank anyway - issues with penetrating the membrane underneath - plus needs cleaning periodically. And the pipes across the roof are really deteriorating in the hot sun.
Can always use the booster pump on the lower floor if we switch to mains.

 

[marconi]

No test yet but to ask your neighbour about her shower spray pressure and flow rate would be useful. Also ask about the diameter of the shower head and hole sizes and number of them - in broad terms. A question for you is what kind of shower experience do you and your family want - personally I do not like being jet washed! My wife and I are content with the rainfall experience. You get the gist. Remember the shower has a 7kW element so flow rate and temperature rise are trade-offs.

 

[Yonny24]

No test yet but to ask your neighbour about her shower spray pressure and flow rate would be useful. Also ask about the diameter of the shower head and hole sizes and number of them - in broad terms. A question for you is what kind of shower experience do you and your family want - personally I do not like being jet washed! My wife and I are content with the rainfall experience. You get the gist. Remember the shower has a 7kW element so flow rate and temperature rise are trade-offs.

My neighbour would have no clue whatsoever about flow rate etc. No man in her house either. She's pretty useless with any aspects of house maint/details.
Our standard shower heads and flex houses are these normally fed by 1/2" thermofusion piping. mains coming in I think is 3/4" then reduces to 1/2 through the house.
My wife loves a jet wash experience!! Just replaced her shower head last week with a larger one! The cold water from the upstairs taps has a good pressure, fortunately.
Hot water is much less which I think is due to that spanish style water tank shown previously limiting the rate.
I think with the cold water entering the shower directly may be better.

 

[Yonny24]

The heater immersion style tank upstairs have these one way valves which have such a small diameter, which does not help the hot water flow.
Cold water flow upstairs and hot water one way valves on tank

I'll post a vid of the mains pressure from the front garden later



View attachment video_2022-07-15_12-09-04.mp4

 

[Yonny24]

Front garden tap - direct from our mains!! Pressure washer!! This can easily be reverted to feed the house instead of the old tank on the roof. I also remember when I had to adjust the stop valve in the tank on the roof - very good pressure even up 8/9 meteres there from the mains.
View attachment frontmains.mp4


This is where they made the modification for the mains to go up to the roof. These are 3/4" for sure. mains up and other down into the house

 

[Yonny24]

Would be a good time also to do some major work on the roof as we've had a leak through the flat roof asphalt membrane sheeting we haven't been able to pinpoint yet. Quite a high chance it's under this massive tank where they just built the bricks on top of the membrane many years ago (previous owner), probably over time penetrated it, and it's seeping under there where the blue highlight is!!! Cowboy job done for sure. Membranes need replacing every 10-15 yrs so they had not planned for this at all.
So only solution is to remove the whole lot



Couple of downsides of not having the storage tank though - when the mains water is cut off it gives us a couple of days reserve, and when supply is high from the street we will lose pressure (this is where adding the booster pump may come in useful)


This weekend if I get time I might try and install the bypass between the 2 pipes - from mains and house inlet, bypassing the pipe to the tank.
This way I can test the pressure and also start repairs on the roof membrane by emptying the tank etc.

Need to buy one of the thermofusion pipe heaters to bond the unions together.

Another observation is that the pipe diameter outlet from the tank is 1/2" after the 3/4" booster pump but then feeds a 3/4" pipe into the house at ground level so they've added an unnecessary restriction! that is about 15 metres long.

 

[Yonny24]

This is a simple diagram of the piping to the roof and tank.
The idea is the make a simple connection/bypass at the ground level where the 3/4 meets the 3/4 inch from the mains.

 

[marconi]

My family plumbers recommend you stick with a roof tank and water pump. I have checked what flows and pressures your shower requires and these are easily met by the tank and pump and in range for minimum and maximum pressure and flow rate. If you dispense with the pump then you risk changes in pressure and flow rate when other taps and water using appliances are drawing water which the shower's stabiliser may not be able to compensate for. If you do without the tank and the pump then with regards to pressure and flow rate you are at the mercy of the local water company and its distribution network plus the consequences of neighbours drawing water at the same time causing lower pressure and thus lower flow rate. The tank and its pump provides you with an accumulator (reservoir) to ride through these variations in street water pressure.

Your pump can provide a flow of 3.2m3 an hour or 50L/min. The shower requires 8L/min or more.

The minimum pressure for the shower is 100kPa. The pump provides 12m head of water pressure which is about 115kPa and this is less than the maximum allowable shower inlet pressure of 1000kPa.

What they did suggest is that you fit a second pump in parallel with the current one but isolated at inlet and outlet using valves. Then if the main pump fails you can quickly bring into service the standby pump. Might be useful since you have a wife and children. You will need isolating valves on the main pump too at inlet and outlet. You get the idea.

 

[Yonny24]

My family plumbers recommend you stick with a roof tank and water pump. I have checked what flows and pressures your shower requires and these are easily met by the tank and pump and in range for minimum and maximum pressure and flow rate. If you dispense with the pump then you risk changes in pressure and flow rate when other taps and water using appliances are drawing water which the shower's stabiliser may not be able to compensate for. If you do without the tank and the pump then with regards to pressure and flow rate you are at the mercy of the local water company and its distribution network plus the consequences of neighbours drawing water at the same time causing lower pressure and thus lower flow rate. The tank and its pump provides you with an accumulator (reservoir) to ride through these variations in street water pressure.

Your pump can provide a flow of 3.2m3 an hour or 50L/min. The shower requires 8L/min or more.

The minimum pressure for the shower is 100kPa. The pump provides 12m head of water pressure which is about 115kPa and this is less than the maximum allowable shower inlet pressure of 1000kPa.

What they did suggest is that you fit a second pump in parallel with the current one but isolated at inlet and outlet using valves. Then if the main pump fails you can quickly bring into service the standby pump. Might be useful since you have a wife and children. You will need isolating valves on the main pump too at inlet and outlet. You get the idea.

OK many thanks for detailed advice. Makes sense.
Next challenge is to get the cold water feed from the current mixer tap in the shower to the electric shower without breaking walls and tiles.

 

[Yonny24]

My family plumbers recommend you stick with a roof tank and water pump. I have checked what flows and pressures your shower requires and these are easily met by the tank and pump and in range for minimum and maximum pressure and flow rate. If you dispense with the pump then you risk changes in pressure and flow rate when other taps and water using appliances are drawing water which the shower's stabiliser may not be able to compensate for. If you do without the tank and the pump then with regards to pressure and flow rate you are at the mercy of the local water company and its distribution network plus the consequences of neighbours drawing water at the same time causing lower pressure and thus lower flow rate. The tank and its pump provides you with an accumulator (reservoir) to ride through these variations in street water pressure.

Your pump can provide a flow of 3.2m3 an hour or 50L/min. The shower requires 8L/min or more.

The minimum pressure for the shower is 100kPa. The pump provides 12m head of water pressure which is about 115kPa and this is less than the maximum allowable shower inlet pressure of 1000kPa.

What they did suggest is that you fit a second pump in parallel with the current one but isolated at inlet and outlet using valves. Then if the main pump fails you can quickly bring into service the standby pump. Might be useful since you have a wife and children. You will need isolating valves on the main pump too at inlet and outlet. You get the idea.

Lot of work in progress here.
Picked up the ground pole today. Lots of work on the water reservoir tank due to the water leakage. Got myself a thermofusion tool to replace some unions.

My family plumbers recommend you stick with a roof tank and water pump. I have checked what flows and pressures your shower requires and these are easily met by the tank and pump and in range for minimum and maximum pressure and flow rate. If you dispense with the pump then you risk changes in pressure and flow rate when other taps and water using appliances are drawing water which the shower's stabiliser may not be able to compensate for. If you do without the tank and the pump then with regards to pressure and flow rate you are at the mercy of the local water company and its distribution network plus the consequences of neighbours drawing water at the same time causing lower pressure and thus lower flow rate. The tank and its pump provides you with an accumulator (reservoir) to ride through these variations in street water pressure.

Your pump can provide a flow of 3.2m3 an hour or 50L/min. The shower requires 8L/min or more.

The minimum pressure for the shower is 100kPa. The pump provides 12m head of water pressure which is about 115kPa and this is less than the maximum allowable shower inlet pressure of 1000kPa.

What they did suggest is that you fit a second pump in parallel with the current one but isolated at inlet and outlet using valves. Then if the main pump fails you can quickly bring into service the standby pump. Might be useful since you have a wife and children. You will need isolating valves on the main pump too at inlet and outlet. You get the idea.

2m ground pole purchased. Lots of work in progress on the roof also

 

[marconi]

Happy days then.


(and some extra words to meet post requirement).

 

[Yonny24]

Happy days then.


(and some extra words to meet post requirement).

Hmm hit another hurdle. Shower says it needs a 15mm brass compression fitting for the water inlet.
Only ones I can find are 13mm compression fittings made from pvc.
Showers are not fitted here so not sure it the 13mm will squeeze on or I'll need to order it from overseas

 

[James]

Could it be that half inch pipe is quoted as diameter inside in some countries and diameter outside in others?

 

[Yonny24]

Could it be that half inch pipe is quoted as diameter inside in some countries and diameter outside in others?

Could well be the case. Always end up with the wrong fittings here.
There are 13,19,20 and 25mm fittings. The 13 is only 1 pound fifty. Worth a shot and exchange it if it looks like the wrong size.

 

[Yonny24]

Could well be the case. Always end up with the wrong fittings here.
There are 13,19,20 and 25mm fittings. The 13 is only 1 pound fifty. Worth a shot and exchange it if it looks like the wrong size.

Looks like I might need to send over the brass compression fitting from the UK. Wish I had bought it with the shower while I was there now! Just not a fitting they have here because they don't sell these showers.
So no fast install here for sure. Maybe by next year my wife will have water on demand! LOL

By the way, installed the 2m ground pole last night, just need to make my own inspection casing for it, will use some concrete around it and a cover.

 

[marconi]

Do you want me to buy some and post to you? You can 're-imburse' me by making an equivalent donation to a Uruguian children's charity.

 

[Yonny24]

Do you want me to buy some and post to you?

Many thanks for the offer. Very kind of you.
I have my Dad in Wales who can arrange that

Need to arrange it carefully maybe with some other items as I can only import 3 times a year with my residence card here (max 200 USD also).
Very strict and all registered.

Unless someone is travelling over here. I'll keep an eye out - sometimes the school kids around our neighbourhood go on cultural trips to the UK> Just missed one big group, unfortunately.

USA fittings are all in inches so probably won't fit unless you know of a company there. (know a group of Americans here who travel a lot)

 

[Yonny24]

Sorry I know I'm digressing from electrical topics a little here (well it is an electrical pump but more to do with the plumbing and location for the flow sensor to work efficiently). The pump installed under the tank does not quite comply with the fitting instructions. The manual says an incorrect installation is with the black control box on the underside. This is exactly how ours is and was installed.
I have always noticed there is always a slight delay in the pump initiating on the upper floor in the bathrooms. Lower floor is faster.
Could this be the reason? Does the flow sensor need to be reversed (repiping and pointing the pump 180 degrees?)
hmm I wonder if the pump would turn on faster if it was rotated 180 degrees, involving quite a bit of odd pipe routing though below the tank. Or the pump located down on the ground floor where it enters the house?





Also, got a diagram of the pump way further down - maybe on the ground level?? Not under the tank. Also could do with a bypass in case it does fail and I can just switch to the bypass.



Clearer photo of the pumps orientation and piping here::

 

[marconi]

I will ask my brother in law this morning. I suspect that it is something to do with the difference in head of water since you say the downstairs is quicker than the upstairs. It is the start of flow of water (and I assume above a minimum flow rate) which is detected by the flow switch to turn the pump on. It is the difference in head of water which accelerates the stationary water in the pipes up to speed to create the flow. Therefore smaller difference in head, lower acceleration rate, longer time to reach and exceed minimum flow rate. Why the flow switch must be on top is presumably to do with its mechanism - I will ask my plumbing guru.

 

[marconi]

https://api.grundfos.com/literature/Grundfosliterature-5439421.pdf

My plumber chums gave a thumbs up to my explanation as the likely reason for the delay. They did not know why the connection box had to be on top. So I did some research.

I reckon the HISER 120 Auto booster pump is very similar if not the same as the Grundfos 120 with integral flow switch. If you look at the second link at section 4 on installation it states in a note that the electrical connection box must not be at the bottom because the ‘pump‘has a drain hole. The risk it seems then is that water could seep over time into the connection box from the sealed pump motor assembly - the wires to the windings have to pass through a sealed hole somehow - and then be unable to drain out of a second hole in the connection bottom located at the bottom of the connection box. Over time this would clearly be a problem. If you continue to use the original pump you should take a look inside the connection box to see if there is any water ingress. Can you see the drain hole?

Please note the requirement for 0.5m difference in elevation between outlet of roof tank and shower head. The minimum pump inlet pressure is 2m see page 3 of grundfos reference - this is the distance from the top of the water in the tank to the inlet of the pump. I think you just about have that. Is the tank pressurised by the mains water pressure or is their a float valve?

I have included an installation video. Hope this helps.

 

[Yonny24]

My plumber chums gave a thumbs up to my explanation as the likely reason for the delay. They did not know why the connection box had to be on top. So I did some research.

I reckon the HISER 120 Auto booster pump is very similar if not the same as the Grundfos 120 with integral flow switch. If you look at the second link at section 4 on installation it states in a note that the electrical connection box must not be at the bottom because the ‘pump‘has a drain hole. The risk it seems then is that water could seep over time into the connection box from the sealed pump motor assembly - the wires to the windings have to pass through a sealed hole somehow - and then be unable to drain out of a second hole in the connection bottom located at the bottom of the connection box. Over time this would clearly be a problem. If you continue to use the original pump you should take a look inside the connection box to see if there is any water ingress. Can you see the drain hole?

Please note the requirement for 0.5m difference in elevation between outlet of roof tank and shower head. The minimum pump inlet pressure is 2m see page 3 of grundfos reference - this is the distance from the top of the water in the tank to the inlet of the pump. I think you just about have that. Is the tank pressurised by the mains water pressure or is their a float valve?

I have included an installation video. Hope this helps.

Many thanks. I knew you'd be the man to ask. Greatly appreciated as always.

Makes sense in regards to the possibility of water ingress into the box.

Now a couple of doubts. The tank is not pressurised, it has a float valve. As the pump is directly under the tank there is not 2 metres between the pump and top of the tank. 1.5 at most.

The only water inlet to the house enters at the ground floor so has to rise to the top floor bathrooms. There is not another pipe branch that enters the upper floor.

Do you think the pump may perform better if it is placed at ground level just where it enters the house? That would be about about 14 metres approx between the tank and pump. 7 metres horizontal across the roof and 7 metres directly down the side to where it enters the house.

Thanks again

 

[marconi]

On Monday I will contact Grundfos technical department to see what a head of 1.5m would mean for the pump as opposed to 2m - there may be some margin. And I will re-acquaint myself with my second year fluid dynamics lectures. So a response in a few days.

Have you already bought a new water pressure booster pump or are you using the original?

 

[brianmoooore]

Maybe a regional thing, but every Grundfos pump I've ever seen that is painted that colour is only suitable for closed circuit applications, where the water is deoxygenated. The pumps for non closed applications are gold in colour, and the working parts are made from materials that won't corrode.

 

[marconi]

I will follow up on brianmoore's helpful post.

 

[marconi]

posted in error and deleted.

 

[marconi]

Good news. The inlet pressure is greater than 2m head of H20. I forgot to include atmospheric pressure acting on the surface of the water in the tank which is a pressure of about 10m head of H20. Thus the head of water at the pump inlet is about 12m head of H20 or 1.2 bar for the pump’s current location.

 

[Yonny24]

Thanks for the replies.
Do you think I'd get a better faster pressure if the pump was installed at ground level, where I've added the circle with the cross rather than under the tank? The bathroom is far, it goes down to the ground level first and then rises up.

 

[marconi]

Rules to Follow to Avoid Pump Problems | Valin - https://www.valin.com/resources/blog/rules-follow-avoid-pump-problems

The pump should be located close to where it draws suction from the cold water tank to ensure the minimum Net Positive Suction Head Available NPSHA of 2m h2o Is exceeded. If a long thin pipe run provides the water feed to the pump inlet there is the risk of the NPSHA dropping below 2m because of friction in the pipe, its bends and joints and turbulence acting to reduce head of water pressure.

The cold water tank also provides a large reservoir of water to provide a short term high flow rate to the shower which is why I do not recommend connecting the pump to your mains water pipe directly. At a high flow rate the water pressure in the mains pipe coming into your home will decrease and thus could fall below minimum inlet head of water of the pump.

Note also that you should avoid sharp bends near the inlet and outlet of the pump. Have long arcs of pipe work so the water flow is not overly disturbed.

 

[Yonny24]

Rules to Follow to Avoid Pump Problems | Valin - https://www.valin.com/resources/blog/rules-follow-avoid-pump-problems

The pump should be located close to where it draws suction from the cold water tank to ensure the minimum Net Positive Suction Head Available NPSHA of 2m h2o Is exceeded. If a long thin pipe run provides the water feed to the pump inlet there is the risk of the NPSHA dropping below 2m because of friction in the pipe, its bends and joints and turbulence acting to reduce head of water pressure.

The cold water tank also provides a large reservoir of water to provide a short term high flow rate to the shower which is why I do not recommend connecting the pump to your mains water pipe directly. At a high flow rate the water pressure in the mains pipe coming into your home will decrease and thus could fall below minimum inlet head of water of the pump.

Note also that you should avoid sharp bends near the inlet and outlet of the pump. Have long arcs of pipe work so the water flow is not overly disturbed.

Brilliant thanks for all the detailed information.
I'll keep the pump set up as it is.
I do believe there was some air in the piping the other day after changing a non return valve on the immersion heater tank on Friday though. Appears to be functioning better on the upper floor bathrooms now. Still the hot water pressure is not great from the upper floor immersion heater. I wonder if it needs an additional smaller booster pump in the airing cupboard where the immersion heater is. That non return valve I believe causes the issues initiating the flow sensor

 

[Yonny24]

Just a quick update. Discovered why we were having issues with the flow sensor on the pump. Pump was fine. Odd discovery with the non return valve and the flexible pipe fitting used.
The hot water was leaking slightly back into the inlet pipe. Noticed the inlet pipe was hot!
Swapped out the flexible pipe on the inlet valve.
One had a protruding washer v shape almost that seemed to be putting some pressure on the internal valve.
The replacement has a flat washer and has solved issue. No backwards leakage and the pump kicks in as it should when opening the cold water tap!
What an unusual discovery.
Left one was the one causing the issues with the valve. Right shows an older one I had hanging around with a flat washer

 

[marconi]

Nice investigative work and solution.

 

[marconi]

I just wondered where you have reached with this shower project?

 

[Yonny24]

I just wondered where you have reached with this shower project?

Unfortunately nowhere yet - been so busy.
Been working on CCTV around the exterior and other bits and bobs that needed more attention.

Also the actual cold water inlet piping could be very messy due to the location of the mixer for the current shower unit, without breaking down the walls and installing a new cold water pipe within the wall it could look unslightly with adaptors and a pipe on the oustide of the wall.

So really on hold for now as I'm undecided.

But as always appreciated all the assistance and replies.