7kw electric shower - 4mm2 too risky?

[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.