Do electric showers contain pumps and what exactly is a 'power shower'?

[JoeyT]

I'm curious why. definitely non-preferred from the installer's viewpoint! Are you going for the single or twin pump?

Twin pump. Best to have equal pressure, rather than one at 3 bar and the other at ~0.1.

 

[fixitflav]

Best to have equal pressure, rather than one at 3 bar and the other at ~0.1.

OK, but that's not how it works. With the single, the pressure of both hot and cold at the mixing valve are nominally equal, determined by the water level in the CWST. It's only 3 bar after the pump.

 

[denso13]

determined by the water level in the CWST

The storage cistern should feed both hot and cold therefore the pressures should be equal.

 

[fixitflav]

The storage cistern should feed both hot and cold therefore the pressures should be equal.

Yes, that's what I meant. The cylinder in between on the hot side makes no difference!

 

[JoeyT]

I may have gotten confused.

The pump is a twin pump, pumping both from the CWST (directly) and from the hot water cylinder directly into the shower. There the pressures should be the same (hence the twin pump pumping both sides).

How would you use a single pump, before the cold water feed for the tank?

 

[fixitflav]

How would you use a single pump, before the cold water feed for the tank?

It's described in the Stuart-Turner instructions, link in your post #11. Figs 3 and 4. The mixing valve is on the pump suction side and takes in hot and cold.

 

[JoeyT]

Got it. Pump after the mixer, before the heads. Not mentioned it yet but we may boost the rest of the taps, they probably don't need it, except for the kitchen hot feed but will decide that later.

Thanks everyone.

 

[Johntheo5]

The single pump with the mixer before the pump is a option but TMVs do restrict the flow under very low gravity supply head, they generally contain check valves which can be removed but are still restrictive IMO, also you have no local control of the mixing temperature and people like different showering temperatures.
I have seen single pumps just boosting the gravity fed HW and mixing with cold water mains in the different mixers, showers etc, and they worked quite well but are dependent on a reasonably constant mains pressure that doesn't fall under ~ 2.0bar dynamically.

 

[fixitflav]

The single pump with the mixer before the pump is a option but TMVs do restrict the flow under very low gravity supply head

The only that would be a problem is if the initial, gravity, flow is less than the 1 l/min needed to kick the pump in. Worth checking but I doubt it would be an issue.

also you have no local control of the mixing temperature

The mixing valve can be located in the shower cubicle as normal.

I have seen single pumps just boosting the gravity fed HW and mixing with cold water mains

I don't think that's being suggested here

 

[fixitflav]

Not mentioned it yet but we may boost the rest of the taps

I don't think that's possible from the shower pump, if that's what you have in mind. No way it could be piped with a single pump. With a twin, in principle the hot and cold pipes after the pump could be tee'd off to taps, but using either tap alone would mean the other impeller dead-headed, which isn't acceptable.

 

[Johntheo5]

The mixing valve can be located in the shower cubicle as normal.

So 4 pipes in all, 2 in to the cubicle/mixer, 1 out to the pump and 1 (mixed) back in?.

 

[fixitflav]

So 4 pipes in all, 2 in to the cubicle/mixer, 1 out to the pump and 1 (mixed) back in?.

That's right. Looking at the Stuart-Turner stuff, that's no more complicated, probably less, than the piping with a twin-pump set-up.
For the single-pump option, I'd probably take both supplies in the loft, hot from the cylinder vent pipe, run them to above the mixer location, and drop straight down.