Energy/water-saving shower head question

[A.Clews]

Just seen this ad in The Independent about energy and water-saving shower heads for power showers:

or

have an Aqualisa Quartz power shower which pumps at the rate of about 12 litres/minute, or 18 litres/min on boost setting.

This shower head is claimed to restrict flow to 8 litres/min. However, surely the shower pump will still be 'trying' to pump at the higher rate, so wouldn't this shower head place a resistive strain on the pump and lead to problems? Does anyone have any experience or technical knowledge on this? Having spent an arm and a leg on this shower, I don't want to risk damaging it, though I like the idea of saving water.

Thanks in advance...

[Lurch]

On Sat, 12 May 2007 07:30:06 +0000 (UTC), [e-mail] mused:

What a load of old bollocks. Save your money, if you wanted to save money you'd have had some crappy low flow shower put in in the first place. I can't see how it can give the same performance but shave 5 litres\second off the flow rate.

[A.Clews]

Thus spake Lurch ( [e-mail]) unto the assembled multitudes:

I certainly can't argue with that, but my main interest is in the effect such a device would have on the operation of the processor/pump, what with the back-pressure created by the restricted flow rate, and whether it would affect my warranty.

[Lurch]

On Sat, 12 May 2007 10:04:42 +0000 (UTC), [e-mail] mused:

In the short term I can't se it would do major damage, however, I wouldn't fit something that purposely restricts flow to a shower outlet. I think all\most shower installation manuals specifically prohibit this. As for the warranty, I'm sure Aqualisa will be happy to declare it null and void once they find out you've been using it with a flow restrictor in the outlet line.

I wonder how much of the environment these will save in the long run, someone who is using a standard shower setup has the same shower for

20 years and never has a problem, but uses a bit more water. Someone who has the same shower fits one of these stupid heads and knackers the shower up every couple of years, so they have a bigger shower fitted each time. So who uses the least energy over the 20 years?

[timegoesby]

It will be a flow regulator, which guarantees flow irrespective of pressure. Pumps are deisgned to cope with a range of flows and resistances. It should be fine, ring the makers. I recall in the USA a water company went around and fitted these flow regulators on all showers for free and saved stand pipes being used. Few people noticed the difference in the showers and most saved money on bills.

[John Rumm]

These usually work by having a more directional shower pattern than a standard head. Hence you get the same force of water but directed in a smaller cone by fewer jets. Some also "cheat" by directing the spray of water using jets only round the periphery of the cone and not filling in the gaps in the middle.

Years ago when I had the poorly designed gravity system that came with the house, I had a problem with the cold cistern running dry while in the shower. I fitted a head similar to this as a "quick fix". I have not changed back to the original head even though I now have mains pressure hot water. I have however changed to the pressure reduction disc on the head to a more aggressive one since it helps improve the controllability of the manual shower valve that was not really designed for mains pressure systems.

I actually quite like the slightly narrow spray since you can point it away from you when trying to lather up or wash you hair etc. (this is on a fixed outlet shower which gives only limited head movement)

[Pete C]

Hi,

Why not call Aqualisa and ask them? I expect it would be OK.

I've done something similar with a normal shower head, but getting a normal shower head to withstand 2 bar pressure isn't easy!

Most people think litres per minute is _everything_ when it's not even half the story...

cheers, Pete.

[A.Clews]

Thus spake Pete C ( [e-mail]) unto the assembled multitudes:

I have emailed them. I'll copy their reply (if any) here.

Would you care to share the rest of the story?

[Pete C]

OK...

The energy contained by the moving water from the shower head, is given by

1/2m * v^^2

half m times v squared, where m is mass of water and v is it's velocity, or speed.

So if the speed is doubled it's energy is quadrupled! Even if you halve the amount of water and double the speed it's energy is still doubled.

The speed of the water is largely down to the pressure it's under as it leaves the shower head. One way to get higher pressure is have a shower head with smaller holes, which is what I did.

Something to bear in mind is that a pump will shift less and less water as it's output pressure goes up. This is the 'flow curve', a chart of flow vs. output pressure. For a centrifugal shower pump it tends to go up in a curve then fall back.

So if the flow is tooo restricted, the increase in pressure won't compensate for the reduced flow, and it's best to have it working below this point.

I also found the size of the jets in the shower head makes a difference too, having few normal size ones under much higher pressure makes for an really unpleasant shower! In the end I settled on 0.4mm jets, and fine tuned the number slightly to get the right pressure. This gave a nice tingling shower without it being stinging.

cheers, Pete.

[A.Clews]

Thus spake Pete C ( [e-mail]) unto the assembled multitudes:

[snipped]

Thanks!