Another Venturi shower question

[robgraham]

Rather than hijack the previous thread on these showers.

The one thing that is not made clear on the manufacturer or related websites for venturi showers is what the *minimum* hot water temperature should be. Has anyone any idea ? We all know what is comfortable for us in the shower - I've just measured our's at 42 C - but if the cold water is coming in at say 6C and has to "suck up" sufficient hot water to raise it to that temperature, then there must be a minimum HW temperature. OK if I measured the flow rates, etc. it could possibly be calculated, but ...

Another thought is that the HW head / pressure is obvious, but the mains pressure would be measured in a static situation only and will be consistent throughout the system regardless of restrictions in the pipework - but there must also be a flow parameter requirement.

Rob

[John]

I've been pondering the same thoughts today as obviously a significant amount of mixing takes place.

[dom]

The answer would be complex, based cold water temperature, cold water pressure and how that pressure rolls off under increasing flow, hot water temperature (which will roll off as the store is depleted), hot water pressure and how that pressure rolls off under increasing flow - calculations sufficient to daunt a physicist.

In practice the manufacturers have a few graphs in the instructions - that are likely to give satisfactory results for domestic situations.

My experience of a single example with good cold pressure and flow, poor hot water head - was that 22mm throughout is essential - and then results are very acceptable.

[robgraham]

Dom Thanks for that - I suppose I guessed it was a bit of a "string" question

When you say '22mm throughout' did that include the mains feed? Also can you remember what temperature your HW tank is running at - that is if it has a stat on it ?

Rob

[dom]

22mm throughout the hot water feed from the tank - 15mm is perfectly adequate at mains pressure.

Immersion heater - as I'm part way through a chapel conversion with no central heating yet.

Hot water at the tap is too hot to keep a hand under for more than a second, but not so hot to burn instantly - say 60 degrees?

The only caveat I would add is that in winter the shower setting has to be tweaked closer to the hot end - and as I do (on my setup) flow is reduced from "gushing" to "very good".

I can't emphasise enough the importance of that 22mm hot pipework with minimum number of bends.

[David Hansen]

On Mon, 26 Nov 2007 07:48:05 -0800 (PST) someone who may be robgraham wrote this:-

When I investigated one thoroughly about a year ago the manufacturer's web site had installation instructions which went into every detail, including minimum hot water temperatures.

[robgraham]

HW temperature question. The distance to the shower from the HW tank I've emailed Trevi on to get their opinion - I suspect that based on the graphs given and that I do have a bit more head than the minimum, that it should be OK.

I suspect from the wording in your answer that you didn't go down this route - why? Or alternatively if my interpretation is wrong, has it been a success ?

Thanks

Rob

[David Hansen]

On Tue, 27 Nov 2007 02:26:17 -0800 (PST) someone who may be robgraham wrote this:-

Because one doesn't need to do everything one investigates thoroughly:-) In this particular case a thermal store had advantages to do with the heating, it could be fitted with a shower coil to take mains pressure water and thus a bog-standard mixer could be used at the shower.

[robgraham]

I've also done the investigation on the thermal store route and decided the upheaval and cost doesn't really justify it, but the =A3200 plus for this shower and a bit of 22mm pipe work seems a better option.

I still hanker after the thermal store but it does seem a lot of effort and cost even on the DIY basis - having said that I haven't come across this idea of the shower coil before and would like to explore that further.

Rather than lose this topic in this thread, I think I will start a new one on the shower coil subject.

Rob

[Doctor Drivel]

I've also done the investigation on the thermal store route and decided the upheaval and cost doesn't really justify it, but the £200 plus for this shower and a bit of 22mm pipe work seems a better option.

I still hanker after the thermal store but it does seem a lot of effort and cost even on the DIY basis - having said that I haven't come across this idea of the shower coil before and would like to explore that further.

Rather than lose this topic in this thread, I think I will start a new one on the shower coil subject.

Rob

[David Hansen]

On Tue, 27 Nov 2007 09:56:34 -0800 (PST) someone who may be robgraham wrote this:-

The upheaval and cost just to get a mains pressure shower is not worthwhile for most people. However, it can become worthwhile if allows other things to be done at the same time.

The effort depends on the changes one is making. I was making a number of changes and thus the effort was higher than just slapping one in.

The cursing, swearing and scratches/bruises were largely due to the changes I was making to the pipework, one of the few exceptions being when a joint I had not done up properly came apart in my hands and a stream of water at 65C, under a head of nearly 10m, hit me in the chest:-(

As for the cost, it is nothing compared to what some/many spend on a kitchen, car, television and so on.

indicates a premium of £320 for a thermal store coil and £125 for a shower coil. The shower coil could be fitted in a conventional vented hot water cylinder should one not wish to have a thermal store.

If I spot one I will join it if I have anything extra to say.

[Doctor Drivel]