This will give an electrician or plumber some unnecessary work:
Lady in the office is convinced her electric shower is faulty or connected up wrong as it gets hotter when she turns it down!
Us blokes can't convince her there is no problem.
Which bit does she turn down, the temp or flow rate?
The message from "John" contains these words:
Have you tried explaining it sensibly instead of just waving arms about?
You put the same amount of heat in all the time. If less water is flowing through the unit then the water will get hotter.
Perhaps she thinks the knob controls the amount of heat going into the shower not the amount of water going through - not an unreasonable mistake as some newer showers do indeed work like that.
On Wed, 04 Oct 2006 06:27:29 GMT someone who may be "John" wrote this:-
Does she also think that if one turns up a thermostatic radiator valve then the room will warm up more quickly?
|The message |from "John" contains these words: | |> Lady in the office is convinced her electric shower is faulty or connected |> up wrong as it gets hotter when she turns it down! | |Have you tried explaining it sensibly instead of just waving arms about? | |You put the same amount of heat in all the time. If less water is |flowing through the unit then the water will get hotter. | |Perhaps she thinks the knob controls the amount of heat going into the |shower not the amount of water going through - not an unreasonable |mistake as some newer showers do indeed work like that.
As everything nowadays uses thermostats, why do electric showers work as described above.
But it does. Every woman knows that.
My wife thinks the boost switch on the CH (that bypasses the cylinder stat) should make the water hot more quickly.
You must have my old flatmate working for you.
She thought the dishwasher was faulty, because it would leave the cups and bowls full of water unless you put them in face down.
Presumably it's still cheaper to vary the flow rate than the power.
Especially if it's done manually. Electric showers are _very_ simple.
And they're also sufficiently weedy that you want full power all the time.
cheers, clive
The message from Dave Fawthrop contains these words:
Because it's probably easier to regulate the flow of water than have the electronics to control the heat input.
Just a bit! It would have to be switching 30A plus in a tiny box. Given the tiny amount of water in the heating chamber, the system would have to have a very low hysteresis to avoid cold/hot/cold/hot water so it would be switching this current very fast. The house lights would flicker and the contacts burn out. A solid state control system probably wouldn't fit and would be expensive. The inlet water is cold enough that it can be run steady state and the flow modified to change the temperature. It's the best way of doing it (possibly the only way). There is an alternative, it's called a hot water tank and a pump, or a combi. Both better in all ways (except when the electric shower is as a backup for when other systems fail)..
The message from "Bob Mannix" contains these words:
The hardest part would be the cooling - unless of course you use the handy waterflow to dump the heat into.
It is a purely resistive load, which helps massively with the design, though.
However, it still isn't easy, especially as you'd have to meet regs with regard to power factor (particularly not degrading the sinusoidal form by chopping).
Christian.
Thats not a problem with electronics 10kW+ dimmers for (stage) lighting are available. There is some loss in the triac(s) but put their heatsink on the cold inlet and you have ample cooling and don't "waste" that heat.
Rubbish, though "expensive" is a relative term. It would be expensive compared to a simple water valve to restrict the flow...
Doh! Brilliant!
Mind you, if you used the water as the conductor and changed its conductivity by adding copper sulphate to adjust the temperature, you wouldn't need any electronics. But you would end up blue. Arse.
That could be a niche marketing opportunity to those of certain footballing affiliations.
Owain
The message from "Bob Mannix" contains these words:
I gather some old 3-phase water heaters were just electrodes into the water.
On Thu, 5 Oct 2006 11:21:02 +0100 someone who may be Guy King wrote this:-
Nothing wrong with electrode boilers, provided the appropriate safety precautions are taken. Small ones may be single phase, larger ones three phase and some use high voltage supplies.
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