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Electric shower, anything I can do?
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paulca:

--- Quote from: MosherIV on July 24, 2019, 07:14:10 am ---If I understand the plumbing correctly, the electric shower is fed from a water tank in the loft  :palm:

Try connecting the electric shower to mains water, run the water in let up to the electric shower heater. Most electric showers are designed to be run from mains water.

Modern house plumbing no longer use a tank in the loft. The whole house is run off mains water.

--- End quote ---

I'm aware of this, but the house has not (yet) been modernised.  I am "assuming" it is run from the header tank in the loft as that's normal for a system of this age.

So I'm resigning myself to put up with it until I can re-do the heating as a pressurized mains fed system.  That's possible to get done this autumn as apparently it should only take 2 days to complete. 

On a related note the choice has been presented to me as to whether I want a "Combi" set up or a "System" setup.  The former has no hot tank and water is heated on demand by the gas boiler.  I have had this before and it's awesome; turn on a tap and you have scalding hot water in about 20 seconds.  However the downside is, I have no hot tank and cannot later take advantage of solar PV water heating.  It also has a more invasive and expensive install as the hot water tap circuit needs replumbed to the boiler.  Going the system approach I have a heat exchanger in the hot tank so the gas can heat it, but I can put a DC immersion in the tank at a later time and as long as I can control the hot water/heating circuit valve and the circulation pump I will save on gas for heating not just the water but the radiators too.  Of course 1kW of solar will not go that far, but it will heat the to tank to 60*C fairly easily during the day.
soldar:
I have designed and modified a few domestic hot water systems of very different nature. My boat, homes with on-demand heaters and homes with tanks. Depending on your aim and needs some may work better than others and all can be made to work relatively well if you make it expensive and complicated enough.

Domestic hot water systems are not complicated to understand for anybody who has the ability to understand electronic circuits and can be modeled very similarly.

On-demand systems intrinsically suck at maintaining water temperature because basically they dump a fixed amount of energy into the water and any change in any parameter will result in a change in temperature. So you need to be able to modulate the energy and have a feedback loop that measures output temperature and modulates energy accordingly. This is possible and is done but adds initial expense and complication and risk of problems and failures.

One advantage of tankless systems is you save a little space but that makes sense only if you have the tiniest of apartments. Another advantage for systems with very little use is you are not maintaining a tank full of hot water which means losses that need to be replaced.

But, on the whole, by and large, a tank system is going to provide better results, better water temperature stability at lower initial cost.

I have seen homes in England with both gas heaters and electric on demand heater. I never understood it. It seems salespeople sell stuff and homeowners buy stuff they don't really need because they do not understand the problem or the system.

If you want to have an electric on-demand water heater and you require stable temperature then there is only one thing to do which is to modulate electric power with a feedback loop that measures output water temperature. And studying the system it will have certain limits, an envelope of pressures, flows, input temperatures, etc.  This is what gas heaters do and they are incredibly complicated and expensive.

Right now water arrives from the mains quite warm and needs very little warming up for a shower but my on-demand heater cannot provide so little heat. It is below the minimum it can do even at the minimum setting. A solution which works but might not be obvious to non tech people is to open the sink hot water and dump some hot water that way. Dump half or 3/4 of scalding water down the drain and use 1/4 in the shower mixed with cold water. Not very energy efficient but with a gas heater there is not much else you can do.

With an electric heater it is trivial to insert a triac power control and regulate the temperature manually but it is better to sense the temperature automatically as it leaves the heater and insert a small tank or long pipe to stabilize any fluctuations.

But, yes, I have seen plumbing and water heating systems in the UK that are hard to understand for anyone with a bit of understanding. I think it may be a combination of patching very old systems and not really understanding how things work.

For a while I was staying in China in an apartment with a gas on-demand water heater which was impossible to get a decent temperature. The water was either scalding or boiling. I very soon learned to use two low stools. Put a tub on one and mix hot and cold water until I got the desired temperature. Then sit on the other stool and use a mug to shower water from the tub over myself. Works pretty well and saves a lot of water.

I was doing the same thing on my boat until I fixed the system which has its own complications, including cycling pumps.


alanb:

--- Quote from: paulca on July 23, 2019, 06:55:35 pm ---
I'm planning on upgrading the whole heating system to a pressurized setup, so this is a temporary problem, but an annoying one!

--- End quote ---

Put your efforts into upgrading the whole heating system. This annoyance is a great incentive to upgrade as soon as possible.
stevelup:
You can get better electric showers - one example is the Mira Advance - this is thermostatically controlled and modulates the heater. Means the temperature is unaffected by water pressure.

Have a look at Triton as well - they do about half a dozen different thermostatically controlled ones.

Triton also do one with a pump. So if your current one is fed from a loft tank rather than the mains, you could go for that.

But to be honest, as has already been said, electric showers are a bit crappy anyway. Is there no way you can get a proper hot+cold feed to the location. The only advantage with putting another electric one in would be simplicity of installation.
richard.cs:

--- Quote from: paulca on July 24, 2019, 08:21:05 am ---I am "assuming" it is run from the header tank in the loft as that's normal for a system of this age.

--- End quote ---
You should check that assumption. This kind of shower is essentially unusable on a header tank and I've never seen one plumbed that way. Even in houses with header tanks they usually tee off the rising cold before it goes into the tank, otherwise they just don't work at all, in most cases refusing to turn on due to low pressure. If it really is on the header tank then rearranging the plumbing is step 0 but I suspect as it sort of works you'll find it is on mains pressure just your mains pressure is crap.

As you describe it you essentially have too big a gap between high and low, you need a "medium" which many of these showers have but not yours. It's probably one element or both with the two of similar power, better ones either have 3 elements or two dissimilar ones to give three power settings e.g. 3 kW, 6 kW and 6+3 kW. You may be able to create a medium setting of 1.5 elements by putting a diode in series with one of them, you'd then have cold, low and medium rather than cold low and high.

They usually have a mechanical pressure regulator up front to take out the worst of the variation when someone uses water elsewhere in the house, and you'll find that changing settings between summer and winter is necessary. Some of the fancy modern ones do active temperature control by varying the input power rather than having a valve to restrict the water flow. Buying one of those or much cheaper buying a 3-step basic one would probably fix your problem, but any electric shower really needs connecting to mains pressure water.

As a side note, be careful with your decision to go with a pressurised system and presumably a combi boiler (instant gas water heating combined with central heating for the international audience). They have a number of disadvantages over a well designed low pressure system with storage and these are often skimmed over by installers wanting to sell the shiny and new.
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