General > General Technical Chat

Electric shower, anything I can do?

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paulca:
Yes.  I have a number of thoughts about the solar heating thermostat issue.  You "can" get DC thermostats, they are expensive though.  The option I have heard used most often is electronic switching.  That presents it's own issues though.

A lot of people just "match" the element to the power point of the panel and connect them direct.  However as I live in sunny Northern Ireland I need proper MPPT to get anything on cloudy days.  So a controller will be required.  This is were it gets complicated as these are not mass-produced consumer items yet.  There are a few projects out there that will sell you a controller, or give you the design files and let you build one.  Currently I am aiming towards that approach.  The output of the buck converter would be made aware of the temperature, much in the same way a solar charge controller is aware of the battery voltage.  It will basically open circuit the panel when the water hits 65*C or so.

Obviously this needs done in a fail safe way and the idea of having a further bi-metallic non-reseting contact thermostat set to a much higher temp does sound like a nice fail safe device.  Even though a DC version will be expensive, in retaliative terms it might be worth paying £50 for it.

paulca:

--- Quote from: soldar on July 24, 2019, 01:47:35 pm ---I like to have independent systems as much as I can and as simple as possible. But people love the idea of saving a little space and having a compact gadget that does five things although it does them all badly.


For simplicity, low cost and reliable service it is hard to beat the American system of having a domestic hot water tank separate from the house heating. 


--- End quote ---

I also want independant systems for certain things.  Presently in 99% of UK homes if the mains electric goes down you will have no heating, no hot water, no light, running water only while the local pumping station's generator runs.  You might have gas, oil and god knows what else, but they all require electric to operate.  Cookers, fridges, everything does. The electric is extremely reliable but power cuts of 1 or 2 hours once or twice a year do happen.

There is of course the potential of a rare but extreme solar flare or other damage which could in the worst case take out a few sub-stations which might take weeks/months to repair.  The local electric board will often use truck sized generators to cover these outages while sub stations are repaired, but following major grid damage how likely is this?

So I already have a source for lighting by using batteries charged on off-grid solar to run small 3W LED lights.  I intend to put a bottled gas hob in.  I intend to put a wood burning stove in the living room.  The only thing I need them is a DC operated freezer (or bottled gas) from a boat or caravan.

It's not exactly prep'ing, but I think we all rely far too much on the electrical grid.  I fear that without electric for longer than a few days and common order will start to break down and riots start.

On the American system I think we have to really consider how much energy they use compared to the rest of the world, I believe the average US household uses 4 times the energy as a UK household.  They pay next to sod all for their energy and probably think nothing of running an electrical heating element in their hot tank 24/7/365!

BMK:
If this is your ubiquitous plastic tanked instant electric shower my Mira / Triton etc.. .
There is no thermostat except a high limit safety to stop the thing from boiling. The outlet water temperature is completely dependent on incoming water temp, element power and flow rate. There are 2 fixed heater powers (hi/low switch) and the main knob actually just adjusts the flow rate. Depending on on the temp of incoming water and the flow rate chosen (seasonally variable as most attics are blazing hot in summer) you get steady water outlet temp.  In my experience the flow gets restricted due to blocked inlet filter and/or scaling of the shower head itself. The effect of the adjustment knob is dominated by the other restrictions. It is a 2 minute job to remove and clean the filter. Google your model.

SteveyG:

--- Quote from: richard.cs on July 24, 2019, 12:08:18 pm ---
--- 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.

--- End quote ---

I would go further and say the pressure switch would not activate on the shower if gravity fed at a height of probably 2m maximum.

Firstly, confirm it is connected to mains water. Secondly, confirm the stop tap is properly open both at the water meter and at the incomer to the house. Finally, upgrade the shower to a Mira Thermostatically controlled electric shower.

If it's been fitted to the header tank, I'd also check the electrical installation as the installer did not know what they were doing.

SteveyG:

--- Quote from: paulca on July 24, 2019, 01:26:15 pm ---
--- Quote from: richard.cs on July 24, 2019, 01:21:07 pm ---System boiler plus storage tank is essentially what you have now, only at the moment you have a low pressure storage tank and you're proposing a high pressure one. This is often a good system as you get mains pressure hot water without the downsides of a combi boiler. It's not a very common approach in the UK mainly because of historical inertia I think but there is not a lot wrong with it. You can generally expect it to behave like a mains pressure version of your current system. Disadvantages over low pressure tank are generally that it's normally a smaller tank holding less hot water and that the tank lasts less long (they're coated steel rather than copper so they corrode out). If your household tends to have baths rather than showers you might prefer a low pressure system (little else has the ability to fill a bath of hot water as quickly as a header tank and large-bore pipes), if your household is small and hot water usage is max one shower at a time then a combi might be better than either storage approach.

Storage (either kind) also gives you free electric backup (immersion heater) and gives you some future options for solar heating.

--- End quote ---

Thanks Richard, this confirms my thoughts.  I expect the conversion plumbing will be easier going to high pressure storage "System boiler" than combi anyway.  And I am interested later in attaching a DC immersion from a solar panel.

--- End quote ---
Difference in effort between Combi boiler installation and Heat Only with a cylinder is minimal. The only thing which may need more work on the combi boiler is the gas supply will be undersized, so more likely than not will need a 22 or 28mm feed from the meter.

Additional complexities from the pressurised tank are related to the safety systems which need plumbing to outside through specific means to comply with G3 regulations.

Both systems have pros and cons, so don't just accept what an installer suggests. Energy costs for a combi boiler will be higher if you use a lot of hot water and for most of the combis available in the UK, there is both a lag between turning on the tap and getting hot water but also a minimum flow rate before you get hot water.
With the unvented cylinder you do have standing losses and of course you lose out on space. You won't have unlimited hot water either, even with a fast recovery coil.

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