Author Topic: Electric shower, anything I can do?  (Read 12560 times)

0 Members and 1 Guest are viewing this topic.

Offline richard.cs

  • Super Contributor
  • ***
  • Posts: 1200
  • Country: gb
  • Electronics engineer from Southampton, UK.
    • Random stuff I've built (mostly non-electronic and fairly dated).
Re: Electric shower, anything I can do?
« Reply #25 on: July 24, 2019, 01:21:07 pm »
Can you elaborate a little?

I was considering going for the System boiler approach which has just a hot water circuit flowing through the heat exchanger coil in the hot tank, which, assuming I fit an electrical routing valve giving me control of hot water only, radiators only and both gives me the best of all worlds.

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.
 

Offline richard.cs

  • Super Contributor
  • ***
  • Posts: 1200
  • Country: gb
  • Electronics engineer from Southampton, UK.
    • Random stuff I've built (mostly non-electronic and fairly dated).
Re: Electric shower, anything I can do?
« Reply #26 on: July 24, 2019, 01:24:47 pm »
Is this a mainland thing?  I have lived in about 5 different places in Northern Ireland with vented/pumped heating systems and there has only ever been one control, heating on, heating off.  If it's on, you get both hotwater and radiators, if it's off you get neither.
Maybe it is. I have lived in four places in the South of England, all had low pressure hot water systems with a choice of hot water only or hot water plus heating. All of my friend's and family's houses are either like this, have a choice of all three, or have combi boilers.
 

Offline paulcaTopic starter

  • Super Contributor
  • ***
  • Posts: 4361
  • Country: gb
Re: Electric shower, anything I can do?
« Reply #27 on: July 24, 2019, 01:26:15 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.

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.
"What could possibly go wrong?"
Current Open Projects:  STM32F411RE+ESP32+TFT for home IoT (NoT) projects.  Child's advent xmas countdown toy.  Digital audio routing board.
 

Offline richard.cs

  • Super Contributor
  • ***
  • Posts: 1200
  • Country: gb
  • Electronics engineer from Southampton, UK.
    • Random stuff I've built (mostly non-electronic and fairly dated).
Re: Electric shower, anything I can do?
« Reply #28 on: July 24, 2019, 01:35:13 pm »
And I am interested later in attaching a DC immersion from a solar panel.
The one to watch there is the thermostat. They won't survive switching DC so an external contactor or similar is needed.

If you have a plastic header tank you also need to have a high-reliability way of ensuring you never boil the tank.* Standard (modern) immersion thermostats have a second set of contacts which fire at about 90 C and are not self-reseting to get double fault to danger, you need to replicate that level of safety so a single contactor driven by the thermostat isn't really good enough.


*There have been a couple of scary incidents in which stuck immersion contacts have boiled the storage tank, forcing circulation into the roof tank until it too is filled with very hot water. The plastic tank then gives way pouring 100 gallons of near-boiling water onto the poor sod asleep below.
 

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Electric shower, anything I can do?
« Reply #29 on: July 24, 2019, 01:47:35 pm »
Every country has its own culture in everything, including solutions to common technical problems. It is interesting to see this as you live in different countries.

In Spain gas water boilers (heaters) have a combined system where they can heat the house radiators and the domestic hot water. In the summer you can have domestic hot water without heating the house. The thought that you either do both or none seems rather crazy to me. If you want domestic hot water you need to heat the house? How crazy is that?  What's the point?

Still, these combined gas heaters are complicated and expensive and when they break down everything goes down.

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.

A friend of mine bought a combined scanner-printer against my advice. Shortly after the printer stopped working and I got a free scanner.

People love buying a laptop computer because they "don't have the space". Then they bitch when the smallest thing breaks and it is too expensive to repair. Or when they can't install that card or whatever.

People love the apparent simplicity and later find out things do not work so well.

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. 

I always bitch about this to my friends. In Spain you can go to a really expensive, luxurious home but you can't take a comfortable shower there because water temperature is wildly unstable. WTF? What kind of luxury is that? I'd rather live in a shack with a good shower.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline paulcaTopic starter

  • Super Contributor
  • ***
  • Posts: 4361
  • Country: gb
Re: Electric shower, anything I can do?
« Reply #30 on: July 24, 2019, 01:52:28 pm »
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.
"What could possibly go wrong?"
Current Open Projects:  STM32F411RE+ESP32+TFT for home IoT (NoT) projects.  Child's advent xmas countdown toy.  Digital audio routing board.
 

Offline paulcaTopic starter

  • Super Contributor
  • ***
  • Posts: 4361
  • Country: gb
Re: Electric shower, anything I can do?
« Reply #31 on: July 24, 2019, 02:00:53 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. 


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!
« Last Edit: July 24, 2019, 02:13:25 pm by paulca »
"What could possibly go wrong?"
Current Open Projects:  STM32F411RE+ESP32+TFT for home IoT (NoT) projects.  Child's advent xmas countdown toy.  Digital audio routing board.
 

Offline BMK

  • Contributor
  • Posts: 48
  • Country: 00
Re: Electric shower, anything I can do?
« Reply #32 on: July 24, 2019, 02:33:27 pm »
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.
 
The following users thanked this post: splin

Offline SteveyG

  • Supporter
  • ****
  • Posts: 997
  • Country: gb
  • Soldering Equipment Guru
Re: Electric shower, anything I can do?
« Reply #33 on: July 24, 2019, 03:11:51 pm »
I am "assuming" it is run from the header tank in the loft as that's normal for a system of this age.
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.

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.
YouTube Channel: https://www.youtube.com/user/sdgelectronics/
Use code: “SDG5” to get 5% off JBC Equipment at Kaisertech
 

Offline SteveyG

  • Supporter
  • ****
  • Posts: 997
  • Country: gb
  • Soldering Equipment Guru
Re: Electric shower, anything I can do?
« Reply #34 on: July 24, 2019, 03:20:54 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.

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.
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.
« Last Edit: July 26, 2019, 09:43:44 am by SteveyG »
YouTube Channel: https://www.youtube.com/user/sdgelectronics/
Use code: “SDG5” to get 5% off JBC Equipment at Kaisertech
 

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Electric shower, anything I can do?
« Reply #35 on: July 24, 2019, 04:35:33 pm »
There's no way I would run a water system without, at least, 30 m water pressure. 40 m is better and 20 m bare minimum. I want to see water coming out of the faucet when I open it.

In the country home I have an automatic pump. It used to be you needed a pressure system with a pump that would cycle on and off and the water pressure would be like sawteeth, up and down, which is a pain if you are using a tankless water heater. Now I have a pump that automagically detects flow and starts itself and maintains constant pressure until flow stops. No pressure vessel, no pressure switches, no nothing, just the self-priming pump.

It maintains a pressure of about 25 ~ 30 m which works pretty well. It is mounted in the garage, over the 1000 L water tank.

Same at home as on the boat the first issue to resolve is maintain good and stable water pressure.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline paulcaTopic starter

  • Super Contributor
  • ***
  • Posts: 4361
  • Country: gb
Re: Electric shower, anything I can do?
« Reply #36 on: July 24, 2019, 04:48:08 pm »
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.

Thanks, good info.

It's this one:
http://secure.tritonshowers.co.uk/media/custom/upload/File-1352735182.pdf

I'll see if cleaning the filter helps.  I also intend to replace the shower head as it's a bit knackered and doesn't actually have the "mode" I like.
"What could possibly go wrong?"
Current Open Projects:  STM32F411RE+ESP32+TFT for home IoT (NoT) projects.  Child's advent xmas countdown toy.  Digital audio routing board.
 

Offline Towger

  • Super Contributor
  • ***
  • Posts: 1646
  • Country: ie
Re: Electric shower, anything I can do?
« Reply #37 on: July 24, 2019, 05:17:55 pm »
You have the wrong model shower for a tank feed system. Yours is designed for mains feed.
The Triton T90 (+various sub versions) is their tank feed shower, it is much the same but has a small (noisy) pump.  The new (si?) version moved to a DC pump motor and is supposed to be much quieter.  In any event the T90 should have it's own feed point from the tank, not 'T'ed from the main outlet.
 

Offline Someone

  • Super Contributor
  • ***
  • Posts: 5154
  • Country: au
    • send complaints here
Re: Electric shower, anything I can do?
« Reply #38 on: July 25, 2019, 07:45:51 am »
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.
This is all dependent on the specific heater, instantaneous/continuous/on demand gas water heaters are widely used in Australia but they have closed loop regulation at the heater. When used with a controller to set the desired output temperature for each use there are no problems with stability other than low flow rates.
 

Offline paulcaTopic starter

  • Super Contributor
  • ***
  • Posts: 4361
  • Country: gb
Re: Electric shower, anything I can do?
« Reply #39 on: July 25, 2019, 08:22:58 am »
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.
This is all dependent on the specific heater, instantaneous/continuous/on demand gas water heaters are widely used in Australia but they have closed loop regulation at the heater. When used with a controller to set the desired output temperature for each use there are no problems with stability other than low flow rates.

I think it depends on how you want to use the hot water.  I 'can' imagine that a shower could send a signal to the boiler to request a temperature so the shower only runs the hot water and varies it's signal to the boiler to achieve the temperature it wants.  However I can't see this as practical unless that boiler is specifically for the that shower alone.  If someone turns on the kitchen hot tap what temperature would the boiler deliver?

The on-demand combi boiler in my last place produced water around 70-80*C and the shower had a bi-metal valve.  As soon as the hotwater was flowing the heating circuit would be shut off, if active and the boiler would produce hot water as hot as it could get it.  The shower bi-metalic valve then regulated the amount of cold water that got added to maintain a temperature.

Anyway, I checked my mains inlet stop cock and found it not fully open, so my water pressure on the cold taps has increased.  This included the bathroom cold tap which tells me the upstairs cold feed has been redirected to the mains and so the shower is most likely running on mains water pressure.  I didn't get to test the shower last night or this morning (long story), but I also bought a new shower head to exclude the existing one was gunked up.  I'll see how it goes tonight.
"What could possibly go wrong?"
Current Open Projects:  STM32F411RE+ESP32+TFT for home IoT (NoT) projects.  Child's advent xmas countdown toy.  Digital audio routing board.
 

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Electric shower, anything I can do?
« Reply #40 on: July 25, 2019, 10:05:07 am »
This is all dependent on the specific heater, instantaneous/continuous/on demand gas water heaters are widely used in Australia but they have closed loop regulation at the heater. When used with a controller to set the desired output temperature for each use there are no problems with stability other than low flow rates.
Yes, they are widely used in Spain too. They are the most used solution here. Some drawbacks I see:

Compared to tanks they are complicated, expensive to buy, expensive to repair and prone to needing repairs. To do all that regulation they have complex electronic systems that can break down and if you are lucky you can find a replacement board very expensively. If you are unlucky you need to replace the whole heater.  OTOH, a water tank just sits there for decades and knows nothing about electronics or repairs.

On demand gas heaters can only modulate power within certain limits, say 35 or 40% at the lower limit and 100% at the upper limit. If it is going to actually modulate then you need your centerpoint to be, say between 50 and 80% of capacity, so you have range to move around. So, really, the modulation range is not that great.

Add to that the great variation in power needs and you can see an on-demand heater is just not suitable for many circumstances.

Assume in winter water arrives at 4ºC and you need 15 L/min at 74ºC.

Assume in summer water arrives at 24ºC and you need 3 L/min at 40ºC.

The ratio of power requirements is over 20 and no on-demand heater can do that or even come close while a tank can do that and more.

The combined heating and domestic water on-demand gas boilers we have here resort to different tricks and they kind of work but they are more inefficient than simpler solutions.

In summary, a complicated solution, expensive, prone to problems, inefficient, expensive to buy, expensive to run, expensive to maintain and repair.

These days we are having a heat wave in Europe and water is coming out of the faucet at over 25ºC. The minimum amount of heating my gas heater can provide is way over what I need for a shower so the only way to take a shower is to open another faucet and dump heated water into the drain while I shower. Not something I like to do. Maybe I can take a bath instead.

I understand the need for complicated solutions in a spacecraft where space is at a premium but I prefer not to spend hundreds or thousands of euros and endure crappy showers just to save a little space and have a nice heater hanging on the wall.

Yes, we have on demand gas heaters here. I don't like them. Personally, I prefer a tank any day but that's just me. Other people have other preferences.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline richard.cs

  • Super Contributor
  • ***
  • Posts: 1200
  • Country: gb
  • Electronics engineer from Southampton, UK.
    • Random stuff I've built (mostly non-electronic and fairly dated).
Re: Electric shower, anything I can do?
« Reply #41 on: July 25, 2019, 10:17:42 am »
Assume in winter water arrives at 4ºC and you need 15 L/min at 74ºC.

Assume in summer water arrives at 24ºC and you need 3 L/min at 40ºC.
...
These days we are having a heat wave in Europe and water is coming out of the faucet at over 25ºC.

Your incoming water temperature range is very wide, here we see much lesser variation though it is still problematic for on demand heating. In the UK our water temperature range is more like 10ºC winter to 20ºC summer.

Are your water distribution pipes run on the surface of the ground (I have seen this a lot in Italy but I have never been to Spain) or very shallow buried? In the UK we bury ours about 1 metre deep to prevent them freezing in the winter and I suspect that may be why we see less variation in temperature. As you said before the variation between how different countries do things is very interesting.
 

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Electric shower, anything I can do?
« Reply #42 on: July 25, 2019, 11:01:11 am »
Water pipes here are buried because we also get hard freezes here. I suppose it is fairly complicated to determine the factors in water temperature. First would be the temperature in the open reservoirs. I suppose there are huge pipes many km long that take the water to the city. I don't think those would add much. Then maybe big tanks and reservoirs and then thinner distribution pipes. I have no idea what the influence of each may be.

It may be that the last riser from the sidewalk to the apartments has most influence as it is the thinnest and most exposed. I don't know.

I am always measuring this kind of thing but it never occurred to me to ask other neighbors. They already think I'm weird enough and I don't need to make it worse.

Receiving the water in winter just above freezing seems logical to me. In the summer I would expect more variation because if you have thin pipes exposed to the Sun the water can get very hot. The good thing then you don't need heating it.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline Someone

  • Super Contributor
  • ***
  • Posts: 5154
  • Country: au
    • send complaints here
Re: Electric shower, anything I can do?
« Reply #43 on: July 25, 2019, 11:25:15 am »
Compared to tanks they are complicated, expensive to buy, expensive to repair and prone to needing repairs. To do all that regulation they have complex electronic systems that can break down and if you are lucky you can find a replacement board very expensively. If you are unlucky you need to replace the whole heater.  OTOH, a water tank just sits there for decades and knows nothing about electronics or repairs.
In this country (before rebates or incentives) instantaneous heaters are around the same price or cheaper to buy and have been showing similar longevity to tank systems. But they cost significantly less to operate over their lifetime, so much so that they have a payback period of just 3 years if you replace a storage system. This will vary on your local energy pricing, tariffs, temperatures, etc.

On demand gas heaters can only modulate power within certain limits, say 35 or 40% at the lower limit and 100% at the upper limit. If it is going to actually modulate then you need your centerpoint to be, say between 50 and 80% of capacity, so you have range to move around. So, really, the modulation range is not that great.

Add to that the great variation in power needs and you can see an on-demand heater is just not suitable for many circumstances.

Assume in winter water arrives at 4ºC and you need 15 L/min at 74ºC.

Assume in summer water arrives at 24ºC and you need 3 L/min at 40ºC.

The ratio of power requirements is over 20 and no on-demand heater can do that or even come close while a tank can do that and more.
All the units I'm familiar with do have power control with ratios over 20, even beyond a factor of 30 so based on your choice of numbers they work fine. This is going back 20 years so its nothing new or exclusive, there are multiple suppliers of products which meet those requirements.

Storage units can't deliver any temperature other than their current point, so most of the time they are being used with cold water mixed in at the load. You're keeping a big pile of hot water hot for the minority use case, its silly and outdated.

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.
This is all dependent on the specific heater, instantaneous/continuous/on demand gas water heaters are widely used in Australia but they have closed loop regulation at the heater. When used with a controller to set the desired output temperature for each use there are no problems with stability other than low flow rates.

I think it depends on how you want to use the hot water.  I 'can' imagine that a shower could send a signal to the boiler to request a temperature so the shower only runs the hot water and varies it's signal to the boiler to achieve the temperature it wants.  However I can't see this as practical unless that boiler is specifically for the that shower alone.  If someone turns on the kitchen hot tap what temperature would the boiler deliver?
Its a simple system, the boiler unit has a well regulated output temperature which can be changed in a second or so. If you can't possibly wash you hands in the kitchen with 43 degree water while someone else is showering, or wait for them to finish their shower before running a washing tub at 60 degrees, then you've got some first world problems.
 

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Electric shower, anything I can do?
« Reply #44 on: July 25, 2019, 12:38:03 pm »
All the units I'm familiar with do have power control with ratios over 20, even beyond a factor of 30 so based on your choice of numbers they work fine. This is going back 20 years so its nothing new or exclusive, there are multiple suppliers of products which meet those requirements.

I am interested in this. I'd like to see a gas water heater that can modulate output from say 12 KW down to say 500 W. Sounds very interesting. 

Other than that there is no need to belittle my preference just as I don't belittle yours. You do whatever you want. I don't care. Just allow others their own choice.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline richard.cs

  • Super Contributor
  • ***
  • Posts: 1200
  • Country: gb
  • Electronics engineer from Southampton, UK.
    • Random stuff I've built (mostly non-electronic and fairly dated).
Re: Electric shower, anything I can do?
« Reply #45 on: July 25, 2019, 12:55:09 pm »
All the units I'm familiar with do have power control with ratios over 20, even beyond a factor of 30 so based on your choice of numbers they work fine. This is going back 20 years so its nothing new or exclusive, there are multiple suppliers of products which meet those requirements.

I am interested in this. I'd like to see a gas water heater that can modulate output from say 12 KW down to say 500 W. Sounds very interesting. 
Same, in the UK I've not seen anything near 20:1, many are more like 4:1 and 10:1 is considered to be very good. Once you go below their minimum they either cycle and the temperature swings wildly, or just turn off and go cold.
 

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Electric shower, anything I can do?
« Reply #46 on: July 25, 2019, 01:45:41 pm »
Storage tanks also are necessary and useful when using solar panels to heat the water. While I lived in America my house had solar panels and a big tank and I hardly ever needed supplemental heat, only a bit in the winter. In the summer though I had more heat than I needed and I would flush the toilet with buckets of scalding hot water. 
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline Nauris

  • Regular Contributor
  • *
  • Posts: 188
  • Country: fi
Re: Electric shower, anything I can do?
« Reply #47 on: July 25, 2019, 07:06:33 pm »
For reference I draw schematic how hot water and heating is arranged here traditionally. (altought these days heat pumps are very much in, oil not so much)
 

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Electric shower, anything I can do?
« Reply #48 on: July 25, 2019, 07:20:13 pm »
For reference I draw schematic how hot water and heating is arranged here traditionally. (altought these days heat pumps are very much in, oil not so much)
The problem with using a heat exchanger in the big heating tank for domestic hot water is that (1) you need the big tank always hot, which makes no sense when you do not need heating, and (2) efficiency suffers.

On demand combined heaters here do that and it works for certain values of "works". One advantage of not heating the domestic hot water directly with the flame but through an exchanger is that is adds a lot of temperature stability but, again, efficiency suffers a lot.

Another thing I would add is that if they are not required by code I would still require thermostatic valves anywhere a person might get hit by that water. All bathroom, kitchen faucets, etc. Most people do not realize how dangerous hot water is and how fast it can scald. I know of a very serious case of a baby in a bathtub who pulled the control lever and got badly burnt. If you do not have Thermostatic valves installed and you have children, old people, distractable people, etc. in the house you should really consider lowering the heater temperature as much as possible.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline paulcaTopic starter

  • Super Contributor
  • ***
  • Posts: 4361
  • Country: gb
Re: Electric shower, anything I can do?
« Reply #49 on: July 25, 2019, 09:19:01 pm »
If you can't possibly wash you hands in the kitchen with 43 degree water while someone else is showering, or wait for them to finish their shower before running a washing tub at 60 degrees, then you've got some first world problems.

So you are suggesting that when I want hot water of X degrees for X purpose I put my shoes on and go out to the boiler and set the hot water temperature manually and when I then want to use the water at Y degrees for Y purpose I go and change the temperature at the boiler again?

Who does that?  In fact most combi boilers with on demand hot water are just set at MAX and you mix hot and cold at the demand with a mixer tap.  They are of course differential, so if you want a low temp, it's mostly cold and very little hot is used.  The boiler will put out hotter water with a lessened flow, but it's really not an issue and surprisingly easy to balance by moving the tap, or shower valve.

The benefit of this approach with a shower is that you must mix a bunch of cold into the hot, which gives you even higher pressure.
« Last Edit: July 25, 2019, 09:26:20 pm by paulca »
"What could possibly go wrong?"
Current Open Projects:  STM32F411RE+ESP32+TFT for home IoT (NoT) projects.  Child's advent xmas countdown toy.  Digital audio routing board.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf