Huge hot water cylinder heating more water than needed

Section62

Starfrog said:

Reed_Richards said:

If you have a hot water tank with an immersion heater you can heat it with your solar array.  If it does not have an immersion heater it might be a lot cheaper to get one inserted than to replace it with a Sunamp unit.  If you get a Sunamp unit, get the type that can either be heated electrically or from your oil boiler so you can choose whichever option is the cheaper on days when the sun does not shine enough.

Bits of the "stuff" inside the Sunamp box can be in one phase and bits in the other.  I imagine you would want to keep it fully charged, it will get partially discharged as you use hot water and then you'll charge it back up again at an appropriate time. 

Thank you for the response and agreed I can heat it with my solar array and use an Eddi ? But its fairly old and I think the method of heating water with an immersion is not as efficient as I think i can have it. 

An immersion heater in water is about as close to a 100% efficient method of converting electricity into hot water as you can get.

The efficiency doesn't tail off with age, the only problem may with an excessive build-up of limescale.  And if the water you want to heat is excessively hard to the point it is a problem for immersion heater efficiency then I wouldn't advise feeding it through an expensive heat store.

Starfrog

Section62 said:

Starfrog said:

Reed_Richards said:

If you have a hot water tank with an immersion heater you can heat it with your solar array.  If it does not have an immersion heater it might be a lot cheaper to get one inserted than to replace it with a Sunamp unit.  If you get a Sunamp unit, get the type that can either be heated electrically or from your oil boiler so you can choose whichever option is the cheaper on days when the sun does not shine enough.

Bits of the "stuff" inside the Sunamp box can be in one phase and bits in the other.  I imagine you would want to keep it fully charged, it will get partially discharged as you use hot water and then you'll charge it back up again at an appropriate time. 

Thank you for the response and agreed I can heat it with my solar array and use an Eddi ? But its fairly old and I think the method of heating water with an immersion is not as efficient as I think i can have it. 

An immersion heater in water is about as close to a 100% efficient method of converting electricity into hot water as you can get.

The efficiency doesn't tail off with age, the only problem may with an excessive build-up of limescale.  And if the water you want to heat is excessively hard to the point it is a problem for immersion heater efficiency then I wouldn't advise feeding it through an expensive heat store.

I'm not an expert on this but I think the age old method of using an immersion electric water heater is not the best start for heating water (gas is cheaper) but where gas isnt available then electric is the only option. heating a giant tank of water is not the ideal situation when you really only want a small part of the heated water. There is a company making a slightly more efficient water tank called Mixergy which seems to address some of the issues.  My thoughts on this are and everyones situation is different but having the water heated on the demand of hot water is probably more efficient than heating it up and then waiting for it to be used when it then has time to cool, while insulation will help keep it warm a large body of water is going cool over time and its that loss that causes the use of immersion heater. There are so many different ways to look at the technology these days and so many options, I'm still doing my research into this and Im open to the various option which will meet my requirements. Electric that I can produce and use of the water when ever i need it without boosting it or switching it on for times i normally use the most hot water are factors that i dont want to keep thinking about. I just want it on demand (like a combi boiler) but as i dont have gas then thats not an option and I want to get rid of the Oil boiler. so the choice is a sunamp or a traditional water tank, in my opinion the sunamp appears to be more efficient with the delivery of hot water ?? 

Section62

Starfrog said:

heating a giant tank of water is not the ideal situation when you really only want a small part of the heated water.

This was discussed earlier in the thread.  Heating a whole cylinder of water is only necessary if you've used up all the stored hot water.  If you only use small amounts then the heating required is only that necessary to heat the replacement water and to replace lost heat.  Getting the cylinder size right is important - it needs to be large enough to supply the required volume of water at the desired temperature.  Too big or too small can be a problem, but generally 'too small' is worse than 'too big'.

Starfrog said:

My thoughts on this are and everyones situation is different but having the water heated on the demand of hot water is probably more efficient than heating it up and then waiting for it to be used when it then has time to cool...

Having the water heated at point of use (both location and time) is more efficient, but (with electric) means having to heat water using peak-rate energy, and in some cases having flow restricted to match rate of heating.

Starfrog said:

I just want it on demand (like a combi boiler) but as i dont have gas then thats not an option and I want to get rid of the Oil boiler.

As above, you can do that with electric water heating, but you would have to accept increased costs.  Using a hot water cylinder as a heat store allows 'instant' hot water, but at off-peak energy prices.

Starfrog said:

so the choice is a sunamp or a traditional water tank, in my opinion the sunamp appears to be more efficient with the delivery of hot water ??

Efficiency will depend on pattern of use and proximity of the sunamp to the appliances using hot water.  The key feature appears to be storing more heat in a smaller volume - something which may be important in a small flat, but perhaps less of an issue in a large house.  Ultimately there may be more effective ways of investing the money that would otherwise be spent on a sunamp - it's a question of looking at everything in the round, not just 'A' vs 'B'.

Starfrog

Section62 said:

Efficiency will depend on pattern of use and proximity of the sunamp to the appliances using hot water.  The key feature appears to be storing more heat in a smaller volume - something which may be important in a small flat, but perhaps less of an issue in a large house.  Ultimately there may be more effective ways of investing the money that would otherwise be spent on a sunamp - it's a question of looking at everything in the round, not just 'A' vs 'B'.

I guess the crux of the matter is how much power is used to heat 200 Ltrs using a traditional water heater and how much is used for the equivalent 200 ltrs using a Sunamp. They will both have the same issue about proximity, so then it comes down to getting it up to heat, then keeping at heat. While I agree that its not just a simple case of A v B, I am still looking for viable options outside of that to provide hot water on demand that is electrically efficient. The Sunamp while costly upfront has a long projected life span with no further maintenance required. The Hot water tank is cheap but does need to be serviced and also needs to go through a legionella cycle every so often. I’d love to see other options and real world energy use for hot water, there is lots of literature out there that a claims one is better than the other but its like the electric radiators people saying that its the wave of the future and super efficient, what they dont tell you is that your electric bills will absolutely sky rocket as its 1000kwh for 1000kwh of heat, they will say its 100% efficient but thats not in a good way as it just means that you will need to run lots of radiators throughout your house at 100% use of electric ! ….. I digress but welcome all data on actual costs for the various hot water options that are available that need electric to heat as that is really the only viable option i have as an energy source (which is offset by my solar and battery storage)  

QrizB

Starfrog said:

The Sunamp while costly upfront has a long projected life span with no further maintenance required. The Hot water tank is cheap but does need to be serviced and also needs to go through a legionella cycle every so often.

I'm not sure I've ever serviced my vented HW tank, although I did once replace a leaking fitting. What servicing do they need?

I am still looking for viable options outside of that to provide hot water on demand that is electrically efficient.

What about a heat pump hot water tank? A similar price to buy *and* cheaper to run than a Sunamp?

There's a current thread over on "other fuels" and there are a couple of different designs available from of UK suppliers.

Here's an example (not intended as a recommendation, just the first I found on Google):
https://coolenergyshop.com/products/cool-energy-ecostore-ce-es300-all-in-one-heat-pump-hot-water-system

And another:
https://rointe.com/uk/water-heaters/heat-pumps/dalis-pro-air-source/
There's an Italian(?) manufacturer too but I can't remember who!

doodling

Hi,

Starfrog said:

Section62 said:

Efficiency will depend on pattern of use and proximity of the sunamp to the appliances using hot water.  The key feature appears to be storing more heat in a smaller volume - something which may be important in a small flat, but perhaps less of an issue in a large house.  Ultimately there may be more effective ways of investing the money that would otherwise be spent on a sunamp - it's a question of looking at everything in the round, not just 'A' vs 'B'.

I guess the crux of the matter is how much power is used to heat 200 Ltrs using a traditional water heater and how much is used for the equivalent 200 ltrs using a Sunamp. They will both have the same issue about proximity, so then it comes down to getting it up to heat, then keeping at heat. While I agree that its not just a simple case of A v B, I am still looking for viable options outside of that to provide hot water on demand that is electrically efficient. The Sunamp while costly upfront has a long projected life span with no further maintenance required. The Hot water tank is cheap but does need to be serviced and also needs to go through a legionella cycle every so often. I’d love to see other options and real world energy use for hot water, there is lots of literature out there that a claims one is better than the other but its like the electric radiators people saying that its the wave of the future and super efficient, what they dont tell you is that your electric bills will absolutely sky rocket as its 1000kwh for 1000kwh of heat, they will say its 100% efficient but thats not in a good way as it just means that you will need to run lots of radiators throughout your house at 100% use of electric ! ….. I digress but welcome all data on actual costs for the various hot water options that are available that need electric to heat as that is really the only viable option i have as an energy source (which is offset by my solar and battery storage)  

The Sunamp will use exactly the same amount of energy as the traditional cylinder, assuming that they are both insulated to the same extent.  The only advantage the Sunamp has is that it is physically smaller and therefore easier to insulate well.

If you are planning to use surplus electric power from your solar system to heat your hot water then unless you have a truly massive solar array (30kW peak or bigger) and are planning to ditch the boiler altogether then you will have no problem getting the cylinder up to temperature; in summer you will have more electrical power than you need and in winter you'll be using the oil boiler.  Spring and Autumn are trickier (reduced loss from storage might move the point at which you start using the boiler to heat the water), but as you're talking about servicing then presumably you have a mains pressure cylinder and therefore the risk of legionella is much reduced in any event.

The cheapest overall solution (including energy costs) is highly likely to be more insulation around your existing cylinder.