Ditching gas, going electric immersion only, a wee project

Solarchaser

Did you check any of your traditional radiators?

See my theory is the modern flat panel are holding the heat longer, rather than radiating. 
So I wonder if you had tested them comparatively if the traditional radiators would have been notably cooler

Yeah mine are pretty much always above 50C

Reed_Richards

@Solarchaser, thinking about comments you made on other threads, what is the "conversion loss" of your system?  

Solarchaser

@Reed_Richards i replied in the other thread just there,  but essentially my conversion loss should be a theoretical zero as the immersion heaters I'm using to heat the tanks are immersed in the liquid they are heating.

There will be some loss in the wiring and in the connections,  and since I'm using ssr's there will be some loss in the relay itself, proved by it heating up as its used, but in reality I'd expect the loss to be less than 1%.

Electric heating is generally reported as 100% efficient, though I must confess I've never interrogated this, just taken it as read.

You could argue there will be loss when running the destratification pump as some of the heat will be lost in the pipes and pump which transport the fluid around, but I've insulated them all, so I'd be surprised if there is much lost.

Happy to plump for a nominal 5% if you want just a figure to play with?

Where sunamp and warmstone and tepeo have my system beat is in standing losses, as they are all better at protecting their heated material than my large metal tanks.
My plan in the next couple of months is to vastly improve the insulation around my system to hopefully significantly reduce my standing losses, but thats a plan, and not right now.
So yeah I think right now I'd be pretty comfortable with a 5% loss figure, and I think if I was storing for over 24 hours, I'd likely be losing out to the other systems due to standing losses.

If your next question is, can I prove it... hmm, not really, for a couple of reasons. 
1. Standing loss is happening all of the time, and increases as the tank heat increases
2. The heating and hot water is in use in the family home even during the tanks heating cycle at the moment, so I can't simply say 10kwh added should equal an increase of 10C and I see 9C so I have a 10% loss etc etc
I could only prove that if the tanks were not in use during heating (so could do it next month as heating will happen when all are asleep)

Reed_Richards

So @Solarchaser , I'm not comfortable with the concept of "conversion loss" so I asked the question about your own system to try to better understand what it means to you.  It's a fundamental law of physics that energy is never lost, just converted from one form to another.  That's why electric heaters are said to be 100% efficient and why this is true. 

As an aside, I suppose fan heaters make noise, noise/sound is a form of energy and if that noise is audible outside the house then some energy has escaped.  But even then the efficiency of a fan heater will be so near to 100% that the noise is not worth worrying about from an energy-loss perspective.

In your case some of your wiring gets hot and you regard that as a "conversion loss".  That's true if "conversion loss" means electricity that does not get converted to heat inside your thermal store.  In your case it still gets converted to heat, just not in the right place.  It could still be useful heat if it helps to keep your house warm or not useful if it gets out of the house.  If that is the sole cause of your "conversion loss" then I think your 5% figure is likely to be very pessimistic

You have stated elsewhere that devices like the Sunamp thermal store and the Warmstone thermal store suffer from "conversion loss" and I don't understand what you mean in this context.  They are (or can be) heated electrically and if you are prepared to believe electric heating is 100% efficient (which it is) then there is nowhere inside the box for that electricity to go continually other than into heat.  Outside the box there will be continuous standing losses as heat is lost through the insulation and down the connecting pipes but we agree that those are different.

Okay, so if "conversion loss" is electricity converted to energy that you cannot use, where does it go in the case of these other thermal stores?  It cannot be trapped heat because then the box would get hotter and hotter until it melted.  It can't be trapped in some physical or chemical process inside the box because the material inside the box is a finite resource and any non-thermal process inside that requires energy will stop once all the material has been used up.  The connecting wires could heat up, as in your case, but hopefully regulations will ensure that they will be made thick enough for this not to happen to any significant degree.

So my question to you is that in these other thermal stores that you believe suffer from conversion losses, where does the lost electricity/energy go?  You don't have to know the answer for sure, just find me a vaguely plausible explanation that is different from the standing loss.             

70sbudgie

I don't know enough about how the Warmstone thermal store, but I can try to explain what the losses are in the phase change (Sunamp) thermal store. My husband is a chemical engineer, so chemical phase change is one of the fundamentals of his job. He has tried to explain it to me, but I am not a chemical engineer, so any errors in the science are due to my understanding (or lack of). 

As I understand it, a chemical changing phase is a matter of probability. At a certain temperature (and pressure) a chemical has a probability that its inter molecular structure will change so that it changes phase. But the phase change temperature is a range, not a sudden cut off. So at that energy level, not all the molecules will change phase. For example, say your phase change temperature is 25°C. At 23°C some of your material will start changing from solid to liquid. At 25°C, perhaps 85% of your material is liquid. Do you put in more energy to get that last 15% to change, or do you accept that only 85% of your material has liquified? This is where your losses are. Because of the physics (chemistry?) of chemical phase changes, it is really difficult to get a material to 100% change phase. And I understand that it is also very difficult to control it. Once the phase change reaction starts, it is like a chain reaction.

I hope that at least helps start the seed of understanding.

Reed_Richards

70sbudgie said:

....I hope that at least helps start the seed of understanding.

Sorry @70sbudgie but I don't think you understand the issue which is: can all the electricity you put in be recovered as heat out?  If not, where does it go and can you use the device repeatedly always getting out less heat kW than the electricity kW you put in?  That's even if it were perfectly insulated so there are no "standing losses".  I would be interested in your husband's opinion on this specific question.

Edit: I accept that the first time you charge and discharge the unit you may end up with some "trapped energy" but that is a one-off and cannot happen every time.

Another edit: I am sufficiently old that I played with clockwork toys as a child.  You supply your own mechanical energy to tightly wind a coiled spring.  Then the spring unwinds driving the motion of the toy.  Friction means the spring never completely unwinds so the first time you wind it up to 100% and it only unwinds to, say, 15% remaining then stops.  But that means the next time and every subsequent time you wind it up you only have to do 85% of the winding you did on that very first time.  So although it always holds 15 % of trapped mechanical energy, every time after the first time you wind it up you get back all the energy you put in.          

Heedtheadvice

Hmmm...well you get back all the energy but not necessarily where you want it! In the clockwork example some of the energy gets converted to heat because of continued friction and thus does not get to move the toy.....

The better we can reduce losses the greater the efficiency we have whatever the cause...so it is well worth discussing to try and improve matters. Keep it up.

Solarchaser

To me, conversion loss is simply the energy that you supply, which you expect to to end up as heat in your final product (hot water), is lost somewhere else in the process.
For instance some sunamps have pumps in order to circulate the heat better through their phase change material, any energy used to run that pump is conversion loss.

If you are asking me why did I state the sunamp as 85% conversion efficiency,  that's because it appeared in a video of Andrew bissel when he was trying to get private funding (iirc) for the sunamp.
Being physics based, I dont know about chemicals really, so when the ceo says 15% conversion, then I say fair enough as I don't understand fully what's involved in the process.

I shared the warmstone blurb in the other thread where they state 98-99% efficient. 
I'm pretty sure I also seen 85% banded about when I was researching this a year ago... but maybe I am " misremembering" as is the popular phrase.
When these things are light on detail you can only apply your own theories I guess.
So for me sunamp says 85% I assume 15% is lost as chemical change of state as something other than heat, perhaps vibration?? (That would be a lot of rattling though), or that the change gives off too much heat which then cannot be retained in its phase change material, and so when turned back to liquid/ solid that heat cannot be harnessed.
That to me said it looses 7.5% converting to solid and 7.5% to liquid.
Heat is heat, but if its not put back into the water during conversion then it is lost.
Or perhaps if the heat applied to get from say 10C ambient to 56C phase change can't be stored in the phase change, and when at 56C it changes all, but then from 56C to 10C again can't be put back into the water running through it, then its lost.

Why would water tanks be different in this scenario,  well they are just water all of the time, so will happily give heat to water at 10C if they are at 15C, then don't need to be at 56C to give heat to the water.

All of this is assuming they are doing water supply rather than heating, just for this answer.

That's my thinking, and why if there is a conversion efficiency, then simple water tanks should/would be better than a process which is more complex.

For me the tanks are not in my heated house envelope, so anything that doesn't come through as hot water is wasted energy if that makes sense?

70sbudgie

Reed_Richards said:

70sbudgie said:

....I hope that at least helps start the seed of understanding.

Sorry @70sbudgie but I don't think you understand the issue which is: can all the electricity you put in be recovered as heat out?  If not, where does it go and can you use the device repeatedly always getting out less heat kW than the electricity kW you put in?  That's even if it were perfectly insulated so there are no "standing losses".  I would be interested in your husband's opinion on this specific question.

Edit: I accept that the first time you charge and discharge the unit you may end up with some "trapped energy" but that is a one-off and cannot happen every time.

Another edit: I am sufficiently old that I played with clockwork toys as a child.  You supply your own mechanical energy to tightly wind a coiled spring.  Then the spring unwinds driving the motion of the toy.  Friction means the spring never completely unwinds so the first time you wind it up to 100% and it only unwinds to, say, 15% remaining then stops.  But that means the next time and every subsequent time you wind it up you only have to do 85% of the winding you did on that very first time.  So although it always holds 15 % of trapped mechanical energy, every time after the first time you wind it up you get back all the energy you put in.          

I understand the issue of conversion losses, I am just struggling to understand enough of the chemistry / physics of phase change materials to be able to explain it in any way that is understandable (apparently!). 

I'll try another way...

(I don't know the actual numbers, so these are just made up as an example)

If you have water and apply 1kWhr of energy (my husband hates me using kWhrs, he says I should use the unit joules), it causes the water to increase in temperature by 5 degrees. If you apply 1kWhr of energy to ice that is at -1°C, the temperature will only rise by 1°, but the ice melts. All that energy has gone into melting the ice, not increasing its temperature.

That is the principle of phase change energy storage - the energy goes into changing the inter molecular bonds / structure of the material and not into a measurable temperature rise. 

In reverse, water at 1°C can be triggered to start freezing. This starts a chain reaction which releases energy. But you won't get all of your 1kWhr of energy back because some of it will remain as bonds in the material. (These are my husbands words paraphrased)

It seems that Sunamp have managed to identify how much of that energy stays within the inter molecular bonds in the material (probably by repeated experimentation) and have put a figure to it. 

And phase change materials don't behave like a spring. A material can change between phases an infinite number of times - there's no limit to how many times water can freeze and melt.

Why a phase change material would repeatedly have similar losses, is definitely beyond my understanding. I think it must be something to do with physical chemistry?

Edit to add: my husband also talked about energy you put in that doesn't cause the material to change phase and that it is impossible to achieve 100% phase change in a material. I understand that improving the efficiency of solid crystalising out of a liquid is a big part of his job.

Reed_Richards

Solarchaser said:

To me, conversion loss is simply the energy that you supply, which you expect to to end up as heat in your final product (hot water), is lost somewhere else in the process.

Agreed.

For instance some sunamps have pumps in order to circulate the heat better through their phase change material, any energy used to run that pump is conversion loss.

Here I don't agree.  The pump is inside the unit and circulates material inside the unit so the energy it uses is ultimately converted to heat which can be used.  It's just an indirect rather than a direct conversion.

If you are asking me why did I state the sunamp as 85% conversion efficiency,  that's because it appeared in a video of Andrew bissel when he was trying to get private funding (iirc) for the sunamp.
Being physics based, I dont know about chemicals really,

But you should know about conservation of energy

 so when the ceo says 15% conversion, then I say fair enough as I don't understand fully what's involved in the process.

That could be true as a one-off but for it to happen repeatedly defies one of the most fundamental laws of physics.  Of course it could be an attempt to disguise what is really a standing loss.  

I shared the warmstone blurb in the other thread where they state 98-99% efficient. 
I'm pretty sure I also seen 85% banded about when I was researching this a year ago... but maybe I am " misremembering" as is the popular phrase.

Again anything other than 100% efficiency which is not down to standing losses just isn't physically possible for anything that does not have a very short life.  The "lost" energy would build-up and destroy the unit.

When these things are light on detail you can only apply your own theories I guess.
So for me sunamp says 85% I assume 15% is lost as chemical change of state as something other than heat,

Could happen but not time and time again because it's a closed system.  If its 15% every time then all the chemical will have changed state after 7 charging cycles and then whatever was happening will stop.
 
 perhaps vibration?? (That would be a lot of rattling though),

Think of a little battery operated radio.  That can make a lot of noise but consumes very little battery power.  Something vibrating enough to consume significant power compared to heating would force you to wear earplugs and have your neighbours coming round to complain.

 or that the change gives off too much heat which then cannot be retained in its phase change material, and so when turned back to liquid/ solid that heat cannot be harnessed.
That to me said it looses 7.5% converting to solid and 7.5% to liquid.
Heat is heat, but if its not put back into the water during conversion then it is lost.

But if it's somehow lost to the water it stays inside the box and the box just gets hotter and hotter until it melts.

Or perhaps if the heat applied to get from say 10C ambient to 56C phase change can't be stored in the phase change, and when at 56C it changes all, but then from 56C to 10C again can't be put back into the water running through it, then its lost.

Again, but if it's lost to the water it stays inside the box and the box just gets hotter and hotter until it melts.

Why would water tanks be different in this scenario,  well they are just water all of the time, so will happily give heat to water at 10C if they are at 15C, then don't need to be at 56C to give heat to the water.

Phase change materials aren't as magically different as you suppose.  They take in heat, they give out heat.  The do this at any temperature and will equally heat water at 10 C if they are at 15 C.  But if they happen to be at 56 C (for this particular material) they give out a lot more heat.    

All of this is assuming they are doing water supply rather than heating, just for this answer.

That's my thinking, and why if there is a conversion efficiency, then simple water tanks should/would be better than a process which is more complex.

I have to tell you that there is no such thing as perpetual motion, summoning energy out of nowhere.  And there is no such thing as conversion efficency, losing electricity or energy to nowhere - except in the restricted sense that some of your electrical energy can be lost outside of the thing you are trying to store heat inside.

For me the tanks are not in my heated house envelope, so anything that doesn't come through as hot water is wasted energy if that makes sense?

That's fair enough and makes standing losses a big issue for you.  That's why you should be looking harder at other options without dismissing them on the basis of something that does not exist.  You may well still conclude that a tank of water is the best option but don't be misled.

I have interspersed my replies in bold text.