How do Sunamp heat batteries work?

waqasahmed

paul991 said:

Then the govt  would have less to tax you on.

There's be a "grid connection fee" similar but more expensive than the standing charge

I'm sure the 5% VAT that they're getting rn wouldn't be opposed much, if they even made sure that people have PassivHaus homes, even if they upped it to an equivalent of say 10% VAT because our electric bills would be hardly anything anyway 

Solarchaser

Reed_Richards said:

AFAIK hand warmers rely on a chemical reaction and you initiate that by causing two chemicals to mix together to produce an exothermic reaction.  If it was a phase change you would have a hand cooler rather than a hand warmer because the initial state is cold and it would need an energy input to cause a phase change so that would suck the heat out of your hands.

I'll continue later  

While I dont propose to know exactly how hand warmers work, I will comment on the phase change part as you seem to be under the impression that a phase change can only happen to cool.

If you cool water to around 0C it changes phase, if you heat it to around 100C it changes phase again... both of these at atmospheric pressure obviously. 

There are materials which change phase at all different temperatures, including hand warmers which change back when you heat them.

In fact here is how hand warmers work
https://www.sciencefocus.com/science/how-do-re-usable-hand-warmers-work/

Reed_Richards

Solarchaser said:

.. id be delighted to read what has prompted your very clear statements with bold writing stating this thermal absorbtion stays the same through sunamps pcm, and that it will accept even greater heat after phase change.

I'd also be happy to read about sunamp supplying heat transfer without the phase change.

The phase change has nothing whatsoever to do with the heat transfer.  The heat transfer comes from flowing water through a hot material (or running an electric current through a resistive element as a means of heating the unit).  All that the phase change gives you is the ability to store more energy in a smaller volume.  It also has the effect that you can extract a lot of heat at one particular temperature, which is useful if you have the right material with the right transition temperature.  I know this, I guess, because I have a background in the science of materials.

Sunamp claim that their units are very well insulated and will lose heat less rapidly than a tank of water with the same heat storage capacity; they don't claim that there is no heat loss.  My feeling is that all claims made by manufacturers of hot water cylinders or their equivalent are not real world because the measurements are made in the absence of any connecting pipes.  We inevitably connect copper pipes and copper is a very good conductor of heat.  AFAIK this cause of heat leakage is never properly addressed in domestic systems.  Your plumber, if you are lucky, might install a "heat trap" pipe loop to guard against convection in the hot water but that's the best you can do.  @Solarchaser, who is reliant of hot water storage tanks, may have found a way of preventing the heat they contain being wicked away down the connecting pipes but I doubt it because I don't think technology designed for this purpose is commercially available.     

Solarchaser

So basically what you are saying is you know something about phase change materials in general,  but actually you don't know about sunamps particular material, and assume it conforms to the materials you are used to dealing with.

My point about the hand warmers was that they are phase change, but are inert until activated and so not capable of heat transfer until activated. You are stating sunamp is not the same, fine.
You are not offering proof of that, but tbh im happy to take that as read, cos really, who cares?
Sunamp in a square box (as long as the insulation isn't bulging) has better heat leakage properties than a cylindrical water tank, ok, but its really really not that straightforward. 

I stop my hot water tanks wicking away heat by a combination of one way valves and loops, all very available to your average Joe public.

Will I have more heatloss than sunamps, probably, but I also have alot more usability, and a far clearer view on the "temperature" of my tanks. An often complained about negative of sunamp is you have no idea if its half full or empty as it has no way of telling you, there is no temperature guage or capacity guage on phase change boxes.

Reed_Richards

Solarchaser said:

... In fact here is how hand warmers work
https://www.sciencefocus.com/science/how-do-re-usable-hand-warmers-work/

The key word in the reference is reusable.  These are hand warmers that you charge up "in a pan of boiling water" (or similar).  They come out boiling hot, cool quite rapidly to the phase change temperature then release a lot of heat at that temperature but eventually cool down completely.  So they start very hot but cool slowly whilst releasing heat.

The sort of handwarmers you can buy at my local supermarket are not reusable and rely on a chemical reaction when you mix two chemicals together.  They are cold until you want to use them then become hot for as long as the chemical reaction keeps going.

I'm reminded that sunamp always feature the hand warmers that are cool to the touch until you initiate the phase change, this has always given me the impression the pcm is inert until a temperature/event that changes it.

I haven't seen this publicity material but it has given you completely the wrong impression.  If your hand warmer is cool to the touch it's either because you have not mixed the chemicals together or because you have not yet placed it in a pan of boiling water.

I'm not under the impression that a phase change will only happen to cool.  If you flow salt water at 2 C in a pipe through a tank of ice it will melt the ice by extracting heat from it (a phase change to cool).  If you flow salt water at -2 C in a pipe though water at 0 C then the water in the tank will freeze and the salt water will be heated to 0 C.  There is no useful domestic application that I can think of for the ice-to-water phase change.  All that Sunamp have done it to find a material where the phase change happens at a temperature that is useful for water heating (around 56 C, I think) and, presumably, the volume of either phase is not too different. 

A phase change is not necessarily just solid to liquid or liquid to gas.  You can have solid to solid phase changes or liquid to liquid.  It's been suggested that Napoleon's army failed in their attempt to defeat Russia because their uniforms had tin buttons. At the cold temperature of the Russian winter tin undergoes a solid to solid phase change from the malleable phase we are familiar with to another phase that is much more brittle.  So the buttons on the soldiers' uniforms crumbled and how could they fight if their trousers kept falling down?

https://www.smithsonianmag.com/smart-news/napoleons-army-may-have-suffered-from-the-greatest-wardrobe-malfunction-in-history-92535444/
https://www.amazon.co.uk/Napoleons-Buttons-Molecules-Changed-History/dp/1585423319
           
  .     

QrizB

Reed_Richards said:

I'm reminded that sunamp always feature the hand warmers that are cool to the touch until you initiate the phase change, this has always given me the impression the pcm is inert until a temperature/event that changes it.

I haven't seen this publicity material but it has given you completely the wrong impression.  If your hand warmer is cool to the touch it's either because you have not mixed the chemicals together or because you have not yet placed it in a pan of boiling water.

We're getting way off topic here but I've got some of those reusable hand warmers and they work exactly as that linked Science Focus article says. They are cold to the touch even when they are ready to use.

When you trigger them, the liquid contents crystallises and it's this latent heat of crystallisation that gives the "hand warmer" effect.

Once used, you heat them in a pan of water to melt the active material before allowing them to cool to room temperature again, remaining liquid as they cool.

Martyn1981

Reed_Richards said:

AFAIK hand warmers rely on a chemical reaction and you initiate that by causing two chemicals to mix together to produce an exothermic reaction.  If it was a phase change you would have a hand cooler rather than a hand warmer because the initial state is cold and it would need an energy input to cause a phase change so that would suck the heat out of your hands.

I'll continue later  

Hiya, is there any chance we are talking at crossed purposes? As I understand it the heat pads and Sunamp both use the same idea/technology, versions based on sodium acetate.

So after use you heat the heat pads back up, and they undergo a phase change from solid to liquid. This is how I understood the Sunamp batteries work too, with the additional energy stored that phase changes bring, such as the enormous amount of energy needed to change ice to water, or water to steam.


Edit - Sorry, should have read ahead, and SC has already replied on this issue.

Martyn1981

Reed_Richards said:

Solarchaser said:

... In fact here is how hand warmers work
https://www.sciencefocus.com/science/how-do-re-usable-hand-warmers-work/

The key word in the reference is reusable.  These are hand warmers that you charge up "in a pan of boiling water" (or similar).  They come out boiling hot, cool quite rapidly to the phase change temperature then release a lot of heat at that temperature but eventually cool down completely.  So they start very hot but cool slowly whilst releasing heat.          
  .     

But that's what I described before you replied:

Hiya. If you think about one of those handwarmers after you've reset it, it will be hot, but will cool down (lose heat/energy), so as you say, after the pcm has changed phase, any additional energy applied will raise its temp (just like the water getting hotter), but also, just like the water, it will then slowly lose some of the heat to the environment.

My bold in my quote to match your bold in yours.

I think we've been talking about the same thing but confused each other, and would have helped immensely if I'd been more clear that I was talking about the re-useable type. I didn't mention that as I thought it was well known, a poor assumption looking back, and one I shouldn't have made.

[Edit - Lightbulb moment following SC's latest post with the vid. That's why I thought it was known as we've seen or discussed this way, way back. But a long enough gap for new discussions. M.]

So going way back, I (and I think SC) haven't been claiming that any losses from the Sunamp are as 'bad' as a hot water tank, but in my waffle v's the economics (back at the start) I felt the economics of the Sunamp with their 'claimed' zero losses, didn't work. And as SC has pointed out, there will almost certainly be some small losses from the nSunamp too.

TBC, as we've all said, any losses in the system, during the heating months isn't really a loss, though there may be different values depending on leccy v's gas heating etc etc.

Solarchaser

QrizB said:

Reed_Richards said:

I'm reminded that sunamp always feature the hand warmers that are cool to the touch until you initiate the phase change, this has always given me the impression the pcm is inert until a temperature/event that changes it.

I haven't seen this publicity material but it has given you completely the wrong impression.  If your hand warmer is cool to the touch it's either because you have not mixed the chemicals together or because you have not yet placed it in a pan of boiling water.

We're getting way off topic here but I've got some of those reusable hand warmers and they work exactly as that linked Science Focus article says. They are cold to the touch even when they are ready to use.

When you trigger them, the liquid contents crystallises and it's this latent heat of crystallisation that gives the "hand warmer" effect.

Once used, you heat them in a pan of water to melt the active material before allowing them to cool to room temperature again, remaining liquid as they cool.

What?????
Off topic? As if we would ever do that on this forum!
I'm shocked at the suggestion. 🤪😁

Anyway Reed, see this video, it's a quickie and tbh I've seen this hand warmer demo on every single sun amp video
https://youtu.be/KIozC2ffxEg

Solarchaser

Martyn1981 said:

Reed_Richards said:

Solarchaser said:

... In fact here is how hand warmers work
https://www.sciencefocus.com/science/how-do-re-usable-hand-warmers-work/

The key word in the reference is reusable.  These are hand warmers that you charge up "in a pan of boiling water" (or similar).  They come out boiling hot, cool quite rapidly to the phase change temperature then release a lot of heat at that temperature but eventually cool down completely.  So they start very hot but cool slowly whilst releasing heat.          
  .     

But that's what I described before you replied:

Hiya. If you think about one of those handwarmers after you've reset it, it will be hot, but will cool down (lose heat/energy), so as you say, after the pcm has changed phase, any additional energy applied will raise its temp (just like the water getting hotter), but also, just like the water, it will then slowly lose some of the heat to the environment.

My bold in my quote to match your bold in yours.

I think we've been talking about the same thing but confused each other, and would have helped immensely if I'd been more clear that I was talking about the re-useable type. I didn't mention that as I thought it was well known, a poor assumption looking back, and one I shouldn't have made.

So going way back, I (and I think SC) haven't been claiming that any losses from the Sunamp are as 'bad' as a hot water tank, but in my waffle v's the economics (back at the start) I felt the economics of the Sunamp with their 'claimed' zero losses, didn't work. And as SC has pointed out, there will almost certainly be some small losses from the nSunamp too.

TBC, as we've all said, any losses in the system, during the heating months isn't really a loss, though there may be different values depending on leccy v's gas heating etc etc.

Hi Martyn I think we are thinking similarly, however reading your post has made me realise that it's me that's caused this confusion right at the start.

I'll try and briefly explain what I understood the sunamp pcm to do and hopefully explain why I think what I think.

My understanding of the sunamp is that the pcm is in liquid state at temperatures below let's say 60C for arguments sake.
And so any heat below that is lost, now RR is saying it isn't, I'll explain why I think it is, in a sec.
It's reported through forums that the pcm wants to be about 65C for phase change and then changes back when... let's say asked to, and the result is 55C water out.

From this I ASSUMED that the pcm in its solid form sits at room temperature (like the hand warmers) in theory for ever, giving great long term heat loss figures as its inert while storing its heat.

I ASSUMED that when hot water is required there is something in the sunamp that commands the material to change phase, (again based on the hand warmers) releasing its heat into the water through heat exchangers. The fact it is changed at 65C and gives back 55C means there is loss in the conversion.

Why do I assume/reason all heat is lost below the phase change, well that's because in the various forums people report the water goes from hot to suddenly cold, not a gradual cooling as you get with hot water tanks which essentially release the same amount of energy as they cool... or at least can we agree its linear, vs the sunamps which *appear* to give all and then nothing suggesting to me that when it's changed all back to liquid at 55-60c then there is no more heat to give and so instead of going from 55 to 50 to 45 etc, it seems they go all goof all good, empty.

RR says I'm wrong and they do absorb heat the whole time.
I'm OK with being wrong, it happens all the time 🤣 ideally though, id like to be proven wrong