How do Sunamp heat batteries work?

2nd_time_buyer

It feels wrong to be converting the most useful form of energy (electricity) to the least useful (heat) without getting any side benefit along the way (e.g. lighting a house, watching TV) or benefitting from increased efficiency from a heat pump. Particularly if that Electricity is generated in a gas power station and there might be 40% lost in generation and transmission.

If I was running a tinpot dictatorship, the first thing I would do is ban all resistive heaters.  The second would be to promote more colorful trousers. 

Martyn1981

Can't fault you on the trousers.

How about HPWH's with external two way venting, instead of 'ordinary' hot water tanks, if full heatpumps aren't possible. Perhaps in conjunction with some A2A units?

waqasahmed

2nd_time_buyer said:

It feels wrong to be converting the most useful form of energy (electricity) to the least useful (heat) without getting any side benefit along the way (e.g. lighting a house, watching TV) or benefitting from increased efficiency from a heat pump. Particularly if that Electricity is generated in a gas power station and there might be 40% lost in generation and transmission.

If I was running a tinpot dictatorship, the first thing I would do is ban all resistive heaters.  The second would be to promote more colorful trousers. 

Mine would be to incentive PassivHaus compliance with 0% loans, and build a decentralised grid, by banging on solar panels on people's houses wherever they are 

paul991

Then the govt  would have less to tax you on.

Reed_Richards

Solarchaser said:

Haha there is always one, yes of course energy cannot be lost, but if you have the energy you want to remain in the phase change material and it does not, then it is lost in the conversion,  ie it does not come back out as the heat you want.

I still believe that you're not thinking this through, @Solarchaser.  Starting from cold, you heat the phase change material up to its phase change temperature, then it stores a lot of heat changing phase at that temperature and it you continue applying power then the changed phase material will increase in temperature again.  All that heat is potentially recoverable if the Sunamp was perfectly insulated, in practise some will leak out.  But there is no such thing has heat that does not come back out.  And heat that comes out when you don't want it to is just down to the fact that no insulation is perfect.   

Solarchaser

OK, so I'm not thinking it through?
To take what you said, starting from cold you heat the phase change material up.... and all of this is waste heat, as under around 65C the pcm stays in its original phase, this is also a good reason why the majority of heat pumps are no use for sunamp because they don't generate the temperature required, any heat that is under the phase change temperature is waste, how that comes out, yeah I can only guess really, perhaps as heat back to the heat pump, so reducing its efficiency,  perhaps thermosyphon on the water pipes.... its all theory 

Heat lost through insulation can be used in the home envelope... assuming you want it, which in winter you do, summer, not so much.
Same as with a hot water tank.

Around 9 months ago I decided I was making the move away from gas, I was 99% sure that it was going to be to sunamp, it's out of the box thinking, it's a Scottish company, born out of Edinburgh uni, which i visit quite often, they are involved in community projects to help those worse off (as well as helping themselves,  sure, but they are a business) all good positive stuff. I had decided where I could fit two of them, and was looking to remove floor boards in an area for another two sitting under the floor so I was pretty much all in on it.
However in doing alot, and I do mean alot of research/searches I began to get concerned that sunamp seemed to make big claims about how much you save each year, but was light on actual data, and it reminded me of the solar sellers of 10 years ago.
So I decided to actually attempt to interrogate the technology, which proved quite hard.
The phase change part is straightforward, but the inner workings of the sunamp not so easy to find.
I searched for videos of the ceo punting his wares to secure funding and in one and only one there was a nod to 85% efficiency. 
I could not verify it, I could not disprove it.
There were comments about an internal pump to ensure adequate distribution of heat to facilitate entire phase change of all material, then others suggesting no pump required (perhaps different models).

Anyway back to your point, once the phase change is getting the right amount of heat, its doing its thing, should be pretty efficient, and long term storage would seem to be a niche market, but there are always losses.

If you search, you will find complaints about the usability, being unable to have hot water if the sunamp was "half charged" rather than fully heated or fully depleted.
Same with if you were heating with solar/off peak, but also wanting hot water.
The box itself being hot to the touch, how if the whole thing states it only loses 500wh/day?

Why is there no efficiency figures?
Surely at some point they have put in say 10L of 65C water to change the phase, then tested how many litres of 55c water comes back out?

So in short, I believe that some of the heat is not absorbed into the pcm and as the heat transfer to the water, to heat it relies on that phase change , if its not retained in the phase change, it cannot be transferred in the opposite phase change into the water, and so would be waste heat.
That's my thinking

Reed_Richards

Solarchaser said:

To take what you said, starting from cold you heat the phase change material up.... and all of this is waste heat, as under around 65C the pcm stays in its original phase,

No that's not waste heat at all, @Solarchaser .  When you heat a thermal store that is a tank of water it remains in its original phase (or you're in trouble) but the heat input is not wasted.  The only difference between a tank of water and a pcm is that with water the same amount of energy input will raise the tank temperature by the same amount throughout the temperature range of operation.  With a pcm the same amount of energy will raise the pcm temperature by the same amount until you reach the phase change temperature at which point you can add a lot of extra energy without increasing the temperature.  After all the material has changed phase it will go up in temperature again as more energy is input.  All that energy can be extracted to heat the water in the pipe passing through it.  You don't rely on the phase change to heat the water, it just increases the energy storage capacity per unit volume.

I'm sure you are correct that Sunamp oversells its products and that is good cause to be cautious but your notion of wasted heat cannot be right because it's not physical.       

Solarchaser

While I kind of understand the point you are making, and while I agree that's true in water, especially as the properties of water under pressure stay pretty much the same through the 65C barrier on the sunamp pcm, 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.

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.

Martyn1981

Reed_Richards said:

Solarchaser said:

To take what you said, starting from cold you heat the phase change material up.... and all of this is waste heat, as under around 65C the pcm stays in its original phase,

No that's not waste heat at all, @Solarchaser .  When you heat a thermal store that is a tank of water it remains in its original phase (or you're in trouble) but the heat input is not wasted.  The only difference between a tank of water and a pcm is that with water the same amount of energy input will raise the tank temperature by the same amount throughout the temperature range of operation.  With a pcm the same amount of energy will raise the pcm temperature by the same amount until you reach the phase change temperature at which point you can add a lot of extra energy without increasing the temperature.  After all the material has changed phase it will go up in temperature again as more energy is input.  All that energy can be extracted to heat the water in the pipe passing through it.  You don't rely on the phase change to heat the water, it just increases the energy storage capacity per unit volume.

I'm sure you are correct that Sunamp oversells its products and that is good cause to be cautious but your notion of wasted heat cannot be right because it's not physical.       

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.

So, as I understand what Solarchaser to mean (aplogies if I've got it wrong), not all of the energy added to the pcm will be stored for later ('permanent') use. Some, like the hot water tank, will slowly leak out. This isn't necessarily a loss, as I mentioned in my post, and you and SC have mentioned, if it's during the heating season. But, if the main selling point of the pcm device(s) is that they have no losses, unlike a hot water tank, then that's not necessarily true.

I also got the impression that SC wasn't saying it was a large loss, nor being pedantic, just questioning the lack of losses, which in context (possibly my fault for raising the issue in my waffle/story) was interesting/fun to note.


On an aside, would it be OK for me to PM you some questions about an ASHP? My sister is running into difficulties getting one approved, or do you think any issues, regardless of how specialised, warrant a thread post for all to 'enjoy'?

Reed_Richards

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