Electric boiler?

[ericmark]

Seem to remember turned to liquid at around 70°C. Sodium maybe? There must have been a problem as it was dropped.

 

[JohnW2]

Seem to remember turned to liquid at around 70°C. Sodium maybe? There must have been a problem as it was dropped.

I've just had a quick look. Sodium and potassium have much lower thermal capacities than water, and lithium about the same as water - but all three of those (particularly lithium) in that 'column' or the periodic table would come with big problems (particularly the tendency for 'spontaneous combustion'!) ... and, as I suggested might be the case, I can't find any solid or liquid which would have a higher thermal capacity than water.

However, I've just realised that you are talking about phase conversions, whereas I was talking about storing heat without a phase change. Hence, as you said, it's the latent heat of materials (not their thermal capacity) which matters - so, when I have a moment, I'll look into that.

 

[Harry Bloomfield]

The lower bath has my wife's e-bike in it, never used.

No, no, no - You are supposed to keep coal in it, not a bike!

 

[JohnW2]

However, I've just realised that you are talking about phase conversions, whereas I was talking about storing heat without a phase change. Hence, as you said, it's the latent heat of materials (not their thermal capacity) which matters - so, when I have a moment, I'll look into that.

I've had a quick look at latent heats of melting/fusion. The first table I found (here) indicates that ammonia has a similar latent heat to water but all the other substances in the list are lower than water, other than aluminium and chromium (both about 18% higher than water) - although their melting points would obviously be far too high to be useful for routine heat storage.

 

[BS3036]

Back at that time (70's) my plan was a house with a large cellar which I would fill with wax, and loads of pipes going through it. It meant the heat could be stored at a constant temperature (melting point) suitable for heating the house for a year. I found that you could choose a wax with a convenient melting temperature. It might have worked but I never got round to it.

 

[JohnW2]

Back at that time (70's) my plan was a house with a large cellar which I would fill with wax, and loads of pipes going through it. It meant the heat could be stored at a constant temperature (melting point) suitable for heating the house for a year. I found that you could choose a wax with a convenient melting temperature. It might have worked but I never got round to it.

I would think far from a crazy idea, but is not one of the problems with any such approach is that it is not very (if at all ) 'controllable'?

 

[Harry Bloomfield]

I would think far from a crazy idea, but is not one of the problems with any such approach is that it is not very (if at all ) 'controllable'?

No less controllable, than storage heaters presently are.

 

[JohnW2]

No less controllable, than storage heaters presently are.

That depends upon what BS3036 meant. It sounded as if he might well have been thinking of storing heat for a lot longer than 12h/24h ...

... the heat could be stored at a constant temperature (melting point) suitable for heating the house for a year.

 

[BS3036]

it is not very (if at all ) 'controllable'?

Assuming the whole think was encased in good insulation, which is obviously part of the plan, then you only remove heat when you run water through the pipes, which then travels on up to your radiators or underfloor heating pipes. At the time I did the calculations and it really just depended on having a decent sized cellar.
At the time, solar thermal tubes were also more prominent than PV, so it was just a case of taking the sun in the summer and using it in the winter.

 

[Harry Bloomfield]

It sounded as if he might well have been thinking of storing heat for a lot longer than 12h/24h

He said a year, but would need to be well insulated, to prevent the heat rising when it wasn't wanted, and could take a very long time to charge up. Would work well, being able to charge up at especially low prices of summer, and off-peak.

 

[JohnW2]

Assuming the whole think was encased in good insulation, which is obviously part of the plan, then you only remove heat when you run water through the pipes, which then travels on up to your radiators or underfloor heating pipes.

Yes, that's roughly what I thought you were saying.

However, I'm not clear as to what temperature you would envisage storing the wax at. If it were to serve the purpose of releasing (latent) heat when it solidified, it would presumably have to be stored roughly at its melting point, so I imagine that you would have to find a wax whose melting point was adequately high for the water travelling to the radiators - in which case the insulation would presumably have to be exceptionally good?

At the time I did the calculations and it really just depended on having a decent sized cellar.

I could perhaps have achieved that, since my my very large cellar is (at a rough guess/calculation) 150 - 200 m³ However, I have far better things to do with it (my 'workshop'!) than fill it up with wax!

At the time, solar thermal tubes were also more prominent than PV, so it was just a case of taking the sun in the summer and using it in the winter.

True - but, as above, if you were going to store the wax, for months, at a temp high enough for feeding the rads, it may have proved unrealistic to install adequate insulation?

... or am I missing something?

 

[BS3036]

am I missing something?

I think what you are missing is the will to take on a challenge. The points you mention (most of which I already pointed out) represent the engineering challenges to be overcome. The storage temperature would have been chosen for optimal trade-off . Bear in mind that these days a lower temperature is considered best for the heat transfer than in those olden times. As for whether it would have been worth it to heat a house all year from the sun rather than paying someone for the energy - I thought that might be good value. However, as you may realise, I also did not find the resolve to take on this challenge, as I expected to move house more often than would have made this practical.

 

[JohnW2]

I think what you are missing is the will to take on a challenge. The points you mention (most of which I already pointed out) represent the engineering challenges to be overcome. ..... However, as you may realise, I also did not find the resolve to take on this challenge, as I expected to move house more often than would have made this practical.

I don't think I missed much. It never really occurred to me that you might ever have seriously considered 'doing it', so I assumed that you were talking about an interesting academic/theoretical 'thought exercise'! When I asked whether I was 'missing anything', I was really asking about 'technical' issues, rather than practicalities or inclination to actually implement such a system!

The storage temperature would have been chosen for optimal trade-off . Bear in mind that these days a lower temperature is considered best for the heat transfer than in those olden times.

Is that true? It's certainly the case that when heat is being supplied by a heat pump, lower temperatures have to be used (typically ΔT30, rather than the traditional ΔT50), necessitating more and/or larger radiators, but I wasn't actually aware of the lower temps resulting in 'better heat transfer'.

In any event, I don't think I've heard of anyone using less than ΔT30, and even that would require a storage temp well in excess of 50 °C - which I imagine would present major challenges, particularly in relation to insulation. On the other hand, if one did choose to go down below ΔT30, one might end up virtually having to 'wallpaper' the entire house with radiators

 

[ericmark]

I have a multi-fuel option for DHW, suppose no reason not to also have a multi-fuel option for CH. As long as both heat the water to around the same temperature. But electric costs too much, even off-peak at 8.5p/kWh.

However, I suppose there is no reason not to use either a direct drive, or liquid fuel/electric drive, with something like the Wispergen. The sterling engine was tried with a gas boiler, but the regulations killed the idea, it was not what they could do or not do, it was how the government rules and regulations are met, and the units did not slot into government incentives.

But in the main, the likes of wind generators are not really practicable for domestic homes, and solar panels do not produce much in the winter, so having a heat pump to cool the home makes sense, if enough solar to heat the home too much, then also enough solar to run the heat pump (AC), but this is not the case in winter, when running the heat pump in reverse.

But installation cost is the big thing, domestic CH in the main is a parallel piped system, and we turn the flow of water on/off to each radiator, but to keep radiators small in physical size, and to use same radiator to heat and cool, we need to move to a fan assisted radiator and control output by fan speed, not the water, which means we want a series piped system. There are two types of fan assisted radiator those with a single matrix, and those with a twin matrix, the latter can heat one side of the building while cooling the other side, but the domestic house is not large enough to require that.

So as a new build, plumbing in series, with fan assisted radiators plus the condensate plumbing to remove water when cooling, may be a viable option, but as a retro fit, the installation cost becomes silly.

I have seen in my time some really great systems, where the cooling water from the 1.5 MW generator fed the boiler for the central heating, and then heated the cold water enough to allow the chemical to work to clear the water, with an installation able to accommodate 1000s of at first workers and then the military on the Falklands.

This system I suppose would work with blocks of flats, but with most domestic housing estates it's a non-starter. It is the same with solar panels, with a home designed from day one to have solar panels, as I saw in Turkey, with a flat roof and access to the roof for maintenance and cleaning, they work well, even if just a walk way around the roof, and homes orientated so to catch the sun or rotatable panels. But as a retro fit no, I have now a problem getting the gutters fixed, where the smooth solar panels allowed the snow to fall off the roof in a massive slide, taking the gutters with it.

The advantage with electric is you don't need to watch how much fuel oil, or LPG you have, you just pay the bill each month. But as yet the supply of electric is not stable enough. While we have reports of massive swades of the country being without power every time we have a named storm, sometimes for a week or more, electric heating is not going to work.

I can get by without lights, and even without cooking, but not without heating.

 

[JohnW2]

.... While we have reports of massive swades of the country being without power every time we have a named storm, sometimes for a week or more, electric heating is not going to work.

For the great majority of people in the UK, loss of electricity also means loss of heating by gas, LPG or oil, doesn't it (unless people have (which few do) 'standalone' gas, LPG or oil heaters that do not require any electricity to 'control' them) ?