Heat Battery

Martyn1981

Reed_Richards said:

Actually you could fill your night storage heaters with a phase change material like they use in a heat battery to make them more compact.  Possibly they would also perform better because all the heat is released at the phase change temperature.  So there you are, @Martyn1981, 'magic phase-change clay'.

Funny you should mention that, I definitely remember (vaguely) something from about 5yrs ago when phase change and Sunamp started to make the news. It was a phase change dining table. It contained a material layer with a phase change temp of around 22C, the idea being that when the room got 'too' hot the material would absorb some heat, and release it as the room cooled down, that way it would help to stabilise the temp around that point.

So ........ rather than filling the storage heaters with it, perhaps build the internal walls/skin with it. 

Fronkle

I used to run an oil fired boiler at least 3 hours a day during the summer just to heat my hot  water. At 40p/litre without using the boiler for room heating, I would use about 1200 litres/year during the summer simply to heat hot water. This cost amounts to about £480 simply to heat hot water in the summer. The cost of servicing the boiler every 12 months was about £300. With the Sunamp, the boiler uses no oil for at least 3 months. I buy electricity on Economy 7 at 9p/KwHr and the incremental cost is low. Know have the boiler serviced every 15 months instead of 12. All in the total annual savings in my case amount to a payback time of about 6- 7 years assuming the cost of oil remains at 40p/litre. Additionally, there is no hot water tank to replace every 20 years or so, no thermostat to replace, and the amount of hot water is greater. 

Reed_Richards

I doubt that there is much information on real-world life expectancy of a heat battery because they have not been around long enough.  My last hot water cylinder was still going strong after 20 years, however.  

40p per litre for heating oil, 11.35 kWh per litre but assume the boiler is 80% efficient works out at 4.83 p per kWh.  It's hard to see how electricity at 9p per kWh can beat that.  If it does it must be because the hot water cylinder was woefully inefficient at storing heat.

Compared to a well-insulated hot water cylinder, a heat battery is compact but expensive.  @Fronkle's economics appear topsy turvy.    

JimHignett

I am sure this has been covered earlier but I have actually got a 9kWh Sunamp and had it for 4 years. It cost 4k to install. It takes up 1/3-1/2 the space if the boiler. It has a very low standing heat loss, due to a) Not needing to keep a tank of water above the legionella kill temperature. b) The energy really only gets released on phase change so not at room temp if the taps are off.
When we foolishly ripped our water cylinder out and went combi 15 years earlier, that cost 4k. Sunamp needs no maintenance and should not lose efficiency due to furring up.
They are rectangular, which means you can fit them in a really small space and they don't need insulating. Really, are you telling me I should go back to a water cylinder?

Reed_Richards

I've heard some bad reports about their reliability but that's hearsay and hopefully you won't experience any issues with yours.  Still, £4k is a lot compared to a hot water cylinder.  Even if the Sunamp is effectively better-insulated it will take a good few years of re-heat cost saving to pay off that extra cost.  You'll have space for some clothes in the airing cupboard but not the heat to air them with.