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Time control for electric radiators
- Thread starter Daveydub
- Start date
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I read some new rule for electric heaters came in force this month and a lot of makers have had to improve there heaters, Lot 20 or something means better controls and a lot of these oil rads like dimplex have had to have timers built in to conform.
http://www.lot20.co.uk
http://www.lot20.co.uk
What a load of crap. Someone should explain to these idiots that electric heating is 100% efficient and can't be increased.
The conversion of electricity into heat is, indeed, 100% efficient but this is not about efficiency in that sense.
If you look, this "Lot 20" is about reducing production of an unnecessary amount of heat (hence using an unnecessary amount of electricity), for example by improving the performance of temperature controls (thermostats etc.).
Kind Regards, john
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And someone should explain to idiots who dismiss the idea of system efficiency as total crap that better controls can indeed reduce the amount of energy used to heat a given location to a required temperature at a required time, and to be able to change those requirements easily, and that the Lot 20 provisions for electric heaters are all about better controls.
Let me know if you ever encounter an idiot who cannot or will not read that for himself, and I'll be pleased to explain to him what a load of crap his opinion is.
Well yes, it will depend very much on the required heating load - a big house will need a big store.
When I put the thermal store in the flat, I specifically did a test to see what teh actual heat load was - by running the store off the immersion for several days and seeing how much the meter clocked up. At the time it barely got above freezing (late 2010 - bloomin 'eck, was it that long ago
), and the average heat load to keep the place warm 24 hours a day was around 2kW - well within the capability of a 3kW immersion.Obviously, things would be a bit different once DHW usage is taken into account - but it's better than what you get direct from the combi boiler when it breaks down
The first obvious thing to do with a new system is to fit oversize rads so they will provide the heat needed at a lower temperature - that means you have more useful heat in the store. The next thing is to note that you can heat the store to much higher temperatures without losing efficiency when using electric - so for the same size store, if you heat it to (say) 90˚ then it takes about 100 minutes to heat up (from 20˚).
But assuming you only get "useful" heat out down to 40˚, then (drawing 6kW) you'll get 70 minutes out from 90˚ but only about 45 minutes from 70˚. So taking the flat with an average load of 2kW, it could probably run the heating from storage with 125l of water @ 90˚ for around 210 minutes (3 ½ hours) - with 250l giving 7 hours.
And don't forget that you can still use an immersion heater to "top up" - and when doing that you are no worse off than when using electric heating direct. There'll be a tradeoff between radiator size (bigger means more useful heat can be stored by a given quantity of water), cylinder size (bigger cylinder means more heat stored), physical space needed, and the ultimate saving (cheap rate vs expensive rate).
Was that with the immersion 'powered' for 24/7, or just for 7 hours per day, as with E7?Well yes, it will depend very much on the required heating load - a big house will need a big store...... At the time it barely got above freezing (late 2010 - bloomin 'eck, was it that long ago
Kind Regards, John
A heat store. A store of heat. That'll be a storage heater then.
Water is actually pretty good as a store, at 90°C https://www.engineeringtoolbox.com/sensible-heat-storage-d_1217.html
Cast iron is almost as good (by volume) but of course can be raised to much higher temperatures. If you could take it from 20° to 170° you'd store twice as much heat as the same volume of water taken to 90°.
There are downsides. It would weigh over 7x as much. You'd need some pretty good and fail-safe controls - leaving the water you're heating lying around in the heat exchanger inside the lump would be a Bad Idea.
Aerogel insulation would do a fine job of keeping the heat in.
A 0.5m³ lump could store the energy of a 6kW heater over 7 hours. Should come in at well under 4 tonnes all in.
The flat only has single rate lecky, the immersion was switched on all the time, but obviously would have been controlled by it's internal stat. If you were designing a system to store heat from off-peak lecky then you'd use larger/more immersion heaters - so in this case you'd be wanting (plucks figure out of the air) something like 9kW of immersion heaters, or more by the time you allow for DHW.
Not really - but I see where you are coming from. There's a fair difference between a "storage heater" in the normal sense where the heat input, storage, and heat output are all in one unit - and a system with a heat store separate from the heat emitters (eg a large water tank supplying a conventional wet heating system).
So while both are "storage heating", I think it would cause some confusion to describe what I was talking about as a "storage heater".
Not sure how you could make that work - safely and reliably. If you try introducing water into it then it will flash boil, and it will also cause shock cooling of the cast iron - which could be "quite spectacular" to see when it failed
But when it's below boiling point of the water* then you'd want to be putting water through it to extract all the useful heat. So you would need a system that could get the heat out without the risk of raising steam while the store is above boiling point, but which can get all the useful heat out as it gets cold. I suppose an intermediate heat transfer medium could do it - perhaps an oil filled loop and a plate heat exchanger to transfer the heat to the water circuit, though that would still need some failsafe system to avoid boiling the water.Doable, but as you say, has a number of downsides - it would also be "considerably more expensive" than water as a heat storage medium.
* Which might be a little above 100˚C if the system is pressurised.
That was obviously my point. One would presumably only contemplate such a system if one could (exclusively or primarily) use cheap rate electricity, which means that one would have to store enough heat during 7 hours to provide heating for 24 hours (or whatever was desired/required) - so, as you say, the E7 equivalent of what you described would probably require 9kW worth of immersion heaters and a lot of (very well insulated) storage capacity - not to mention (as you have already mentioned) large radiators.
Kind Regards, John
Well yes, you'd aim to cover most of the heating with cheap rate - but even if you do have to top up with standard rate at times, it's still going to be (hopefully, compared to "all day rate"*) cheaper than doing all the heating on day rate; and a lot more controllable than conventional storage heaters.
* Yes I know, standard rate on E7 (and similar) tend to be more expensive than single rate tariffs.
* Yes I know, standard rate on E7 (and similar) tend to be more expensive than single rate tariffs.
If the amounts of heat storage and insulation were comparable, then I suppose it would be more 'versatile', in that one could control where the heat was 'released' (e.g. by having TRVs on radiators, if not formal 'zoning'). I haven't attempted the sums, but I still think that one would need a very large, and very well insulated) heat (water) store if one was hoping to do most (if not all) 24h heating using 7/24h electricity.
I think that 'tend' is an understatement, since it surely in inevitable. If dual-rate tariffs offered the same day-time rate as single-rate tariffs, but cheaper night-time rates, then it would be a no-brainers which would mean that virtually everyone sensible would go for the dual-rate one.
Kind Regards, John
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