Economy 7 or Single Rate?

GasAttacK77

I've switched to OFTM SR but may switch to their E7 tarrif in November.

A few queries regarding the Quantum heaters:

1) If I set them to charge for just 6 hours overnight, would they store enough heat for the day? If not, what happens?

2) Would they require more or less charge for the following:

*On for 24 hours at 20

*On for 4 x 4 hour periods (total 16 hours) at 22

3) If I stay on SR, is there any benefit to changing the charging hours from 12am to 7am?

QrizB

GasAttacK77 said:

1) If I set them to charge for just 6 hours overnight, would they store enough heat for the day? If not, what happens?

Quantums, like most UK storage heaters, are designed to store a specific amount of heat. The heating element is sized such that it takes seven hours to store the intended amount. If you only allow them to charge for six hours, you'll reduce their maximum capacity by one-seventh.

Imagine a storage heater with a 21kWh capacity. It will have a 3kW heating element; 3 x 7 = 21. If you only allow it to charge for six hours, it's maximum charge will be reduced to 18kWh; 3 x 6 = 18.

For a correctly sized system, you'll only need the maximum capacity during periods of prolonged cold weather. During milder periods, you won't need to the full capacity and probably won't notice the effects of reducing the charge period.

Note that Quantums will only take the amount of charge they expect to need, so there are unlikely to be any practical benefits from reducing the charge period.

GasAttacK77 said:

2) Would they require more or less charge for the following:
*On for 24 hours at 20
*On for 4 x 4 hour periods (total 16 hours) at 22

That will depend entirely on the weather, the ambient temperature, and the thermal properties of your house.
Do you want your room to be at 22 or at 20? If you want your room to be at 22, a setting of 20 will feel cold. On the other hand, if you're happy at 20 why would you set to 22?

GasAttacK77 said:

3) If I stay on SR, is there any benefit to changing the charging hours from 12am to 7am?

On single rate, there's little to gain from charging your Quantums at all.

Scot_39

GasAttacK77 said:

I've switched to OFTM SR but may switch to their E7 tarrif in November.

A few queries regarding the Quantum heaters:

1) If I set them to charge for just 6 hours overnight, would they store enough heat for the day? If not, what happens?

2) Would they require more or less charge for the following:

*On for 24 hours at 20

*On for 4 x 4 hour periods (total 16 hours) at 22

3) If I stay on SR, is there any benefit to changing the charging hours from 12am to 7am?

Quantums if operating correctly are fairly cool to tge touch- but they do go wrong at times and can get warmer lose more heat when not demanded.

A conventional nsh would be constantly hot to the touch in use after overnight charge - too hot to touch for many on higher settings.

1)  properly rated 6 hrs will be fine most of the time.  Dimplex sizing calcs assume -3 C external.  For North of Border they recommend changing to -5. And defaults iirc to 21 living room 18 others.

I don't heat to anywhere near 20 - but my nsh generally only charge for 2 hrs on milder days and maybe 5 max after wind up for a really cold snap (like minus day time). 
But at 20+ they could cap out.
Mines arguable sized for upto 10 hr charge split 3 times a day as house built with EMEB heatwise rts installed.
And only cover living room and halls - bedrooms have own panels,  kitchen and bathroom wall mounted fan heaters.

Most of the year in most of UK temps - aren't that low - so will seldom need their full capacity.

But in the limit - you would need to rely on boost mode - manual / automatic - blockable ?? Not sure

2) Heating to 22 - I guess on the basis that the room will tgen cool to 20 between - just adds a little more to losses.  All other things being equal the temp differential controls losses and so costs - lower is normally better.  

If you only wanted 22 4 hrs a day you might save but over 16 to achieve I assume 20 min for 20-24 hrs anyway in between- that's just likely adding a bit to home losses.

3) Why would anyone spend on expensive hhr storage heaters - that cost upto £1000 supply only plus fitting - because they can timeshift cheap rate electric - and then run on single rate.

Do you really use so little heating (and hot water if that off peak immersion het cylinder) that SR works better for you - many E7 deals only need c35% night use to beat cap svt.

And even in summer for many with hot water storage cylinders just hot water will make e7 cheaper.  Especially if tank feeds shower.

My hw tank and shower add to c3-4kWh per day over half my summer average use.

And again you might save a (i suspect very) small amount on losses from a cooler cool surface by heating just before heat demanded but that heat is still in your rooms anyway.

Ildhund

Scot_39 said:

Do you really use so little heating (and hot water if that off peak immersion het cylinder) that SR works better for you - many E7 deals only need c35% night use to beat cap svt.

It's easy to check the break-even point, so long as there's no big difference in standing charges: just work out

[Day rate — Single rate] / [Day rate — Night rate]

That gives a figure between 0 and 1 which is the proportion of total consumption used during offpeak hours above which E7 will be cheaper.

E.g. using the SVT p/kWh figures for my own region*: E7 Day 27.55, E7 Night 19.09, Single rate 25.11

[27.55 — 25.11] / [27.55 — 19.09] = 2.44/8.46 = 0.288 ≈ 29%

So long as more than 29% of total consumption is used during offpeak hours - not difficult for an electrically-heated household - this Economy 7 tariff will be cheaper. Of course, heating cost will be not much during the summer semester, so it would have to be significantly more than 29% during the winter for this plan to work.

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*  East Midlands. The difference in standing charge is less than £1 p.a., in E7's favour.