economy 7 on prepaid meter for a 1.6kw heater Does this sound correct?

oneiloneil

if a single 1.6kW storage heater will use £0.37 per hour x 7 hours = £2.60 per 24hr period (as 7 hours charge should provide enough).

And, do you know what it is for prepayment meter on economy 7 also please?

oneiloneil

Im asking if my calculation is correct, but also I wondered what the rate is for eco7 on prepayment meter for a neighbour.

Jyana

oneiloneil said:

Im asking if my calculation is correct, but also I wondered what the rate is for eco7 on prepayment meter for a neighbour.

Where do they live, who is their supplier, and are they running it overnight or using the day time boost that some storage heaters have? It could be anything from (roughly) 10p to 80p an hour depending on those answers.

ETA: Seven hours over night should be enough if it is sized for the space it is heating, and the controls on it are utilised well. 

ariarnia

agree with jyana your math looks right but if its actually right depends on your region and supplier (theres not much difference with single rate energy under the cap but theres still a lot of difference with e7 and there also changing from jan)

also dont forget the standing charge on your electric in your total sum for your bill. and 5% vat. 

oneiloneil

the supplier is sse / ovo. the area is Corsham, Wiltshire. The heaters are modern elnur hhr40. 
My Neighbour hardly ever uses his heater, but did so during the sub zero temperatures two weeks ago. The ancient building with 2ft thick rubble filled walls, heated from just one heater in just one room, (understandably or not), didn't raise his room temperature above 17 degrees. He's now turned it off saying it cost him £12 a day which I disputed, as I assumed the unit would only consume 11.2 kWh. 
It's probably running for much longer than the initial 7 hours eco charge time setting. 

ariarnia

yes. if the unit is contantly on using the boost function because the person is cold then it will use more than the 7 hours of night rate energy and will be charged at the higher day rate. to work out your sums we would then need to know how long it was actually on during the day and during the night. 

if you are saying it SHOULD be enough just the 7 hours then one thing that might be worth thinking about is heating a cold house takes more heat than keeping a warm house warm. sp that could be why the 7 hours wasnt enough. 

we have thick walls and in winter if we go away for a few days we turn the (gas boiler) heating off or down to that frost protection setting. when we come home the house can be not 'to temp' for a good 48 hours because we have to heat the bones of the house and chase out any damp before it gets back to just maintaining the background level if heat in the air.

it will be the same with the storage heater heating 2 foot thick walls. if your neighbour runs the heater every night to charge and uses that energy in the day to heat they might find it doesn't get past 17 on the first couple of days but after that the 7 hours is enough to keep the house comfortably warm all day and night. 

Scot_39

oneiloneil said:

the supplier is sse / ovo. the area is Corsham, Wiltshire. The heaters are modern elnur hhr40. 
My Neighbour hardly ever uses his heater, but did so during the sub zero temperatures two weeks ago. The ancient building with 2ft thick rubble filled walls, heated from just one heater in just one room, (understandably or not), didn't raise his room temperature above 17 degrees. He's now turned it off saying it cost him £12 a day which I disputed, as I assumed the unit would only consume 11.2 kWh. 
It's probably running for much longer than the initial 7 hours eco charge time setting. 

a) It could well be using far more than a peak of 1.6kW / 11.2kWh during E7 charge

The one link I found to an Elnur HHR40 - suggested it was a 3.5kW input model.

https://www.elnur.co.uk/wp-content/uploads/2020/04/Elnur_ECOMBI-HHR_User-Guide.pdf

The 1.6kW is actually quoted in the manual p10 - but this is its heat / i.e. output rating  - not the input power taken whilst charging.

That manual - if correct device - actually states 24.4 kWh input on E7 - thats maximum of 7 hrs @ 3.484kW.

b) Boost Mode ?

Difficult to say - but looks like if the £12 due to just the one heater - maybe have been on day rate boost too for part of time.

These modern heaters are not the same as old charge bricks to temp devices.

They are often by design part NSH / part panel heater - as implied by Combi in this model names' case ?

Day unit use is part of the new heaters design - if wired / configured to do so - if not able to achieve set temperature based on night charge alone (the manual says default 21 degree daytime programmed)  (or as often the case initially - after switch on - or a fast loss change - e.g. external temperature drop).

Other Smart HHR's have a daytime boost mode - and wired by preference to day and night switched supplies - not delved into the programming manual - in full detail - but this implies it also does - via the 1.1kW "balancing" element

"the percentage of charge
the heater tried to take last period and how long the
balancing element has been used for during the last on
peak time."

Perhaps they could look at that figure the next time they try - or just compare their day and night usage before / after - preferably in kWh - not £/p.

c) Pricing varies a great deal between E7 suppliers within and between regions - and also by payment method - so actual price difficult to predict.

E7 tariffs vary wildly - seen c5p-20p+ quoted ( night rates - days c55p->40p to balance) - depending on supplier / very regional / payment dependent with EDF - others ?.

Even at say a highish 24p/kWh E7 night rate - 25kWh = £6 - not the quoted £12.

If the balancing element is as appears a 1.1 kW heat boost - that could in theory use another (17*1.1) 18.7kWh - at day rate - and that could in theory be another - say £8 at 45p/kWh day. 

Obviously this mix could start very high on balance power (peak rate?) if just switched heater on - say in morning without a prior night charge - but over say days - the off peak charging should take over - so most - if not ideally all - charge is via E7 rates.

Comparing and talking kWh (energy used) more likely to provide useful guide answers than prices - that can then be multiplied by their tariff rates.

You are however basically right - Energy Used (kWh units) = Rated Power (kW) * Time Device on (hours)

As long as you use the correct power - the input power for NSH the key.

Total Power Needed

** The heater should have ideally been rated for the space size and house type - but it seems unlikely to have been assumed the only heater in the flat/home etc

Others with a more similar wall type - may be able to give their typical whole house daily kWh.

My 3 NSH heaters were in total using 20-25 kWh during the recent cold snap - and by no means in coldest part of UK - for a pretty small 2 bed modern mid terrace with old DG etc. And that was to get fairly low temp = keeping Living Room at 17-18, other rooms 15.

And in order to charge initially - add say 5kw+ or c20%+ on top for 1st 24-48hrs - in my case all off peak.  In your cases - possibly not.

Scot_39

One thing I forget to add was, based on 1.1kW balance and 3.48kW main storage element.


That device could in theory take 18.7 peak +24.4 off peak kWh = 43.1 kWh.

As to whether it really ever would is perhaps questionable.

Sounds a lot, but the quoted heat output is a nominal 1.6kW, which if were to be maintained for 24 hrs = 38.4 kWh.


So the true cost answer is likely to be far more than your 11.2 kWh.

But probably less than the theoretical max.

But as room never got fully hot, to match the set temperature ?, it may well have been regularly over the 24.4kWh E7 max (* assumed off peak feed).

Itself over double your 11.2 figure.



May well be worth your neighbour checking time and temp profiles if not tweeked after install.

Manual Default 18 night, 21 day profile seems a little high for many.  But does match age uk for elderly or nhs upto for young and old / immobile etc etc.

15/ 18 for instance might be enough for many.

And a 1C change been estimated to save £100-150 by some annually on generally cheaper (unless have a very cheap E7 night rate ) GCH home.

Gerry1

Is the neighbour's heater connected to two supply circuits (one E7, one 24-hour) or just one (24-hour)?  If there's only one circuit it relies on the Elnur having been correctly programmed to mimic the meter's E7 switching times.

Unless the neighbour is something of an anorak, a single-circuit heater will almost certainly not have been programmed correctly.  Even if the installer was knowledgeable and diligent enough to have checked the switching times in the relevant DNO area, that may not be sufficient: the actual times can vary from meter to meter, and meter timings can drift.  It's highly unlikely that the installer was present to confirm the meter switching times around midnight and 7am !

Similarly, the user guide does not not explain how to program the switching times for a single circuit, it's only in the installation guide which the neighbour probably won't study or it may not even have been left by the installer.  The default times are midnight to 0700 so if there is any variance from the actual switching times then the neighbour will be paying too much.

The default setting allow five hour of peak rate topping up, so this could also wipe out most or all of the E7 savings.

Clever HHR NSHs such as Elnur and Quantum can be a good solution for small all-electric properties, but can be an expensive nightmare on a single circuit unless perfectly programmed.

oneiloneil

Thank you all. Your answers have cleared up many of my wrong assumptions. 
I'll offer to check his 24hr consumption the next time he uses the heater. 
It has 2 separate power feeds, and the off peak time clock matches the off peak set up on the unit. 
From what's been said here, it will potentially draw 7 x 3.5 KW (24.5 KWh) during off peak, and release this at 1.6 KW per hour for 24 hrs (38.4 KWh). meaning it will draw a further 14 KWh from the peak rate electricity.

My advice will be to turn his unit on at least 2 days before the cold weather hits again, running it at a constant 18 degrees. When the cold arrives, his comfort override can be used when he feels he needs a boost. 

ariarnia

oneiloneil said:

Thank you all. Your answers have cleared up many of my wrong assumptions. 
I'll offer to check his 24hr consumption the next time he uses the heater. 
It has 2 separate power feeds, and the off peak time clock matches the off peak set up on the unit. 
From what's been said here, it will potentially draw 7 x 3.5 KW (24.5 KWh) during off peak, and release this at 1.6 KW per hour for 24 hrs (38.4 KWh). meaning it will draw a further 14 KWh from the peak rate electricity.

My advice will be to turn his unit on at least 2 days before the cold weather hits again, running it at a constant 18 degrees. When the cold arrives, his comfort override can be used when he feels he needs a boost. 

remember thats up to the settings (three things really). and that's the bit thats hard to get right. 

if the input on the night rate circit isnt set to max then it wont draw as much as it can overnight. if its cool but not freezing in spring or autum then you might not want to fully charge them every night. 

if the input on the second feed is turned off then it wont draw extra power when it gets low during the day (and you can choose just to boost it for an hour if you need to by manually turning it on). it'll just release the heat from overnight thru the day until it goes cold when it runs out.  

and if the vents are closed first thing in the morning and opened when it starts to get dark then it wont release the heat until later in the evening. or you can even open them a bit in the morning then close them down and not open them again until evening. like setting the timer on a gas boiler. so the room can cool a bit when you're not in there and you can 'save' the heat for when you want it later in the day.