Off-peak circuits for storage heaters

[Tim Streater]

I'm trying to get to the bottom of why our Village Hall is using lots of daytime kWh even though the hall's not being used and it has Economy 7.

Looking up the storage heaters it's using, the User Manual talks about that they should be connected to an "Off-Peak circuit". Is this supposed to mean a circuit that is only live during off-peak hours? There is a radio-unit to switch to off-peak, but I can't tell whether that's just switching the meter or enabling power to a particular circuit as well. The wiring is complex (someone else is getting a sparks to take a look), so I can't tell whether the three storage heaters are all on the same circuit or not.

I was assuming these things had timers but they haven't, so my theory that the frequent outages here meant that the timers needed resetting is obviously wrong.

[Chris Hogg]

In my previous bungalow, I had E7. There were three storage heaters (I soon took out two of them). At approximately midnight, the whole house, including storage heaters, went over to E7, so as well as the heaters you could run a washing machine, dish washer etc. on E7. But after the seven hour period, the storage heaters were disconnected and the rest of the bungalow returned to the standard rate (actually a slightly higher rate). So the storage heaters had to be on a separate circuit to the rest of the bungalow but one that was controlled by the same time clock. IYSWIM!

[Michael Chare]

To benefit from Economy 7 you need something to ensure that most power is used during the off peak period. For example you could have a timer for the storage heaters that ensures that they only operate during the off peak period. The timer or timers would need to be suitably rated for the amount of current that the storage heaters are likley to draw.

[Mark Carver]

Yes. My parents 1966 house is like this. There's a spring reserve time switch, which energises the 'Off Peak' circuits. It has drifted over the years to such an extent, that the heaters now come on during the day. The October 1987 hurricane, and 6 day long power cut, saw to that !

[Tim Streater]

I suspect timers will be needed, except that like the one that we have at home to occasionally control the immersion heater, it would be mains powered so any outage means it will go out of sync. If there really is a circuit which is only live during off-peak, then any connected to that wouldn't need a timer, obvs.

[Tim Streater]

The switch at the Village Hall is radio controlled so it will switch at the right time, but it's useful to know that circuits meant for off-peak such as storage heaters are actually only live during off-peak.

[Fredxx]

I thought E7 meters had a switched output, and the supplier gets to choose your 7 hours.

[tim...]

that would be the normal way of wiring them

It should also be configured to switch on the SR circuit

It really shouldn't be (unless they are the sort of SR with a fan)

During the day time the SR circuit should be completely dead.

It isn't difficult to check with a circuit tester

OTOH if the have a fan then they should have two circuits - one to power the heating elements and another to power the fan

This can't have just gone wrong

If it is wired wrongly you would have noticed before

It should be using the same timer that switches the day/night rate

so if it does go wrong then you will simply be getting you night rate at the wrong time. The SR should switch on/off at that time

OTHO if the are on a different timer then they can get out of sync. but that wouldn't be the normal way of doing things

[Martin Brown]

Now there is no real danger of frost why not isolate them for the summer? Fitting an Owl monitor to your supply will let you figure out what the power hogs are. About £40 will easily save you that much in the first year if our experience is anything to go by.

Hot water for kitchen or toilets would by my first guess. We have been running heating on frost stat most of the winter but that is mostly using night time electricity to hold a minimum of 8C.

Daytime the feeble winter sun through double glazing almost holds it at that. Now it is spring the sun is enough to warm it up nicely.

Newer ones seem to have two feeds. One off peak and one for use at other times. Ours are not storage heaters but they are fed by a two phase mains system that somehow treats evenings and weekends as different from daytime. I have never entirely understood how it does that. The smart meter knows the time (previously it was a clock in a jamjar thing).

Ours heaters have individual timers although they can also be controlled by a common control wire from a single external master controller. I caught one trying to warm the room up for non-existent classes a while back. User error when reprogramming hadn't cancelled some events.

Their programming interface leaves a lot to be desired. The most useful manual one is "advance" which puts them on until the next set point (or for a multiple of hours if you press several times). I have set points on them for end of typical sessions so it is difficult for casual users to accidentally leave them on. Academic at the moment.

[Jack Harry Teesdale]

The Economy 7 installation in premises such as village halls can be somewhat different to domestic premises as they will be classed as 'commercial premises'.

The consequence of this is that dependant on whether the Supplier has fitted a meter with a full load switching timer or more commonly just a 'Tele-switch' which will only switch the meter register over. In these cases a load switching 'contactor/timer' would be required to actually switch the storage heater load on an off. This could mean the haters could be 'on ' out of synch with the meter timer.

[Tim Streater]

By complex I mean that today I went to have a look at it, assuming naively that I'd be able to figure everything out. Wrong. The wiring is complex because it's an old hall, used to be a post office but now isn't, has had wall heaters added some years ago, then a single storage heater, then two more. So there are three customer units, with some but not everything labelled. I'm in no position to deduce what is connected to which circuit.

My job is limited to reading the meter and choosing the next supplier when the contract expires. It costs a lot to run in winter, as it's a wooden structure with walls about a micron thick. Everyone had put the cost down to the poor insulation, along with needing to have some low level overnight heating in winter to preserve the structure.

What's happened now is Covid. So we have a long period with the hall unused which therefore started *after* last winter. So now this winter my expectation was that the night consumption would be more or less as usual, the day consumption would be just a few kWh or less between monthly reads, as odd bods popped in to check things. What I in fact see is average *daily* usage as follows:

Day: 22.3 kWh Night: 11.5 kWh

Obviously incorrect. So I've escalated this to the Hall management.

The storage heaters (Dimplex, 2 x XLS6N and 1 x XLS18N) have no timers. Which is just as well else every time the volts go off we'd need someone to go in and reset them. That this was the problem was my initial assumption.

[Martin Brown]

It might be right if your hall is as poorly insulated as you imply.

Do check that you haven't got an immersion heater on somewhere though.

FWIW as another datapoint our large hall on frost stat was averaging daily use during the cold snaps this year (I only have weekly numbers):

Day: 11kWh Night: 6kWh

That is for a solid wall Victorian brick build with a fully insulated loft and double glazing but obviously solid walls with no insulation.

I have just this week isolated them but left the frost stat settings in place just in case there is another cold snap. You could easily triple or quadruple that if the hall was actually in use. Heating it up uses

20kW continuously until it reaches working temperature ~1-2 hours.

[Tim Streater]

Yebbut the hall is not used. No reason for any daytime consumption at all.

This is a good point to check.

[Martin Brown]

Frost stat may well override all other considerations (and you want it to) a burst water pipe due to a penetrating frost would be expensive. It depends on the limit set but our insurance requires a minimum set of 8C. (and weekly logged inspections)

It has been colder than that during daytime for a few weeks and only recently become warm enough for it to back off to almost nothing.

I recommend putting an Owl on the service supply so you can see in real time how much current the building is drawing. Stops people walking away and leaving the plate warmer or immersion heater on. The sensor has a wireless display so you can put it near the exit point to remind people.

[Alan]

You need to read the user manual of the heater. The ones I fit do have an in built timer, to allow the user to adjust when it is on/off etc. The peak supply should be live at all times, this controls the fan and possibly timers within the unit. If the peak supply is turned off, they will not work at all. Make sure the peak and off peak supplies are connected to the correct terminals. The off-peak supply will come at around midnight until 7am. There is a boost facility on the ones I fit which uses the peak supply to warm an element and blow the hot air out with the fan. This can get expensive if used a lot. Also, the temperature they are set to makes a difference, if they are set to full power, they will likely go cold around 4pm, so may be using the peak supply to top them up.

We had a problem with a new heater, which was only getting lukewarm. A call to Dimplex's call centre got me sent a Tech. Document, which showed that if the temperature is set to, say, 10 degrees, the heater is smart enough to know it only needs to warm up the bricks to , say, 100 degrees, rather than the 200 degrees if set at 20 degrees. The Tenant was turning the heater down to 10 degrees when she went to bed,then, the next day at 8am, she'd turn it up to 22 degrees, and the heat would be gone at 12 noon. None of that was listed in the User / install manual.

[alan_m]

I have timers with inbuilt backup batteries/cpacitors that maintain the time (but not necessarily any switching) during a power cut.

[Paul]

There's a couple ways to get time info.

1) LF radio transmissions.

2) GPS.

At least the LF radio method, is available in retail goods (wall clock with self-synchonizer).

I don't know if there are any broad product lines of self-synchronizing timers for switching loads or not. If such existed, it would save you trips to adjust the dial on the old electromechanical kind.

I have a GPS set up here, and it sets the time on this computer (instead of NTP). The GPS just "looks out the window", and isn't a proper external mount.

Paul

[AnthonyL]

I had an office with storage heaters on the Off-peak circuit. When I had new meters installed (not at my request) Eon connected them the wrong way round. My daytime usage, a few cups of tea and a couple of computers and lighting went through the roof and my nighttime usage dropped to - well a few cups of tea etc worth. It took quite a bit of persuading that firstly I was right and then they should come and fix it but I think I got some compensation for the trouble in the end.

Surely you can experiment by turning heaters off/on?

[invalid unparseable]

My off-peak time switch has done the same thing after several power cuts in recent times. If I get the electricity company in to re-set the clock will they try to instal a smart meter (which I don't want)?

- Mike

[Tim Streater]

<noise of sucking through teeth> Not my department, Squire. More than my job's worth etc etc.

More seriously - I have told the Chairman of the Managemnt Cttee. He arranged for the installation of more storage heaters in the first place, and is getting an electrician in to check everything related. He should know what questions need answering.