Economy 7

[hard-work]

There are two basic types, vented and unvented, the latter needs to be serviced more often, he had two I think around 300 litres each, with all the bits looked more like this

product Diameter 545 mm product Height 1980 mm you are looking at around £2000+ for a system like this plus fitting, in the main they are used when people want to also use wood burners, the major problem with all fires burning unprocessed wood or coal is particular emissions, to stop this either you burn charcoal or coke or run the wood burner at a set rate so neither is a lot of heat wasted up the flue nor does it produce particular emissions. So wood burner used once a day and the heat is stored and distributed when required.

This is really the same as using off peak power, it's a way to store heat until required. However those who use wood burners are either a bunch of thieves stealing wood from anywhere they can find it, or save the earth nuts, and even if the money it costs to fit the wood burner will take 50 years to get back, they will still fit them so show off to visitors how ecological friendly they are.

£2000 will buy a lot of electricity, so in real terms can't see one of these paying for its self in a flat, in a 5 bedroom house with solar panels on roof and wood burner in main room these may be an option, but in a flat just a pipe dream.

Can only be electric. How big is his house to warrant two 300 litre stores? I am considering a DHW only thermal store and a thermal store/buffer for UFH. So maybe 140 litres of DHW only thermal store and a UFH cylinder, both open vented. Cannot be more than say 5 foot high for either. With UFH the floor temperature is setback overnight. When operating overnight it will be on Economy 7 direct, not operating on stored energy for an energy store, that is reserved for day use. So the store has to be big enough to cope with day demand of UFH.

 

[JohnW2]

Mine used to make a fair old "bang" when it engaged also. Was quite alarming at first but you did get a clear indication of when it was off-peak!

In fact, I never had a contactor, but the electro-mechanical time-switch made a "bang" that could be heard in most parts of the house when it switched!

ISTR the timings did used to go a bit off around BST changes - although I can't remember specifically, I'm sure it sometimes shifted a week earlier, but I'm struggling to see why it would do now!

Throughout the 30+ years I've had E7, both with the electro-mechanical time switch and the electronic timing I now have, the E7 timings have remained on GMT throughout the year. Hence my cheap-rate period is roughly 00:30 - 07:30 (clock time) during the winter and 01:30 - 08:30 (clock time) during the summer.

Kind Regards, John

 

[JohnW2]

Can only be electric. How big is his house to warrant two 300 litre stores? I am considering a DHW only thermal store and a thermal store/buffer for UFH. So maybe 140 litres of DHW only thermal store and a UFH cylinder, both open vented. Cannot be more than say 5 foot high for either.

As I've said, even given a very large house, a 140 litre hot water cylinder (only 1050 mm tall, 450 mm diameter) is plenty for my DHW - but I have no idea what would be required in addition to that for however much UFH you would want to service.

Kind Regards, John

 

[SimonH2]

Note that if your E7 setup has a radio teleswitch (which I believe has been standard for ages) then cheap rate times will be indeterminate. AIUI your supply contract will not specify when you get cheap rate, only that you'll get at least 7 hours, in no more than 2 periods, between certain times overnight. If you use a simple timer then you run a good risk of having something turned on when you are on expensive lecky.
The setup in the offices where I used to work had a circuit (B6 MCB) in the CU in the office, with a T&E going down to the meter room where it went through a switched FCU (for isolation) and then to the switch contacts in the meter. Red core live feed, black core switched live return which operated a contactor. In the office, the circuits for the storage heaters went through contactor contacts - ie the contactor didn't switch a supply to a separate CU, the connections from MCBs were routed through it.

Is there really no way to route even a 1mm² T&E, or even a 0.75mm² round cable between meter room and flat ?
Failing that, I suppose it would be possible to use one of the radio remote control products to relay the meter state to the flat - but it would be messy.

 

[jg321]

Throughout the 30+ years I've had E7, both with the electro-mechanical time switch and the electronic timing I now have, the E7 timings have remained on GMT throughout the year.

I had one that stuck to GMT, and one that shifted. The one that shifted was E10 actually, rather than E7.

Oddly both were in the same DNO area, Rochdale and Manchester City Centre, so both former Norweb. As I may have mentioned before, being in both meter cupboards around the time of switching was quite interesting; hearing them all switch one by one with differing offsets.

 

[JohnW2]

I had one that stuck to GMT, and one that shifted. The one that shifted was E10 actually, rather than E7. Oddly both were in the same DNO area ...

Were they both the same technology? I don't think that there were ever any electro-mechanical ones that had a 'calendar' as well as a clock, so they could not have been changed to/from GMT without human intervention (unthinkably expensive, twice per year for millions of customers). Those with electronic clocks (or radio-controlled tele-switches) presumably could do GMT/BST switching, but my current electronic meter doesn't (as confirmed by E.ONs label on it).

As I may have mentioned before, being in both meter cupboards around the time of switching was quite interesting; hearing them all switch one by one with differing offsets.

Even when I had the electro-mechanical time switch, I've never had any time-related load switching. Albeit extremely clunky and loud, all that time switch was doing was instructing a dual tariff meter to change tariffs.

Kind Regards, John

 

[ericmark]

I am sure it can be worked out, but easy way is look at last years bill. I know my house uses a lot more power than this house I am in now, but it does not make sense, this house is detached and mine is a semi, and this house has a very poorly fitting front door, so one would expect to use less in my house than this house of my mothers, but that is not the case.

It will depend on where the storage tank is, centre of house it does not really matter if some heat escapes, and I suppose you could always add a second latter. But you want whole tank hot not just the top, so look at Willis system, this puts the immersion heater outside main tank and it heats from top down, so after just 10 minutes you have hot water but it will in fullness of time heat whole tank. But you would need to be Irish to understand how it work! It seems English plumbers are too tick.

Oh and I am Welsh. The Willis system (From Ulster) is really good I am told, but for some reason it has not been in general used in rest of UK.

 

[hard-work]

The Willis system is nice for sure, but it is bulky as it is an exterior add on. Being exterior is has more heat dissipation. This new https://mixergy.co.uk is in another league.

 

[SimonH2]

And just to add - the radio controlled systems are also sometimes used for load control. The obvious one is switching loads off when demand is excessive, but also turning them on at odd times (we certainly heard our contractor humming a few times during the day) if it's convenient to add load (yes it does happen).

 

[JohnW2]

And just to add - the radio controlled systems are also sometimes used for load control. The obvious one is switching loads off when demand is excessive, but also turning them on at odd times (we certainly heard our contractor humming a few times during the day) if it's convenient to add load (yes it does happen).

I suppose that's fair enough if what is being switched is metered by a separate meter (at 'low rate' rate) or if the radio-controlled system switched a dual tariff meter (to low rate) whenever it was on - but if it were being used to turn on ('behind my back') large loads which were being metered as 'peak rate', I think I would have something to say (or would thwart the system with some time-dependent additional switching of my own)!

In any event, I thought that we were waiting for the last of the spare valves for the BBC's Droitwich transmitter to fail, and therefore potentially spell the end of the Radio Teleswitching system as we know it - at least implemented as it currently is?

Kind Regards, John

 

[JohnW2]

It will depend on where the storage tank is, centre of house it does not really matter if some heat escapes, and I suppose you could always add a second latter.

Even if the storage tank is in the middle of the house, heat loss can be undesirable (and wasteful) during summer months and during the night in winter. Extremely good insulation is therefore highly desirable.

Kind Regards, John

 

[crystal ball]

No wearing out, cause for a fire if malfunctions, or buzzing because of excessive wear.

If you switch off the meter will not change over to off peak, you would be permanently on the higher rate

 

[SimonH2]

I suppose that's fair enough if what is being switched is metered by a separate meter (at 'low rate' rate) or if the radio-controlled system switched a dual tariff meter (to low rate) whenever it was on

That's what he teleswitch does - it switches the meter over to cheap rate. The meter itself contains a pair of contacts which can be used to control your loads.
So when the teleswitch turns on, the meter switches over to cheap rate, and your connected off-peak loads can turn on.

My reference to the teleswitch turning these loads on/off as load control was to using this mechanism to switch you to/from cheap rate and turn on/off your off-peak loads accordingly. So there is no question of switching on large loads to use peak rate lecky, just potentially giving you extra off-peak time - as I say, we've heard our contactors in the office humming a few times during the day, and been "a bit surprised" by the clonk of them operating.
Of course, we can't rule out a teleswitch just picking up some interference and randomly switching ...

 

[ericmark]

There were some council house built around here with a central heat store, in middle of house there was in essence a very well insulated room with bricks and heater in it, and thermostatic and timed controlled fans which as and when required moved the energy from the central store to rest of the house, the heat store if not used and switched off would keep warm for a week. True electric central heating, however like most hot air systems it has to be installed as the houses are built, it is not really a system you can install latter.

The hot water system however lends itself to being fitted after the building is completed. Also any hot air system moves air to cold areas, so really important to have double glazing, or the costs go up.

The maths is also a problem, we look at a house and we do the calculations and put them into an on line calculator and it tells us we need a 28 kW boiler, so that means since economy 7 only runs for 7 hours every 24 then we need 28/7x24= 96 kW or 417 amp, we know that must be wrong, as only 100A is supplied to a house, the error is with economy 7 we never let the home get cold, so not looking at energy required to heat house from 10°C to 20°C in an hour, it does not matter if it takes 100 hours to heat home as we never let it get cold.

So now move to heat store, we are now allowing house to get cold, then reheat, however there has to be a limit, which is of course amps supplied times 7 hours, so with two immersion heaters, you can use 6 kW so 42 kWh, = 36113500.08 calories, and calorie = the energy needed to raise the temperature of 1 gram of water through 1 °C. So 85°C is upper limit and 25°C lower limit so 60 degrees we can cool the water, so divide by 60 = 601892 now get into litres so divide by 1000 and we have 600 litres of water required to store 42 kWh. Now tank will hold 300 litres so two tanks will hold 42 Kwh.

Now my house originally had a single gas fire in centre of main room which heated whole house, at the time we got largest that would go with a flue brick, what was 5 kW and it did heat whole of house, now your not heating a three bedroom house, so likely only need 3 kW which is a single 300 litre tank, added to that you can use a boost or other electric fires in extremely cold weather, so you only have to calculate for normal.

So why 28 kW boiler with gas, well in the main so it will work an instant shower, you can get 12 kW gas boilers for central heating, but they would not really give enough water for a shower, it would be like using an electric shower and you know how hopeless they are.

OK I have shown the idea of calculating, but clearly every home is different, can't really do it for your flat, but to maintain the temperature you don't need that much power. At 7.1 p off peak 42 Kwh = £3 a day, at 12.6 p normal it would cost £5.30 a day so yes off peak can save you £2.5 a day, but that is the max, it seem likely you will only use half of that or less, and that is only on really cold days, so the saving average through year more likely £1 per day or less. Now for peak you pay 15.2 p not 12.6 so 2.6 p extra so 36 kWh per day time use to break even. As the off peak power use average goes down, so does the break even point.

So if fitting off peak costs £3000 then if you save £1 per day then 11 years before break even, add to that cost of borrowing £3000 and likely it will never pay for it's self. So why bother?

 

[SimonH2]

The maths is also a problem, we look at a house and we do the calculations and put them into an on line calculator and it tells us we need a 28 kW boiler

Not these days ! Mainly (as you mention later) the reason for such oversize boilers these days is to run a shower - leading to a boiler that is grossly oversized for the heating and (because they still don't design boilers for even the 20th century ) will run inefficiently (designed to not condense most of the time).

, so that means since economy 7 only runs for 7 hours every 24 then we need 28/7x24= 96 kW or 417 amp, we know that must be wrong, as only 100A is supplied to a house, the error is with economy 7 we never let the home get cold, so not looking at energy required to heat house from 10°C to 20°C in an hour, it does not matter if it takes 100 hours to heat home as we never let it get cold.

So now move to heat store, we are now allowing house to get cold, then reheat, however there has to be a limit, which is of course amps supplied times 7 hours, so with two immersion heaters, you can use 6 kW so 42 kWh, = 36113500.08 calories, and calorie = the energy needed to raise the temperature of 1 gram of water through 1 °C. So 85°C is upper limit and 25°C lower limit so 60 degrees we can cool the water, so divide by 60 = 601892 now get into litres so divide by 1000 and we have 600 litres of water required to store 42 kWh.

You still have the same issue - only 7 hours to provide the heat needed for the whole of the day. But the house heated 24/7 will need more energy than one that is allowed to cool off when not occupied - simple physics says that a room at (say) 20˚C will lose heat faster than one at (say) 15˚C. The difference with a wet system is that the heat storage is essentially only limited by your space for the tanks and it can provide very rapid heatup with good control. But you still have the same issue of that 7 hours to reheat the tanks - taking your example of 42kWh then that's 6kW, or around 25A. Clearly there's a difference somewhere between the need for a 28kW boiler and tanks that can be reheated with 6kW

I strongly suspect that very very few gas installations actually have any calculations at all - it'll be a case of "house is well insulated, pick a combi and it'll be OK for the heating" I suspect a large proportion of "plumbers" wouldn't know where to start with such calculations anyway.