economy 7 ponderings

[JimK]

at what point does it start to make sense to be on Economy 7 leccy?

any thoughts/ pointers etc welcome

Cheers JimK

[tim....]

Assuming that you are talking about an existing installation, when your night usage is more than about one half of your day time usage.

Or are you asking about getting a ROI on the costs of updating your space/water heating to store heat overnight, instead of running instantaneously during the day?

tim

[js.b1]

Generally the answer is...

- Do the thermal loss calculations

- Do the capital install & depreciation cost for GCH

- Do the capital install & depreciation cost for E7

The reality is...

- You need insulation levels to current standards

- You are at home all day (work from home or retired)

- You have a flat or bungalow

- You do not have gas available

- You do not want the disruption of GCH re solid floors

The killer for electric heating is any peak-rate requirement :-)

E7-only storage heaters (Automatic):

- Insulation - CWI & Lost Insulation essential

- Size critical - otherwise cold at night

- Reliable - 25yr without maintenance

- Low Depreciation - =A310/yr typically

- No Servicing - =A30/yr

- Ugly - fronts should be "pressed" to look like a radiator, bring back the old folded punched aluminium grills

- Overall - risk of too hot overnight as they "leak" 60% (3 Tog duvet)

E7+Peak storage heater (Duoheat):

- As above

- Reliable - risk of 5-10yr due to electronics & thin film front elements

- Depreciation - risk of 3-5x higher

- No Servicing - =A30/yr

- Overall - less risk of too hot overnight as they reduce E7 charge by using more peak charge

Consider an automatic E7 heater plus separate panel heater is just the same as a Duoheat either without the cost or potentially the same 25yr no-failure reliability of the capillary automatic type.

E7 fan storage heater (Commercial):

- Actually the only type that really work

- Costly - =A3700 for 24kWhr, =A3950 for 40kWhr and a stupendous =A31300 fo= r

48kwhr storage

- Size - 285mm depth is really big

- Wall thermostat or programmer - turns on fan to pull heat out

- No cook overnight - you get heat when you want it

Examples are Creda TSR, Dimplex VFMi, Elnur do a cheaper one without peak-rate boost element. The fan outlet is at the bottom, they hold heat for 3 days, heating on demand. So you would say set a 15oC background temperature, then boost to

16-18-20oC by manual push-button or programmer or occupancy sensor. Germany does a lot of fan storage heaters, lots of variations.

The problem remains even with GCH that there is no (true) radiant source. It is worth considering that when looking at alternatives, it's not just the visual focal point but the radiant heating.

21oC in a room with fan heaters is pretty miserable even whilst warm, 19.5oC with a radiant heater is better (not the halogen rubbish, I mean a proper radiant type like Tansun - not practical indoors).

The future will eventually be electric heat pumps with CO2 compressors (twin scroll, DC invertor, continually varying output vs cycling). They will be 9-14kW output feeding a large thermal store. Potentially used in series to boost output temperature - existing R410A heat pumps suffer due to low CoP at low temperature and so really need underfloor heating re 45oC output or two heatpumps in series for conventional undersized radiators. There will still need to be a boost on cold days unless CO2 heatpump (they go to CoP parity only at -25oC), that could be handled by E7 element with some peak usage.

E7 is good for hallways with leakage into bedrooms, in an otherwise well insulated house. E7 in a living area really needs a balance of E7 combined with peak, Duoheat has breakdown risk & cost, conventional Automatic have ugly aesthetics but reliability and ease of adding another heater. Size correctly E7 NSH work ok, just not brilliantly. The only systems that really work are the big commercial units - but their depth is an issue. Germany "fits them in many packages" and variations re leakage levels. A widespread E10 system would work well - that requires nukes because the windmill crowd just can't create the kW required for an entire country (nor could the distribution system handle it). We are adding future cost to the grid, without considering how to pay for it. Nukes are the only practical solution.

[js.b1]

Oops, you mean E7 electricity.

E7 Day/Night rate varies around the UK.

- eg, Non-E7 unit may be 10p

- eg, E7-Day unit 12p, Night 5p

Say you use 7000 units per year.

- 7000 at standard rate 10p =3D =A3700/yr

- 7000 at 30% Night at 5p =3D =A3105, 70% Day at 12p =3D =A3588, Total =A36=

93

- 7000 at 40% Night at 5p =3D =A3140, 60% Day at 12p =3D =A3504, Total =A36=

44

- 7000 at 45% Night at 5p =3D =A3158, 55% Day at 12p =3D =A3462, Total =A36=

20

- 7000 at 60% Night at 5p =3D =A3210, 40% Day at 12p =3D =A3336, Total =A35=

46

E7 Day/Night is a 7hr period typically 12am-7am. Norweb I believe do E8, no idea if still available (or legacy).

There is E10, but it can have restrictions and only a few offer it re competition.

Tumble Dryer.

- Auto-Sensing Tumble Dryer is 3.7kW usage

- Used daily for 365 days =3D 1350units

- 1350 at standard rate =3D =A3135/yr

- 1350 at E7 Night at 5p =3D =A368/yr

- 1350 at E7 Day at 12p =3D =A3162/yr so beware running during day :-)

Washing machine uses less. However you have other baseline loads like fridge-freezers, perhaps water heating etc.

Note that on-peak heating is 20% more expensive during day than non- standard rate.

Typo re other post E7 heating, Creda TSF (commercial) not TSR (domestic).

[JimK]

Yes, I was toying with the idea of doing just that but it seems space heating is the only realistic way of reaching that tipping point?

Cheers JimK