Economy 7 Trick

pob1976

Hi, if you are on Economy 7 and have a freezer, try getting a timer and setting it to switch off at 9pm and back on at 1pm, freezers are so well insulated they hardly lose any cold and if they lose a few degrees in this time it dosn't make much difference. During Economy 7, the freezer switches on and gets to its original temperature quickly, but in the cheaper tariff. I have been doing this or 6 months now, and you don't get any extra frost build up, so 4 hours a day in Economy 7 soon adds up over a year.

Cardew

p!!!976 wrote: »

Hi, if you are on Economy 7 and have a freezer, try getting a timer and setting it to switch off at 9pm and back on at 1pm, freezers are so well insulated they hardly lose any cold and if they lose a few degrees in this time it dosn't make much difference. During Economy 7, the freezer switches on and gets to its original temperature quickly, but in the cheaper tariff. I have been doing this or 6 months now, and you don't get any extra frost build up, so 4 hours a day in Economy 7 soon adds up over a year.

I assume you mean back on at 1am? (not 1pm!)

Whilst the principle is sound, the savings are nowhere near the difference between 4 hours at Economy7 rates compared with 4 hours at daytime rates.

This is because the thermostat cycles the compressor on and off and most of the time the freezer is using no power.

The average freezer will use about 1kWh(i.e. 1 unit) per day. So in any 4 hour period the freezer will use on average 0.16kWh.

So your savings per month would be approx 5kWh on E7 rates as opposed to daytime rates - say 35 pence.

Valli

I've always just left mine on - and always found I made a saving anyway. At one time it was the ONLY thing I had running through the night (when I first left home and got my own house) and I still saved...

pob1976

Cardew wrote: »

I assume you mean back on at 1am? (not 1pm!)

Whilst the principle is sound, the savings are nowhere near the difference between 4 hours at Economy7 rates compared with 4 hours at daytime rates.

This is because the thermostat cycles the compressor on and off and most of the time the freezer is using no power.

The average freezer will use about 1kWh(i.e. 1 unit) per day. So in any 4 hour period the freezer will use on average 0.16kWh.

So your savings per month would be approx 5kWh on E7 rates as opposed to daytime rates - say 35 pence.

Hi there, was an example, my freezer manual says it can be off for 11 hours without the food spoiling, so its possible to increase the off time, although the saving might be small, it adds up if many people do it.

grahamc2003

p!!!976 wrote: »

Hi there, was an example, my freezer manual says it can be off for 11 hours without the food spoiling, so its possible to increase the off time, although the saving might be small, it adds up if many people do it.

You have to be careful(ish) with this. It's a problem which smart meters face when, in the future, deciding whether or not to turn your fridge or freeze off. You could easily breach the temperature range you have set by your strategy (admittedly it probably wouldn't be the end of the world if you did, but may leave those implementing the 'smart' grid - which effecitvely could do the same thing - open to legal action if someone got ill.

The problem is your fridge (better to use this as an example rather than a freezer) may be set to keep temperatures between 2C and 4C (for example). If you come along at 9pm and turn the supply off, then there's a risk you're already at the upper end of the tempertaure range(4C) and the fridge was just about to click on. Obviously, the fridge will continue to rise in temperature, breaching the upper limit, for another 4 hours when your timeswitch again supplies the power and thr fridge turns back on. The internals may then be at 6C, or even higher if the door has been opened a few times and it's a warm evening.

I'm sure, these days, elf and safety would have something to say (should they ever be able to understand the situation). In terms of a 'smart' grid, it illustrates the problems those implementing it may face. If someone falls ill the next day, you can bet at some stage, someone will sue the 'smart' grid people if they turned their fridge off. Presumably, the smart grid logic would ensure the upper temp limit was never breached by continual monitoring of it, but with your strategy and doing a similar thing manually with a timeswitch, that monitoring would be missing.

zeupater

grahamc2003 wrote: »

You have to be careful(ish) with this. It's a problem which smart meters face when, in the future, deciding whether or not to turn your fridge or freeze off. You could easily breach the temperature range you have set by your strategy (admittedly it probably wouldn't be the end of the world if you did, but may leave those implementing the 'smart' grid - which effecitvely could do the same thing - open to legal action if someone got ill.

The problem is your fridge (better to use this as an example rather than a freezer) may be set to keep temperatures between 2C and 4C (for example). If you come along at 9pm and turn the supply off, then there's a risk you're already at the upper end of the tempertaure range(4C) and the fridge was just about to click on. Obviously, the fridge will continue to rise in temperature, breaching the upper limit, for another 4 hours when your timeswitch again supplies the power and thr fridge turns back on. The internals may then be at 6C, or even higher if the door has been opened a few times and it's a warm evening.

I'm sure, these days, elf and safety would have something to say (should they ever be able to understand the situation). In terms of a 'smart' grid, it illustrates the problems those implementing it may face. If someone falls ill the next day, you can bet at some stage, someone will sue the 'smart' grid people if they turned their fridge off. Presumably, the smart grid logic would ensure the upper temp limit was never breached by continual monitoring of it, but with your strategy and doing a similar thing manually with a timeswitch, that monitoring would be missing.

Hi

I tend to agree with the referenced post. The freezer thermostat could possibly be reduced in order to extend the period which the unit could safely store without power, however, attempting to do this with a refrigerator will cause frost damage to some foods (salad etc) and freeze liquids such as milk, so it's not really a viable option.

Regarding the 'smart-grid', it's almost certain that smart-grid operators will be required to both have a maximum 'off' time and a minimum period between 'power-saving' events in order to protect consumers (and themselves !) against any such issues ...

HTH
Z

pob1976

grahamc2003 wrote: »

You have to be careful(ish) with this. It's a problem which smart meters face when, in the future, deciding whether or not to turn your fridge or freeze off. You could easily breach the temperature range you have set by your strategy (admittedly it probably wouldn't be the end of the world if you did, but may leave those implementing the 'smart' grid - which effecitvely could do the same thing - open to legal action if someone got ill.

The problem is your fridge (better to use this as an example rather than a freezer) may be set to keep temperatures between 2C and 4C (for example). If you come along at 9pm and turn the supply off, then there's a risk you're already at the upper end of the tempertaure range(4C) and the fridge was just about to click on. Obviously, the fridge will continue to rise in temperature, breaching the upper limit, for another 4 hours when your timeswitch again supplies the power and thr fridge turns back on. The internals may then be at 6C, or even higher if the door has been opened a few times and it's a warm evening.

I'm sure, these days, elf and safety would have something to say (should they ever be able to understand the situation). In terms of a 'smart' grid, it illustrates the problems those implementing it may face. If someone falls ill the next day, you can bet at some stage, someone will sue the 'smart' grid people if they turned their fridge off. Presumably, the smart grid logic would ensure the upper temp limit was never breached by continual monitoring of it, but with your strategy and doing a similar thing manually with a timeswitch, that monitoring would be missing.

Thanks for that info, I wouldn't do it with a fridge as the temperature is much higher and a fridge is no way as well insulated as a freezer, so it would warm up too quickly which isn't good for your food.

zeupater

p!!!976 wrote: »

Hi there, was an example, my freezer manual says it can be off for 11 hours without the food spoiling, so its possible to increase the off time, although the saving might be small, it adds up if many people do it.

Hi

Regarding this ... the manual will be written to inform the user that the freezer contents will still be safe after a power failure of this period. Freezer storage times without degradation of food quality are related to the storage temperature, that's what the star rating on a freezer describes. A four star freezer maintains a temperature of -18C which will store most food for 12 months, but if, as a result of your energy saving measures, the temperature regularly rises to -12C your food will degrade by the same amount in around one month, and at -6C in around a week, so depending on the value of the contents of the freezer, this could possibly be a very poor moneysaving idea .....

HTH
Z

Cardew

zeupater wrote: »

Regarding the 'smart-grid', it's almost certain that smart-grid operators will be required to both have a maximum 'off' time and a minimum period between 'power-saving' events in order to protect consumers (and themselves !) against any such issues ...

HTH
Z

I think the intent of the 'smart-grid' it is only the items with heavy consumption that will be switched off and then only for minutes.

This is some information for my place in the USA where peak demand is late afternoon in summer when aircon is required.

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Ben84

Freezer manufacturers may advise that their contents are safe for a certain amount of time during a power cut, but this advice wasn't given with the expectation of a power cut every day.

I'd be concerned about problems from ice crystals forming in food (crunchy ice cream is the worst!), to reduced life span of food, as well as thawing and refreezing water possibly causing an ice build up inside the freezer that could stop it working.

The actual cost to use your freezer may not be that much either. Very old models may use £100 a year, newer ones with high ratings may cost £30. Potential savings with a modern appliance are small. However, while savings look better with an older one, the lower insulation, which is largely why it uses more, makes the potential for increasing in temperature while off much greater.

podcake

there is another thought here, that suggests this could well be false economy. Its the old you never get anything for nothing scenario.

Firstly: apologies if this sounds too technical, i've tried to make it accessible to all

the way heat transfer works is not linear, it is all to do with the difference between the hot place and the cold place. it will drop off faster the bigger the difference. By the same token it takes more and more energy to keep the difference greater (imagine how it takes more fuel to drive faster). This is helped along the way by the insulation used, because the rate of drop off is relative to the conduction of the insulation ( if its thicker/better the freezer stays cooler for longer). This works exactly the same in reverse because all of the things in the scenario are attempting to hit equilibrium ( get the same).

it is generally the case that it is better to keep the difference in temperature 'topped up' because you are just using a small extra bit of energy every so often. The key point is that the fridge/freezer can only provide a given amount of 'cooling energy' because the pump is only a given power. It is designed to provide that small extra bit of cooling every so often. If you let your fridge/freezer cool off to the point where the pump HAS to kick in now it may well not be capable of cooling the thing enough in the time required before the 'unsafe' temperature is met, not to mention that it could be on for a LONG time trying to 'catch up' on what it is meant to be doing. So instead of little bursts to keep it going you are making the device work hard every day, putting it under extra strain which will wear it out faster, risking your food not being kept frozen and otherwise saving a few pence..

to use the car analogy, its like setting off up the M1 (lets assume it to be empty) and accelerating to 70, turning the engine off (assuming you don't need it for brakes etc..) and coasting for a while until you hit what you think is about 20mph (the minimum speed for motorway use), turning the ignition back on and accelerating hard until you get to 70 again.. repeat ad-infinitum, I will guarantee that you will certainly not save any fuel this way...

Another point of note is that this method might work to some degree on a chest freezer that is kept closed throughout the 'off time' as the cold will tend to collect in the body of the freezer. an upright ('hot air rises'), if you open the door, will lose a vast quantity of its 'cool' out onto the floor as the hotter air comes in to replace it (ever noticed how freezers tend to have solid drawers? its an attempt to minimize this effect). So an upright that you use during the day (i'm willing to bet) WOULD become unsafe for food, and would need some sort of emergency kick in to prevent any harm to the user..


A FAR better scenario if you wish to save some money in this way is as follows:

replace your freezer with a 12v model (they DO exist) and install a large lead acid battery, sufficient to power the thing all day, once that is in place connect a decent sized battery charger to the mains on a timer, which will charge the battery at your cheap rate. This way you get cheap electricity, safe food and little wear and tear to your freezer.. win win. (although the cost of setup, the life of the battery and the electricity saved will most likely cost you far more than just leaving the freezer turned on)