Wednesday, May 18, 2011

Save £15 per month - check the fridge and freezer

Knowing how much your house uses, without your activity, can be a useful fact for managing costs at home.

Background electricity and refrigeration:

An 'A' rated freezer might be rated with a maximum consumption of 60 watts, however it should still be checked.

Today an energy efficient refrigeration appliance should use 1 kilowatt per day or for really modern appliances, only 500 watts per day.

( Reference links provided at the end of this article )

So per hour that freezer or fridge should be taking 20 watts to 40 watts of power.

It might peak at 60 watts, but that short burst (after you stood with the freezer door open then shut it again), should not affect the hourly average too much.

'A' rated or otherwise - what happens when appliances get old?

Signs of age or wear and tear - refrigerator / freezer:
  • They breech the maximum 60 watts and might even peak at over a kilowatt when refrigerator cycle is triggered.
  • They fail to drop to an acceptable 20 -> 40 watts after the moving part buzzing has stopped.
In the house here, the landlord has an 'A' rated freezer that was left locked on 'overdrive' by the previous tenant. Not sure for how long, but it seems to have affected the efficiency.

The background usage for that freezer alone never falls below 100 watts.

The background usage for that fridge and freezer together sometime sticks at 300 -> 400 watts - way too high.

The fridge has been located next to the cooker, so I imagine it has not had the best time of things either.

Predicting costs - the simplest mathematics you will see:

Get an electricity usage monitor - the type that has a clip you loop around the cable leading to the meter, with a separate display you read off in another room.
( See "What if I don't have a 'clip to supply'" section if you don't have one and don't want to spend out )

Turn off all the devices that are non-background (laptops, computers, televisions, whatever).

What do you read? 100 watts, 200 watts, 300 watts?

Take whatever you read and divide by ten.

( You can round to the nearest hundred and then drop a zero if you find it easier )

Here you have the monthly electricity bill (assuming you all went away on holiday for a month)

Was yours 300 watts so £30? Frightening.

If yours was 500 watts so £50, then you probably have a garage or utility room with some extra fridges or freezers? No. Well seek out an explanation.

The mathematics is simply assuming a 14 pence per kwh cost - not unreasonable in the UK in year 2011.

Rechargeable devices - constant drain:

Modern rechargeable devices should not 'constant drain', once the battery in the main unit is charged, they should draw 1 watt or less.

Rechargeable Caravan vacuum cleaner - a counter example.

The Caravan vacuum upright sits in a recharge housing and uses 8 watts constantly. It is a fault with the design or just wear and tear, but the charging circuit never drops to zero watts.

Going back to the mathematics - that is costing 80 pence per month, whether the device is ever used or not.

Older devices that have constant drain > 20 watts:

  • Non usb scanner ( 25 watts )
       [ lide scanners that plug into a usb port do not waste power in this way ]
  • Sky+ box ( 25 watts )
The Sky+ box is probably a design fault :-
    The hard drive (used for live recording playback), runs constantly rather than spinning up and spinning down again.

If you have a Sky+ box and a non usb scanner, then there is £5 a month in electricity right there.

Do switch them off when not using them, or upgrade to more energy efficient alternatives, which don't 'constant drain'.

What if I don't have a 'clip to supply' electricity monitor - they are expensive?

In that case you probably have time rather than money at your disposal - you will need an hour.

Pick a time when all the people in the house are out and you only have background electricity usage.

Read off the current kilowatts used on the electricity meter, wait an hour, read again.*

*Remember that often the rightmost dial (sometimes coloured differently) is tenths of a kilowatt rather than whole kilowatts

Do your subtraction (now kilowatts used - then kilowatts used) and you have a figure you can use.

Was it 1 tenth of a kilowatt - so £10 per month
Was it 3 tenths of a kilowatt - so £30 per month
Was it 5 tenths of a kilowatt - so £50 per month

Notes and Further Reading:

Adjust the mathematics to suit your situation. If your standard electricity rate is 28 pence per kwh, then double the figure you get using my formula.

I used the word formula in the sentence above - a bit grand for a simple division operation, however I intend this article to be useful to people having all levels of mathematical ability. 

Notes about the calculation - 100 watt example - method 1:

730 hours per month; 14 pence per kilowatt hour; 100 watts constant usage

100 watts is a tenth of of a kilowatt so begin with 0.1

730 hours per month and 14 pence (£0.14) per kilowatt hour is 730 * 0.14 is 100 approx. 

Multiply 0.1 by 100 gives £10

Notes about the calculation - 100 watt example - method 2:

Suppose for a moment that your background usage was 1 kilowatt.

There are 730 hours in a month. So that background usage would cost you 730*'rate per kwh'

Rate per kilowatt hour is 14 pence (£0.14) so to get a pound figure we replace
730*'rate per kwh'  with 730*0.14 giving £102.2

£102.20 is roughly speaking £100

100 watts is one tenth of a kilowatt.

So we take our £100 calculated figure and divide by ten, which gives £10.

Here is one story that demonstrates just how big a portion of your monthly electricity can be taken up by a faulty fridge or freezer.

Large Upright Freezer - non 'A' rated - real world measured example:

120->134 watts when the motor is running.

2 watts when idle / at temperature.

Cooling override (struggling to maintain temperature), can see temporary surges of 995 watts.

Measured usage during single day in June was 1.5 KWh

1.5 * 0.14 * 1.2 gives £0.25 rewritten 25 pence.
( Note: The 1.2 final multiplier is VAT )

25 pence per day is roughly £8 per month

This particular upright freezer is outside in a shed which does get extremely warm, when there are two consecutive days of unusually warm weather.

Realistically my hunch is that during June, July, August, that upright freezer will consume £12 per month.

And £5-£6 per month averaged over the other 9 months of the year.

Budget for £90 per year to run that 7 cubic feet upright freezer.

A new 'A' rated upright freezer that is kept inside in a room that does not get excessively warm, should have annual consumption around 250KWh per year.

The large upright in this example is not 'A rated' and has an annual consumption double that of any new replacement.

That £90 per year budget buys around 550 KWh per year of running.

Buying a replacement (assuming current electricity costs remain static), the replacement will have paid for itself in 3 to 4 years.

A house with 2 fridges and 2 freezers - options for reducing power:

Some families who have utility rooms and outside storage, but a small kitchen, may have small fridge / freezer in the kitchen, and extra cold storage elsewhere.

For this example, I will use a house that has small fridge + small upright freezer in the Kitchen, and larger versions of the same in outside storage.

Fridge capacity: 4.5 + 7 = 11.5 cubic feet
Freezer capacity 4.5 + 7 = 11.5 cubic feet

That amount of storage, if managed effectively should be enough for 5 or 6 people.

Options for reducing power consumption:
  • Turn off one of the 4.5 cubic feet small units during June, July, August.
  • Rearrange kitchen to house one large+one small, rather than two small
  • Buy a new 'A' rated fridge freezer to replace two of the current units.
In the days when electricity was reasonably inexpensive, having extra storage was not much of a financial issue.

This year and in the coming 5 years, electricity prices are more in tune with actual generating and cleanup costs, and extra cold storage is a luxury that may be reviewed in your family budget.

I mentioned earlier that 23 cubic feet or cold / freeze storage is more than enough for a family of 4 or 5 people.

Students often have the reverse problem - lack of cold / freeze storage.

People wonder why students eat plenty of food 'on the go' - Subway, chilled food, take away.

Usually these student shared houses have a single fridge freezer for 5 or 6 people.

Roughly speaking that is 10 cubic feet of cold / freeze storage between 5 or 6.

Having other people eat your ready meals is a hazard in any shared house with some friends, some strangers.

But having only 2 cubic feet of cold / freeze storage per person can also be limiting to any 'health eating' good intentions.

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