## Kettles and cookers

Britain, being a civilized country, has a 230 volt domestic electricity supply. With this supply, we can use an electric kettle to boil several litres of water in a couple of minutes. Such kettles have a power of 3 kW. Why 3 kW? Because this is the biggest power that a 230 volt outlet can deliver without the current exceeding the maximum permitted, 13 amps. In countries where the voltage is 110 volts, it takes twice as long to make a pot of tea.

If a household has the kettle on for 20 minutes per day, that's an average power consumption of 1 kWh per day. (I'll work out the next few items "per household," with 2 people per household.)

One small ring on an electric cooker has the same power as a toaster: 1kW. The higher-power hot plates deliver 2.3kW. If you use two rings of the cooker on full power for half an hour per day, that corresponds to 1.6 kWh per day.

A microwave oven usually has its cooking power marked on the front: mine says 900 W, but it actually consumes about 1.4 kW. If you use the microwave for 20 minutes per day, that's 0.5 kWh per day.

A regular oven guzzles more: about 3kW when on full. If you use the oven for one hour per day, and the oven's on full power for half of that time, that's 1.5 kWh per day.

Figure 7.1. A flock of new houses.
Figure 7.2. The water in a bath.

Microwave: 1400 W peak

Fridge-freezer: 100 W peak, 18 W average

Figure 7.3. Power consumption by a heating and a cooling device.

Fridge-freezer: 100 W peak, 18 W average

Device power time energy Table 7A Energy consu^ion per day per day figures for heating and cooling --devices, per household.

 - kettle 3 kW 1/3h 1 kWh/d - microwave 1.4 kW 1/3h 0.5 kWh/d - electric cooker (rings) 3.3 kW 1/2h 1.6 kWh/d - electric oven 3 kW 1/2h 1.5 kWh/d Cleaning - washing machine 2.5 kW 1 kWh/d - tumble dryer 2.5 kW 0.8 h 2 kWh/d - airing-cupboard drying 0.5 kWh/d - washing-line drying 0 kWh/d - dishwasher 2.5 kW 1.5 kWh/d Cooling - refrigerator 0.02 kW 24 h 0.5 kWh/d - freezer 0.09 kW 24 h 2.3 kWh/d - air-conditioning 0.6 kW 1h 0.6 kWh/d