Dishwashers

History

American socialite Josephine Cochrane was frustrated at the way her servants were damaging her fine bone china by scrubbing it in the scullery sink. She is said to have remarked: “If nobody else is going to invent a dishwashing machine, I’ll do it myself.”

Working in a shed behind her home, she developed and patented a design employing water jets and a rack that would hold the soiled tableware in place inside a copper boiler. Powered by a motor, a wheel turned and squirted soapy water over the dishes to clean them. In 1886, Josephine patented her design, set up a manufacturing company, and began to supply the machines to restaurant businesses.

It was not until the social changes of the 1950s and the development of effective detergents, that ordinary households would acquire a dishwasher.

The UK dishwasher market

By 2018, 49% of British homes had dishwashers[1].

Innovation

Most of the energy use in dishwashers comes from heating up the water. So, the less water that there is to heat, and the lower the temperature difference between the water supply and the temperature at which it is used, the lower the overall energy consumption.

So the most energy efficient appliances and programmes tend to use water very efficiently as that keeps the energy use low. As a result, ‘Eco’ or energy-efficient programmes tend to take longer, sometimes up to two and a half hours. The lowest temperature programmes are usually 40-45C.

A few dishwashers allow ‘hot fill’ connections from the hot water system, which may mean that the water can be heated more cheaply by the central boiler or by another source such as solar panels. In practice, due to the small amount of water used in modern, efficient washes and the length of pipes from the hot water cylinder, these are only worthwhile for households that use hot washes. Research suggests that a well-organised dishwasher can use a small proportion of the energy and water used to wash by hand.

Labelling

Dishwasher labels display their energy efficiency on a visual scale (currently D to A+++). The annual calculated average energy use is also shown in the number of kWh (electricity units) consumed per cycle.

The label also shows:

how energy-efficiently the machine dries (rated A to G)
the water consumption per year (in litres)
the noise emitted in-use (dB)
the number of place settings that it can accommodate.

[1] ONS, Family spending in the UK: April 2017 to March 2018, Table A45, Percentage of households with durable goods