Case study: Laundry drying systems

In preparation for the development and marketing of new laundry drying products, a Life-Cycle Assessment was performed (Gensch and Rüdenauer 2004). Megatrend analyses and consumer research had identified interesting new developments which needed assessment: Gas-fired laundry driers for private households and heat-pump driers presented new technologies or applications promising high energy savings; laundry driers were the only type of household appliance expected to generate major growth in sales; on the other hand, because of the high energy consumption of conventional laundry driers, many target groups had a very sceptical stance towards them; there was a growing number of reports on mould formation caused by inappropriate drying in living spaces, and increasing levels of thermal insulation were expected to further heighten this problem; on the other hand, everyday experience showed that many consumers avoided mould formation problems by drying laundry even in winter with windows opened for hours on end.

The goal of the LCA was therefore to compare new laundry driers with conventional laundry driers and with hanging laundry up to dry in indoor spaces (unheated basement; heated living space). The literature cited contains the great array of input parameters considered (air change rates, heating periods, spin rates of the washing machine, drier loading etc.) as well as sensitivity analyses. The figure beside shows the results.

The findings of the comparison of different drying systems were surprising in several respects: Drying by hanging laundry up in heated (living) spaces (“drying room, normal”) consumes the most energy, which, as a “grey” proportion of energy used for space heating, is not noticed by consumers. Optimized drying by hanging laundry up in heated rooms (i.e. with targeted, brief airing of rooms etc.), which is practised rarely, yields an energy consumption lower than that of conventional laundry driers but above that of the new drier types. When laundry is hung in other types of room (basement, attic; calculated with different parameters as reference rooms 1 and 2) heat is lost through ventilation etc. The option with the lowest energy consumption was the new heat-pump drier, which, with its very low consumption, is close to the value needed in terms of basic physics simply to “evaporate” the water from the laundry.

Comparison of the cumulated energy requirement (CER) of the systems analysed