23 May 2011

Cold Water Washing

When we bought cloth nappies we considered the instructions about how to wash them somewhat over the top, and scaled our practice down a great deal. However, I did sufficiently listen to their advice to 'wash in very hot water' to set the washing machine temperature to about 35 degrees (Celsius!) - less than half the recommended temperature, but definitely not cold. Recently I decided to try washing the nappies on cold for a while and see if it made any difference. Results: no difference whatsoever to the quality of wash. (Tyson now tells me he has always washed on cold and had no idea I was using hot water) Our washing machine is now permanently set to cold.

Initial Time: Fractions of a second to turn the dial. Several weeks of assessing whether the nappies were really coming clean, but that was testing rather than time taken to make the change.

Initial Cost: Zero.

Ongoing time or cost commitment: Zero.

Impact:  We estimate this is saving about 1.42 units of energy per day (1.42kWh). That's a total of 517 units per year, or 513 kg of carbon dioxide.

This calculation is based on our estimate that a wash uses about 70L, which is about how much we could capture last summer when we were bucketing from the washing machine, if we emptied buckets between the wash and rinse cycles. It takes 1 unit of energy to heat 20L of water by 42 degrees, and water generally starts at around 18 degrees. As cloth nappy users, we wash pretty much every day. 

The information we could find on either the washing machine itself or the web claims our Whirlpool WF665 front loader uses only 307kWh per year to heat an undefined amount of water to 'warm' every day (presumably the hottest setting) and suggests the machine uses somewhere between 55 and 60 L per wash, varying depending on the size of the wash load. Our experience of catching the water, and the physics of heating water, suggest these claims are not accurate. 

It is not possible to calculate accurately how much we are saving if the 307kWh claim is true, as we can't tell how much of that energy is for heating the water and how much for operating the machine. However, newer machines that Tyson has seen through his energy auditing work show energy use for both cold and hot washes, and he says that generally hot washing is rated as using 5-8 times the energy of cold washing. At five times the energy, based on 307kWh per year, changing from hot to cold would be saving us 245.6 units per year (244kg of CO2). Possibly a little less as we were not previously using the highest possible temperature setting.

Its not about the money, but just to give an idea: that's between $60.10 (based on Whirlpool's figures) and $126.51 (our figures) per year at the current cost of electricity.

1 comment:

  1. I cold water wash for my cloth nappies too. I haven't done the experiement to see if hot was better, so glad to find you did it for me.
    I find that the most critical part is line drying - preferably in the sun for the bleaching!