DIY aircon

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Wish you had aircon in the bedroom in these heat waves?

1. Get yourself a cheap fan.
2. Get a two litre bottle of water or lemonade and consume the product. Fill the plastic bottle with tap water and put in in the freezer.
3. Come the evening, remove the frozen 2L bottle, take it to the bedroom and place it on a flannel (condensation) just behind the fan; turn the fan on.

The result is a continuous cool flow of air over the bed which has the additional advantage of wafting mosquitos away too.

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Update: how much cooling does this actually provide?

A two-litre bottle of water frozen to about −20°C can absorb roughly 850,000 joules of heat as it warms to 0°C, melts, and the resulting water then warms to about 12°C (GPT-5.6 tells me). If that happens over, say, 10.30 pm to 5 am, it represents an average cooling power of about 36 watts.

That isn't much as an air-conditioner for an entire bedroom, but the fan itself makes little difference to the calculation. At its lowest speed it probably consumes only about 1 watt, so the combination still provides net cooling of roughly 35 watts.

So this solution is really a personal cooler, not a room cooler. The fan passes air over the very cold bottle and directs the cooled moving air across the bed. The combination of slightly cooler air and increased convective and evaporative cooling from the skin can make a substantial difference to how comfortable you feel, even though the temperature of the room itself barely changes. And you could always use two bottles...

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