“I can honestly say it’s the best thing I’ve ever spent my money on,” says 30-year-old Stephen about the unassuming waist-high plastic pillar that sits in the bedroom of his converted bungalow in Nottinghamshire. The retail worker has always found the room uncomfortably hot in summer, and his attempts to cool down using freestanding fans, electric air coolers and reading up on rudimentary fluid dynamics never seemed to cut it. When peak temperatures began creeping towards the 40C (104F) mark a few years ago, he splashed out on a portable air conditioner and has never looked back. “If it were...