Many communities lack reliable electricity, which is why we’ve seen a number of projects that work without it, such as a portable medical sterilizer and an underground refrigerator. In Bangladesh, recycled, make-it-yourself air conditioning units called Eco-Coolers are helping thousands of people stay cool during the country’s scorching summers.

Invented by Ashis Paul, a creative supervisor at advertising company the Grey Group, the Eco-Coolers are zero energy, make use of ample amounts of available waste and can quickly cool a home by five degrees Celsius. With the majority of Bangladeshis living in tin homes, five degrees Celsius can turn a home from unbearable to comfortable. Recycling is uncommon in the country, so the Eco-Coolers’ use of empty plastic bottles helps the environment as well as keeps the units affordable.

Able to be custom-fit for any sized window, makers cut plastic bottles in half and insert the necks into holes cut into the chosen size of board. When placed in a window, the wider part of the open bottle faces outside, drawing hot air into the funnel. Air pressure changes when passed through the bottle neck, releasing cooled air into the room. Blueprints and a how-to guide are available on the Grey Group’s website.

What other appliances could be made electric-free and eco-friendly?