A few years ago, when I bought two Midea U window air conditioners on sale online at Costco, I didn’t know that I had just made the biggest quality-of-life improvement purchase ever.I was replacing the dinky, underpowered window units that had come with my apartment and had excelled at only one thing: waking me up every few minutes with the guttural sound of their motors. As someone who has the misfortune of being a restless sleeper — and is a drag to be around whenever the temperature rises above 75 degrees — I knew that something needed to change.On an afternoon in late May, just as the summer humidity was blooming and the air was portending what would become the hottest summer in New York City history, two big boxes arrived at my apartment.