(Photography by Ema Peter) Around the turn of the 20th century, it became trendy for North American cities to build conservatories to show off tropical plant species, no matter how untropical the locale. Winnipeg’s version was the Palm House, a botanical garden in Assiniboine Park filled with exotic foliage. But by 2009, the once-fashionable brick-and-concrete structure had aged into a dilapidated energy hog. When the Assiniboine Park Conservanc…