Emily Chung, CBC News
Using local energy sources such as lake water, wood waste or even garbage to heat and cool buildings is one way for communities to cut their greenhouse gas emissions — the goal of this week's UN climate summit.
In district energy systems, instead of having an individual heating and cooling system for each building, multiple buildings are hooked up to a central system — similar to how buildings are connected to the municipal water service instead of each one relying on individual wells. Heat is distributed to buildings via pipes that typically carry hot or chilled water.
It's an idea endorsed by the United Nations Environment Programme, or UNEP, which calls district energy a "key measure for cities/countries that aim to achieve 100 per cent renewable energy or carbon neutral targets."
Once the distribution is set up, almost any energy source can be plugged in, depending on what's available locally and what will benefit the community.
Here's a look at what six communities across Canada have done.