They’re worse than cars, buses and trucks for the amount of greenhouse-gas emissions they produce.

And now Vancouver is aiming to tackle these planet-killing monsters – the buildings we live and work in – by encouraging private companies to find lower-carbon ways to heat them..

And, since it’s hard to come up with a cost-effective way to do that for a single building, the city’s engineering department is offering to work with companies who can devise district energy systems that could serve large parts of the densely populated downtown.

“There are two major contributors to city greenhouse gases: transportation and buildings, which account for more than 50 per cent,” says Peter Judd, the city’s general manager of engineering. “We have a strategy for new buildings [to make them more energy efficient]. But to make changes, you have to deal with existing buildings.”

So the department has a bidding process going on now, asking companies to come up with plans to do two things.

First, find a lower-carbon system for Central Heat, a private company that now heats 200 downtown buildings with steam heat created by burning natural gas.

Second, design new district energy systems that could serve other parts of the downtown.

Mr. Judd said there has been a lot of interest in the project from local companies that specialize in sustainable energy. But the city is not saying how many applied in the project’s first phase, which had a deadline of Feb. 28.

“I know there is interest for sure,” he said. “We’ve built up a good level of expertise.”

He said that even though the city wants a private company to build the system, the city is running the bidding process because any district energy system is only possible if the city facilitates access to underground systems.

While many people think of motor vehicles as a main source of emissions causing global warming, the reality is that buildings account for 55 per cent in any city because of the natural gas typically burned to heat water and run furnaces.

The city is aiming to reduce its overall carbon-dioxide emissions by 1.1 million tons per year by 2020.

Of that total, about 35 per cent should be achieved by making all buildings more efficient.

New buildings built to better standards will help account for about 25 per cent of the total, with the remaining 10 per cent coming from a combination of new low-carbon district energy systems or old systems that are converted to lower carbon methods.

District energy systems are becoming increasingly popular in cities, because they’re seen as a way to tap into local, renewable sources of energy rather than being dependent on supplies from outside the city whose sustainability might be questionable.

The systems serve a defined geographic area through a system of buried pipes that use steam or water to provide heating and cooling to a number of buildings.

Cities, universities and developers are using a number of sources for energy:

garbage incinerators;

geothermal pipes that go far underground and capture heat through the temperature differences at different levels;

wood-chip burners;

buildings whose functions produce heat, such as data centres or refrigeration units;

and sewer pipes, which have hot water from showers and washing machines running through them constantly.

Surrey just passed a bylaw to mandate that new development in its planned new downtown district be compatible with a district energy system, and it’s offering incentives for early adopters.

In Vancouver, the Olympic Village has a district energy system built and maintained by the city. Council voted recently to require new developments nearby to hook into it.

As well, private developers – ParkLane in the River District and Westbank and Ivanhoe at Oakridge – are planning district energy systems for their massive projects in the southeast and central districts of the city.