In summer, an underground network of pipes cools the major buildings downtown using frigid water from the bottom of Lake Ontario. In winter, another network of pipes heats those buildings, using steam from a central plant. The Ontario Society of Professional Engineers (OSPE) arranged a tour for engineers who might find this interesting.
Centralized steam heating for cities can be very economical, reliable, and efficient. If you run a hospital, hotel, or office building, you'd have to devote space and a dozen employees to run a boiler room 24/7. You'd have to buy extra-big boilers to handle your maximum load, so most of the time they'd be running at less than peak efficiency. Plus if your boiler broke down, your building would get chilly. It's much less stressful and expensive to just buy your steam heat from a utility.
On a side street downtown, there is what appears to be a rather dull office tower. The entrance is understated, and the ground level has blank walls rather than storefronts. Once past the lobby and multiple security gates, you enter a shabby control centre. A few engineers peer at dozens of SCADA computer displays. The screens vibrate slightly, as do the thick-paned glass windows looking out onto the steam generation system. Four of these buildings are connected to the piping network heating much of Toronto. Each plant has a different output when at maximum efficiency. To maximize efficiency and minimize cost, the load is continually switched from one to another.
Once you leave the control room, a blast of noise shakes your internal organs. Several stories below the level of the control room, huge rumbling pumps bring back condensed steam through underground pipes. Tap water is forced through chemical treatment beds and added to the hot condensate, making up for water lost in leaks. The water then is pressurized with more pumps, and forced through pipes in a furnace, exposed to a roaring fireball, fed by squealing squirrel-cage air blowers and natural gas jets. The water flashes to steam, is superheated, and is then squirted through insulated underground pipes to buildings across the city.
It doesn't seem like a complicated operation, until you get inside and see all the things that can go wrong. The engineering team is continually working to improve efficiency, reduce equipment downtime, and perform preventive maintenance. Removing asbestos insulation around the steam pipes is an ongoing chore that will take decades to complete.
The steam distribution system isn't as advanced as it could be - using co-generation would be a big step forward. Right now, natural gas is just burned to make steam. It would be better to use a natural-gas turbine (basically, a stationary jet engine) to turn a turbine to create electricity. The hot exhaust from the turbine could then be used to generate the steam. However, upgrading the existing steam plants would take money, and any work would have to be done in the summer months when steam heating requirements are lowest.
This wasn't one of the most exciting engineering tours I've been on, but it did show me how many buildings in Toronto keep from freezing in winter.