Lake water cools Canadian city

A giant cooling system using water from the depths of Lake Ontario is slashing the energy consumption of Toronto's financial quarter.

The system is one of just a handful of mega-projects of its kind and several cities have similar set ups but what makes this one unusual is its scale.

“There’s nothing innovative or unique about this system,” said a spokesman for Enwave, the company which runs it.

“It’s just very, very big.”

Unique or not, the system is impressive in its size and simplicity – adding up to major energy savings, particularly during peak demand in the hot, summer months when air conditioning is needed most.

In a nut shell, the Deep Lake Water Cooling project takes advantage of low temperatures at the bottom of the lake to chill a network of pipes which carry water for use in air conditioning systems around the city.

The cooling system starts out deep in Lake Ontario, with a city-owned treatment plant pulling in water from the lake bed.

The intake pipes extend for 5km into the lake and plunge to a depth of 85m, where the water is close to freezing.

“We have source of 4°C water all year round,” said the spokesman.

The city’s cold potable water is passed through a bank of heat exchangers – arguably the world’s biggest system of its kind – where it chills water in a second self-contained network of pipes owned by Enwave.

Those pipes carry the cold water to dozens of large offices in the city, including the courts and government buildings, where more heat exchangers work their magic to provide cooling for thousands of workers in those buildings.

The warmed water is pumped back to the Enwave’s lakeside plant, where it is passed through a final set of heat exchangers and the energy is absorbed by the city’s potable supply with no noticeable effect on its temperature due to the huge volume of water passing through the municipal pipes.

“The city’s water flows on one side of each unit and Enwave’s runs on the other,” said the spokesman.

“Heat is transferred between the two.”

The capital costs of running the intake pipe deep into the lake, and installing the infrastructure on shore, were fairly high – almost C$250m – but once the system is up and running, it is relatively inexpensive to maintain.

“There are no moving parts except for the pumps and it’s all designed for heavy industrial use,” said the spokesman.

Pressure is lower in the Enwave pipes so that, in the case of a breach between the two systems, city-treated potable water flows into the cooling system rather than the other way round.

Even in a city with cold Canadian winters, the system is well-used throughout the year as the cores of office blocks and server rooms require cooling even in the coldest months.

It reduces electricity use by up to 90% compared with conventional air-conditioning, eliminating 79,000 tonnes of carbon dioxide annually and removing the need for 45 tonnes of polluting refrigerants.

It saves more than 61 MW of electricity annually – the equivalent power demand of 6,800 homes.

Full details of the system can be found on the Enwave site.

Sam Bond

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