Deep below the surface of Lake Ontario is Toronto’s most valuable source of renewable energy. Enwave’s Deep Lake Water Cooling System harnesses the cold temperatures from Lake Ontario to cool hospitals, data centres, educational campuses, commercial towers and residential buildings in Toronto.
This innovative project uses water from a depth of 70 m to reduce the amount of energy-intensive air conditioning required to cool the downtown core. It displaces 55 MW of energy from the grid per year, equivalent to powering eight hospitals.
As the demand for this service increases, Enwave requires the installation of a fourth intake pipe. The pipe is a 1600mm DR 21 HDPE Pipe supplied & fused by Sandale Ontario under the supervision of the marine construction contractor, Dean Construction.
The Sandale Ontario Challenge
The depth at which these pipes are buried would cause costly maintenance if something went wrong. Any fouling in the pipe would decrease flow capacity and increase the pumping cost, negating the purpose of the system. Also, there needed a solution to avoid excavating a 600m long trench (through marine habitat) from the beach at Centre Island into Lake Ontario.
Due to the size of the intake line (approximately 3,350 m), all the fabrication had to occur off-site. Once the pipe had been fused, transporting it via tug across 50km of Lake Ontario, then across a public beach and 500 m offshore to tie in and sink to its final location, possessed various challenges.
Excavation from the steel sheet piling pit (installed on the south shore of Toronto Island) to a location offshore would require two parallel rows of sheet piling into the lake. This would require a large amount of excavation and material handling issues. It would also require additional environmental permits and attract easement issues.
The existing 1.85m dia. steel intake pipe was constructed of riveted sections of steel plate. The rivets in the 16mm plate protruded into the pipe, reducing the available clearance and creating obstructions. The fourth intake needed to be robust enough to be maneuvered through the steel intake’s debris, humps, dips and turns.
Tensiometer readings obtained during a test pull of a 21m long pipe segment indicated that a 100-ton pull could be required to facilitate the pulling of a section of 570m long, fused HDPE pipe. The flow through the new HDPE would create a significant negative pressure. The pipe needed to withstand collapsing on itself.
The Sandale Ontario HDPE Solution
A new 1600mm DR 21 HDPE 4710 pipe supplied and fused by Sandale Ontario was slip-lined through the existing steel intake for 570m. HDPE is a corrosion-free monolithic piping system that is perfectly suited for this challenge. By slip-lining the new HDPE pipe, from the onshore pit to the break-out location, Enwave was able to perform the work without additional environmental permits and within their own easement.
A steel sheet piling cofferdam was installed onshore to permit the excavation to uncover the existing intake pipe. The existing intake pipe/sheet piling interfaces were jet-grouted to make them stable and more watertight.
Offshore, divers cut out 30m of the existing intake, including parallel rows of steel sheet piling, the existing pipe, and its concrete encasement. Obstructions and debris were then cleaned out of the pipe.
A custom domed pulling head and fittings capable of a safe 100-ton pull were constructed. A winch capable of 100-ton pulls was installed near the onshore pit. A two-parted 2-1/4” wire rope was threaded through the existing intake. Various sheaves and monitors were required and installed. The pull was successfully completed in August of 2021.
The possibility of the pipe collapsing under negative pressure was eliminated by grouting the annulus between the existing steel pipe and the new HDPE for the entire length of the pipe. All the grouting between the existing steel pipe and the new HDPE was performed underwater.
With the project’s challenges fully addressed, the system now once again pumps cool water into downtown Toronto, helping to reduce costs and provide a more efficient solution to maintain the comfort of those in some of Ontario’s most crucial buildings.
Learn more about slip-lining metal or concrete pipes with long-lasting HDPE pipes and how this innovative and cost-effective approach can help your project.