A Halifax-based engineer has looked to the sea for an energy-efficient solution to heating and cooling a 500,000-square-foot mixed-use complex under construction on the city’s waterfront.
The system follows the principle of geothermal heating/cooling but uses seawater, instead of groundwater from deep in the soil.
“Twelve metres below the ocean’s surface, the temperature is fairly stable, year-round,” says Denis Morris, president of M & R Engineering.
His firm has designed a system comprised of a polyethylene pipe that runs 600 metres offshore into the Halifax Harbour to draw in seawater from 12 metres deep.
The seawater runs through a titanium plate heat exchanger “just like you would draw groundwater through a geothermal heat exchanger,” says Morris.
“We use conventional heat pumps that are optimized for the temperatures the ocean will give us.”
The design, which is free of conventional mechanical cooling, incorporates a network of “active chilled beams” and large cooling coils.
“We are using the harbour for free cooling in summer and heat pump heating all winter,” he explains.
Morris calculates the innovative system will be 52 per cent more efficient than requirements under the National Energy Code 2011.
While the seawater system costs more than conventional heating/cooling, it eliminates cooling towers, fossil fuels and relies on electricity off the building grid.
“There are no emissions from our building,” he states. “The only emission is where you are rejecting heat into the water in the summer.”
He predicts a payback in 10 years or less.
The innovative cooling/heating system is for the Queen’s Marque, a multi-purpose development that includes offices, a hotel, retail and residential space in downtown Halifax. The project is a development by the Armour Group.
Morris says the pipeline will be moved into place on barges and then sunk to the seabed. The intake, to be attached by divers, will be “turned up” about 12 feet away from the seabed to eliminate sand and silt from entering the 16-inch diameter pipe.
He says it will include a fish screen and an “anti-fouling” coating to prevent the growth of barnacles and other sea creatures at the inlet. The pipeline will draw 1,300 gallons of seawater a minute.
Morris adds the design takes into account rising sea levels. At building entry, the pipe will be elevated to prevent leakage during high tides.
Laying the pipe will involve co-ordination with various local authorities as well as Fisheries and Oceans Canada. Location of the pipeline will be put on charts to ensure sea vessels “don’t drop an anchor on it,” he says.
To be completed in 2020, the Queen’s Marque is being built by Armour in partnership with Bird Construction.
Morris says prior to deciding on the design his firm looked at buildings with unconventional heating/cooling systems in Boston, Chicago and Bermuda.
“They all do various things. We are combining the best that we see,” he adds.
The seawater intake has been sized to accommodate future buildings in “a mini-district heating system” to accommodate other buildings in the Armour Group’s portfolio.
“They are investing in improved technology now as a hedge against increased costs later,” Morris says.
The seawater project is M & R’s second, following one for the Nova Scotia Power Headquarters in Halifax built in 2012. The headquarters won a LEED Platinum award.
“We’ve learned lessons from that building and this new one is incrementally improved, but the Nova Scotia Power building is running really well and they are using the same technology for their next building, so they are happy with it,” he says.
M & R recently completed a similar design for the Cape Breton Coast Guard College. The federal government project will be tendered in 2019.
Morris says he’s evaluating a proposal to build a heat pump energy centre on the harbour for 17 buildings.
“It might be too expensive, but we have to study it,” he says. “Fifteen years ago…people thought there were too many barriers for seawater heating and cooling. Now look what is happening.”
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