Canadian Consulting Engineer

Feature

Tapping into Sewage

In some ways it seems so obvious. Instead of letting the warmth simply drain away, a new facility in downtown Vancouver is salvaging heat from sewage pipes below the streets and using it to supply heat and domestic hot water to buildings.




In some ways it seems so obvious. Instead of letting the warmth simply drain away, a new facility in downtown Vancouver is salvaging heat from sewage pipes below the streets and using it to supply heat and domestic hot water to buildings.

The False Creek Energy Centre in downtown Vancouver is the first utility in North America to harvest heat from a wastewater system for domestic use. The neighbourhood energy utility (NEU) currently distributes the heat to 12 mid-rise mixed-use buildings in the Southeast False Creek community. It presently supplies about 70% of the thermal energy demand of 1,400 residential units (some of which were originally the 2010 Winter Olympic Village housing).

Uncharted territory

Since this was a North American “first,” the consulting engineering companies, FVB Energy and Ausenco Sandwell, together with Chris Baber, project manager for the city of Vancouver, had to steer their way through uncharted engineering territory.

One of the first issues was finding a suitable heat pump system and heat exchanger. Ray Tarnai, P.Eng. of Ausenco Sandwell explains: “The exchanger had to achieve a higher heat transfer rate than could be accomplished through a two-stage system. We also had to feed raw sewage directly into the heat pump, which makes it unique.” The team searched worldwide for a supplier and eventually found one in North America that provided performance guarantees and a 10-year maintenance contract.

The potential sewage fouling of the heat exchanger meant that solids could clog the equipment, while oils and fats could lead to the growth of biofilm and compromise its efficiency. To solve those issues the heat exchanger has a 2-mm travelling screen that removes solid particles before the sewage passes through it.

To reduce the biofilm build-up the team chose a shell and tube system that can be adapted to include an automated brush cleaning system. A four-way valve allows the operators to periodically reverse the flow of the wastewater to flush it out. After over a year of operation, these tools have proved effective.

Another concern was that the local sewage flows in the neighbourhood vary dramatically over the course of a day and night. There needed to be enough wastewater to provide 2.7 MW of energy. To “top up” the supply, a connection was made to the main sewer line serving downtown Vancouver. Automated controls also maintain the flow through the exchanger.

After the heat exchanger has done its work, the removed solids are returned to the waste stream by being deposited in the centre of a specially designed self-cleaning trench-type wet well. Pumps are periodically run at high speed to clean the solids and grit from the wet well areas.

Better than geothermal

The waste stream runs at an average of 20°C which is much warmer than the temperature of the earth, making it more useful as a source of energy than a geothermal field. Tarnai sees no reason why sewage heat recovery should not become widely used. What’s needed is “a significant heat demand, a nearby source of sewage and an acceptable location for the central heat plant,” he says.

Originally Vancouver had considered other renewable energy sources for the Southeast False Creek Community, including a geothermal collection field. But the field needed to be extremely large and would have been too costly. There isn’t enough sunlight in Vancouver to produce enough solar thermal energy, and the community had concerns about a biomass energy source.

The architecture of the utility building is so attractive it won a Royal Architectural Institute of Canada award in 2010. The most dramatic feature is the stainless steel exhaust flues that extend 20 metres above grade near the adjacent Cambie Street Bridge. The flues are from the boilers, a generator and an odour control unit. LED lights on the flues change from blue to red as the demand for energy rises.

The NEU system took three years to build and cost $30 million. It can be operated by a staff of two. The project has won 2010 awards from Consulting Engineers of B.C. and the Association of Professional Engineers and Geoscientists of B.C. — BP cce

 Client:City of Vancouver Neighbourhood Energy Utility

Design basis and detailed design of distribution system:

FVB Energy (Robert Doyle, P.Eng., John Chin, P.Eng.)

Design of central heat plant:

Ausenco Sandwell (Ray Tarnai, P.Eng., Joseph Chacko, P.Eng., Minoo Colah, P.Eng., George Szabo, P.Eng.)

Mechanical/wastewater:

Omni Engineering

Architecture:

Water Francl Architecture

Suppliers:

Trane (sewage heat pump); Eaton (medium voltage switchgear, motor control centres)