ENMAX’s Downtown District Energy Centre in Calgary is a district heating plant which has been in operation since 2010. The Centre contains a series of large natural-gas-fired boilers generating hot water that provide heat to many buildings in Calgary’s downtown core and East Village. The hot water is pumped through a buried, welded steel, insulated piped distribution system. Heat exchangers transfer energy from the hot water to the building heating systems, thus replacing the need for boilers or heat generating equipment in each building.
In 2014, ENMAX approved a Combined Heat and Power (CHP) system to expand their diversified electricity generation capacity and increase revenue from the Centre, while also reducing greenhouse gas emissions. The CHP system burns natural gas in a large reciprocating engine to generate electricity. Heat from the engine cooling jacket and exhaust gases is recovered to reduce boiler operation at the Centre. The system generates 3.3 megawatts of electricity and 3.0 megawatts of thermal energy with an overall efficiency of 85%.
ENMAX engaged Associated Engineering to complete a design basis memorandum and detailed design, and provide construction and commissioning services for the CHP system. Project Manager, Aled Jones, tells us, “There were several challenges to integrating the CHP system with the existing facility. The physical space available was very tight to fit in the engine. Engineering many system components into an operating facility without any plant downtime, beyond one regularly scheduled outage, was also very challenging.”
The logistics and timing of lifting the engine into the building over the CP Rail train tracks had to be closely engineered and planned. Bringing the 25 kilovolt transformer into the second floor, high voltage room, through a wall, also required an engineered lift. For the Centre, a package CHP solution was impossible due to space and integration restrictions. Mechanical and Project Engineer, Aaron McCartie, says, “As a result, we designed a custom CHP system based on loose shipped components from the supplier.”
Another major design hurdle was ensuring the CHP heat recovery system worked seamlessly with the boilers, boiler economizers, and District Energy distribution temperatures and flow rates. Custom, upgraded heat exchangers were specified for the CHP package to best match the heat recovery temperatures to the Centre’s existing operations.
The CHP engine carries the entire District Energy System summer load (baseload) from approximately May through September. Following commissioning in May 2018, the Centre plant boilers were able to shut-down completely, while the CHP system was running.
Currently, approximately 45% of Alberta electricity is generated from coal. By shifting from coal to natural gas, the CHP system reduces greenhouse gas emissions. The facility also increases the efficiency of energy generation from approximately 35%-40% to 85% by recovering the majority of generated heat.
Facility will displace approximately 4,000 tons of carbon dioxide emissions per year
Key personnel on this project included Aled Jones, Aaron McCartie, Joe Lisella, Elizabeth Wollbaum, Scott Witzke, and Sean Bolongaro.