Canadian Consulting Engineer

By Ruben Arellano, P. Eng. Hemmera Energy   

Beaver Barracks Geoexchange

Buildings Energy Building Mechanical & Electrical (HVAC) Systems Green, Alternative Energy

In the Centretown neighbourhood of historic Ottawa, Centretown Citizens Ottawa Corporation is developing Beaver Barracks as a sustainable affordable housing community. The complex has five buildings w...

In the Centretown neighbourhood of historic Ottawa, Centretown Citizens Ottawa Corporation is developing Beaver Barracks as a sustainable affordable housing community. The complex has five buildings with over 240 residential units.

A central element of the project’s sustainability mandate is an innovative geoexchange district energy system.

Geoexchange, also known as geothermal heat pump technology, takes advantage of the abundant low-grade solar thermal energy that is stored in the ground year-round — literally free energy under your feet. This energy is captured by use of a ground-heat exchanger (GHX) and standard heat pump technology. Only a small amount of electricity is used to operate the system, resulting in overall energy efficiency 300 to 500% greater than common natural gas or electric equipment. Greenhouse gas emissions are reduced dramatically by the same degree.

The geoexchange system at Beaver Barracks includes 60 boreholes drilled 137 metres deep through soil and limestone bedrock. The individual loop pipes are thermally fused together into a continuous parallel piping network that forms one large geoexchange field. The field feeds to a single central energy plant, which provides heated and chilled water and domestic hot water to the individual buildings.

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The central energy plant uses modular high-efficiency heat pumps to maintain a two-pipe central loop tempered to 23-31C (73-87F), This feeds a secondary loop in each building, maintained at 21-32C (70-90F). Small individual heat pumps in each apartment draw from the secondary loop to maintain the temperature desired by the occupant.

Once final commission checks are completed this summer, the geoexchange district energy system at Beaver Barracks will be the largest of its kind in Canada

Uncommon features

• Common field and central plant for several buildings — an uncommon feature in geoexchange systems.

• Primary and secondary loop design for maximum efficiency in running low-temperature distribution and to allow energy sharing in shoulder seasons.

• Central domestic hot water generated primarily with heat pumps.

• Deep borehole loops using newly formulated and CSA-approved PE4710 HDPE pipe resin compound, allowing for a reduced GHX field footprint and no risk of exceeding pipe pressure rating.

• Central plant design with three energy source options to maximize the plant efficiency depending upon building use, energy demands and utility costs. The multiple source redundancy ensures residents are always provided with heating, cooling and domestic hot water.

• Use of “thermally enhanced” borehole grout, with strict construction quality controls.

Geoexchange system: Corix Utility Services (design-build-own-operator); Hemmera Energy, Vancouver (design).

Architect: Barry J. Hobin Associates.

Supplier: Multistack (heat pumps)

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