Case study: Aquifer Thermal Energy Storage System at Pacific Agri-Food Research Centre, Agassiz, B.C.

An $18 million office/laboratory at the Pacific Agri-Food Research Centre under construction in Agassiz, B.C. will be the first office laboratory building in Canada to use ground source heating and cooling. The 7,100-m2 building consists of a two-storey laboratory wing, a large single-storey industrial area for crop processing and two greenhouse wings.

The centre uses an aquifer thermal energy storage (ATES) system as its primary source of heating and cooling. Cohos Evamy Interplan/CEI is prime consultant, with Golder Associates, Canadian Environmental Technologies Inc. and G. F. Shymko and Associates on the design team.

The chosen system has five wells. Two wells with pumps supply groundwater during the heating season and are used as injection wells during the cooling season, and two other wells perform the opposite function. The fifth well with no pump is located down gradient and is used to compensate for any imbalance in the yearly heating and cooling loads.The two warm and cold wells are approximately 60 metres below ground level. Each well consists of four well screens approximately 3 to 4 meters in length and 200 mm in diameter, and has been placed along the sandy formation of the aquifer. The dump well was completed at a depth of 37 metres below grade. The ambient temperature of the aquifer is 10C.

Each pump is controlled through a variable frequency drive and can deliver between 4.5-9.0 L/sec (75-150 gpm). The groundwater is pumped through a duplex stainless steel heat exchanger located within the building. It is anticipated that groundwater will be injected back into the aquifer at 4C to 5C.

The chilled/condenser water system consists of a primary loop and three secondary circuits, each equipped with duplex pumps. The primary loop circulates water through the titanium plate and frame heat exchangers while the secondary piping circuits distribute water to: (1) coils in the air handling and fan coil units, (2) water-cooled freezers and coolers, and (3) the central heat pump evaporator.

The primary loop allows energy to be transferred between the secondary circuits and groundwater is used to compensate for the difference between the building heating and cooling loads.

As a secondary heating system, three high efficiency fully modulating natural gas-fired boilers (2000 MBTU ea.) provide 82C hot water to the greenhouses. In extreme cold weather, a hot water return from the greenhouses can be diverted to provide supplemental heat to the laboratories and office.

The ground source heating system will be shut down during the shoulder seasons as the electrical demand charges for the central heat pump would not be cost beneficial.

In September 1998 the total incremental capital costs between the ATES and conventional heating and cooling systems were estimated to be $215,000. Energy savings should be approximately $35,000 annually, providing a payback of six years. The payback will be confirmed two years after the system has been commissioned.

Scott Maynard, P.Eng., project manager, Agriculture & Agri-Food Canada

Charles Woo, P.Eng. Cohos Evamy Partners