In December, Metro Vancouver's new water filtration plant in the Lower Seymour Conservation Reserve began providing the Lower Mainland with pristine water drawn from the Seymour and Capilano watershed...
In December, Metro Vancouver’s new water filtration plant in the Lower Seymour Conservation Reserve began providing the Lower Mainland with pristine water drawn from the Seymour and Capilano watersheds in the mountains north of Vancouver.
One of the largest water filtration plants in North America, the Seymour-Capilano Filtration Plant will process 1.8 billion litres per day. Efficient processes and equipment are used throughout the facility.
One of the efficiency components is the use of a central ground source heat pump system (GSHP), or ‘geoexchange’ system, to heat and cool space throughout the complex. The GSHP system provides environmental control for the 2,400-m2 operations and maintenance building, as well as for the various process buildings in the plant, which amount to 7,500 square meters of enclosed space. The GSHP system is also used to preheat the complex’s domestic cold water.
The geoexchange system reduces the plant’s required electrical capacity as well as its electrical energy consumption. Also, since the plant is a post-disaster facility it has back-up diesel generators in case it is cut off from the utility power supply during a seismic event. Under these conditions, it was found appropriate to heat and cool the entire complex by a central GSHP.
The central GSHP system includes water-to-water heat pumps configured as chillers in a heat pump application. The switchover from heating to cooling is achieved on the water side, without the need to reverse the refrigeration cycle (common for the traditional heat pump operation).
A unique aspect of the GSHP system is the ground loop, also referred to as the field. This is a horizontal field located below the plant’s clear well. Over 40 kilometres of HDPE pipe was installed in a “mud-slab” below the structural concrete that encases the clear well (see above). The pipe exchanges heat with the surrounding ground. The body of water in the well acts as a 200-megalitre water supply buffer, but it also has a significant thermal influence on the surrounding ground. It helps to stabilize the temperature swings in the ground over different seasons as heat from the GSHP ground loop pipe is either extracted or rejected.
Locating the ground loop beneath the clear well saved excavating elsewhere and had construction advantages. The exposed ground provided a ready-made bed for the mud slab holding the geothermal pipe, so the clear well structural slab could simply be built on top.
The GSHP centralized system allows the antifreeze loop (fluid in contact with the cold evaporator and field loop) to be separate from the heating and cooling loop (fluid circulated through the buildings). The system also allows simultaneous heating and cooling, as both services are available at all times.
In winter, the spare cooling capacity is used to recover heat. Waste heat from the main electrical room is recovered using the cooling coil.
The heating and cooling is generated by a modular plant of three banks, each with five heat pump modules. Each module of 105 kW (30 tons) nominal capacity consists of two separate refrigeration circuits. As the overall capacity is broken down to 30 independent loops, simple on-off controls for each module allow reasonable step control of the capacity in ~3.4% increments. The large volume of water in the system also helps achieve a stable capacity control.
The modular concept provides reliability as well as ease of operation and maintenance. If a compressor fails, a single refrigeration loop is affected. All other compressors continue operation. The maintenance does not require immediate response, which is often very costly. Also, since small loops are common, the refrigeration mechanics do not require specialized training or certification.
Although the building GSHP system has not yet gone through a full year’s seasonal cycle, it proved itself during the commissioning of the water treatment process. The performance so far has shown that even during the cold period when the evaporator loop was at sub-freezing temperatures, a significant amount of renewable energy was extracted from the ground and used for heating, replacing the need for fossil fuels. The control system permits monitoring and will provide reliable data on the heat pump system performance.
Mechanical (HVAC) consultant: SSBV/ Stantec (Dejan Radoicic, P. Eng.)
Architect, structural, electrical: SSBV
General contractor: North American Construction.