WestJet Corporate Campus Geo-Exchange Design
Geo-exchange system paybacks are challenged in markets with low cost natural gas. WestJet’s corporate headquarters located in Calgary considered a cost of $1.4M for a traditional vertical borefield. To overcome the economic challenge, the designers pursued a creative solution. Harnessing the deep caisson piles as thermally active piles was a first for Western Canada and only the second such installation built in Canada at the time. As the piles were so-called sunk costs already, adding geothermal piping to the rebar cages was a cost-efficient solution.
Controlling the geo-exchange system to provide simultaneous heating and cooling allowed for less energy required from the geofield. The massive thermal piles stored more heat near the pile due to the thermal capacitance of the concrete. Owing to the large diameters of the caissons, some as large a 1.2m in diameter, there was excellent thermal contact with the ground.
“…designers had to use innovative thinking and sophisticated control algorithms to achieve the optimum efficiency necessary to make the geoexchange system worthwhile.”Canadian Consulting Engineer
The mechanical system was simulated using the transient thermal analysis tool TRNSYS. This allowed the control sequences to be optimized to provide the most energy from the equipment. Had high temperature heat pumps been available at the time, even the domestic hot water load could have been met by heat pumps which would have made the system even more economic.
Integrating the thermal storage literally inside the foundations of the building required some careful control logic as well. This was managed using a detailed TRNSYS model which allowed full optimization of the system. Designing such complex systems and finding cost effective solutions is the core of ETA Energy Solutions service offering.