©2013 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 55, no. 12, December 2013.
By Caroline Paquet, ing., Member ASHRAE
About the Author
Caroline Paquet, ing., is project manager at Bouthillette Parizeau in Montreal. She is a member of ASHRAE’s Montreal chapter.
The new Biodiversity Centre at the Botanical Gardens in Montreal is a joint venture between the city of Montreal and the University of Montreal. The 4180 m2 (44,993 ft2) Centre houses high-tech, state-of-the-art laboratories, an exhibition hall, classrooms, art collection storage, and offices.
The design process involved meetings with occupants to accurately define their needs and using that information to calculate heat loads and air circulation requirements of the building. A heat balance analysis and an energy simulation were used to determine and customize the most suitable and effective energy-efficiency strategies. These tools provided important information about the building that aided in the design of the solar wall and energy recovery systems.
To meet the heating requirements of the building, a rigorous energy analysis resulted in the design and installation of a closed loop geothermal system that meets 100% of heating needs when all of the energy recovery systems are operational. Indeed, the total calculated heating load is met by the sum of the geothermal field contribution, the energy recovered from the chillers and laboratory exhaust, and the solar energy obtained passively through the solar wall.
Nevertheless, high-efficiency condensing natural gas boilers (η = 95%) are also installed within the distribution network. These boilers are primarily used for redundancy to ensure enough heat is provided in the event that any of the energy recovery systems fail during extreme winter peak conditions (i.e., –28.9° C [–20°F]). This strategy reduces the initial infrastructure costs by limiting the need for additional geothermal wells while maintaining capability of meeting the heating requirements under any circumstance.
Studies showed that the soil composition in the area is of silt clay and limestone with a thermal conductivity of 2.93 W/m·°C (0.58 Btu·ft/h·ft2·°F). The resulting geothermal field design consists of 18 wells with a depth of 122 m (400 ft).
During the summer, two chillers are used to meet the space cooling requirements. R-410 refrigerant is used, which is in accordance with the Kyoto Protocol. The first chiller is coupled with a conventional cooling tower for a cooling capacity of 271 kW (77 tons) (EER of 15.8). The second chiller uses the geothermal system for heat rejection and has the capacity to provide 48% of the cooling load, or 250 kW (71 tons) (EER of 16.2). Therefore, the geothermal well is solicited at its maximum at all times to answer the load demands while preventing the ground around the wells to become thermally unbalanced (i.e., 18 wells meet 100% of the heating loads and 48% of the cooling loads at peak conditions).
This design is the product of multiple iterations in order to obtain the optimum configuration and maximize the equipment capacities (temperature differentials and efficiency) while achieving the best possible cost-benefit ratio.
The geothermal and other loops use a 25% propylene glycol solution to maximize energy transfer, decrease project costs, and eliminate the need for intermediate equipment that could have adverse effects on the overall performance. It is also an advantage for the operation and maintenance team since it eliminates the need for purchasing and handling chemical treatment products.
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