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Bridging the Gaps

©2012 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 54, no. 5, May 2012. 

By René Dansereau, Member ASHRAE, and Chantale Bourdages, eng.

About the Authors
René Dansereau is director of expertise in HVAC and the main designer of this project and Chantale Bourdages is a mechanical engineer at DESSAU, in Longueuil, QC, Canada. Dansereau is a member of ASHRAE's Montreal chapter.

Adorned with a $125-million, 16-story glass tower, the Université de Sherbrooke's new Longueuil Campus is one of the tallest structures on Montreal's South Shore. Inspired by an innovative view on education, the university sought to offer an open study environment to encourage interdisciplinary mingling and promote the development of new and emerging disciplines. The campus' bold architectural design focuses on open spaces and gathering areas to promote a sense of community and cohabitation throughout the grounds. Its translucent building envelope maximizes the use of natural light and enhances a majestic view of the green rooftop oasis. By blurring traditional boundaries between indoor and outdoor spaces, the new building bridges the gap between man-made structure and its environment.    

Getting Into the Mechanics

The casual observer is often unaware of the dynamic systems behind the scenes, working to ensure their comfort and enabling them to appreciate architectural displays. From a mechanical viewpoint, all the glass and open spaces translated into a complex web of interrelated challenges. Moreover, the fact that the university wanted its new campus to be a model of sustainable development pushed energy challenges even further.

Therefore, designers opted to harness the power of geothermal energy. Ground source energy is not only renewable, but it has proven itself as an economically viable source of energy. About 25% of the building's heating/cooling capacity is extracted from the ground by means of a 165 ton (580 kW) screw chiller, which functions essentially like a heat pump and is connected to 37 vertical boreholes. Depending on the building's needs, the geothermal system can work in heating or cooling mode throughout the year. During spring, the cold ground can even provide free cooling by bypassing the compressor.

However, before tapping into geothermal energy, designers wanted to recover as much energy as possible. Despite harsh winter temperatures in Québec, most buildings require year-round cooling in their central areas. Typically, excess heat, deemed unusable because of its low temperature, is thrown out, even in the dead of winter.

Wanting to reconcile these apparently discordant cooling and heating needs, designers devised a low-temperature heating loop that recovers the excess heat from the center of the building, via two heat recovery chillers (Figure 1), and redirects it to the colder areas where it is needed.

To reduce summer cooling loads and downsize overall cooling equipment, mechanical designers worked with architects to select a low SHGC glass, consequently increasing occupant comfort in the process. A third chiller, which can achieve excellent part-load performances (NPLV as low as 0.368 kW/ton [0.105 kW/kW]) thanks to a variable speed drive installed on its compressor, was selected to supply the building when in cooling mode.

The control system allows cooling needs to be monitored and met through a sequence of operations that ensures that the most efficient combination of chiller/cooling tower and/or geothermal energy is used. Needless to say, the low NPLV chiller is frequently used during cooling season.

The single control system manages all HVAC equipment, as well as security and electrical systems, through the building's fiberoptic telecommunication network. Since the control system is routed through the telecommunication network, close coordination between the mechanical designers and the university's computer technicians was essential.

Low-temperature water loops are often key components of high-performance mechanical designs because they are capable of exploiting heat coming from many sources.

Read the Full Article

Figure 1