©2013 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 55, no. 8, August 2013.
By Laurier Nichols, P.E., Fellow/Life Member ASHRAE; Marc-Olivier Lacoursière, P.E., and Mathieu Courchesne, P.E.
About the Authors
Laurier Nichols, P.E., is senior energy analyst and Marc-Olivier Lacoursière, P.E., and Mathieu Courchesne, P.E., are energy analysts at DESSAU, Longueuil, QC, Canada.
Nestled on the southern slope of Montreal’s Mount Royal, McGill University’s McIntyre Pavilion is a cutting-edge medical research and teaching facility. The installation features world-renowned research laboratories in fields including oncology, pharmacology, biochemistry and infectious diseases. Built 50 years ago, this 16-story, 30 000 m2 (320,000 ft2) building was in need of major renovations (about $25 million).
In addition to replacing the McIntyre Pavilion’s electromechanical infrastructure, the designer’s mandate included upgrading building facilities to meet current bio-safety standards. Figure 1 details the extent of the work completed.
Medical research facilities are extreme energy consumers for a number of reasons, including the significant amount of fresh air required to replace exhaust air expelled by lab fume hoods, their high-density lighting, as well as frequent use of specialized electronic equipment and cold rooms for research activities. This enormous energy use drives up the demand for air conditioning and, despite Quebec’s harsh winters, such facilities experience year-round internal cooling loads.
In the case of the McIntyre Pavilion upgrade, the new air-handling units had to supply 100% fresh air. Therefore, the overall outside airflow had to be increased by 150%, requiring an additional capacity of 56 634 L/s (120,000 cfm). These changes, coupled with the replacement of the building’s core systems, provided several interesting opportunities to improve the building’s overall energy efficiency.
Heat Recovery and Low-Temperature Water Loops
Due to the increase in outside air supply, the new design had to include a great deal of extra heating capacity. An interesting option involved recovering the heat generated by interior air conditioning to help heat peripheral areas and incoming fresh air. Water supply systems must be kept at low temperatures 43°C (110°F) to fully benefit from energy recovery potential. However, the McIntyre Pavilion used a high-temperature system 79°C (175°F) supplied by a steam/water exchanger connected to the steam system serving the entire McGill Campus. Therefore, to process the sizeable quantity of outside air admitted by the units, high-temperature heating coils had to be installed.
The designers chose coils with a large temperature differential (ΔT = 36°C [65°F]), which meant that return water could be used as a low-temperature system to supply the new heating system coils. Return water from the terminal coils is then preheated by excess heat from two new 530 kW (150 ton) recovery chillers before being heated via steam/water exchanger to resupply the fresh air coils. The new high/low temperature system retains the university’s existing steam system while benefiting from available regenerative energy. The two new screw chillers were selected to provide maximum recovery performance and produce water heated to 51°C (124°F) in winter. They also support the two existing 2,920 kW (830 ton) chillers in cooling interior heat gains and outside air during the warmer summer months.
To recover energy from the exhaust air, a total of 13 glycol-based recovery coils were installed in the various exhaust vents and a network of pipes connects them to the preheating coils for the fresh air supply systems. The designers opted for eight-row coils to achieve maximum heat transfer and a recovery efficiency of 45%. This measure provided a recovery capacity of 3,640 kW, which is substantially more efficient given the sizeable increase in outside air supply.
The creation of a low-temperature heating system based on an existing high-temperature system made for an innovative design. This design made it possible to satisfy the enormous heating load caused by the increase in fresh air intake and recover energy from the internal building heat gains.
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