©2014 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 56, no. 6, June 2014.
By Pascal Michaud, ing., Associate Member ASHRAE, and Sebastian Maynard, ing.
About the Authors
Pascal Michaud, ing., and Sebastian Maynard, ing., are mechanical engineers at Dessau in Rimouski, QC, Canada. Michaud is a member of ASHRAE's Quebec chapter.
The Notre-Dame of St. Rosary Convent in Rimouski, QC, Canada, required a sizeable expansion to reflect its growing role as a senior care center and residence. A total of 86,100 ft2 (8000 m2) of floor space was added to accommodate 63 new bedrooms, three dining rooms, several common areas, as well as activity spaces for the residents. To comply with LEED requirements, a number of efficiency measures were implemented with an end result of a building whose energy consumption is 42% lower than Canada's Model National Energy Code for Buildings' Reference Standard.
Senior care residences tend to be among the highest energy consumers largely due to the elevated rates of outdoor air and ventilation that they require to ensure the health and comfort of occupants.
In accordance with the Canadian Model National Energy Code for Buildings (MNECB), the design team created a model of the building and its electromechanical systems using EE4 and DOE2. Simulation software accurately demonstrates the energy savings and cost effectiveness of the proposed design options. EE4 is an analysis program created by the Canadian government, powered by DOE2. An analysis of the various simulation options allowed the team to select the optimal course of action.
Ground Water Loops
The building’s heating and cooling system is composed of heat pumps connected to a geothermal loop. Twenty-five boreholes were drilled that are 152 m (499 ft) deep, and 23 heat pumps are connected to the geothermal loop. Seventeen water-to-air heat pumps (cooling EER ranging from 13.5 to 17.5 and heating COP ranging from 2.9 to 3.7) are used for both heating and cooling the rooms, one water-to-water heat pump (cooling EER of 13.5) is used for cooling water to supply fan coils, two water-to-water heat pumps (heating COP of 3.0) are used for heating water to supply the radiant floor, two water-to-water heat pumps (cooling EER of 13.2 and heating COP of 3.1) are used for the preheating, as well as heating and cooling of water to supply three fresh air-handling units and one water-to-water heat pump (heating COP of 3.0) is used to preheat domestic hot water.
Heat pump systems also offer the advantage of moving energy from one zone to another, and in this manner contribute to reducing energy consumption. Also, an electric boiler serves as a backup during winter peaks. Due to the short summer season, no backups are required in cooling mode.
Water Loop Temperature
Different water loop temperatures were selected to obtain greater energy performances from the heat pumps. The supply and return temperatures of chilled water are respectively 44°F and 54°F (7°C and 12°C), while the temperatures of the heating loop are respectively 110°F and 100°F (43°C and 38°C). These temperatures represent optimal performance settings for the heat pump system described earlier.
Hot Water Preheat
As senior care centers such as this one consume large quantities of hot water, the design team opted to preheat domestic hot water as an added energy-efficiency measure. A geothermal water/water heat pump is used to preheat domestic hot water. The heat pump preheats hot water up to 110°F (43°C). The water then passes through a water heater tank that increases the temperature of the water until it reaches 140°F (60°C). This approach is more efficient than the conventional use of electric water heaters.
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