©2012 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 54, no. 8, August 2012.
By Chantale Bourdages, Eng.; and Olivier Brodeur, Eng., Member ASHRAE
About the Authors
Chantale Bourdages, Eng., is a mechanical engineer, and Olivier Brodeur, Eng., is a project manager at Dessau in Longueuil, QC, Canada.
The Cartierville YMCA is an 88,000 ft2 (8180 m2) building that offers aquatic, sports and recreation facilities. The project was made possible due to an innovative public-community partnership between the Quebec government, the City of Montreal and the YMCA. The owners mandated an energy-efficient HVAC design that would become a focal point of this environment-friendly building. By combining renewable geothermal energy and heat recovery systems, the mechanical engineering team was able to craft a self-financing project designed to reduce energy consumption by 54%, which translates into savings of $200,000 a year on energy-related costs.
Choosing Efficient Systems
To help designers target the most energy and cost-efficient HVAC systems, energy simulation models were used to evaluate different scenarios. The simulation software simultaneously takes into account weather data, building envelope parameters and complex building HVAC system interactions, which are practically impossible to estimate using traditional calculation methods. Using DOE2.1e simulation software, the mechanical design team was able to accurately analyze peak loads, as well as the building’s hourly loads throughout the year, enabling them to pinpoint potential heat recovery capacity.
Due to their elevated hot water consumption (pools, showers, whirlpools, etc.), as well as extra air conditioning and dehumidification needs, recreation facilities tend to have high energy bills. Therefore, designers wanted to focus on potential energy recovery systems before tapping into the grid or even renewable energy. Simulation models helped confirm that heat recovery equipment and geothermal energy constituted the most cost-efficient combination. By providing data on part-load building behavior and available excess heat, building simulations proved essential to the design and sizing of geothermal and heat recovery equipment.
Interactive Water Networks
Typically deemed unusable, excess heat is often discarded by conventional HVAC systems by means of air condensers or cooling towers, even in winter. By carefully analyzing the building’s heating, cooling and dehumidification loads throughout the year, designers used building simulation models to create a sophisticated multiple water network system that prioritizes heat recovery.
Flexibility between water networks is one of the key elements to fully recovering internal energy before tapping into geothermal or grid equipment to supply the building’s varying needs (Figure 1). First, a mixed water loop supplies the building’s 21 water-to-air heat pump units. Heat pumps were designed to supply the thermal zone, enabling the system to heat or cool according to actual zone needs, therefore avoiding wasteful terminal reheat typical of traditional multizone systems. The mixed water loop directly transfers excess internal heat to the colder areas of the building. A second network consists of a chilled water loop used to dehumidify air in the aquatic center and cool the mechanical room year-round, as well as supply the fresh air cooling coil. An 84 ton (300 kW) recovery chiller rejects excess heat into the heating network (third network). Heat is rejected only when energy can no longer be recycled throughout the building, either by means of the geothermal loop or the two dry coolers on the roof. The third water network, as mentioned, is a heating loop that can preheat and heat fresh incoming air, as well as the building’s pools, domestic hot water and heat pump units during winter.
Citation: ASHRAE Journal, vol. 54, no. 8, August 2012
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