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43 Percent Energy Savings

©2012 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 54, no. 12, December 2012.

43% Energy Savings

By Geneviève Lussier, Eng., Member ASHRAE; Victoria Lakiza; Jean-François Dubé; and Pierre Lévesque, Eng., Member ASHRAE

About the Authors: Geneviève Lussier, Eng., is a project manager, Victoria Lakiza is a project manager and junior engineer, Jean-François Dubé is a professional technologist and project manager, and Pierre Lévesque, Eng., is president of SMi-Enerpro at Enerpro, division of Le Groupe SM International in La Prairie, QC, Canada. Lussier and Lévesque are members of the Montreal Chapter of ASHRAE

A nearly 30-year-old condominium complex near Montreal wanted to reduce its largest monthly expense, which was its electricity bill. So, the Les Verrières sur le Fleuve complex decided to optimize its mechanical systems in the public spaces, which saved 43% of the total energy consumption.

The complex has two 18-story twin towers with 120 apartments each, totaling 495,000 ft2 (45 987 m2). The lowest levels house public spaces such as an indoor swimming pool, two levels of heated interior parking and a number of multiuse rooms and storage areas.

Improvements were made to the domestic water booster pump, the exhaust and makeup air ventilation system, the cooling towers, the indoor swimming pool ventilation system, the outdoor swimming pool water heating system as well as the ventilation of the interior garages.


Domestic Water Booster Pump

The domestic water booster pump system was optimized by installing a variable frequency drive on the 10 hp (7.5 kW) booster pump to modulate water flow according to domestic water demand. Since this pump operates year-round, the speed modulation saved about 50% of its energy consumption.


Cooling Tower System

The cooling tower system includes four 20 hp (15 kW) water pumps and two dual 25 hp (18.5 kW) fan water cooling towers. These pumps and towers run when the air-conditioning units installed in each apartment start operating, which is from April to late October, about 5,000 hours annually. Two pumps (one in each tower) circulate the air-conditioning unit’s condenser water to both cooling towers (one in each tower).

In this project, one variable frequency drive was installed on one of the pumps (the other one is only used for backup) to modulate the flow according to the condensing water temperature in the cooling towers’ basins. This means that this pump only runs at full speed when outside temperatures are exceptionally high. In addition, the cooling tower fans were equipped with frequency drives so that their airflow can modulate in response to the heat charge instead of starting/stopping to maintain the water temperature setpoint.


Makeup Air and Exhaust Systems

Every apartment’s exhaust from its kitchen hood, bathroom and dryer is discharged into a series of exhaust ducts, which are exhausted outside by a 15,000 cfm (7080 L/s), 10 hp (7.5 kW) main fan in each tower. This exhaust air is compensated by one 100% fresh air ventilation system of 14,000 cfm (6000 L/s) that supplies public corridors on each floor. Heat pipe heat recovery was already installed on these systems.

To maximize heat recovery, two 6 ton water-source geothermal heat pumps were installed on the fresh air supply system. The heat pumps use a portion of the air downstream of the heat pipe, heating and discharging it before the electric heater. A new heat recovery coil was installed downstream of the heat pipe in the exhaust air. The new heat pump evaporators cool a glycol loop that goes through the new coil and cools the exhaust air. This allowed heating all of the fresh air without using the electric heater most of the time.

As for the fans, new variable frequency drives were installed on their motors to adjust the exhaust and fresh airflows in off-peak periods. The exhaust fan modulates to maintain a given negative pressure setpoint in the exhaust while the fresh air fan varies to track the exhaust airflow. In the summer, the heat pumps cycles are reversed, and the fresh air is cooled, improving occupant comfort in the corridors.


Indoor Swimming Pool Water Heating & Ventilation System

The 502 ft2 (47 m2) indoor swimming pool was dehumidified by a 100% fresh air system equipped with a 50 kW electric heater. The water was heated by a 35 kW electric heater. To reduce electricity consumption, a new air-to-air heat exchanger was installed on the fresh air system and exhaust duct. This heat exchanger is used to recover energy from the hot, moist exhaust air and transfer it to the fresh air intake where it heats the incoming fresh air.

A new 4 ton (14 kW) heat pump was installed in the return duct of the ventilation system and is used to dehumidify the swimming pool air. The heat rejected by the heat pump’s condenser is used to heat the swimming pool water. These measures resulted in entirely heating the introduced fresh air and the swimming pool water without using the existing electric heaters. Furthermore, indoor air quality of the spaces adjoining the swimming pool was improved because the interior pressure of the swimming pool room now is maintained at a negative pressure. This way there are fewer chloramines and odors transferred to the surrounding spaces.

Citation: ASHRAE Journal, vol. 54, no. 12, December 2012


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