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Article-lussier.jpg

©2014 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 56, no. 12, December 2014.

Geneviève Lussier, Eng., Member ASHRAE

About the Author
Geneviève Lussier, Eng., is director, technology and design at SMi-Enerpro in Longueuil, Quebec, Canada.

Canadian winters are harsh, resulting in high heating loads. But a new office building (nicknamed “Jonxion”) near Montreal is entirely heated using only heat recovery measures and renewable energy from the ground. The design of the envelope and mechanical systems helped lower capital costs and energy consumption of the building to only 9.7 kWh/ft2 (104 kWh/m2) per year.

The building envelope design was crucial to heating the whole building and fresh air supply using only recovered heat from interior spaces and from the ground. All floor-to-ceiling windows are triple paned to limit heat loss and heat gain. Smaller windows (5 ft high and less) are double paned, low-e with argon gas space. These specifications obtained a uniform and low perimeter heat loss and heat gain per linear foot, making the mechanical design simpler. 

 

Mechanical Systems Description

The gross building area is 117,918 ft2 (10 955 m2) distributed on five floors. The refrigeration systems are located in a roof penthouse. A mechanical room is located on each floor for the secondary ventilation systems. A dedicated outdoor air system (DOAS) of 16,000 cfm (7551 L/s) is located on the roof and distributes fresh air to the secondary systems. The DOAS is also equipped with an exhaust fan that exhausts air from the restrooms and general spaces.

A heat recovery wheel is installed in the DOAS to recover heat from the exhaust air. This wheel also recovers latent energy from the exhaust air, which eliminated the need to install a humidifier in the DOAS. To prevent freezing of the wheel when outdoor temperatures are very low (less than 10°F [–12°C]), the speed of the wheel is reduced. Each floor of the building is air conditioned by a secondary system equipped with a cooling coil. This system mixes return air with treated fresh air from the DOAS. On every floor, for the building periphery, six fan coils cool or heat the air according to the envelope load. As a result, since the fan coils offset the envelope load, the full occupied space becomes an internal zone, resulting in a sizable cooling load year-round in the building, even in winter.

The heat removed from these interior spaces (by two 80 ton (281 kW) centralized chillers) is rejected (from the chiller condensers) in a heating loop to heat the fan coils located in the peripheral zones. Basically, in winter, these chillers are used as heat pumps. This means that heat generated from the internal spaces is transferred to the peripheral spaces.

The chillers operate at high evaporator temperatures (±48°F [9°C]) and low condenser temperatures (±95°F [35°C]), which results in a lower kW/ton. In this case, after a one-year study, we observed that only one of the 80 ton (281 kW) chillers is needed, and it operates at a 60% average load (±48 tons [169 kW]). At this operation point, the chiller’s energy consumption is approximately 0.65 kW/ton. Furthermore, if the heat gain from the internal spaces is not enough to satisfy the heating load, the chiller extracts energy from the ground using the 28 geothermal closed loop vertical 500 ft (152 m) deep boreholes. All the heating coils were designed to use low temperature heating water, making it possible to use heat rejected by the chillers without adding any energy and thus increasing the efficiency of the chillers by operating at lower condenser temperatures.

All of these sources of heat recovery resulted in the ability to heat the air from the ventilation systems without using boilers. This means that the whole building is heated without using an external energy source (fuel, gas or electrical energy), resulting in a significant reduction of CO and CO2 emissions and energy consumption.

 

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