ASHRAE Journal - November 2010 - 31

technology award case studies

Preheating Coil Outside Air

Electric Heating Coil

Supply Fans

Supply Toward Tower Perimeter Induction Units Electric Heated Pan Humidifier

Mixing Box in 100% Fresh Air During Day and 100% Return Air During the Night

Filters ER ER

Water Cooling Coil Pump Return Fan

Exhaust Air

General Exhaust

Figure 1: Original dedicated outdoor air system (DOAS) for the North Tower. The system had an electric coil, a chilled water coil, a runaround glycol loop for heat recovery on the exhaust air and an electrically heated hot water humidification pan.

Heat Recovery Coil

induction units. This system was fitted with an electric coil, a Implemented Modifications chilled water coil, a runaround glycol loop for heat recovery on Traditionally, in a northern climate such as Montreal, the exhaust air and an electrically heated hot water humidifica- inexpensive air conditioning for internal spaces comes from tion pan (Figure 1). The induction terminal units have an electric airside economizer cycles. However, heating for the perimeter coil and a chilled water coil to maintain adequate perimeter zones and heating and humidification of the outside air are still zone air temperature. needed. Consequently, the airside econoOn each floor, an air-conditioning unit mizer is basically wasting a lot of warm Building at a Glance draws its return air from close to the peenergy that could be reused if harnessed Name: Complexe Desjardins rimeter (obtaining its required outside air correctly. In this existing building retrofit, from there), supplying air conditioning to the cooling loads described in the previous Location: Montreal the floor’s internal zones using chilled water section had to be harnessed to contribute to coils. Complexe Desjardins is an all-electric building heating and humidification loads Owner: Desjardins Gestion building (Quebec’s electricity is mostly using decentralized chillers acting as a heat Immobilière renewable hydroelectricity) and, as such, pump and adiabatic humidifiers. the hot water used in the pan humidifiers In the North Tower, a 330 ton (1160 kW) Principal Use: Office was heated using an electric heater. Also, heat recovery water source heat pump on the Includes: Retail, Storage chilled water was produced centrally and chilled water network was installed. It uses distributed to the various HVAC rooms return chilled water to produce hot water Employees/Occupants: 10,000 throughout the complex. used to heat and humidify outside air and to Substantial Completion: 2008 At night, the dedicated outdoor air satisfy a part of the building envelope heatsystems operate as a 100% recirculation ing load. The hot water pan humidifiers were system to provide perimeter heating. Also, replaced with one-pass adiabatic humidifiers, another 100% DOAS supplies outside air using warm air to evaporate the water and to the commercial retail spaces (23,000 cfm [10 850 L/s]). producing humidification, while preconditioning the return air This system was identical to the previous system, though for sensible cooling purposes. smaller in size. Finally, two recirculating, dual-duct systems The installation of a 330 ton (1160 kW) chiller (to act as (77,500 cfm and 58,000 cfm [36 600 L/s and 27 400 L/s]) a “heat pump”) in the main ventilation mechanical room supply conditioned air to spaces located within the lower reduced required pipe lengths and installation costs (Figure levels of the tower (180,000 ft² [16 750 m²] of office spaces 3). This chiller cools chilled water returning from the recirand storage areas). Those systems had a dual supply fan, an culation air-conditioning units located on each tower floor, electric coil in the hot duct and a chilled water coil in the cold using it as a heat source and precooling the chilled water duct (Figure 2). returning to the chiller plant (reducing its load). Condenser
November 2010 ASHRAE Journal 31

ASHRAE Journal - November 2010

Table of Contents for the Digital Edition of ASHRAE Journal - November 2010