ASHRAE Journal - December 2014 - 49

2014 ASHRAE TECHNOLOGY AWARD CASE STUDIES

ABOVE Main entrance.
LEFT Lobby.

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.
All ventilation systems' fans are equipped with variable frequency drives. Since the fresh air is supplied by a
DOAS and the secondary systems do not exhaust air, no
return fans were necessary. Airflows to zones are varied
depending on heating and cooling loads. The peripheral
fan coils are equipped with ECM motors. The minimum
fresh air amount introduced in the systems was determined using ASHRAE Standard 62.1-2007. CO2 levels are
monitored on each floor as well as high occupant density
rooms (for example, conference rooms). High induction
diffusers were used to increase comfort levels in each
zone. Furthermore, during construction, all sealants,
adhesives, paints and glues had low or no VOCs in their
composition. Figure 1 illustrates the ventilation systems
configuration.
Both chilled and heating water are produced using two
80 ton (281 kW) high efficiency twin screw compressor
chillers. The fan coil systems can either cool or heat the
D ECEM BER 2014

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