ASHRAE Journal - May 2022 - 62

Residence Hall Design Features
Geothermal, Chilled Beams
BY MASSINISSA OURTIRANE, P.ENG., ASSOCIATE MEMBER ASHRAE
B
ishop's College School, a non-profi t
independent boarding prep school in
Sherbrooke, Quebec, Canada, features
geothermal energy and chilled beams in a new
student residence built in 2018. The 2230 m2
(24,000 ft2) building, the Mitchell House, is a threestory
residence that includes 18 dormitories for 36
students, apartments for supervisors and visiting
parents, bathrooms and common areas.
The design team evaluated several alternative
heating sources with the criterion that the heat
source be stable and renewable. Given the fact that
the ground temperature is relatively warm and
stable in winter despite the cold Quebec winter
temperatures, the design team opted for geothermal
energy.
To mitigate the risk of energy imbalance between
the amount of heat extracted in winter and that
rejected in summer, a calculation was made to
ensure that the amount of energy extracted in
winter and rejected in summer were balanced. In
addition, the location of the geothermal wells near
a river allows the system to be optimized, as it is
known that the fl ow of groundwater near the geothermal
wells allows the ground temperature to be
rebalanced between seasons.
The closed loop geothermal system consists of
150 m deep (500 ft) vertical wells in which a water
and propylene glycol mixture is circulated and
heated using the ground's heat itself thanks to the
good thermal conductivity of rock and soil the wells
are located in. The geothermal system is designed
to meet 60% of the annual heating load. To even
further optimize the geothermal system, high effi -
ciency polyethylene piping fi lled with highly thermally
conductive nanoparticles were installed to
increase the heat exchange between the fl uid and
the ground. The thermal conductivity of this specifi c
Student residence building at Bishop's College School in Montreal.
pipe is 60% higher compared to the conductivity of
regular high-density polyethylene (HDPE) piping.
Hot and chilled water are provided by a geothermal
heat recovery chiller central plant system. In
the cooling mode, geothermal wells are used to
store energy from the condenser loop (waste heat).
When the building is in heating mode, geothermal
wells are used to inject heat in the heating loop
and the domestic hot water. In addition to the heat
recovery chiller, a geothermal water-to-air heat
pump was used in the design of this building. One
dedicated outdoor air system (DOAS) was provided
with a heat recovery coil to precondition the
incoming outdoor air by recovered energy from the
exhaust air.
The rest of the heating was performed by the geothermal
water-to-air heat pump. The facility also
uses a direct digital energy management and temperature
control system that monitors and controls
all HVAC and domestic water heating equipment.
On the ventilation side, the building owner preferred
to use active chilled beams for the resident
rooms. A chilled beam consists of a coil contained
in a housing that is recessed in the ceiling. Primary
air (fresh air in the case of this project) is supplied
within a plenum to be discharged through induction
nozzles, mix with entrained air and ventilate
the room. Active chilled beams provide space heating
and cooling without the use of a fan within
Massinissa Ourtirane, P.Eng., is energy effi ciency engineer at ORT Energy in Montreal.
62
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