ASHRAE Journal - May 2020 - 58

2020

ASHRAE TECHNOLOGY AWARD CASE STUDIES

TOP The heating and cooling plant contains three heat
recovery geothermal chillers (featured at left) and two
magnetic bearing variable speed chillers (featured in
center).
BOTTOM The ventilation system is connected to occupancy
sensors, allowing airﬂow to speciﬁc rooms to be reduced
when a room is not occupied.

PHOTO ALINA CORNEA ARCHITECTURAL PHOTOGRAPHY

individual thermostats, allowing
space temperatures to be adjusted to
patient preference.
The heating and cooling systems
were designed to CSA Standard
Z317.2-2010 temperature and
humidity levels, as required by the
OBC. Clinical and nonclinical spaces
comply with ANSI/ASHRAE Standard
55-2010, Thermal Environmental
Conditions for Human Occupancy, to
accommodate a variety of activity
levels, clothing thermal resistance levels, and comfort
for both patients and staff.

Innovation

The project team employed several innovative solutions in order to meet energy targets, including the use
of geothermal ﬁeld technology.
The heating and cooling plant contains three 108.7 ton
(382 kW), 1,042 MBtu/h (305 kW) heat recovery geothermal chillers, three 5,500 MBtu/h (1.6 MW) condensing
boilers, two 400 ton (1407 kW) magnetic bearing variable
speed chillers, and one 2,000 MBtu/h (586 kW) condensing boiler for low demand (Figure 3).
The geothermal system supplies a portion of the
building's heating load and all of the 24/7 cooling load
through a geothermal heat exchanger, with a total
unit capacity of 3,142 kBtu/h (921 kW) for cooling, and
3,044 kBtu/h (891 kW) for heating. The peak demand
of the geothermal system is 94.9 kW for cooling and
235.1 kW for heating. The geothermal ﬁeld is made
up of 100 boreholes that each reach a depth of 600 ft
(183 m), with a total length of 6,000 ft (1829 m) of piping. A propylene glycol ﬂuid is pumped through the
4 in. (102 mm) borehole piping underground. During
the summer months, the geothermal water loop rejects
heat into the surrounding soil, charging the ground as a
heat sink. The ground is then a heat source in the winter,
when the geothermal water loop absorbs the captured
heat.

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The condensing boilers were designed with a low
heating water return temperature of 100°F (38°C). At
this low temperature, the heating water loops can be
integrated into the condenser water loop to efﬁciently
service the heat recovery chillers.
The magnetic bearings in the chillers create less friction than standard oiled bearings, reducing energy loss
and improving the heat transfer efﬁciency by preventing
oil contamination into the condenser and the evaporator. The efﬁciency of the chiller is NPLV 0.337 kW/ton
(0.096 kW/kW).
Each of these systems is connected to a customdesigned central plant optimization (CPO) control
system. The CPO models energy use based on historic
building demand loads, time of day, building occupancy
schedules, and weather forecasts. Following these data,
the CPO maximizes the use of the heat recovery chillers

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ASHRAE Journal - May 2020

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