ASHRAE Journal - May 2023 - 27

FIRST PLACE 2023 ASHRAE TECHNOLOGY AWARDS
Energy Efficiency
The design was required to meet stringent energy
efficiency outcomes in order to secure Federal National
Housing Strategy funding. The overall energy goal of the
project was to achieve an energy and greenhouse gas
reduction of 50% or greater compared to a traditional
natural gas-based National Energy Code for Buildings
(NECB) 2015 reference building. To meet this target, a
variety of design options were reviewed and modeled by
the design team's energy modelers. Energy compliance
with the Ontario Building Code 2015 was demonstrated
through the performance path of SB-10 using NECB 2015.
A vertical geothermal system with a closed-type
ground heat exchanger was implemented as an energy
source and sink for heating and cooling the building
(Figure 1). Due to their superior heat recovery performance
during shoulder seasons when compared to
two-pipe fan coil units and conventional water-source
heat pumps, 241 hybrid heat pumps were chosen to
provide heating and cooling to the building's suites.
When in cooling mode each hybrid heat pump's internal
compressor is on, and when in heating mode it is off.
Because of this, in shoulder seasons each hybrid unit's
heating load can be satisfied entirely by recovered heat
from the building loop. When the overall system is in
a net heating mode and absorbing heat from the geothermal
field, a central heat pump in the lowest parking
level is used to absorb heat from the geothermal loop.
The energy recovered between hybrid heat pumps
during shoulder seasons, where some units are in heating
and some are in cooling, improves overall efficiency
of the building. Instead of consuming additional energy
to heat a space, heat being rejected from a space being
cooled is essentially transferred to spaces requiring heat.
This is achieved indirectly from the net heating or
cooling requirement of the building loop as a whole. As a
result, less natural gas is consumed annually to heat the
building, more energy is recovered between hybrid heat
pumps during shoulder seasons, and less overall heat is
rejected to the geothermal field annually.
A wastewater energy recovery system was designed to
extract heat from outgoing sanitary wastewater and use
it to preheat domestic water. For more on the wastewater
energy recovery system, see the Innovation section.
Hybrid heat pumps in each residential suite have
CASE STUDY
energy recovery ventilators to provide fresh air and
exhaust for the suites. This minimizes heating and cooling
ventilation loads by transferring both sensible and
latent energy (both heat and humidity) between the
incoming and outgoing airstreams, reducing the overall
heating cooling requirements of the building. In the
winter, the incoming air doesn't require as much heating;
in the summer, the incoming air doesn't require as
much cooling and dehumidification from the evaporator
of the hybrid heat pump. This also improves occupant
comfort, as it helps to deliver consistent humidity
levels in the suites. Internal rather than external energy
recovery ventilators were used, resulting in a cleaner
installation, less ductwork, simpler controls and less
overall space required.
Compared to a standard OBC-compliant building
utilizing the NECB 2015 path of SB-10, 500,117 kWh
of electrical energy was saved through the building
design, with a peak reduction of 820 kW. The amount
FIGURE 1 Seasonal heat transfer via geothermal and hybrid heat pump system.
Backup/
Trim Boilers
Heat
Recovered
Heat
Heat From
Storage
Central
Heat Pump
Geothermal
Field
Hybrid Heat Pump In Heating Mode
(Central
Heat Pump
Bypassed)
Heat To Storage
Geothermal
Field
Hybrid Heat Pump In Cooling Mode
Compressor
of natural gas saved through the implementation of the
final design totaled 5,793 m3 (204,578 ft3).
Indoor Air Quality
Maintaining comfortable indoor temperatures and
indoor air quality (IAQ) is important to the design of residential
buildings. To maximize occupant comfort, each
residential unit contains a vertical hybrid heat pump,
and is ventilated through a dedicated energy recovery
Adrianne Mitani, P.Eng., is an associate, and Greg Snaith, P.Eng., is a senior project manager at Smith + Andersen in Ottawa, Ontario, Canada.
M AY 2023 ashrae.o rg ASHRAE JOURNAL
27
Recovered
Heat
COURTESY OF SMITH + ANDERSEN

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ASHRAE Journal - May 2023

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