ASHRAE Journal - June 2022 - 57

FIRST PLACE | 2022 ASHRAE TECHNOLOGY AWARD CASE STUDIES
The existing school is equipped with water-cooled
chillers and gas-fi red condensing boilers, but they were
at maximum capacity and could not be used for the
new system. The design engineers engaged the school
to compare and prioritized various system options that
would rank in importance to meet their goals. These
criteria include fi rst cost, architectural integrity, operational
cost, ease of maintaining the system, health of the
occupants and energy consumption, etc.
Variable air volume (VAV) was eliminated early on as it
did not measure up in energy effi ciency and did not conform
with the architectural vision for the project since
it required more plenum space. The local heat pump
option was eliminated to reduce the need for additional
maintenance/replacement associated with compressors.
In the end variable refrigerant fl ow/dedicated outdoor
air system (VRF/DOAS) was chosen for this project.
Energy Effi ciency
Energy effi ciency was an important factor in determining
the type of system used. The VRF condensing
units operate at a part-load effi ciency between 22.0 to
22.9 IEER, and locating the units inside a penthouse
allowed for COP of over 3. The energy model for the
building indicated a 35% improvement over the baseline
(ASHRAE/IESNA Standard 90.1-2007 was used for LEED
v3). In addition to selecting effi cient systems, a key factor
in energy savings was the control strategy.
A common sequence would have the DOAS provide
outdoor air fully dehumidifi ed and then reheated to
room-neutral temperature. The design team made use of
the dehumidifi ed and cold air to actively cool the space.
The VRF setpoint and the VAV setpoints were interlocked
so the VRF would come on only when the outside air (OA)
cfm, dictated by the CO2 sensor, delivered at approximately
55°F (13°C) could not maintain setpoint. This
ensured that the VAVs satisfi ed the ventilation requirement
but also allowed reduced use of VRF cooling.
HVAC System
The all-electric system includes a DOAS unit with VAV
boxes that serves the ventilation needs of the building.
The 75 ton (264 kW), 11.8 EER, DOAS unit is equipped
with DX cooling with variable speed compressors, electric
heating with SCR controls, an enthalpy wheel at
74% total effectiveness, MERV 8 pre- and MERV 13 fi nal
fi lters and hot gas reheat. Each space is served by a VAV
FIGURE 1 Energy consumption (actual, with PV and modeled - kWHh).
Predicted Consumption
100,000
90,000
80,000
70,000
60,000
50,000
40,000
30,000
20,000
10,000
Actual Consumption
Actual PV
Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
2020
Actual EUI: 32.34 kBtu/ft2·yr Actual EUI with PV: -3.75 kBtu/ft2·yr
Modeled EUI: 35.85 kBtu/ft2·yr
box, which is controlled by a CO2 sensor located in the
space, except for the lab VAVs that are controlled by an
occupancy sensor instead. The labs are also equipped
with exhaust VAV boxes that are interlocked with the
supply VAVs to maintain the space at a negative pressure
when occupied. The building has no exhaust fans as all
exhaust was routed through the DOAS unit to maximize
the benefi t of the enthalpy wheel.
Air-cooled heat recovery VRF serves the comfort needs
of all the spaces. The condensing units for the VRF system
are in a mechanical penthouse in lieu of outside to
improve the effi ciency in the heating season.
The building has two two-story living walls. They
humidify the space in winter, and a dedicated dehumidifi
cation unit ensures indoor humidity levels are within
the comfort range in summer.
The school engaged with Illinois Clean Energy
Community Foundation (ICECF) to receive a grant of
$1 million if net zero was achieved. The building was confi
rmed certifi ed net zero energy by International Living
Futures Institute (ILFI), the fi rst building recognized as
such in Illinois. One condition was that the project does
not use any fossil fuel to operate the system, including
natural gas. The operation of the entire project is electric.
The building addition includes educational learning
spaces on the roof that included a greenhouse and roof
garden. The technology includes sensors in the roofi ng
system that allows students to understand and study
the relationship between green roof and R-values. The
greenhouse provides education on plant growth. While
on the green roof, the students can also view the PV
arrays and its impact on energy.
J U N E 2 0 2 2 ashrae .o rg ASHRAE JOURNAL
57
| 2021
kWh
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ASHRAE Journal - June 2022

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