ASHRAE Journal - May 2021 - 59

SECOND PLACE | 2021 ASHRAE TECHNOLOGY AWARD CASE STUDIES

FIGURE 1 Alice West Fleet site energy, Aug. 2019 through July 2020.

1,000

Site Consumption (MBtu)
Site Generation (MBtu)
Net Zero Tracking (MBtu)

800
600
Site MBtu

As the building rises vertically, it steps back toward the
northern portion of its footprint. This serves the dual
purpose of reducing shading on the photovoltaic system
on the roof, while simultaneously creating roof overhangs on the building's south side to shade portions of
the building from direct solar rays to further reduce the
cooling load.
A number of early energy models run with different
HVAC systems for comparison helped determine that
a water source heat pump system using a geothermal
well ﬁeld would be the most efﬁcient. The geothermal
well ﬁeld, comprised of 72 vertical bores at a depth of
560 ft (171 m) each, provides the school's main source
of cooling and heating.
On average, each heat pump serves two classrooms
that share nearly identical internal and external load
conditions along with similar occupancy schedules.
This helps reduce the total HVAC tonnage by rightsizing the equipment closer to calculated HVAC loads.
Each heat pump is also equipped with dual stage
compressors and the ability to unload excess HVAC
tonnage. Their ability to run at part load a majority of the time is a main reason for this system's high
efﬁciency.
Another critical element reducing the HVAC system's energy consumption is the use of a variable ﬂow
dedicated outdoor air system (DOAS). Decoupling the
ventilation airﬂow from the heat pump units greatly
reduces the energy consumed. Demand-control ventilation (DCV) and an enthalpy wheel also reduce
energy consumption. The enthalpy wheel helps
reduce load, while using DCV reduces conditioned
outdoor air being sent to empty classrooms when it is
not required.
The building's energy use intensity in the school's
ﬁrst year was 17.2 kBtu/ft2·yr (195.3 MJ/m2), a
reduction of almost 68% of the energy used by the
ASHRAE/IES Standard 90.1-2010 baseline system.
With a roof photovoltaic system sized at 582 kW, the
school will generate 727 MWh yearly. This results in
a building capable of generating 9.5% more energy
than it is modeled to consume. The ﬁrst year's energy
consumption and PV production are shown in Figure 1.
Since the PV system came online in February 2020 the
building has been producing more energy that it has
consumed, illustrating its projected path toward zero
energy.

400
200
0

Aug Sep Oct Nov Dec Jan

Feb Mar Apr May Jun Jul

-200
-400
FIGURE 2 Indoor air quality control schematic.
PHOTO: VMDO ARCHITECTS-SAM KITTNER PHOTOGRAPHY

Carbon Scrubber
Exhaust Air
Outdoor Air

DOAS

From Classroom Spaces
Relief Air
Outdoor Air
To VAV
Variable Air
Terminal Units
Volume

Relief Air
Outdoor Air

CO2
Sensor
Thermostat

Return Air
Geothermal
Heat Pump

Supply Air
Geothermal
Water
Loop

Classroom

IAQ

An important design feature intended to increase the
IAQ is the use of DCV sequences with the DOAS. This
system uses carbon dioxide (CO2) sensors in the building that operate variable air volume (VAV) boxes to regulate the ﬂow of ventilation air, as allowed by ASHRAE
Standard 62.1-2010. The sensors can detect rising CO2
levels in classrooms and open the VAV damper to allow
more fresh air to be delivered to occupants (Figure 2).
The desire to keep the CO2 levels in the school low is
driven by the Standard 62.1-2010 requirement for fresh
air and also by a study1 that showed that the quality of
indoor air is critical for students' physical health and for
their ability to learn and retain knowledge. Therefore,
the ventilation airﬂow was set to maintain a maximum
setpoint of 800 ppm CO2 and a minimum of 400 ppm
(outdoor air condition).

Thermal Comfort

The HVAC system was designed with local occupant
control in mind to ensure occupant comfort under
ASHRAE Standard 55-2010.
M AY 2021

ashrae.org

ASHRAE JOURNAL

http://www.ashrae.org

ASHRAE Journal - May 2021

Table of Contents for the Digital Edition of ASHRAE Journal - May 2021