ASHRAE Journal - October 2024 - 53

2024 ASHRAE TECHNOLOGY AWARDS CASE STUDY
reduction in energy use.
The mechanical system was carefully designed to be
energy efficient, effective and maintenance friendly.
The school is on a traditional schedule where the
students are not in the building during holidays
and the summer, but some of the administration
occupy their offices during those times. The areas
that are occupied while school is in session, such as
the classrooms, cafeteria and multipurpose room,
are served by air handlers, but the spaces that will be
occupied year-round, such as the administration office
or data rooms, are served by packaged air-to-water heat
pumps. This approach saves energy as the large fans and
pumps that serve the air handlers can be shut off when
school is out. Smaller pumps are used to serve the airto-water
heat pumps allowing the school to save energy
while still conditioning the areas that will be in use.
The air handlers are also designed to be energy
efficient. In heating mode, each air handler uses an
energy recovery wheel to preheat ventilation air with
exhaust and relief air. In cooling mode, the air handlers
use four stages of cooling. The first stage of cooling is
the economizer mode using 100% outdoor air up to an
outdoor temperature of 65°F (18.3°C). The second stage
is free cooling, using the ground loop heat exchanger.
The third stage of cooling is to use direct evaporative
cooling, and the fourth and final stage of cooling is
indirect evaporative free cooling from the cooling tower.
This building also uses a thermal displacement
ventilation system that only requires a cooling supply
air temperature of 65°F (18.3°C). This higher supply air
temperature also eliminates the need for mechanical
cooling, further reducing energy use.
HYDRONIC SYSTEM
The hydronic system consists of multiple hydronic
loops that are interconnected through heat exchangers.
The ground loop system is a closed loop system
consisting of 40 bores that are 300 ft (91.4 m) deep. In
cooling mode, the ground loop provides free cooling as
the second stage of cooling. A heat exchanger is used
to transfer heat from the air-handler coils and air to
water heat pumps in the building loop to the ground
loop. In heating mode, the ground loop is pumped
through a water-to-water heat pump. This heat pump
generates 130°F (54.4°C) water for the building's
heating water loop.
TABLE 1 Values used in calculations for AHRHAE standards.
Space Occupancy
Standard 55 Values
Clothing Insulation
Summer Winter
Classroom
Media Center
Multiuse Assembly
0.5
0.5
0.5
1.0
1.0
1.0
Metabolic Rates
1.2
1.2
1.2
Standard 62.2 Values
Ventilation Rates
cfm/person
10
10
7.5
cfm/ft2
0.12
0.12
0.06
The cooling tower has its own loop and provides free
cooling to the building through a heat exchanger as the
fourth stage of cooling.
The heating water loop provides hot water to the
building. The water-to-water heat pump is the
primary heating equipment and generates 130°F
(54.4°C) water for the building, but the building
also has gas fired boilers. These boilers primarily
serve to assist during morning warm-up and provide
redundant heating capacity.
INDOOR AIR QUALITY (IAQ) AND THERMAL COMFORT
The thermal displacement ventilation system supplies
air at a low velocity directly to the occupied zones. This
displacement ventilation creates stratification as the air
warms up and rises around the occupants due to their
body heat. This upward flow also carries contaminants
with it, thus there are " higher concentrations of
contaminants above the occupied zone than in the
breathing zone. " * Thermal displacement also provides
an improved air distribution effectiveness of 1.2 while in
cooling mode. This system also provides 100% outdoor
air in all cooling modes, continuously providing fresh
air to the building.
The building was designed to meet the ventilation
rates of ASHRAE Standard 62.1-2016. Ventilation rates
used for typical spaces are shown in Table 1. The school
has multiple occupancy categories, and each was
zoned and designed to receive adequate ventilation
during occupancy. Demand control ventilation is also
used in classrooms and large group spaces to allow
for a reduction in ventilation air when the space has a
reduced number of occupants.
To create a comfortable environment and comply
with ASHRAE Standard 55-2017, the design space
temperatures were 75°F (23.8°C) in summer and 70°F
(21.1°C) in winter with a relative humidity of 50%. The
clothing insulation values and metabolic rates are
*2019 ASHRAE Handbook-HVAC Applications. Chap. 58.10.
O CTO B ER 2024 ashrae.org ASHRAE JOURNAL
53
http://www.ashrae.org
ASHRAE Journal - October 2024

Table of Contents for the Digital Edition of ASHRAE Journal - October 2024
