ASHRAE Journal - June 2020 - 19

TECHNICAL FEATURE

FIGURE 3 The primary energy conservation device is a heat pipe energy recovery coil.

Thermal Efﬁciency ~60%
Energy Savings
Summer: 720,000 Btu/h (211 kW)
Winter: 970,000 Btu/h (284 kW)
Evaporative
Cooling
Air from Outside
100°F - Summer
5°F - Winter

Exhaust Air From Building
75°F - Summer
70°F - Winter

Coil

Air to Building
72°F-Summer
44°F - Winter

CREDIT: NATHAN JOHNSON

protects the main cooling loop from research operational issues (leaks, unattended open valves, etc.). The
process chilled water is piped to each lab individually
and was sized to provide up to 3 tons (11 kW) of cooling
per lab.
Heat is provided using two condensing natural gasﬁred boilers, each sized at 100% of the peak design load
for full redundancy. The boilers operate at a maximum
supply water temperature of 140°F (60°C), and all terminal heating units were selected on that basis. The supply
temperature is reset based on outside air temperature.
This ensures that even at part-load conditions the return
water temperature remains low enough for the boilers
to operate in condensing mode, maximizing the energy
efﬁciency.
Heating and cooling for the mechanical room,
mechanical mezzanine and electrical room is provided by dedicated fan-coil units. The unit serving the
mechanical room includes an outdoor air intake with a
motorized damper, controlled by a wall-mounted timer
switch. Although the mechanical room is normally
unoccupied and does not require outdoor air for ventilation, maintenance personnel are able to manually operate the switch to provide ventilation as desired when
they are working in the space.
Individual labs often have widely varying temperature and humidity requirements. Occasionally, speciﬁc
requirements for temperature stability must be met, for
example equipment or processes that cannot tolerate
temperature variations of more than 1.5°F (0.8°C) over a
24 hour period. In addition, cooling is usually driven by
internal loads rather than envelope loads. PNNL uses a
design cooling load of 10 W/ft2 (108 W/m2) for equipment
and plug loads. To satisfy a wide range of conditions,
each lab at GPCL is a separate temperature control zone
with dedicated heating and cooling coils. With this conﬁguration the primary heating and cooling coils at the
central air-handling unit only meet part of the thermal
loads.
System air temperature is optimized and reset
between 60°F and 65°F (16°C and 18°C) for much of the
year, and the zone coils provide heating and cooling to
satisfy the thermal loads of the individual labs. Rather
than resetting system supply air temperature based on
the demand of the warmest (or coolest) zone, the zone
coils modulate to satisfy individual space demands without reheating or recooling system air. This strategy also

Pump

enables humidity control at the lab level instead of the
system level.
Although the local utility electrical power is generally
very reliable, electrical power is ensured at GPCL using
an uninterruptible power supply (UPS) and a natural
gas-ﬁred standby generator. On loss of primary power,
the UPS is able to maintain the operability of critical
systems such as the lab exhaust system, building DDC
controls and various lab equipment for up to 30 minutes, while the standby generator is capable of serving
the entire facility.

Energy Efﬁciency
Fume hoods are energy hogs. In fact, on an annual
basis the energy consumed by tempering the makeup
air for a single 6 ft (1.8 m) fume hood may be three
times as much as used by an average-sized single-family
home.4 Thus, reducing fume hood airﬂow is a primary
strategy to reduce energy use. At GPCL, fume hoods are
VAV restricted bypass with rotary potentiometer type
sash position sensors that signal the venturi air valve to
modulate the exhaust airﬂow between minimum and
maximum settings as the sash position changes. The
sensors also activate a local, audible alarm to alert users
if airﬂow and hood face velocity drop below the minimum required. In addition, the facility's controls system
tracks the sash positions and sends an alarm to operators if sashes remain open during unoccupied hours.
This is used to train and remind research staff to close
the sashes whenever possible.
The primary energy conservation device at GPCL is
a heat pipe energy recovery coil (Figure 3). Heat pipe
J U N E 2020

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ASHRAE Journal - June 2020

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