A fresh flow of air supply solutions could answer one of the leading design
conundrums facing laboratory designers.
An HVAC engineer’s prime concern when planning or constructing any laboratory building is
the safety of the building’s occupants. The system must operate to specification and meet
appropriate regulations. To this end, many older laboratories were designed with little regard
to energy efficiency. That’s no longer true, and designers must account for operating costs as
well as functionality.
A typical laboratory building consumes five to ten times more energy than a typical office
building or school. HVAC systems consume almost 70% of a laboratory’s energy, according to
Labs21, a voluntary partnership program dedicated to improving the environmental
performance of U.S. laboratories. The majority of this HVAC energy consumption originates from
cooling (22%) and ventilation (44%) loads that help the laboratory function safely.
“This high energy use can be attributed to high outside air requirements, large internal
heat gains from laboratory equipment, and, in many cases, continuous hours of operation,” says
Jeffrey L. Linde, PE LEED AP, Newcomb & Boyd, Atlanta, Ga.
With a push toward a more energy-efficient laboratory environment, vendors are developing
new technologies—or adapting older ones—to help reduce HVAC energy consumption. Before they can
apply their expertise, questions must be answered. What HVAC techniques or technologies can
reduce energy use? How effective are they? How much do they cost? Can these technologies be
improved?
The problem with extra air
Lighting and electrical loads account for 11% and 23%, respectively, of a lab’s total energy
consumption, according to Labs21 data. But the lion’s share of a lab’s electricity bill is
connected to the need for plenty of outside air. This impact, in relation to the total HVAC
energy consumption of a typical lab, is about 80%, or about 60% of the total energy use of the
lab building, according to Gordon Sharp, chairman of Aircuity, Newton, Mass.
The metric with the most impact on lab HVAC system efficiency is the minimum air change, which
can vary. The U.S. Environmental Protection Agency’s minimum recommendations range from 4 to 12
air changes per hour (ACH).
“The overall energy consumption of any laboratory is closely tied to its minimum air change
rate, which makes the difference between 4 ACH and 12 ACH almost triple the energy
consumption,” says Linde.
A common strategy to mitigate outright energy use is take advantage of the gap in energy or
heat between the outgoing exhaust air in a laboratory and the incoming supply air. Technologies
that attempt to leverage this differential include air-based systems such as run-around coils,
heat pipes, cross flow heat exchangers, heat wheels (mainly enthalpy wheels)—and chilled beams,
a chilled water-based system.
When these approaches are implemented individually, results can be seen but are often
incremental. According to various lab design experts, the appropriate approach for a sizable
reduction in laboratory energy use is to take a holistic or integrated systems approach to
energy-efficient technologies.
“Combining different technologies can often create a situation where the whole is greater
than the sum of the parts,” Sharp explains.
A good example are active chilled beams, which have been used in European facilities for
several years, and just recently gained traction in the United States. Chilled beams are
ceiling-mounted diffusers that use building supply air to induce room air to pass through an
integral water coil. The induced room air is cooled by the coil above the ceiling tile to
provide local cooling in the laboratory.
This additional local cooling nets three main positive effects for a lab’s HVAC
system—reduced supply air flow, less reheat energy, and lower system first costs. However, with
typical fixed minimum dilution ventilation rates of 6 to12 ACH, a good amount of conditioned
air still has to be brought to the lab, even at the lower end of this range.
“Where cooling loads are low to moderate, this might increase energy consumption due to the
extra fan power and reheat energy that would be required for that redundant air flow,” says
Sharp. A demand-based control system can reduce the ventilation requirements and air flows to
between 2 to 4 ACH of air flow, he explains. The chilled beams can then handle the cooling load
above this point to save fan energy and reduce reheat.
Energizing incentives
In the past, laboratories did not take many or any steps to monitor energy use beyond the
review of electric, gas, and water bills. As large consumers of energy, laboratory owners are
learning that they can benefit from the Leadership in Energy & Efficient Design (LEED) green
building certification program by U.S. Green Building Council.
The program encourages both energy-efficient and environmentally-friendly building features
and offers credits toward certification for building features or techniques. The guidelines to
measure and verify energy savings have motivated lab owners to install more elaborate energy
metering systems to track ongoing energy consumption. The information collected can be compared
to the performance predicted by a calibrated computer model of building energy use, potentially
leading to large energy savings.
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Diagram shows how Aircuity's OptiNet technology works within a laboratory setting.
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To meet goals set forward by programs such LEED, Labs21, or even a lab owner’s bottom line,
better air management systems have been in constant development. These are typically
systems-based approaches that either evolve from established air management practice or rely on
new technologies such as sensors and embedded systems. One such solution is the centralized
demand-control ventilation system (CDCV).
In a typical demand-based control system, sensors are placed in each room in the lab to
measure contaminants and make system adjustments in real time. A CDCV uses a different
approach. A sample of each room’s lab exhaust air is captured and brought to a centralized
sensor suite for analysis.
In the case of Aircuity’s OptiNet CDCV system, every 40 to 50 seconds
a sample of air is routed through a common air sampling backbone—a tube within a structured
cable—to the sensor suite for measurement. These sequential measurements are then
“de-multiplexed” for each sampled area to create distinct sensor signals that can be used for
monitoring and control.
The number of required sensors is reduced by a factor of 20. Monitored labs can run overall
air change rates as low as 2 ACH when the air is clean, but can increase the airflow rates to 8
to 16 ACH when contaminants are sensed.
The OptiNet system was used in the Feigin Center of Texas Children’s Hospital, a facility
recognized in R&D Magazine’s 2010 Laboratory of the Year competition. But not every lab
requires the latest in air-handling technology to benefit, and many labs simply transfer from
constant air volume (CV) reheat systems to variable air volume (VAV) technology.
Over the past 25 years, VAV systems have largely displaced CV as the HVAC approach of choice
for labs that require a significant throughput of outside air. The VAV system takes advantage
of the fact that cooling loads in most laboratory spaces are not constant. As the cooling load
decreases from its design peak, the need for supply air also decreases.
“The decrease in supply air is accomplished with variable frequency drives that control the
speed of the supply fans. The energy consumed by these fans decreases as the supply air
capacity decreases,” says Linde.
The need for speed control
As the need for supply air decreases, so does the need for general exhaust. A VAV exhaust air
system uses variable frequency drives, which use less energy than constant speed drives, to
control the exhaust fan speeds.
Siemens Building Technologies, Zug, Switzerland, manufactures a line of
variable speed drives, called SED2. This, according to Jim Coogan, principal application
engineer at Siemens, “is one of the biggest energy savers that can be implemented into a
laboratory setting.” The technology’s low harmonic disruption to the power quality of other
equipment and small footprint set it apart from other variable speed drives, he says.
If a laboratory distributes AC power continuously at a steady frequency of 60 cycles per
second, the SED2 will vary the speed of motors by varying the power that comes from the power
source. The motor will turn at a different speed, lowering overall power and energy
consumption.
When a VAV system reduces the air flow rate in a laboratory, “it saves energy at every
component in the HVAC system,” says Coogan. “VAV systems are also likely to reduce the need for
reheat in a room, so the energy saved at the reheat coil is actually saved twice.”
Fixes for existing systems
In addition to the previously mentioned strategies, laboratory fume hoods can also help
mitigate airflow requirements in labs. While fume hoods primarily are safety devices, energy
savings and safety don’t have to be mutually exclusive.
A lab using a CV exhaust system with standard fume hoods operating at 100 fpm baseline face
velocity has several choices to raise efficiency, says Bob DeLuca, Jr., vice
president—technical products at Lab Crafters, Inc., Ronkonkoma, N.Y. The first
are high performance hoods operating at 50 to 60 fpm face velocity.
“High efficiency, low-air-volume hoods, also known as low velocity hoods or high performance
hoods, are designed to operate with lower volumetric flows and low face velocities compared to
conventional hoods,” says DeLuca. These hoods can reduce the heating/cooling demands on the
HVAC system without operator interaction required. However, savings can only be seen in
laboratories where all loads in an HVAC system are driven by the hood population and density,
DeLuca says. These hoods work well with both CV and VAV systems.
Kewaunee Scientific, Inc.’s, Statesville, N.C., Supreme Air LV fume hood is
one example and was designed to operate safely at a face velocity as low as 55 fpm vs. the 100
fpm of a conventional hood.
“The sash on an LV hood locks open to full height for set up procedures then self-closes to
18 inches for normal operation, allowing a VAV system to exhaust air at a reduced rate,” says
Kurt Rindoks, vice president of engineering and product development, Kewaunee Scientific. A
Cartesian baffle system, a dynamic barrier bypass, a flush airfoil, and a new shape for the
sash handle and fascia panels achieve the energy efficiency.
A second alternative, according to DeLuca, is a two-position exhaust system, which has one
designated airflow during occupied time and another when the hoods or lab are not in use. These
two-position systems “can incorporate standard fume hoods or high performance fume hoods for
greater efficiency,” says DeLuca.
One of the most common solutions in today’s laboratories is to install a VAV fume hood,
which can modulate between maximum and minimum set-points for fpm as the fume hood sash
position is adjusted by the user. By reducing the size of the operating sash opening, a lower
exhaust flow is required of the HVAC system. American Auto Matrix’s (Export,
Pa.) Auto-Flow, a fume hood control system, can automate these sash adjustments.
“With our Auto-Flow controller, one can implement sash-pots, face velocity and exhaust duct
sensors, hood presence detectors, and even select the damper style preferred,” says Paul
Jordon, CTO, American Auto Matrix. “The ability to have full and complete control over what is
running in a laboratory is crucial to saving energy and money.”
The demand for energy efficiency, highlighted by spiraling utility expenses and incentives
offered by government agencies, has created a new demand for lab owners: control. By exercising
control over an HVAC system, whether through a Supreme Air LV fume hood for an existing CV
system, an Auto-Flow controller for a VAV installation, or an OptiNet CDCV, the energy savings
can be realized.
Published in R & D magazine: Vol. 52, No. 4, August, 2010, pp.
20-24.
