An HVAC engineer’s first goal when planning any laboratory building is always the safety of
the occupants. However, the secondary focus has become creating energy-efficient laboratories
that meet the owner’s expectations for functionality and cost control.
A typical lab building consumes five to 10X more energy than an office building or school.
Almost 70% of a laboratory’s energy consumption is attributable to HVAC systems, according to a
report by the federal Labs21 sustainability program, with electrical load representing an
additional 23% and lighting about 11%. Most HVAC energy consumption originates from cooling
(22%) and ventilation (44%) loads that help the laboratory function safely and ensure user
comfort.
“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, of Atlanta-based engineering firm Newcomb & Boyd.
Vendors are responding to sustainability concerns by developing new technologies—or adapting
older ones—to help reduce HVAC energy consumption. What HVAC strategies can be implemented to
reduce energy use? How far have we already come in meeting this objective? And what can be done
to improve on the HVAC technologies already present?
The problem with extra air
The need to provide outside air to labs—most often in a once-through rather than recirculated
fashion—accounts for about 80% of the HVAC energy consumption of a lab, or about 60% of the
building’s total energy use, according to Gordon Sharp, chairman, of the Newton, Mass.-based
firm Aircuity.
Thus one of the biggest benchmarks determining lab HVAC efficiency is the minimum air change
rate. Various authorities propose diverse guidelines and standards for this key number. For
instance, the EPA’s recommendations range from as low as four air changes per hr (ACH) to as
high as 12 ACH, depending on the lab’s function and purpose.
“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.
Exhausting air that has been tempered at great expense, after passing through a space only
once, is obviously an expensive proposition. Though systems for improving heating and cooling
efficiency are important (see the sidebar, Energy recovery and chilled beams), lab HVAC
efficiency remains largely dependent on air volume. Thus most of today’s forward-thinking
energy management strategies hinge on eliminating the use of arbitrary ventilation values.
Instead, the goal is providing ventilation at levels that more accurately match actual lab
usage patterns and contamination hazards.
Energy recovery and chilled beams
A common enhancement for a laboratory HVAC system is the use of energy or heat recovery
between the outgoing exhaust air and the incoming supply air. These technologies, in effect,
capture heat energy (sensible heat), moisture energy (latent heat), or both, from the exhaust
airstream and transfer it to the supply airstream. Thus the energy expended in the initial
tempering of outside air is maximized.
Technologies for energy recovery include run around coils, heat pipes, cross flow heat
exchangers and heat wheels (mainly enthalpy wheels), all of which are air-based systems.
Efficiency on the cooling side can often be maximized with chilled beams—a chilled water based
system.
Active chilled beams have been implemented in European facilities for several years, and
just recently have been implemented in North American labs. By definition active chilled beams
are ceiling-mounted diffusers “that use building supply air to induce room air to pass through
an integral water coil,” explains Jeffrey L. Linde, of Newcomb & Boyd. The induced room air is
cooled by the coil above the ceiling tile and provides local cooling in the laboratory.
The local cooling provided by the beams has three positive effects: the potential reduction
of supply air flow, the reduced need for reheat energy, and lower system first costs. However,
because minimum ventilation rates are often fixed in the six to 12 ACH range, a large amount of
conditioned air still has to be brought to the lab even at the lower end of this range, though
it would not be required for cooling. Generally, the prescribed ventilation rate, rather than
cooling load, is driving design.
“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
Aircuity’s Gordon Sharp.
“However, with the ventilation requirements and air flows reduced using demand-based control
to between two and four ACH of air flow, chilled beams can then handle the cooling load above
this point to save fan energy and reduce reheat.”
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Ventilation systems of the past and present
Before the 1990s, the most common HVAC systems used for laboratories were constant air volume
(CV) systems, which supply and exhaust air at a fixed rate. However, variable air volume (VAV)
systems have gained significant popularity during the past two decades. VAV requires more
complex infrastructure, including VAV fume hoods, but the savings for many labs that have
implemented it have been impressive. It has rapidly become the industry standard for
hood-intensive facilities, particularly if occupancy is sporadic.
The common theme seen in energy conservation within laboratories is variable response to
dynamic demand. A VAV system takes advantage of the fact most hoods are not constantly in use.
As lab use decreases from its design peak, the need for supply and exhaust air also
decreases.
In modern VAV systems, hoods and controls work in synergy with air supply and exhaust—for
instance, ramping airflow up when hood are in the full-open sash position. When sashes are
closed, the airflow ramps down to a lower level. “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.
A VAV system uses variable frequency drives to control air handlers and exhaust, reducing
energy needs. Instead of connecting fan motors straight to the line current, the current first
passes through the variable speed drive, which then controls the motors. If a lab receives AC
power at a steady frequency of 60 cycles per sec, the variable speed drive will vary the speed
of motors by governing the power that comes from the source. This setup is not only more energy
efficient but also safer, since the airflow is based on the real-time needs of the lab and its
personnel.
Siemens Building Technologies, a global firm, manufactures a line of variable speed drives
named SED2, which according to Jim Coogan, principal application engineer, “is one of the
biggest energy savers that can be implemented into a laboratory setting.” 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.”
The SED2 technology has two qualities that, according to Coogan, set it apart from other
variable speed drives: low harmonic disruption to the power quality of other equipment, and a
small footprint.
In addition to VAV, with its variable speed drives, modern engineering design for labs calls
for low pressure drop within the ventilation system. See the Labs21 best practices guide at
www.epa.gov/lab21gov/toolkit/bp_guide.htm for tips and guidelines on low-pressure-drop
design.
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Aircuity's OptiNet CDCV system diagram.
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Basing airflow on air quality
VAV marked a major change in the way many designers thought about lab HVAC—notably, basing
design on actual need rather than conventional wisdom or arbitrary guidelines. More recently, a
new approach—demand control ventilation—has begun to gain acceptance.
OptiNet, Aircuity’s centralized demand-control solution, has been implemented in both of R&D
Magazine’s 2010 Laboratory of the Year winners and other laboratories around the nation to
monitor and detect air contamination and adjust ventilation accordingly, to create a safe
environment with low air change rates at a low cost. The centralized demand-control (CDCV)
technology incorporates many different sensors to measure real-time contaminants in a
laboratory, safely controlling the dilution ventilation (or air change rate) of a lab room. VAV
design is required so ventilation can be varied according to measured air quality.
A sample of each room’s exhaust air is captured and brought to a centralized sensor suite
for analysis, rather than relying on multiple sensors within in each room to analyze that
specific environment. To install three or four sensors in every lab room would be very costly,
both in capital expense and ongoing maintenance. “All energy savings would be wiped away by
operating costs,” says Sharp.
With the OptiNet technology, one sensor suite can monitor multiple areas (usually, about 20
rooms per sensor suite). Every 40 to 50 sec, a sample of air from different areas is routed
through a common air-sampling backbone, consisting of 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 ventilation
control.
The unique structured cable includes special tubing known as “microduct,” made from carbon
nanotubes mixed with a special inert plastic fluoropolymer. Most HVAC plastic tubing cannot
pass the particles that need to be sensed as part of demand-based control, due to static that
attracts contaminant particles to the inner walls, causing buildup. Adding carbon nanotubes to
the plastic creates electrically conductive tubing that prevents the static charge and
subsequent particle buildup. In addition, the mixture of carbon nanotubes and the fluoropolymer
plastic is much more chemically inert and non-absorptive than conventional tubing. As a result,
this material does not affect the VOCs or chemical vapors that are flowing through, allowing
accurate contaminant measurement.
With continual environmental monitoring, air change rates can be reduced to as low as 2 ACH,
according to Sharp, providing up to an 80% reduction of energy use while protecting personnel.
If contamination is sensed, such as with a chemical spill, the lab airflow rates automatically
increase to a purge rate of 8 to 16 ACH. Since lab air in a well-designed building is “clean”
of contaminants more than 98% of the time (according to measured averages), considerable energy
can be safely saved.
Fume hood efficiency improvements
In general, fume hoods continue to drive airflow requirements in labs. Thus hoods need to be as
efficient as the other components of the HVAC infrastructure.
With traditional CV design, fume hoods operate at a fixed 100 ft/min (FPM) face velocity,
consuming a large amount of supply air. During the past decade or so, vendors have begun to
change this paradigm with hoods created to protect users at much lower face velocities.
Introduced in 1997, high-performance hoods have proved a safe and energy-efficient alternative
to conventional hoods.
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Variable-speed drives modulate power coming to HVAV system motors, allowing equipment to more closely match actual building conditions and needs. Photo courtesy of Siemens Building Technology.
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Lab Crafters Inc., Ronkonkoma, N.Y. pioneered this approach, with the initial
energy-efficient alternative being a CV exhaust system with high-performance hoods operating at
50 to 60 FPM face velocity. “High-efficiency, low-air-volume hoods are designed to operate with
lower volumetric flows and low face velocities compared to conventional hoods,” says Bob DeLuca
Jr., VP-technical products. However, significant savings can only be seen in laboratories whose
HVAC loads are primarily driven by the hood population and density.
A second alternative within CV design is a two-position exhaust system, which provides
reduced airflow during specified periods of low occupancy or unoccupied conditions (often
referred to as “night setback”). Two-position systems “can incorporate standard fume hoods or
high-performance fume hoods for greater efficiency,” says DeLuca Jr.
The third alternative is the previously discussed VAV design, where fume hoods modulate
between the maximum and minimum set-points as the fume hood sash position is adjusted by the
user or by occupancy-sensor-based positioning systems. The ability to reduce airflow safely
when sashes are down can create major energy savings.
Many manufacturers now offer a range of high-performance (low face velocity) hoods, with
models that can work with both CV and VAV design. Kewaunee Scientific Inc.’s Supreme Air LV
fume hood is a good example. “The sash on an LV hood locks open to full height for set up
procedures then self-closes to 18-in. for normal operation, allowing a VAV system to exhaust
air at a reduced rate,” says Kurt Rindoks, VP engineering and product development at the
Statesville, N.C., company. Achieving energy efficiency with a combination of a unique
Cartesian baffle system, a dynamic barrier bypass, a flush airfoil, and a new shape for the
sash handle and fascia panels, the Supreme Air LV is designed to “operate safely at a face
velocity as low as 55 FPM vs. the 100 FPM of a conventional hood,” Rindoks says.
American Auto Matrix’s Auto-Flow fume hood control system provides control of multiple
parameters for better efficiency. “With our Auto-Flow controller, one can implement face
velocity and exhaust duct sensors, hood presence detectors, and even select the damper style
preferred,” says Paul Jordon, CTO of the firm, which is headquartered in suburban Pittsburgh.
“The ability to have full and complete control over what is running in a laboratory is crucial
to saving energy and money.”
In addition to controlling airflow, efficient lab buildings incorporate advanced design
strategies for other aspects of energy management, including heating, cooling, equipment
electricity use and lighting.
Monitoring for efficiency
Lab equipment power use—including direct electrical use as well as heat generation that then
prompts the need for air cooling—is one of the next frontiers in sustainable lab design. In the
past, many labs did not monitor energy use, beyond the review of electric, gas and water bills.
However, with the push toward LEED certification for laboratories, that has changed. This has
especially become important with the LEED credit called “Measurement and Verification,” which
according to Linde has motivated lab owners to install more elaborate energy metering systems
to provide a detailed account of a lab’s ongoing energy consumption.
Labs21’s new equipment wiki is an emerging resource intended to help owners and design teams
select and specify more energy-efficient equipment—from large items such as freezers and
refrigerators to smaller items like centrifuges. For details on this effort to help labs reduce
their plug loads, see
http://labs21.lbl.gov/wiki/equipment/index.php/Energy_Efficient_Laboratory_Equipment_Wiki.
A measurement and verification plan incorporating metering and monitoring systems helps
ensure that buildings are operating as designed. Stats can be compared with the performance
predicted by a calibrated computer model of building energy use, says Linde, and can lead to
large energy savings.
Lindsay Hock is the managing editor of R&D Magazine, the parent publication of
Laboratory Design newsletter (www.rdmag.com). The Labs21 program of the EPA and Dept.
of Energy provides a variety of best practice guides and technical bulletins addressing many
energy-saving technologies for labs, including heat recovery, chilled beams, high-efficiency
modular boilers, low-pressure-drop design and other topics:
http://www.epa.gov/lab21gov/toolkit/bp_guide.htm.
Published in Laboratory Design newsletter: Vol. 15, No. 8, August, 2010, pp. 1,
7-10.
