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pumping skid implements heat exchangers to
transfer energy from the heating and cooling
systems to change the temperature of the recovery loop. By eliminating the heating and cooling
coils, there’s an air pressure drop reduction up
to 1 in water column. The pumping skid has an
intelligent control system that monitors all
air temperatures in the supply and exhaust;
all water temperatures in the energy-recovery, chilled water and heating water loop to
perform optimization of the energy-recovery
water temperature; and pump speed and
control valve operation. This control system
performs a numerical simulation once per second, using the aforementioned inputs, inputs
from the BMS and 3-D performance maps
of the coils, pumps and valves. Using direct
evaporative cooling in the exhaust increases
the summer time efficiencies in Colorado by
another 40%. The primary manufacturer of
this energy-recovery system, Konvekta, offers
a financial guarantee on the annual energy
savings of this system.
Since this system is much more expensive
than a conventional energy-recovery system,
it’s imperative to review the potential reductions in system cost to bring this system into
cost neutrality for projects that can’t afford
increased cost. The preheat and cooling coils
are removed. This allows the air-handling
units to be reduced in size and removes the
controls, coil piping hook-up costs, coil pumps
and two piping networks to these air-handling
units. The need for glycol in the chilled and
heating water is also eliminated, along with
the glycol feeders for these systems. For the
continued on page 24
Univ. of Colorado Boulder SEEC project, there
was a glycol preheat system that was removed,
as well as a heat-recovery pump. Another large
cost-savings item is the reduction in pipe size
for the energy-recovery loop piping. Lastly, if
allowed by the owner, reductions in boiler and
chiller plants can be accomplished due to the
peak load reduction from the amount of energy recovered from this system.
One AHU coil design winter performance schematic. Image: Konvekta USA Inc.
In conclusion, we were able to find ways to
save $1,200,000 from a conventional system
in order to implement an intelligent high-efficiency energy-recovery system.
Sean T. Convery, PE, is a Mechanical Principal
at Cator, Ruma & Associates in Denver, Colo. His
19 years of mechanical design experience include
energy-efficient mechanical systems for higher
education campuses and research labs.
Your toolkit for good lab exhaust design
By: Mark Hallman, LEED AP, Senior Project
Engineer, Rowan Williams Davies & Irwin Inc.
It’s no secret lab facilities carry the burden of a large energy demand. Reasons for this high demand include the significant plug loads of
specialized lab equipment, the high ventilation
air change rates often implemented in lab spaces and the large volumes of hazardous exhaust
air that must be moved out of the building.
Of course, proper equipment and adequate
ventilation in labs is essential for the success,
health and safety of the building and its users.
However, no less important is the safe release
of hazardous exhaust air from the building so it
doesn’t adversely impinge on nearby air-sensi-tive locations or the lab building itself via re-in-gestion into air intakes.
Many labs have addressed this concern by situating manifolded exhaust fans on the building
roof, which is an excellent design step. However,
the optimum fan design that harmonizes safety
with fan energy and cost is less straightforward,
given the many factors that contribute to the
best possible dispersion of hazardous exhaust.
The exhaust fan design is of great importance as it dictates how well hazardous contaminants will be dispersed away from the building.
It will also determine how much energy will be
Exhaust fans can be operated in two primary
ways: constant air volume (CAV) and variable
air volume (VAV). In CAV mode, the fan always
exhausts the same air volume to maintain a
constant momentum. If fume hoods that feed
into the exhaust fan are turned down/off, fresh
bypass air is provided to the fan to maintain the
same air volume. Conversely, VAV mode reduc-
es the air volume released from the fan during
low fume hood usage, saving fan energy.
Manifolding fume hoods together so they
discharge from a common exhaust fan is an
excellent design step for a few important reasons. First, the resultant exhaust plume released
from the fan is much larger in volume, which
means the plume will have much improved
dispersion momentum. Second, less ductwork
and fewer fans are required for installation and
maintenance, thus saving on first and ongoing
costs. Third, additional internal dilution of the
contaminants is afforded to the exhaust plume,