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Enhanced Laboratory HVAC System
Tal Rabiah, University of Michigan
View Tal Rabiah's full
paper (10 pp., 838KB)
Laboratory VAV system design has been a prevalent choice for many
laboratory buildings, new or renovated, for the past 25 years. The
most popular system has been a single-duct VAV with a central air
handling unit of 100 percent outside air, VAV box, and hot water
reheat coil for each lab space. A thermostat controls the reheat
coil and perimeter heat, lab pressurization panel controls the lab
supply air, the lab space exhaust, and fume hood exhaust VAV box,
without any return air.
The enhanced VAV is of a similar concept, except a vertical, floor-mounted
fan coil unit (FCU) is provided for each lab space. This FCU is
connected to the main VAV make-up air unit, VAV return box from
the lab space to the FCU, and exhaust VAV box from the fume hood
to the building fume hood exhaust system.
Each FCU is provided with a cooling coil and hot water (or steam
coil). A variable speed drive controls the FCU's fan speed. The
lab space DDC panel is provided to control the VSD signal to the
fan motor, exhaust hood VAV box, heating and cooling electronic
valves actuators, and the lab space return air VAV. This concept has the advantage of the lab space clean air to the
FCU in lieu of exhausting it, when the fume hood sash is lowered
or closed. This will lead to substantial reductions in sizes of
the exhaust system, the energy recovery system, and the make-up
air system. Electrical energy will be saved when the hood sash is
lowered or closed due to the reduction of the FCU's supply fan speed.
When lab space is not occupied, trough light switch sensing, DDC
panel will lower the FCU fan speed to the set minimum on the variable
speed drive. The DDC panel also controls lab space pressurization
through the a lab/corridor pressurization sensor.
The corridor space is environmentally controlled and pressurized
through a dedicated FCU. Each FCU accessibility for maintenance
is from corridor space so that lab space is not disturbed. FCU room
walls are acoustically treated to reduce any sound transmission
from the FCU system to the lab space.
In order to make the overall laboratory building more energy efficient,
all pumps, make-up air units, and FCUS speeds are controlled through
variable speed drives. The DDC system is an open protocol type.
The fume hoods are of high performance type, with reduced face velocity
requirements.
Comparison in initial cost, life cycle cost, energy performance,
monitoring, space requirements, and reliability will be presented
between the conventional make-up air/VAV reheat system and this
individual VAV FCU system.
Labs21 Connection:
The aspect of the approach is that this system is actually partially
applied at the University Natural Science Building. The technology
is reasonably new. However, it is not unusual to the HVAC industry.
Biography:
Tal Rabiah is a registered mechanical engineer and a senior
engineer in the design, operation, and commissioning of labs, as
well as fume hood design. Mr. Rabiah holds a BSc and MSc in mechanical
engineering and has 26 years of experience in laboratory designs
(HVAC, plumbing, and fire protection). He has several publications
for ASHRAE and the Association of Energy Engineers in the field.
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