with Single Duct VAV: Built-in Inefficiency of the Common Lab HVAC
Michael Morehead, P.E.,
Many laboratory building HVAC systems are designed as Variable
Air Volume, Single Duct Reheat (VAV Reheat) systems. The VAV Reheat
system uses a single duct to supply all cooling and ventilation
needs for the laboratory and office spaces. This system has inherent
energy efficiencies that contribute to the high cost of laboratory
The inherent inefficiency of the VAV Reheat system is that it
uses a single air supply for both ventilation and cooling. If the
demand for ventilation air is greater than the demand for cooling
air, energy is wasted from overcooling supply air then subsequently
One example of this inefficient operating condition is when fume
hoods are open and large quantities of air are supplied to the
room to offset the exhaust, yet there is minimal cooling load from
equipment. A second example is during un-occupied periods, when
minimum ventilation rates are being maintained but there is not
a cooling load.
This presentation will review the inherent inefficiency of VAV
Reheat systems and look at a specific strategy for improvement
by designing the HVAC system with separate cooling and ventilation
capabilities. Included will be cost evaluations, design challenges,
synergy with other energy efficiency strategies (such as heat recovery
and thermal storage), and opportunities for future development.
Not available at this time.