Original Date: 03/17/1997
Revision Date: 01/18/2007
Best Practice : Variable Air Volume Heating, Ventilating, and Air Conditioning System
In 1990, Polaroid began retrofitting the heating, ventilating, and air conditioning (HVAC) distribution systems at its Integral Coatings Division and installed energy-efficient, integrated, self-contained, thermally-activated diffusers on the variable air volume (VAV) distribution system for its comfort cooling applications. The modifications eliminated the need for zone thermostats and provided an energy-efficient way to maintain consistent, comfortable cooling.
Typically, VAV distribution systems are installed such that the air discharged from the HVAC unit is kept at a constant dew point temperature of 52°F; the static pressure in the duct is kept constant between 0.2 and 0.25 inches of water; and the volume of the air delivered through the diffuser is varied by a damper located in the respective branch distribution duct and controlled by a space thermostat. The result is an energy-efficient delivery system which requires no additional heat sources and makes optimal use of the sensible heat energy from the lights, equipment, and people in the conditioned space. The constant dew point temperature, cooled air is simply delivered variably. When the air is too hot, additional cool air is delivered to the space while conversely, when the air is too cold, less cool air is delivered. The drawback, however, is the higher capital costs and maintenance of the VAV boxes, and the need to install space air thermostats.
For Polaroid’s needs, engineers installed integrated, self-contained, thermally-activated diffusers directly connected to the distribution branches which eliminated the need for mixing boxes and thermostats. The diffusers are designed with a hydraulic mechanism which drives the diffuser blades open or closed, depending on the ambient space air temperature. The mechanism contains a cylinder with a heat-sensitive wax material that reactively contracts or expands, thereby increasing or decreasing the pressure in the cylinder proportionally. The result is an even, consistent, energy-efficient delivery of cool air without using thermostats that require constant calibration and adjustment.
Polaroid gained many benefits through its VAV HVAC system. By eliminating space air thermostats, Polaroid lowered its capital and recurring maintenance costs, and the need for constant calibration to ensure energy efficiency and comfort cooling. Other benefits include the elimination of higher capital costs associated with installing VAV boxes; increased diffusing performance which exceeds standard diffusers at equal cost; and greater energy savings associated with a maintenance-free VAV distribution system compared to standard VAV systems.
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