Four-Pipe VAV System With Neutral Air Handling System
The four-pipe VAV system design eliminates wasteful reheat and associated coincidental cooling energy by using only the minimum required heating or cooling energy to achieve air temperatures that are specific to each conditioned thermal zone within the building . Reheat is the process by which cold air is supplied throughout the building to satisfy spaces with the highest demands for cooling , where spaces that do not need cooling are then required to reheat the air temperature to keep the room from being over-cooled . Modern VAV systems can minimize the energy penalty of this process to differing degrees of success , but not eliminate it . The thermodynamic process involved in conventional VAV reheat systems is similar to driving with one foot on the accelerator pressed down and the other foot throttling the brake pedal to maintain speed . By making the coldest air needed , the most demanding thermal zone is always satisfied , but at the expense of all other spaces requiring additional heating energy to avoid being overcooled .
Eliminating reheat energy waste is made possible by providing “ neutral ” air from the central air handling system that regulates the supply air within a boundary of no colder than 55 ° F ( adjustable ) and no warmer than 72 ° F ( adjustable ). These parameters were selected as they coincide with the lowest potential supply air temperature that could be demanded from a space that requires cooling as well as the warmest supply air temperature that could potentially be provided for a space that is lightly loaded and only requires airflow for ventilation purposes . When the air entering the air handling units is between 55 ° F and 72 ° F , no heating or cooling energy will be expended by the central air handling units . By minimizing the tempering of the central air supply , much of the heating and cooling is performed at an individual thermalzone level . This allows the HVAC system to avoid a scenario where simultaneous heating and cooling occurs . By synchronizing the central air handling system supply air temperature boundaries with the space demands within the building , wasteful reheat energy consumption can be eliminated .
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