پايگاه علوم و تحقيقات صنعت تاسيسات تهويه مطبوع، سرمايش و گرمايش

Underfloor & Overhead

Early air-conditioning systems used air-distribution systems with constant volume and variable temperature to control space temperature. In the 1970s, variable-air-volume (VAV) revolutionized how commercial buildings were air conditioned. The market drivers for VAV were increased zone control and reduction in energy consumption. Now, another revolution is underway—ductless VAV systems.

By eliminating ducts while augmenting the benefits of VAV, these systems have the potential to further improve comfort and reduce energy costs, while providing a more sustainable and flexible HVAC system. Additional benefits include easier layout, improved air quality, reduced life-cycle cost, and, potentially, reduced capital cost. This article describes these ductless systems and explores their benefits.

The Two Types of Ductless Systems The two main types of ductless VAVsystems are underfloor and overhead. Both systems replace branch ductwork with broad airways, so we will refer to them as airway systems. (Main shaft ductwork is still required to deliver air to the airways.) Both systems operate at low static pressure, which reduces air leakage and saves energy. Static pressure of 0.05 in. w.g. (12.5 Pa) has been proven effective in today’s underfloor-airway systems, and is now being applied to the new overhead-airway systems. Underfloor system. An underfloorairway system is used in conjunction with an access floor (Figure 1).