Energy Savings with Enhanced VAV System Concepts


Conventional variable air volume (VAV) systems have very significant problems maintaining the desired minimum of outside air for ventilation throughout the year under the wide range of operating conditions normally encountered. The major problem lies in the basic operating principle of the VAV system: as the system turns down (reducing the total amount of supply air to meet the load for the space), the amount of outside air may also be reduced in proportion to the turn-downed amount of total supply air. This problem with the outside air supply leaves the designer facing the design/off-design dilemma. A system that provides the proper amount of outside air during design conditions may fall short during off-design conditions; while a system that always provides the required minimum amount of outside air at all times may do so at the added energy expense of exceeding the desired minimum much of the time. By using a series of hour-by-hour simulation programs, this study verifies and quantifies the design/off-design dilemma of conventional systems. It also shows the improvements available with enhanced systems. The enhanced systems attempt to provide the desired amount of outside air without oversupplying, under all load conditions. The systems studied are a conventional return fan system, a return fan system with an injection fan, and a return fan system with the return air damper controlled by an outside air flow sensor. The results focus on relative energy requirements for systems meeting the minimum performance criteria. The study examined a four-zone building in three geographical locations (hot, cold, and temperate climates).


Mechanical and Aerospace Engineering

Keywords and Phrases

Air conditioning; Energy conservation; HVAC; Variable air volume (VAV); Ventilation

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version


File Type





© 2024 The Authors, All rights reserved.

Publication Date

01 Dec 1998

This document is currently not available here.