Pressure controlled variable air volume system

There is one primary goal and several secondary goals to fulfill when designing a heating, ventilation and air conditioning (HVAC) system. The main goal is to create an indoor climate that satisfies the user and this should be achieved in the most energy efficient way and with a system that also function in a long-term perspective. Higher supply air flow have the potential of increasing office workers performance and decreasing short-term sick leave. To increase the supply air flow, a cooling function is added to the air and 100% outdoor air is supplied. The main objective of this paper is to give the fundamentals for a system design that takes good indoor climate, energy efficiency and long-term operation into account. When controlling the static pressure at branch level, it is possible to vary the air flow to different zones without measuring the individual flow and without affecting the air flow to other zones. An equation for the placement of the pressure sensor is shown and the relative flow difference between the diffusers on the branch is calculated and measured. These principals are the fundamentals for a pressure controlled variable air volume (VAV) system. The fan pressure set point is optimized resulting in a decreased fan power requirement and sound generation. The flow to each zone is controlled at the diffuser outlet which prevents draft and therefore a wide range in supply air temperature can be used.