Fresh air is a necessary requirement in building ventilation systems, but too little can lead to poor air quality and an excess wastes energy. Previous research has shown that levels of fresh air in buildings can often vary greatly from that intended. This technical note describes how a building and energy management system can be used to improve the control of fresh air levels. Different control strategies were tested on an air handling unit over a range of air flow rates, required fresh air levels and damper arrangements. The test results showed that flow rate feedback gave the most accurate control. It was also one of the most expensive to implement due to the cost of velocity/flow rate measuring devices. However, the benefits included improved control and a constant display of the quantity and percentage level of fresh air. This is the preferred control strategy. System characteristics gave good results, but initial work is required in measuring the system characteristics to set it up. These strategies are only really valid for the supply flow rate at which the dampers are calibrated.
If a variable supply flow rate is used, the accuracy of control should be checked across the whole flow rate. The costs of implementing a new BEMS control strategy can be minimized by using existing hardware and the skills of in-house staff. All the information is clearly presented in this BEMS publication.