Demand control ventilation: Influence of terminal box minimum airflow setting on system energy use

• Resetting the terminal box minimum airflow to a lower rate may cause lower system ventilation rate.
• However, setting the minimum airflow too low will lead to a high system ventilation rate.
• Resetting the minimum airflow from 30% to 20%, a reheat energy savings as great as 40% is achieved.
• An annual energy savings of up to 30% were reached when resetting the minimum airflow from 30% to 20%.

Demand control ventilation is one of the most energy efficient ways to achieve the optimum indoor air quality (IAQ). The interest in it has led to a lot of research and publications particularly for single duct VAV system with terminal reheat since the update of the ASHRAE standard 62 in 2004. However, the VAV terminal box (TBX) control algorithms have been given less attention and the influence of the VAV TBX airflow setting on the system energy use has not been quantified. Thus, this study investigated how the VAV TBX minimum airflow setting influences system energy use as well as building IAQ. First, the DOE developed benchmark building model and EnergyPlus software were used to simulate the building annual hourly thermal load. Then, the system control, energy use and IAQ models were developed for the selected building. Two VAV TBX control methods, the single maximum and dual maximum control methods, were investigated in further detail using two different minimum airflow settings from ASHRAE Standard 90.1-2010. The results indicated that when the TBX minimum airflow is reset from 30% to 20%, a reheat energy savings as great as 40% was achieved and an annual system energy savings up to 30% was reached.