Impacts of humidity measurement uncertainties and an uncertainty-tolerant economizer control strategy for air-conditioning systems

Economizer control is a practical and very important measure to achieve energy savings for air-conditioning systems during moderate seasons. The enthalpy-based economizer control approach is appreciated in Hong Kong due to hot-humid climates, but its performance is often affected by sensor uncertainties. Humidity sensors are especially prone to drift out of calibration, their uncertainties are critical and cannot be ignored. This study quantitatively analysed the impacts of humidity measurement uncertainties on enthalpy-based economizer control and found that they may lead to an increase of up to 35.56% in the total energy consumption of an air handling unit. An uncertainty-tolerant economizer control strategy is proposed to reduce the impacts. The measured relative humidity of fresh air and return air can be corrected online and used to calculate the fresh air and return air enthalpies. The proposed uncertainty-tolerant economizer control strategy has been validated systematically on a virtual platform. The results showed that the average root-mean-square error of the fresh air and return air enthalpies were reduced by 87.92% and 91.39%, respectively. Compared with the total energy consumption of the air handling unit using conventional control strategy, it was reduced by 1.02% - 24.58% when using the uncertainty-tolerant economizer control strategy.