Damper authority estimation and adaptive flow control.

Knowledge of the authority of control dampers in HVAC systems may be used for diagnostic purposes or to enhance control performance. In this paper, a method of estimating damper authority in air distribution systems is described. The method only requires measurements that are normally available in modem HV AC systems with digital controls. The method is based on a technique that allows the static pressure drop across a branch to be regulated even if that pressure is not measured. Experimental results on a Variable Air Volume (VA V) air handling unit demonstrate the efficacy of the method. A flow control strategy that uses feedforward compensation to eliminate the sluggish behavior of conservatively tuned feedback controllers is described. The algorithm is based on a quasi-equilibrium model of the flow characteristic and makes use of knowledge of the authority. The maximum flow rate, which is generally unknown, is estimated from position and flow rate measurements. Therefore the controller is adaptive. The feedforward commands are combined with feedback commands to ensure robust behavior in the presence of model uncertainty. Computer simulations demonstrate the improvements in control performance.