A thermal model of an active chilled beam

Active chilled beams (ACBs) have gained increased recognition as a feasible technology for comfort cooling during the last decades. One of the advantages with such systems is utilization of high temperature cooling. This provides exergetic benefits and also reduces the need for individual room control. However, individual room control normally serves as compensation for the safety margin applied when dimensioning the cooling systems. Therefore, the absence of individual room controls calls for accurate dimensioning tools. This paper presents a model to be used to calculate cooling capacities of ACBs. The model is based on NTU analysis and is a hybrid of first principles and empirical data in order to ensure high accuracy without requiring extensive measurements for model calibration. The model explicitly captures the influence of buoyant forces acting on the air passing the chilled coil in the beam. Output from the model also includes temperature and flow of supply air. The model shows good compliance with measured data in a wide range of operating conditions (average error of 1.7% if six cases is used for model calibration). The model can be appropriately implemented in building performance simulation tools, thus improving the design of ACB systems.