Experimental and numerical testing of an induction variable air volume (VAV) controller with two damper blades

A VAV (Variable Air Volume) air conditioning system without reheat of the air supplied is generally regarded as energy efficient. Re-heat can be avoided when induction VAV controllers are used instead of conventional controllers since primary airflow can be reduced to about 10-20% of its nominal value without a draught risk. The aim of the present tests was to determine the induction and efficiency characteristics of a compact square induction VAV controller with two damper blades and to find relationships between flow ratio and governing independent variables such as: inlet airflow, inlet pressure and terminating elements flow resistance. The aim was also to find a method of flow ratio interpolation for any values of independent variables within the range of tests. A controller of new construction with two damper blades was tested experimentally in a physical model using the tracer gas method and numerically using the CFD method. In order to approximate and interpolate the induced airflow for any values of governing independent variables, a set of relevant relationships was found. CFD calculation results can be approximated using a set of equations with the expanded uncertainty of 5 m3/h. This method can be implemented in the codes for VAV controller selection. The tested construction meets the most important requirement for an induction VAV controller i.e. for the lowest inlet airflow the amount of induced airflow is higher than the required minimum value (NV=2-3). When comparing efficiency characteristics of the tested model of induction VAV controller with test results of jet pumps, it can be concluded that the controller of the tested construction may reach similar efficiency and thus the new construction seems appropriate. There is a satisfactory agreement between CFD and measurement results. CFD method can be successfully used for optimization of the induction VAV controller construction.