Calorimetric flow sensors based on thick-film printed thermopiles for air conditioning system monitoring

Air conditioning systems need permanent monitoring of the mass and energy flows in the air ducts to assess their proper operation and detect and correct changes that may occur with time. This is a prerequisite for energy efficiency and demanded by recent legislation such as the Energy Performance of Buildings Directive issued by the European Union. Such distributed monitoring systems require low-cost and robust flow sensors that need not be extremely precise, but give a good indication of the flow distribution within the air conditioning system. In this paper we present a technology feasibility study to implement flow sensors based on thick-film thermopiles printed by silk screen printing on a plastic carrier film. Finite element simulation studies using Cu-Ni thermopiles prove the viability of the sensor concept. Within the scope of a thorough analysis of the sensor design space, an optimized layout could be found which together with a feedback control operating mode allows for a substantially enlarged dynamic range of the sensor.