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To undertake a heat balance on confined livestock facilities, the heat gains and losses of the unit must be measured. The heat loss due to the ventilating air is one of the most difficult parameters to measure because of the fact that the air flow for each fan in the ventilation must be measured simultaneously. In many situations the heat loss due to the ventilating air accounts for the major proportion of the heat loss from a livestock facility. Therefore, an accurate measurement of the ventilation rate is of prime importance. The equipment used to measure air speeds or velocity pressures existing in livestock units, as described by Feddes and McQuitty (1977), was found to be inadequate. Velocity pressures were measured by pitot-static tubes in the calibration ducts which were positioned downstream from each exhaust fan. At lower ventilation rates and duct air speeds of less than 7.5 m/sec (1500 ft/min, the velocity pressures were too low to determine an accurate air-flow rate in the duct. A logical solution to this problem was to substitute pitot-static tubes with air-flow meters that utilize horizontally positioned, omni-directional probes. However, to place these commercial air-flow meters in each duct and also within the zone of animal occupancy was simply too expensive since simultaneous measurements were of interest. The only apparent alternative to this high cost was to design a less expensive set of air-speed sensors compatible with the existing data acquisition system described previously (Feddes and McQuitty 1977). This paper describes the components of the air-speed sensor unit developed and the procedures used to establish a calibration curve for each sensor.
design of an air-speed sensor system
Feddes, J.J.R. and J.B. McQuitty 1980. DESIGN OF AN AIR-SPEED SENSOR SYSTEM. Canadian Agricultural Engineering 22(1):97-99.
97 - 99