Study on the cooling metering of fan coil units in central air conditioning systems

The cooling metering of fan-coil units plays a key role on the charging of cooling supplying in the central air conditioning systems, which improves the energy efficiency of systems and decreases the controversies between the owner and the user. In order to achieve both of accuracy and affordability on metering, a new metering method is proposed by analyzing the principle and application of water-side measurement and air-side measurement which are existing methods at present. The theory of the new method is studied based on heat transfer of the fan-coil unit. The temperature of the inlet water as well as the temperature and humidity of the inlet air are determined as data collected for cooling calculation. The effect of sensors' positions on the accuracy of the cooling metering is studied by experiments and the error of this metering method is analyzed. The appropriate data collection position is suggested according to the size of systems. It shows that the new method can meet the requirements of real projects, resolving difficulties of data acquisition accurately and economically. The total error of the experiment system is about 8%–12%.