Table 14 Temperature sensors

4.2.1.1 Temperature and Humidity Sensors

Temperature is the most widely measured variable in HVAC. Temperature sensors give guidelines to the AC system to provide the supply air with the desired temperature. Different types of sensors are listed below in Table 14. Due to its high accuracy, stability and reliability, platinum resistance thermometers (PRT) have been chosen to measure the temperature in the building. An accuracy of 0.6K achieved over a 15 to 25 range is suitable for zone air temperature measurement, while an accuracy of 0.25K is needed for control of chilled water temperature.

Table 14 Temperature sensors

Another important variable that needs to be taken into account is the humidity. Excessive humidity levels can cause discomfort, health issues and affect productivity. There is also a risk of condensation. Thus, appropriate humidity control is essential, especially in Singapore.

Table 15 shows two types of humidity sensors that are most widely used in HVAC control. The capacitive polymer film sensor provides a direct measure of relative humidity. However, drift occurs when exposed to high RH. The dew point sensor, on the other hand, has a very high accuracy control. Thus, the chilled mirror dew point sensor has been selected to measure the dew point directly.