Air Temperature and Relative Humidity Sample Clauses

Air Temperature and Relative Humidity. ‌ The air temperature is an important factor for the calculation of the receiver efficiency. The temperature of the air near the earth’s surface (dry bulb temperature) is commonly measured in °C (or in ° Fahrenheit, depending on the country). Finally, temperatures have to be known in the thermodynamic scale of temperature, in Xxxxxx. Relative humidity is a relevant parameter for cooling and receiver efficiency, depending on the technology. It can also affect optical temperature measurements. Relative humidity is the ratio of the observed vapour pressure to the saturation vapour pressure with respect to water at the same temperature and pressure [WMO, 2008]. It is usually given in per cent. Relative humidity is measured with hygrometers and dry bulb temperature with thermometers. From the various existing methods for temperature and humidity measurements we focus on recommended methods for CSP testing: electrical temperature measurement with temperature dependent resistors or band gap sensors and capacitive or resistive humidity measurements. The principle of operation of these sensors relies on the systematic change of the electric properties of the sensor material with the temperature or the relative humidity. Other methods are acceptable, too, if the method allows the automatic recording of the signal with a data logger. Temperature and relative humidity sensors can be acquired as combined sensor (hygro- thermometers) including radiation shield and optional ventilation. Electrical thermometers or hygrometers have to be installed with a radiation shield, in order to avoid that the sensor is heated up artificially above the air temperature. For very low wind velocities measurement errors can occur if no active ventilation is used in order to exchange the air inside the shield with the ambient air.