VU01

The VU01, manufactured by Hukseflux Thermal Sensor, is a high-quality ventilation unit for use with pyranometers and pyrgeometers. Its purpose is to improve the dependability of the measurement. The measurement accuracy improves because the offsets are reduced. The reliability benefits from the prevention of dew and frost formation, as well as the quick evaporation and sublimation of water and snow. ISO/TR 9901 “Solar Energy - Field Pyranometers - Recommended practice for use” recommends the use of ventilators where high accuracy and reliability are required. The VU01 is designed in agreement with the recommendations of ISO/TR 9901 and BSRN.

The VU01 uses a 7.8 W fan and inlet filter to draw clean air over the pyranometer’s outer dome. The fan should operate continuously to reduce dust and dirt settling, to dissipate raindrops, and to stabilize the dome temperature.

The VU01 has dual 5 W heaters, which are used to raise the temperature of the dome slightly above ambient temperature and prevent the formation of dew and frost. Relays are recommended to control and source the appropriate power to the ventilator and heaters separately.

Improved Measurement Dependability

Ventilation promotes thermal equilibrium between all components of radiometers, and thereby reduces zero offsets. Dew and frost formation is prevented. Additional heating will promote the evaporation of water droplets and sublimation of snow. It should be noted that heating in combination with pyranometers will lead to increased thermal offsets, so heating is only recommended if necessary.

Operation

Using the VU01 is easy. The footprint of the VU01 is small, which prevents accumulation of snow. The ventilator power is relatively high to increase the airflow. The ventilator is generally used continuously; the heater is typically controlled by the data logger. Ventilation is typically used with high-accuracy measurement requirements. In such cases, the need for a high level of instrument maintenance and dome cleaning still exists; evaporating droplets of water might leave stains on the instrument domes. The bottom of the VU01 provides access to the removable dust filter.