ARM PROGRAM SOLAR RADIOMETER VENTILATOR UPGRADES

Poster PDF

Description

A key set of broadband shortwave (solar) and longwave (infrared) radiation measurements performed in the Atmospheric Radiation Measurement (ARM) program provide continuous irradiance data for the downwelling and upwelling components of radiation. The ARM program operates three types of stations performing these measurements: 15 SIRS (Southern Great Plains) stations and 6 each SKYRAD and GNDRAD (NSA, TWP and ARM Mobile Facility) stations. The Solar Radiation Research Laboratory (SRRL) at the National Renewable Energy Laboratory (NREL) is the designated mentor organization for solar radiometry activities within the ARM program and is tasked with calibration of these systems as well as ensuring implementation of improvements which reduce uncertainty in radiometric measurements. Each ARM station uses Eppley Laboratory radiometers and those used for downwelling horizontal irradiance measurements are operated with a ventilator. The ventilator is used to blow air over the dome to reduce accumulation of frost, snow, dew and moisture on the radiometer dome surface. Observation of radiometers in field operation have indicated that improvements in the performance of measurements may be achieved by reducing leakage of ventilator airflow and by utilizing DC powered fans that have a higher flow rate than the AC fans that are normally installed in the ventilators by the manufacturer. Tests of a variety of candidate DC fans have been underway at SRRL for the purpose of selecting a suitable 12 volt DC fan replacement. The 80mm-square 120 volt AC fans that are provided with the Model VEN by the manufacturer are nominally rated with a free-flow air flow rate of 35 cubic feet per minute (cfm). The 12 volt DC fans that are being tested at SRRL have a range of specified free-flow air flow rates between approximately 50 and 58 cfm. Initial results at SRRL are consistent with previous investigations (unpublished Long, Vignola) that have showed that reductions in thermal offset responses (up to 3.5 W/m2) as well as reduced scatter in the raw signal can be achieved by utilizing the higher flow DC powered fans. This poster provides background information, and results of the candidate DC fan testing. Transition to the DC fans for incorporation into ARM program solar radiometer ventilators is planned to begin prior to the start of the 2014 radiometer calibration season.