Evaluation of Methods to Correct for IR Loss in Eppley PSP Diffuse Measurements
The IR loss in diffuse measurements made by thermopile pyranometers is examined. Diffuse measurements are used for the study of IR losses to minimize the effects of beam irradiance and therefore much of the cosine response error influences. Specifically, diffuse measurements of an Eppley PSP pyranometer are compared to those made with a Schenk Star pyranometer. Eppley B&W and Star type pyranometers suffer minimal IR loss because the reference and receiving junctions of the thermopile are at the same thermal level. The difference between diffuse values can be attributed to calibration and cosine response errors as well as IR loss. Therefore it is necessary to separate out the various sources of error and examination of the differences over various times of the year can help, at least for systematic errors. Several methods of correcting for IR loss will be examined. First subtracting out the average nighttime offset during the day will be tested. Next an extrapolation between early morning and late evening offsets will be tested. This should help eliminate the IR offset in both the morning and evening, but underestimate the IR losses during the rest of the day. Correlations of the remaining IR losses with temperature, relative humidity, and irradiance will be evaluated. In addition, the IR losses will be studied both for clear days and for totally overcast periods. Pyrgeometer measurements will also be compared to the estimated IR losses. The above measurements and comparisons will help quantify the magnitude and variation of the IR losses.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 962050
- Report Number(s):
- PNNL-SA-56395; KP1205010
- Country of Publication:
- United States
- Language:
- English
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