Davis Instruments Corp.

A study of radiation shield effectiveness


Courtesy of Davis Instruments Corp.

A brief comparison of temperature readings in two passively-ventilated and three fan-aspirated radiation shields under conditions of low wind and relatively high insolation is presented.

From each of two periods of study, two days were chosen for conditions of high insolation and low wind to illustrate a reasonable sample of the performance of the shields. A single sample of each shield was used in each of the two tests.

The results presented here are not represented as being conclusive. we believe, however, they corroborate results of tests we have been conducting over a period of several years. These results are being presented to encourage similar evaluation by others.

The first test was conducted on four shields:

  • RM Young Model 41002: passively-ventilated.
  • Davis Instruments Model 7714: passively-ventilated.
  • Davis Instruments Model 7755: fan-aspirated, solar powered.
  • Qualimetrics Model 8150A: fan-aspirated, AC-powered.

Tlie second test was also conducted on four shields, with the RM Young Model 43408 fan-aspirated, AC-powered shield replacing the Qualimetrics shield.

Units were mounted in close proximity at equal heights above irrigated close-cropped grass and positioned such that no shield was wind-shaded when the wind was in the prevailing direction and such that the fan-aspirated shields did not aspirate other shields. Figure 1 shows the setup for the second test.


The maximum recorded instantaneous wind speed during the selected days was 5 mph (Z2m/s) for the first test (Qualimetrics) and 4 mph|l.8m/s) for the second test (RM Young).


During the specified period, the insolation1 values (intensity of solar radiation) ranged between 1050 and 1200 W/m2 for the first test and between 800 and 1050 W/m3 for the second test. Both days were essentially cloudless.


Davis Instruments Model 7818 Temperature Probes with 6055 NIST Certification & Characterization. The temperature sensors were characterized in a uniform temperature environment between 80°F (27°C) and 110°F (43°C). Differences in readings between the individual probes were measured and determined. These differences were eliminated in the final data by adding correction values to the recorded values. Each temperature was measured every 20 seconds, and these measurements were averaged and logged every 5 minutes with 0.I°F resolution (Note 1).

Davis Instruments Model 7911 Standard Anemometer. Wind speed was measured every 2.5 seconds and the highest value in each 5-minute period was logged with 1 mph resolution.

Davis Instruments Model 7821 Standard Solar Radiation Sensor. Insolation was measured every 20 seconds; these measurements were averaged and logged every 5 minutes with I W/ma resolution.

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