Design and Evaluation of a Low-Cost Horizontal Tube Radiation Shield for Temperature and Humidity Measurements in a Tropical Urban Environment

Abstract. Climate change and rapid urbanization have increased the need for dense air temperature and humidity monitoring networks in tropical cities. Although low-cost sensors are widely available, the cost of radiation shields remains a major barrier to large-scale deployment. This study presents a low-cost horizontal tube radiation shield (H-Tube) constructed from commercially available pipes and fittings combined with a small number of 3D-printed components. Two versions were developed: a bright-annealed stainless-steel shield (H-Tube_SS) and a PVC shield covered with aluminum foil (H-Tube_PVC). Material costs were approximately USD 25 and USD 11, respectively, making them about 8 and 18 times less expensive than typical commercial radiation shields (>USD 200).

Performance was evaluated through comparative field experiments in a tropical urban environment in Bandung, Indonesia, using identical Vaisala HMP155A temperature-humidity probes. Measurements from the H-Tube were compared against a Cotton Region Shelter (CRS) reference and two commercial radiation shields: a multiplate (MP) shield and a vertical tube (V-Tube) shield. Under non-aspirated conditions, daytime temperature biases exceeded 4 °C and relative humidity biases exceeded 15% during periods of strong net radiation. In contrast, aspirated operation substantially improved performance, with temperature biases generally remaining within ±1 °C and relative humidity biases within ±5%, comparable to those of the commercial MP and V-Tube shields. The aspirated H-Tube_SS achieved a temperature RMSE of 0.49 °C relative to the CRS, comparable to the MP shield (0.53 °C) and slightly lower than the H-Tube_PVC (0.58 °C).

Simple bias-correction methods based on linear temperature regression and saturation-vapor-pressure adjustment for relative humidity were also developed and evaluated. For the H-Tube designs, temperature RMSE was reduced from 1.35-1.46 °C to approximately 0.56 °C under non-aspirated conditions and from 0.49-0.58 °C to 0.30-0.35 °C under aspirated conditions. Relative humidity RMSE was reduced to approximately 2.6-3.2% after correction. The correction methods also reduced temperature-measurement uncertainty, particularly for the non-aspirated configurations.

These results demonstrate that the aspirated H-Tube provides a practical, scalable, and low-cost alternative to commercial radiation shields for distributed temperature-humidity monitoring networks in tropical urban environments.