This study investigates the thermal efficiency of a solar air heater (SAH), when it was mounted on a custom-made support frame, and was operated under different air mass flow rate. This SAH is composed of a transparent polycarbonate cover plate, a felt absorber layer, a perforated aluminium back plate and an aluminium frame. The ambient inlet air of this SAH is heated as it passes through the perforated back plate and over the felt absorber layer. The heated air is blown out through the outlet. Studies of SAHs with a similar design to this SAH were not found in the literature. The experiment was carried out at Massey University, Auckland campus, NZ (36.7° S, 174.7° E). The global horizontal solar irradiance, the ambient temperature and the wind speed were recorded using an on-site weather station. Temperature and velocity of the air at the outlet were measured using a hot wire anemometer. During the experiment, the air mass flow rate was between 0.022 ± 0.001 kg/s and 0.056 ± 0.005 kg/s. Results showed that when the SAH was operated at the airflow between 0.0054 kg/s and 0.0058 kg/s, the inlet air temperature and the wind speed (between 0 and 6.0 m/s) did not impact the temperature difference between the outlet air and the inlet air. The thermal efficiency of the SAH increased from 34 ± 5% at the airflow between 0.021 kg/s and 0.023 kg/s, to 47 ± 6% at the airflow ranging from 0.032 kg/s to 0.038 kg/s, to 71 ± 4% at the airflow of 0.056 ± 0.005 kg/s. The maximum thermal efficiency of 75% was obtained at the airflow of 0.057 kg/s. The effective efficiency of the SAH was 32 ± 5% at the airflow between 0.021 kg/s and 0.023 kg/s, 42 ± 6% at the airflow ranging from 0.032 kg/s to 0.038 kg/s, and 46 ± 11% at the airflow of 0.056 ± 0.005 kg/s.

Providing a good quality classroom environment where children can breathe in fresh air is important. However, investigating the Indoor Air Quality (IAQ) in large numbers of classrooms is often too costly because currently available commercial brands are too expensive for the majority of schools. We have been developing a low-cost Indoor Air Quality (IAQ) platform called SKOMOBO which can monitor important IAQ parameters such as classroom temperature, relative humidly, particular matter and carbon dioxide level. Because our platform is designed in-house and utilizes low-cost sensors, there is a significant cost reduction and is affordable. In this paper, we discuss the design and implementation of SKOMOBO with the focus in several hardware and software engineering issues to explore the right set of strategies for developing a practical system. Through extensive experiments and evaluation, we have determined the various characteristic and issues associated with developing a low-cost sensor platform and their practical implications and mitigations.

A low-cost, low power consumption indoor environment monitoring instrument, called SKOMOBO (school monitoring box), was developed and tested. SKOMOBO includes sensors to monitor temperature/relative humidity, carbon dioxide (CO ₂ ), particulate matter and motions. SKOMOBO was developed using the open source hardware Arduino Pro Mini. This paper describes the process of building SKOMOBO, including sensor selection, printed circuit board design, sensor programming and performance evaluation. Two co-located tests have been undertaken; one in the controlled environment and one in the uncontrolled environment. Results show SKOMOBO measurements have high correlations with their commercial equivalents. In the two different testing environments, the R ² of temperature measurements for all six SKOMOBOs were 1. The R ² for relative humidity and CO ₂ measurements were above 0.9. The result of this work shows the reliability of SKOMOBO on monitoring indoor air quality.