An investigation into improved thermal comfort in Kuwait schools using natural ventilation and evaporative cooling
Kuwait has a hot desert climate, where the energy demand for cooling dominates the country’s energy requirements. Air conditioning accounts for more than 60% residential energy use and more than 85% peak consumption. Hence, the Kuwaiti government has set a target to reduce buildings energy demand by 15% by year 2030 (Cerezo et al., 2017). In this context, this project presents a cooling system based on natural ventilation and evaporative cooling that is estimated to significantly reduce the cooling energy demand in school classrooms, whilst providing adequate thermal comfort and indoor air quality. It was hypothesized that using a split system for cooling while relying on single-sided window opening for ventilation could lead to poor indoor air quality, thus adversely affecting student learning and health. The natural ventilation technology chosen is the ‘wind-catcher’ which provides indoor ventilation using both dynamic and stack wind pressures. The wind-catcher is modelled for a school classroom with single-sided ventilation. In this project, a total of four scenarios have been modelled: Baseline Scenario 1 – Air conditioning only; Scenario 2 – Wind- catcher only; Scenario 3 – Wind-catcher with evaporative cooling; Scenario 4 – Wind-catcher with evaporative cooling and AC for backup cooling. In each scenario, the thermal comfort, indoor quality and energy use were analysed. After validation of the baseline scenario using field collected data, all four scenarios were simulated over a year. The results revealed that the optimal scenario was the third, wind-catcher with evaporative cooling. Based on the adaptive ASHRAE standard for thermal comfort, it is predicted to provide 98% comfortable hours in the summer, and 86% comfortable hours all year round. Additionally, in comparison with the baseline, this system is predicted to reduce energy use by 53%, as well as dramatically improving air quality (acceptable CO2 ppm level from 20% to 90%). A computational fluid dynamics (CFD) based analysis was carried out for this scenario to assess the air velocity and air temperature distribution within the classroom in greater detail – which showed that the average air speed in the classroom is expected to be 0.78m/s. It was noted in the study that controlling HVAC systems such as the evaporator fan and the air-conditioner using thresholds based on air temperature resulted in significant overcooling and energy wastage during the cooler periods of the year. Therefore, it is proposed in future work to use thermal comfort metrics, such as Fanger’s PMV to control such HVAC components to avoid overcooling and energy wastage. Along with other recommendations, a practical demonstration of this design within a commercial, educational or hospital building in Kuwait is proposed as key future work.
- PhD