Assessment of indoor air quality and thermal comfort performance of the low-energy cooling windcatcher "UNI-FREECOOL": Numerical and field test study

Windcatchers are natural ventilation systems based on the design of traditional architecture, intended to provide ventilation by manipulating pressure differentials around buildings induced by wind movement and temperature difference. Though the movement of air caused by the wind catcher will lead to a cooling sensation for occupants, the high air temperature in hot climates will result in little cooling to occupants. In order to maximise the properties of cooling by wind catchers, heat transfer devices were incorporated into the design. This work will investigate the performance of a roof-mounted cooling windcatcher integrated with horizontally-arranged heat transfer devices (HHTD) using Computational Fluid Dynamics (CFD) and field test analysis. The windcatcher model was incorporated to a 5mx5mx3m test room model. The study employed the CFD code FLUENT 15 with the standard k-model to conduct the steady-state RANS simulation. Unlike most numerical simulation of windcatchers, the work will simulate wind flows found in sub-urban environment. The numerical model provided detailed analysis of the airflow and temperature distribution inside the test room. For the indoor CO2 concentration analysis, a simplified exhalation (constant exhalation) model was used and the room was filled with 12 occupants. The CO2 concentration analysis showed that the system was capable of delivering fresh air inside the space and lowering the CO2 levels. A supply rate of 1m/s and higher is sufficient to reduce the pollutant concentration below the guideline value. Thermal comfort analysis using the Predicted Mean Vote (PMV) was conducted whereby the measurements ranged from slightly-cool (-0.96) to slightly warm range (0.36 to 0.60). Field test measurements were carried out in the Ras-Al-Khaimah (RAK), UAE during the month of September. Numerical model was validated using experimental data and good agreement was observed between both methods of analysis. The average error between the results was 3.15%. Field testing measurements conducted in the Ras-Al-Khaimah (RAK) demonstrated the positive effect of the integration of heat transfer devices on the cooling performance.