Experimental and numerical study of wind tower integrated with solar heating unit to meet thermal comfort in buildings during cold and sunny climate conditions

Abstract

Natural ventilation techniques are increasingly being adopted in recent times due to the need to cut down on greenhouse gases emission and energy cost. A classic natural ventilation technique, the wind tower, may be utilised to minimize the load on typical HVAC systems. One of the major disadvantage limiting the deployment of wind tower is the additional heating load it demands on the HVAC system during the winter months. The work focusses on improving the year-round capability of a wind tower by attaching a solar heating unit (SHU) that would heat the incoming ambient air through a conjugate heat transfer system before being circulated into the space to be ventilated. For performance validation, the numerical technique was utilised initially, then an experimental setup was created based on the numerical results to validate for practical situations. Using the CFD simulation, ventilation performance of this tower system was evaluated in terms of mean age of air (MAA) and air change effectiveness (ACE). The commercial ANSYS Fluent was used to solve the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) turbulence model. The results showed that SHU has been able to heat up the incoming air of 18 °C by 5 °C–23 °C which is generally considered as a comfortable temperature range. According to the analyses of airflow rate at different incident angles through the four quadrants of tower, the maximum flow rate (0.45 m3/s) of air steam was observed at 45° incident angle. The ACE values in the inhabited space were typically near to 1.0, indicating that the ventilation air mixed up well in the ventilated zone. The wind tower performance was experimentaly investigated in terms of solar radiation variations, wind velocity variations, temperature variation in SHU and inside wind tower, and air change rate (ACR) on the experimental setup. Experimental study shows a variation of 2–4 °C in the indoor temperature and thereby ensuring optimal thermal comfort. The recommended wind speed for an effective mass flow rate is in the range of 3 m/s, and an average ACR of 25 per hour indicates that the air is being ventilated properly.