Abstracts Category : Other

Trombe Wall Conditioning for Nepal

by Philip Edwards

Climate comfort is often taken for granted. However even in moderate ambient conditions, indoor climates can lack comfort without the use of appropriate resources. Around Nepal the average climate conditions range from -10 to 40C with relative humilities ranging from 37% to over 80%. This is coupled with limited economic resources and access to grid electricity, which restricts the use of active modern conditioning systems (such as heat pump airconditioning). This report explored passive conditioning methods in climates around Nepal to improve climate comfort. These methods include evaporative cooling, use of ground source thermal energy and solar heating. A trombe wall model was then analysed in detail due to a simple design, utilising solar energy to drive convection currents within an air gap. Standards were compared to achievable climate comfort conditions provided by the American Society of Heating, Refrigeration and Air Conditioning Engineers (AHSRAE). A trombe wall model was solved by considering an iterative solution method of onedimensional heat transfer and an efficiency of heat removed by convective airflow. Important inputs included the ambient temperature, room thermal resistivity and solar irradiance. The incident solar irradiance has been modelled as varying throughout the day, according a method outlined by ASHRAE and subsequent locational data. The room temperature was modelled over a day by considering room thermal resistances from 0.004K/W to 0.05K/W, and the ambient temperature variation. Results showed that a wall area of 1.4m x 2.5m can provide 6 hours of thermal comfort with ambient daily temperatures between 5.7 and 15C in Okhaldhunga, Nepal, given 0.03K/W room thermal resistance. The same comfort condition was achieved for an ambient daily temperature range from -10.1 to 6.9C in Lhasa, China with a 5m x 2.5m wall, and 0.03K/W room thermal resistance. 6 hours above a minimum ventilation flow rate, as recommended by ASHRAE was also achievable. This was modelled as exhaust flow vented to the outside, with a wall height of 2.5m and lengths between 3.5m and 4.1m depending on location.