Phase change materials for a windcatcher natural ventilation system

The management of comfort in natural ventilation systems can be difficult because of the variable nature of the driving forces. Excessively high temperatures in summer can cause discomfort to occupants. If some of the excessive heat could be stored during extreme temperature conditions then released when the temperature is reduced, the indoor air temperature may be controlled more easily. A phase change material (PCM) melts or solidifies at a specific temperature and either absorbs or releases latent heat as its phase changes. An experimental rig was designed and built to test a PCM system compatible with a natural ventilation system. A PCM with phase transition temperature of 27°C was selected. The test results showed that under varying inlet conditions, the heat transfer during melting was less than the heat transfer during freezing. A temperature difference of about 5°C was achieved during melting with a decline over time. A temperature difference of 5°C was achieved during freezing but the temperature gradient was maintained for an extended period. The system achieved a cooling capacity of 500-600W with a temperature gradient of 5°C over a short period (8 hours) and achieved a heating capacity of around 750-1000W at a temperature gradient of 5°C for a longer period (13 hours). The system can be installed into multiple windcatcher type ventilation systems, but would be most effective in parallel with a windcatcher, where the air flow across the PCMs can be controlled independently of the naturally induced air flow to enhance the cooling effect.