Modelling and simulation of a ventilated double window

Double windows are a currently adopted construction system in Portuguese residential buildings to prevent air leakage and thermal discomfort. We have changed this construction system so that it could be able to pre-heat the ventilation air between the windows. Simple changes consist in introducing vents at the base of the outer window to allow a supply of fresh air. Heat that escapes from inside through the inner window and solar radiation heat up the air between the two windows. Due to wind pressure and stack effect, the air rises and enters the room through a vent at the inside top of the system warmer than the outdoor air. A simulation program was built and validated with the use of test facilities, where different configurations of the system were tested. This paper presents the mathematical model and some results of a simulation work based on it. Parametrical studies were carried out by varying the airflow rate, the outdoor air temperature and the solar irradiance to predict the temperature rise and the useful energy of the delivered air. Results indicate an encouraging thermal performance of the ventilated double window offering itself as an alternative to cold natural ventilation. ► The temperatures and airflows are the result of many simultaneous thermal and flow processes, influenced by the climactic conditions, the geometric and physical properties of the various components of the ventilated double window. ► A mathematical model to predict the thermal performance of a ventilated double window is suitable to building designers. ► A ventilated double window is capable of reducing the heating load of the building due to pre heating the ventilation air.