Ventilation and window opening in schools, Experiments and Analysis

Abstract: The objective of this thesis is to study the application of ventilation in schools buildings. A number of studies of the application of different forms of ventilation are presented. The main part of the thesis focuses on window opening in a classroom. Analytical models for calculation of the air change caused by window airing are proposed. The models are intended to be a tool for designers and occupants which they can use when they want to know how long a window should be open and how many windows should be opened. Tracer gas experiments have been performed both in a small test room and in classrooms. The specific conditions concerning airing require a special calculation method to determine the air change obtained during the tracer gas measurements. New methods for dealing with this have been proposed. The analytical models have been compared with the measurements. The results show that agreement is quite good and that the models can be used when rough estimates are of interest. The effect window airing has on a mechanical supply and exhaust system has been investigated by calculations with the computer program PFS. It is only when wind velocities are high that airing disturbs the flows in the system. The thesis include two studies concerning mechanical ventilation. A duct system with no means of balancing has been studied by calculation with the program PFS. A number of classrooms are assumed to be located next to each other. It is assumed that the flows to each room are equal and that the branch ducts to each room are equally spaced. The results show that a supply duct system may be designed without balancing. An exhaust duct system however requires balancing if the flows exhausted from the classrooms are to be of the same magnitude. Heat recovery in a ventilation system has also been studied by calculations. The energy need and the total costs including the whole service life have been calculated. It was found that heat recovery pays off even for a rather limited operating time. A sensitivity analysis has shown what factors are of significance when a heat exchanger is designed.