Airflow performance characteristics of ventilators in hybrid ventilation systems

Part of the task in the design of ventilation systems involves selection and specification of system components - components sizes and expected performance characteristics or criteria to achieve specific ventilation objectives for anticipated environmental conditions. Careful selection of these components is required to ensure that they are able to react to changes in environmental conditions. For ventilators (air inlets and outlets) this implies that the airflow performance characteristics need to be established in relation to the widely varying pressure driving forces (in natural ventilation mode the pressure differentials are typically less than 10 Pa whilst for mechanical ventilation the driving force can be as high as 100Pa). At present "pure" hybrid ventilators are non-existent hence, a combination of natural and mechanical ventilation components are used for hybrid ventilation applications. The desire to initiate interest of manufacturers to consider development of hybrid ventilators was the motivation behind this paper. To gain some fundamental understanding of potential airflow characteristics of such hybrid ventilators this study resorted to basic elements (slots and orifices) and employed general natural ventilation theory to predict how these components would behave when subjected to the range of pressure differentials expected in hybrid ventilation applications i.e. 0 to say 100 Pa. The study investigated via a series of laboratory experiments variations in airflow performance characteristics of simple ventilators comprising rectangular slots and round-wire mesh screens. The main objectives were to investigate and quantify variations in characteristic equations of ventilators in relation to the whole range of pressure differentials expected and also with regard to changes in dimensions of the ventilator. Results obtained indicate that the characteristic equations are not only influenced by the pressure range from which they are generated but also by the constituent components of a ventilator.