Almost all existing analysis methods for building ventilation airflows, such as the simpleanalytical methods, multi-zone methods and computational fluid dynamics (CFD), give onlyone unique solution for one set of identical input parameters when started with zeroinitialization or zero initial conditions. This can be shown to be incorrect in some situations.Multiple stable solutions are found in some very simple buildings, which indicate that thebuilding airflows are of a nonlinear dynamical system.
This paper is based on the results of Subtask B of the HybVent Project. It presents a critical review of the literature and recent developments in analysis methods for natural and hybrid ventilation in buildings. Ideally, analytical methods aimed at modelling hybrid ventilation systems should incorporate at least three key aspects i.e: the natural ventilation mode, the mechanical ventilation mode and the control strategy. Depending on the input parameters used within the control strategy, thermal comfort and indoor air quality related parameters may also need to be predicted.
An innovative and potentially energy efficient approach to ventilating and cooling buildings is represented by hybrid ventilation. Discusses the application of hybrid ventilation strategies to building design in the USA.
States that natural ventilation systems do not sometimes perform well in conditions of high wind and/or low external temperature. Occupants shut down the system to prevent draughts. In contract, in warm summer weather the lack of air movement is a problem. Hybrid ventilation helps mitigate some of these problems. The paper outlines problems in connection with hybrid systems and indicates solutions for them. Gives examples of hybrid system, some in use and some under construction.
Presents the main features of a preliminary HVAC system project relative to a university complex, based on principles of sustainability. The design involves installation of a cogeneration system. It is proposed to incorporate hybrid and natural ventilation for energy efficiency. Gives examples of architectural designs for the various areas.
States that hybrid ventilation systems use the strengths of both mechanical and natural ventilation strategies. In the absence of many studies of the operational experience or performance monitoring of the systems, an school in Sweden was retrofitted with a hybrid ventilation system controlled by a building energy monitoring system. The main ventilation power source for this system was the six metre high solar chimneys, which were equipped with low-energy exhaust fans to supplement stack effect where necessary.
'Fan in wall' is a new ventilation system under investigation for hot and humid climate to assist natural ventilation. Temperature, relative humidity, air velocity, and thermal radiation affect thermal comfort of a person in hot climate. Installation of an air conditioner reduces air temperature and relative humidity to reach a certain level of thermal comfort. Under favourable conditions, increasing air velocity at unchanged temperature and humidity can result in the same perception of thermal comfort.
Natural and hybrid ventilation concepts are today the mean items of some international researchers about the behaviour in the innovative buildings. In fact they are utilised to contribute to the thermal comfort and the indoor air quality control. Besides there are other advantages as the low use of the energy and the reduction of noise levels. In the last years the study of the hybrid ventilation systems in the office and in the school buildings has in progress as the principal aim of Annex 35, organised by IEA. The present work wants to value the fluid dynamic phenomena organised by IEA.
The aim of this paper is to verify the applicability of coupling thermal and multizonal simulation codes to the study of hybrid ventilated buildings. One of the main problems in hybrid ventilation building design is the evaluation of ventilation control strategies. This point has rarely been adequately developed during design phase by means of dynamic simulations analysis; often actually an insufficient analysis of control strategies it has revealed to be the first cause of complaints from the occupants. This paper aims at demonstrating a satisfactory solution of this problem.
Based on measured wall temperatures made by an infrared camera the flow and temperature fields were computed for an atrium. The nature of this atrium is a large enclosure inside a school building surrounded by halls and classrooms. Within a hybrid ventilation concept the stack effect during the summer time is used to form the main driving force for the night cooling of the classrooms. Time dependant computations were carried out to obtain the flow and temperature fields inside the atrium under various boundary conditions.