Behovsstyrd ventilation i lokalbyggnader-Innebörd och strömningstekniska konsekvenser

Licentiatavhandling, 2005

In today’s society energy efficiency and energy savings are becoming increasingly important. The building sector represents a major part of Sweden’s total use of energy. Furthermore, ventilation constitutes the single largest factor in the energy balance of buildings. Hence, demand controlled ventilation, DCV, is an interesting and important field to study. The present work deals with DCV in general and the air ducting of DCV systems in particular. Principal aims are to define the concept of DCV and to analyze the technical consequences of variable airflows for the purpose of design guidance. DCV implies that airflows are controlled on demand. But it can also include the actual design of the ventilation system so that it can be adapted to future changes of demands. By controlling the amount of air energy can be saved. Heating energy is saved in direct proportion to the decrease in airflows and hours of operation. The drive energy for the operation of fans, however, does not automatically decrease when the airflows decreases. Thus, heating energy is always saved if the airflows goes down but not necessarily the drive energy for fans. The thesis includes definition and design criteria for duct systems regarding airflows and pressure conditions in. It describes the pressure levels in different parts of the air distribution system and the pressure conditions in low-pressure level and in low-pressure loss systems. The results show that it is possible to apply DCV to different structures of duct system. However, the duct system must have certain characteristics. These characteristics also result in additional advantages such as flexibility, stability and symmetry regardless of whether or not the system is a DCV – system. This also means that if the system does not have these characteristics, the effect on the ventilation systems functionality and energy usage can be substantial. There may also be consequences for the flexibility and stability of the system. This study highlights the need for further knowledge regarding pressure levels and losses in duct systems and basic data for correct calculation of pressure losses in duct systems. At present these calculations can only be done approximately and this can lead to systems with higher then necessary pressure levels and consequently higher use of energy.