Ventilation of nZEB
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Ventilation is the process of the dilution of indoor air pollutants by exchanging the indoor air with the exterior air. This can be done because, in general, outdoor air is less polluted that indoor air. With ventilation, the amount of indoor air pollutants must be lowered to a level that does not affect the perceived quality of the indoor environment, decrease the productivity or influence the health of residents. Several hundreds of pollutants can be found in indoor air because they are emitted from human bodies, animals, plants, as well as building materials and processes. Water vapour, CO2, CO, solid particles and odours are the most indicative pollutants in residential buildings. Requirements and methods for the determination of amount of supply fresh air needed to reach the desired category of indoor air quality (IAQ) are presented in Chap. 1. In this chapter, the principles and types of ventilation, design of ventilation systems, energy performance indicators and measures for increasing energy efficiency of ventilation systems are presented. When determining the energy needs for ventilation, as described in Sect. 5.3, it is assumed that supply air is delivered into the building at the indoor air set-point temperature (during heating and cooling periods). Consequently, energy needs for ventilation are included in the energy needs for heating (QNH) and cooling (QNC) and the final energy demand for ventilation is only related to the energy use of electricity for the operation of the fans in the case of mechanical ventilation. Ventilation systems can be extended to air-heating or air-cooling systems. In such systems, heat is delivered or extracted by air that is supplied into the building (rooms) at higher (up to ~40 °C) or lower temperatures (down to ~18 °C) in comparison to the indoor air set-point temperature. Air-conditioning systems are another type of extended ventilation systems using air as a heat transfer fluid for heating and cooling. In contrast to air-heating and air-cooling systems, such systems also regulate the humidity of the indoor air. Besides providing the required indoor air quality, the process of ventilation can be used for the removal of the heat of internal sources and solar radiation to cooling the building’s thermal mass during summer nights to avoid overheating and decrease the energy needs for cooling the building. It is common for all those processes that a much larger quantity of supply air is required in comparison to IAQ requirements. Only “pure” ventilation systems will be presented in this chapter.
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