Abstract
The knowledge of the air flow and air exchange in the building is critical both on the design and operation stage of the building. Infiltration of air interferes with the mechanical ventilation and determines the proper functioning of the natural ventilation system, still commonly used in the standard buildings. The building airtightness can be described by n50 parameter, however it does not specify the real air exchange in natural conditions. According to the simple procedure of the standard EN ISO 13789, factor n50 may be easily converted to the monthly averaged air change rate. However, it is difficult to accept the same value of air change rate in any month of a year, as it is often done in the certification procedures. More precise, climate dependent conversion procedures have been elaborated in USA, but they were developed for the specific local building technology and local climate conditions. This paper presents the results of the preliminary measurements conducted in a single family house in Poland, built in a heavy-weight technology. The real air exchange rate was measured in various climatic conditions by means of gas tracing method, with CO2 as the tracer gas, in order to prove a relationship between the enhanced procedure and the external conditions. Acceptable agreement between the results of the measurement and model calculations was obtained. Based on the preliminary results, the authors determined the more realistic influence of the enhanced algorithm on the ventilation energy demand. The use of the simplified model resulted in case of the analyzed object in 15% overestimation of the ventilation thermal losses.
Highlights
Due to the increasing concerns regarding building energy demand, reduction of energy losses related to ventilation is one of the main targets in the designing process
The knowledge of the air flow and air exchange in the building is an indispensable source of information both on the design and operation stage of the building
The real air exchange through the building envelope can be determined with a gas tracing method
Summary
Due to the increasing concerns regarding building energy demand, reduction of energy losses related to ventilation is one of the main targets in the designing process. Ventilation cannot be analyzed without influence of infiltration This uncontrolled and unintentional airflows affects significantly total volume of exchanged air and energy losses. Infiltration is a nonlinear phenomenon dependent on the quality of external building shell as well as its environment and driving forces. It is driven by the pressure difference caused by the weather dependent terms: wind speed and direction and temperature difference. The real air exchange through the building envelope can be determined with a gas tracing method. This measurement is complicated and the results are strongly related to the momentary external climatic conditions. The second goal is to assess to what extent a more accurate method of determining infiltration affects the building's energy performance
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