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.
The knowledge of the air exchange and building air-tightness is an indispensable source of information, both on the design and operation stage of the building use. Properly functioning ventilation system affects significantly internal thermal comfort and internal air quality. Infiltration of air determines the proper functioning of the gravitational ventilation, still the most commonly used system in Polish single-family housing. However, the most popular and easy to measure parameter: building airtightness (n50), does not specify the real air exchange in the actual climatic conditions. The real air flow rate may be determined with much more troublesome gas tracing method. Air flow rate, n, is in this method obtained from the decaying curve of gas concentration after injection of tracer gas into the building. This paper presents the results of the airtightness measurements conducted in a single family house with natural ventilation. Both, n
50 parameter and building air flow rate n have been measured. The results of the measurements were used as a model calibration tool in the annual computational simulations carried out in the Design Builder program for the Polish climatic conditions. Based on these simulations the authors determined the influence of building airtightness on the internal thermal comfort and the potential scenario of its control.
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