Blower door
With the differential pressure method (also: Blower Door Test), the air tightness of a building is measured. The procedure is used to detect leaks in the building envelope and to determine the air exchange rate. Due to the pressure differences, a constant wind load is simulated on the measured building.
Legal requirement
The goal of every construction project should be to achieve optimum living comfort and to minimize the energy used for this purpose. Therefore it is necessary to provide a relatively air-tight outer shell of each building. In the German DIN 4108, part 7, such as the "mounting an air-impermeable film over the entire area " is required. The DIN sets binding limit values for air change rate n50, thus has a new building to qualify for a certain amount of air tightness, which can be detected by the differential pressure measurement. Each building must have by today's standards a planned, continuous, sealing plane between indoor and outdoor use. This is achieved by increasing insulation levels and more important, since the heat transfer by transmission through well-insulated components is indeed very low, but loses its efficiency when a large part of the supplied energy is lost by convection through leaks. The leakage detection in shell condition with the help of a vacuum drawn in the building reveals leaks. This can be solved without much effort before installing the skins. It can therefore be sustained save energy and reduce the risk of structural damage and reduce the insulating effect due to condensation in the insulation during the winter period.
Standardized difference is the printing process in the ISO 9972:1996 and the acts building upon EN 13829 Thermal performance of buildings - Determination of air permeability of buildings. Differential pressure method, German takeover DIN EN 13829:2001-02.
Principle of measurement
By a fan, air is forced or sucked out into the building to be examined. To adapt the delivered air flow to the building tightness serve different sized orifice plates for the delivered volume flow. By calibrating the size of the volume flow is displayed. The variable speed fan is adjusted so that the ambient pressure results in a pressure difference of 50 Pa ( Pascal ). Pressure differences also occur naturally, such as when wind blows; 50 Pa approximately correspond to the wind force, the fan 5 is inserted by means of an adjustable metal frame, which is surrounded by an air-impermeable awning, in a door or window opening. The frame is pressed down firmly on rubber seals in the door or window frame. By measuring in a door of the name blower door test came ( German: blower door measurement) about. The door or window in which the measuring device is used, then of course can not be measured with. Since it is often very important to measure also the most large front doors with, can be used for installing the Blower Door device also eg a balcony door.
Through the orifice plates, the fan itself creates a positive pressure in the fan. Measuring instruments determine the two pressure differences:
1 ) pressure difference between the outside and inside,
2 ) in fan pressure - and therefore the size of the air flow which conveys the fan.
The speed of the fan is controlled so that a certain pressure between the outer and interior builds. He must move in the vacuum measurement much air to the outside, such as to penetrate through the existing leaks in the building. The measured air flow is divided by the volume of the building. This value, the air change rate n50, you can now compare with other buildings and standards. The blower door method offers the opportunity to:
Measurement phases
The blower door test is divided into three phases:
For the full results of the over-and under pressure of the building, the average air exchange rate ( n50 - value ) is calculated. This indicates how often the air is changed in the building due to leakage measured at a reference pressure of 50 Pa in an hour. An N50 - value = 2.5 h-1 for example, means that the air is replaced in the building at a pressure difference of 50 Pa to 2.5 times an hour due to air leakage. The exact sequence of the measurement is regulated in DIN EN 13829. For a blower door test on a single-family house on-site for a time of about 3 hours must be estimated. This requires that the volume and the base areas of the building within the sealing plane is determined. After the measurements, the homeowner receives a certificate on the quality of the measured building envelope, if the limit values according to the standard were not exceeded. These currently stand at 3.0 1 / h for residential buildings and 1.50 / h for residential buildings with ventilation system.
Fundamental considerations
The differential pressure measuring procedure should be performed on each new construction and remodeling, to locate any existing defects in the building envelope. The Energy Saving Ordinance ( Energy Saving Ordinance ) was paid for the implementation of the blower door measurement. If the limits are adhered to, a reduced air change must be recognized and in buildings with ventilation system includes the blower door measurement standard, as only with leak detection, this technique should be considered in the energy demand proof. For low energy and passive houses the proof is mandatory.
When measuring it comes to two goals. First, the amount of air that supports the fan and the inevitable escapes through joints etc. than 3.0 may, once per hour, the air exchange in the building (Default by the German Energy Saving Regulation - Energy Saving Ordinance, in buildings with ventilation systems at most 1.5 times) and secondly, should the one who performs the measurement, locate the defects and document so that they can be eliminated. So there is nothing to conduct a blower door test, then determine that the standard is not adhered to carry out ( no release of this certificate available), without a precise location of the leaks. The last requirement is not directly law, but one of the generally recognized rules of technology, on the observance, for example, a builder without special agreement is entitled. Therefore, defects must be detected and eliminated in time.
Typical air exchange rates as a result of building tightness measurements are: leaky buildings at 4 to 12 h -1; in new buildings without special care 3-7 h -1; in low-energy houses 1 to 2 h -1 and passive houses 0.1 to 0.6 h -1. In passive houses the air-tightness is particularly important, therefore, a limit of 0.6 h -1 given there is ( in each case measured at 50 Pa).
A building must be released ( eg, for moisture removal ) - but only on the proposed ventilation options. Indoor air flows (which is always wet ) due to deficiencies in the construction (unintentional gaps, slots, etc.) to the outside are almost always structural damage ( mold, etc. ) pre-programmed. Flows, for example, humid air through mineral wool, so it comes to condensation failure: According to the function of the mineral wool for thermal insulation one side of the mineral wool is warm - and the one that is facing the room - and the other side is cold in winter. If the air in the cold area, the air is cooled considerably, the dew point is below and condensation water is the result. Because of the lack of accessibility, this condensation not - be wiped - as the window. The only option is to carefully avoid airtight design of the structure on the warm side ( air-tight layer).
Air tightness should not be confused with vapor diffusion leaks. A normal interior plaster on a masonry example is sufficient airtight but vapor permeable - the same applies to air seal papers. When producing an airtight layer is not about absolute tightness, but to avoid convection, which is caused by the rapid escape of large quantities of air through leaks.
It should be noted that also the sound insulation is often improved by the air-tightness. Airtightness in terms of soundproofing and odor are often between different apartments within a house is an important aspect. With the differential pressure measuring individual apartments can be assessed for their tightness out.