Air Permeability Testing of Building Exterior Doors and Windows

Air permeability performance testing of building exterior windows and doors mainly conducts scientific testing and analysis on the air permeability performance classification, air infiltration volume determination, pressure deformation testing, preliminary pressure testing, additional air infiltration volume determination and repeated pressure testing, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Air permeability performance classification: According to the national standard GB/T 7106-2019, the air permeability performance of the building exterior windows and doors is divided into the multiple grades. The core of the testing is to determine the air infiltration volume per unit opening seam length or per unit area of the windows and doors under the standard pressure difference, serving as the classification basis, and providing the quantitative indicators for the engineering design, product selection and acceptance.

Air infiltration volume determination: This testing item aims to precisely measure the air flow through the window and door specimens under the positive pressure or negative pressure states. The testing needs to be carried out under the stable pressure difference conditions, and the air infiltration volume at the specific pressure points (such as 100 Pa) is recorded. This is the direct data for evaluating the air tightness of the windows and doors. The lower the value, the better the sealing performance.

Pressure deformation testing: During the air permeability testing process, the conditions of the window and door specimens during the step-by-step pressurization and depressurization need to be synchronously observed. This item focuses on the deformation, opening obstacles or permanent deformations of the window and door frames, sashes, glass panels and sealing systems under the wind pressure, evaluating their structural stability and the effectiveness of the sealing systems.

Preliminary pressure testing: The pre-testing link carried out before the formal testing. The purpose is to eliminate the errors caused by the installation gaps and the initial deformations of the sealing materials. Usually, three pressure pulse loadings are carried out to stabilize the state of the specimen, ensuring the accuracy and repeatability of the subsequent formal testing data.

Additional air infiltration volume determination: To obtain the real infiltration volume of the windows and doors themselves, the "additional air infiltration volume" through the gaps between the testing device and the specimen installation frame must be deducted. This item needs to be separately tested for the installation cavity before the installation of the specimen or after its removal, and is the key step of the data correction.

Repeated pressure testing: Simulates the sealing performance retention ability of the windows and doors under the repeated wind loads. During the testing, the pressurization and depressurization need to be repeated for multiple times under the pressure difference of the classification index value (P3), observing and recording whether the air permeability performance decays during this process, evaluating the durability of the product.

Testing Scope

Exterior windows and doors of the various materials: The testing is applicable to all the exterior window and door products of the various materials, including the aluminium alloy windows and doors, plastic (PVC-U) windows and doors, wooden windows and doors, aluminium-wood composite windows and doors, steel windows and doors and FRP windows and doors. The structures and sealing methods of the windows and doors of the different materials are different, but the evaluation standards and methods of the air permeability performance are unified.

Windows and doors of the different opening forms: Covering the various opening methods such as the sliding, casement, top-hung, bottom-hung, tilt-and-turn and fixed windows. For the windows and doors of the different opening forms, the main paths of the air infiltration (such as the sash-frame lap joints and locking point gaps) are different, and the testing needs to emphatically evaluate their sealing weak links.

Whole window and door products: The testing objects are the complete, installed window and door specimens, including all the components such as the frames, sashes, glass, sealing strips and hardware locking systems. The whole-unit testing can most truly reflect the comprehensive sealing performance of the product under the actual use state.

Windows and doors of the new and existing buildings: The testing is applicable to both the product performance certification and incoming re-inspection of the windows and doors of the new buildings, and the energy-saving renovation evaluation or fault diagnosis of the windows and doors of the existing buildings. During the on-site testing, the dedicated devices need to be used on the building openings.

Buildings in the different climate zones: The requirements for the air permeability performance of the windows and doors are different in the severe cold, cold, hot summer and cold winter, hot summer and warm winter and mild regions of China. The testing needs to determine the corresponding performance grade requirements according to the climate zones and energy-saving design standards of the project locations.

Special function windows and doors: Including the high-performance energy-saving windows and doors, windows for the passive buildings, fire-resistant windows and doors and explosion-proof windows and doors. While meeting their special functions, the air permeability performance is often one of the key basic performance indicators of these windows and doors, and the testing requirements are usually more stringent.

Testing Methods

Laboratory static pressure box method: This is the most standard and most precise testing method, carried out in accordance with GB/T 7106. The window and door specimen is installed on the testing opening of the pressure box, a stable pressure difference is formed inside and outside the box through the fan system, and the air infiltration volume through the specimen is precisely determined with the flow measuring devices, calculating the infiltration coefficient.

Graded pressure procedure: During the testing, the stable pressure method is adopted. Starting from the preliminary pressure, the pressure is increased step by step according to a certain pressure grade difference (such as 50 Pa, 100 Pa and 150 Pa) to the target pressure (usually 100 Pa or the design wind pressure value). After each pressure level is stabilized, the air infiltration volume data under this pressure difference are collected, drawing the "pressure difference-flow" curve.

Positive pressure and negative pressure testing: The air permeability performance testing needs to be carried out under the two states of the positive pressure (outdoor pressure higher than indoor) and negative pressure (indoor pressure higher than outdoor) respectively. Because the deformation trends of the windows and doors and the force directions of the sealing parts under the two pressures are different, the performance can be comprehensively evaluated only by combining the data of the two aspects.

Additional infiltration volume deduction: To obtain the real infiltration volume of the windows and doors themselves, the "background deduction method" must be adopted. That is, before the installation of the specimen or after its removal, the installation opening is sealed with the plates or films, measuring the additional infiltration volume of the testing device itself and the installation frame, and finally deducting it from the total infiltration volume.

Data processing and calculation: After collecting the air infiltration volume data at the various pressure points, the values need to be converted to the standard state (temperature 293 K and air pressure 101.3 kPa). Then the air infiltration volumes per unit opening seam length and per unit area are calculated respectively, and finally, comparing with the classification table of the national standard, the air permeability performance grade of the specimen is determined.

Testing Standards

Domestic Standards:

1. GB/T 7106, Test methods of air permeability, watertightness, wind load resistance performance for building exterior windows and doors

International Standards:

1. EN 1026, Windows and doors — Air permeability — Test method

2. ASTM E283, Standard test method for determining rate of air leakage through exterior windows, curtain walls, and doors under specified pressure differences across the specimen

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Building window and door physical performance testing equipment (pressure box system): The core equipment, composed of a sealed pressure box body, variable frequency speed-regulating fan system, air flow measuring device, pressure control and measuring system and data acquisition and processing system. The box body needs to have the sufficient rigidity and sealing performance, and can simulate the wind pressure environments of the different intensities.

Air flow meter: Used to precisely measure the air volume flow through the specimen. The common types include the orifice plate flow meters, Venturi flow meters or standard nozzles. The flow meters need to be regularly calibrated, ensuring that their measurement precision within the testing range meets the standard requirements (generally better than ±5%).

Micro differential pressure sensor: The key sensor for the high-precision measurement of the pressure difference between the inside and outside of the pressure box, with the range usually of 0-500 Pa or 0-1000 Pa, and the precision grade not lower than 0.25. During the testing, two independent sensors need to be used for the measurement and monitoring, ensuring the accurate and stable pressure difference control.

Specimen installation fixing frame: Used to firmly and hermetically install the tested window and door specimen on the opening of the pressure box. The frame needs to have the sufficient strength and rigidity, and its connection with the pressure box and the fixing method with the specimen must ensure that no leakage and obvious deformation occur under the maximum testing pressure.

Data acquisition and control system: Composed of a computer, dedicated software, PLC or data acquisition modules. It realizes the functions such as the automatic control of the pressure procedure, real-time acquisition of the pressure and flow data, automatic calculation and processing of the results and generation of the testing reports, and is the key to ensuring the standardized testing process and the accurate and reliable data.

Auxiliary measuring instruments: Including the thermometers, barometers and hygrometers, used to monitor the temperature, humidity and atmospheric pressure of the testing environment, so as to correct the measured data to the standard state. In addition, the displacement meters also need to be equipped for monitoring the deformations of the key parts of the specimen under the pressure.