Building physics laboratory

An airtight building envelope is part of the professional construction of a building. Corresponding requirements are formulated in the Energy Saving Ordinance (EnEV), among others. The term blower door stands for a procedure with which a building can be examined for its airtightness. The system consists of a fan that is installed in an exterior door or window with the help of an airtight tarpaulin and a flexible frame. This includes a measuring and control unit with which the necessary pressure differences can be adjusted and the conveyed volume flows can be determined. For leak detection, the building is brought to a negative pressure of 50 Pa relative to the surroundings. While this pressure difference is kept constant, the entire building is examined for leaks.

Any leaks found are recorded and can be rectified.

During the actual air tightness measurement, both an overpressure and a negative pressure measurement are carried out and the so-called n50 value is determined. This describes the air exchange, i.e. the volume of air exchanged per unit of time, in relation to the air volume of the measured building, at a pressure difference of 50 Pa. Limit values for the n50 value are specified in the EnEV and DIN 4108-7.

Infrared (IR) thermography is currently probably the most important method for detecting thermal weak points in buildings. The principle of thermography is based on the fact that every body emits characteristic electromagnetic radiation - also called temperature or thermal radiation - due to its temperature. In thermography, measurements are taken in two so-called atmospheric windows of 2 - 5 μm (mid-infrared, short-wave) and 8 - 12 μm (far-infrared, long-wave). The evaluation of the measurement is based on the so-called Stefan-Bolzmann law, which can be used to infer the surface temperature of the body. The camera used (Varioscan, Jenoptik) is a scanning system that works in the long-wave infrared and has a temperature resolution of less than 0.03 K. The camera is also used to measure the surface temperature of the body.

In houses with ventilation systems, e.g. passive houses, it is generally necessary to adjust the supply and exhaust air valves to the projected volume flows. Using an air velocity measuring wheel with standardised attachment funnel, the volume flows can be measured directly at the supply or exhaust valves.

When renovating buildings, it is advantageous to have detailed knowledge of the thermal properties of exterior and interior components.

In many cases, the age of the building and the region in which it is located can be used to roughly infer the structure of the exterior component and thus the U-value (formerly k-value). The only method to determine the thermal resistance of exterior building components with a high degree of accuracy is the method described in DIN EN 12494. Here, the surface temperatures of the building component are recorded using thermocouples or an infrared measuring device and the heat flow through the building component is recorded using heat flow measuring plates. Since the evaluation requires stationary conditions, measuring times of more than 48 hours are necessary. When carried out properly, the method leads to relatively accurate results with an overall uncertainty in the range of 5 to 10 %.

The so-called passive house is a consistent further development of the former low-energy house standard (NEH). Its heating requirement of only 15 kWh/(m²a) is significantly below the legal requirements of the Energy Saving Ordinance. It can be heated with the equivalent of about 1.5 litres of heating oil per square metre and is therefore often referred to as a 1.5-litre house. The passive house standard is not a utopia, but can be realised in almost any building project with consistent planning. Planning should be based on the following principles:

• excellent thermal insulation and compactness
• South orientation and freedom from shading
• Triple glazing and insulated window frames
• airtightness of the building
• highly effective recovery of heat from the exhaust air
• Use of renewable energies

Due to extensive experience, also in the long-term monitoring of completed Passive Houses, assistance in planning and construction can be offered with accompanying scientific research.

The air temperature and relative humidity in rooms can be recorded electronically by small measuring devices and recorded over longer periods of time. After use, the data is read out from the devices and displayed over time in evaluation programs. The result is a time-dependent representation of the respective room climate.

The sound insulation of double-shell building components can be considerably reduced by so-called sound bridges. The localisation of these sound bridges is a necessary prerequisite for improvement. Sound bridges are localised by placing microphones at different positions on the surface of the building component and exciting the component with sound.

The Norsonic RTA 840 measuring system can be used to determine building acoustic parameters such as airborne sound insulation, impact sound insulation and reverberation times in buildings. For this purpose, sound levels are generated in the rooms concerned with loudspeakers or a standard hammer mill and measured with microphones. The measurements are carried out in parallel in all relevant frequency ranges. The evaluation is based on the DIN EN ISO 140 series of building acoustics standards. The results of the airborne or impact sound insulation can be compared with projected values and thus represent a quality test of the affected building components. Reverberation times measured in rooms are required for the above-mentioned evaluations, but can also be used as a basis for room acoustic planning, which is required, for example, for sufficient speech intelligibility.