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Coefficient of thermal transmittance (U value)

Analyzing the building shell: with U-value determination and flow velocity measurement

Thermal transmittance, also known as U-value, is the rate of transfer of heat (in watts) through one square metre of a structure divided by the difference in temperature across the structure. It is expressed in watts per square metre per kelvin, or W/m²K. Well-insulated parts of a building have a low thermal transmittance whereas poorly-insulated parts of a building have a high thermal transmittance.

In order to calculate the U-value, three temperature values are required: the outside temperature, the surface temperature of the inside wall and the room temperature.

Using the multi-function measuring instrument model 435, the U-values as well as the smallest air flow velocities, such as occur at badly sealed windows, can be reliably measured.
With the new, patented U-value probe, the other necessary temperatures can be recorded with only one probe.

In order to measure the surface temperature, the three wires of the U-value probe are attached to the inside wall with modelling clay.The air temperature is determined via a sensor in the probe plug. The three required temperatures are recorded by the connected temperature probes and transferred. The instrument then calculates the U-value from them, and shows it directly in the display.
Flow velocity measurement

With the 435, in combination with a thermal measurement probe, it is also possible to detect the smallest airflows in rooms, e.g. from poorly sealed windows and electrical sockets. The accurate hot wire probe detects even the smallest airflow velocities.