U value measurement for evaluating energy efficiency/heat losses of
walls & windows in old buildings:
What is U value?
Heat losses are unavoidable, but they can be significantly reduced through
clever building and living. Materials retain heat to differing degrees. Just
how much is indicated by the U value – Heat Transfer Coefficient (formerly
known as the k value). It is an important indicator in the assessment of the
thermal properties of materials and defines the heat losses, in other words the
transmission losses, caused by a component.
The unit of the U value is W/(m²K), and results from the
flow of heat that flows through 1 square metre (m2) of outer wall or
window when it is 1 degree (in Kelvin = K, corresponds to 1 degree Celsius)
colder outside than inside. The smaller the U value, the lower the heat loss
through the building component measured.
Significance of U
value
The U value is a key characteristic value for assessing the energy
efficiency of a building shell and is particularly important in respect of
redevelopment or renovation. U value lays foundation for the renovation work. Information
about the U values of a building provides useful clues about possible or
necessary structural modifications. The measurement is carried out on site.
Measurements can be performed on walls, windows or other such elements.
The Challenge in U
Value Measurement
To determine the U value, measurement of three temperatures is required: the
air temperature inside, the temperature of the inside wall surface and the air
temperature outside. The U value is determined across the entire element,
regardless of the individual material layers of the wall structure. The
challenge over here is one needs to know the structure of the wall, what
thickness and what material was installed and what is the thermal conductivity
of the individual materials. Calculating the U-value of an older building
presents a greater measurement challenge: the walls are often made of unknown
materials; it is difficult to measure their thickness; and the idea of drilling
to take material samples can meet with scepticism or even refusal on the part
of the owners.
The Solution
U value probe of testo 635-2 measures the inside wall surface temperature via three
wires that are attached to the inside wall with an adhesive modelling clay.
There is no need to damage the building substance by drilling boreholes. Inside
& outside temperature is measured with temperature sensor or thermocouple
that is attached to the instrument. The measuring instrument testo 635-2
automatically calculates the U-value from the three values and shows this on
the display. You are able to follow the detailed measurement curve graphically
and as a time progression via the testo ComSoft software installed on the
connected laptop.
The Testo Advantage
- Easy
attachment of the probes – even on difficult-to-access components
- Graphical
representation & easy analysis by software
- No manual
calculation
- Accurate U
Value lays foundation of renovation work
- Proof of
service thanks to report creation
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