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.
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