EN 15976-2011 pdf download.Flexible sheets for waterproofing – Determination of emissivity.
This EN 15976 specifies the method to determine the emissivity of plastic, rubber and bitumen vapour control layers, underlays for walls and underlays for discontinuous roofing.
It also defines a conditioning procedure for these product families in order to quantify the sensitivity of emissivity to humidity and temperature.
2 Normative references
The following referenced documents are indispensable for the application of this European Standard. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
EN 13416. Flexible sheets for waterproofing — Bitumen, plastic and rubber sheets for roof waterproofing — Rules for sampling
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply
emissivity
emissivity of a material (usually written t) is the ratio (proportion) of the energy radiated by a surface relative to the energy radiated by a blackbody at the same temperature. It is a measure of a materials ability to radiate heat
3.2
blackbody
blackbody is a theoretical object that absorbs all electromagnetic radiation that falls on it at all wavelengths. No electromagnetic radiation passes through it and none is reflected
NOTE A blackbody is also a perfect emitter with a normal and corrected emissivity of I
3.3
TIR
Thermal Infrared Radiation principle
4 Symbols
For the purposes of this document, the following symbols apply
specific heat capacity is the measure of the heat energy required to increase the temperature of a unit quantity of a substance by a certain temperature interval.
A the wavelength A is the distance between repeating units of a propagation wave of a given frequency.
NOTE In this document it is understood the wave length s limited to the infrared light spectrum.
EN 15976:2011 (E)
a (alpha) represents the absorption coefficient of a surface and is the ratio of the radiant energy absorbed by that surface relative to that of a blackbody at the same temperature.
E (epsilon) emissivity (see above definition of emisslvity) (0 ≤ E ≤ 1).
p (rho) reflectivity coefficient is the proportion of the incident electromagnetic radiation reflected
from a surface or an optical element.
t (tau) transmission coefficient is the proportion of incident electromagnetic radiation (light) passes through a surface oi an optical element.
ft emissivity for the low emissive calibration standard.
emissivity for the high emissive calibration standard.
U sensor signal of the specimen in Volt.
U.. sensor signal of the high emissive calibration standard in Volt.
U1 sensor signal of the low emissive calibration standard in Volt.
5 Principle of low emitting surfaces
Flexible sheets for waterproofing with a low emitting surface are commonly referred to as radiant or reflective barriers. The pnnciple of a radiant barrier is based on its ability to reflect radiant heat instead of absorbing it. Radiation (radiant heat) is the transmission of electromagnetic rays through space and in this context “radiation refers only to the energy of infrared rays. At any temperature, all objects radiate infrared rays, which travel in all directions until they are reflected or absorbed by another object. The heating of objects excites the molecular surface structure, resulting in an emission of infrared radiation fron the surface.
The radiative flux through a body will satisfy the conservation-of-energy equation:
6 Hemispherical blackbody radiator
6.1 Principle of hemispherical blackbody radiator
The hemispherical radiator (half sphere) ui the Ioriii ol a blackbody uses the thermal infrared radiation principle (TIR-principle). The temperature of the blackbody is set and controlled at 1000 (+1- 0,5 °C). The hemispherical shape of the radiator is necessary in order to achieve a complete and homogerious illumination of the measuring surface allowing even the emissivity of rough and structured surfaces to be measured correctly. Part of the energy reflected and emitted by the sample passes through a smafl opening in the hemispherical radiator and is focussed onto an infrared sensor by an infrared lens. The infrared sensor changes the incident thermal radiation into a voltage signal in a broad band and linear manner (the voltage signal is proportional to the reflected thermal energy).
At any given temperature of a blackbody. the spectral distnbution of the thermal radiation is given by Plancks law. The radiators temperature has been chosen to be 100° (± 0.5 °C) so that the corresponding spectrum
has its peak at a wavelength (A) of ca 8 pm and more than 97 % of the radiant energy is in the wavelength range from (2,5 to 40) pm.EN 15976-2011 pdf download.