EN 15026:2007

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Wärme- und feuchtetechnisches Verhalten von Bauteilen und Bauelementen - Bewertung der Feuchteübertragung durch numerische SimulationPerformance hygrothermique des composants et parois de bâtiments - Evaluation du transfert d'humidité par simulation numériqueHygrothermal performance of building components and building elements - Assessment of moisture transfer by numerical simulation91.120.30WaterproofingICS:Ta slovenski standard je istoveten z:EN 15026:2007SIST EN 15026:2007en,de01-julij-2007SIST EN 15026:2007SLOVENSKI
STANDARD
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 15026April 2007ICS 91.080.01 English VersionHygrothermal performance of building components and buildingelements - Assessment of moisture transfer by numericalsimulationPerformance hygrothermique des composants et parois debâtiments - Evaluation du transfert d'humidité parsimulation numériqueWärme- und feuchtetechnisches Verhalten von Bauteilenund Bauelementen - Bewertung der Feuchteübertragungdurch numerische SimulationThis European Standard was approved by CEN on 28 February 2007.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the CEN Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as theofficial versions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2007 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 15026:2007: ESIST EN 15026:2007

Benchmark example – Moisture uptake in a semi-infinite region.18 A.1 General.18 A.2 Problem description.18 A.3 Results.19 Annex B (informative)
Design of Moisture Reference Years.22 Annex C (informative)
Internal boundary conditions.23 Bibliography.24
The following examples of transient, one-dimensional heat and moisture phenomena in building components can be simulated by the models covered by this standard: ƒ drying of initial construction moisture; ƒ moisture accumulation by interstitial condensation due to diffusion in winter; ƒ moisture penetration due to driving rain exposure; ƒ summer condensation due to migration of moisture from outside to inside; ƒ exterior surface condensation due to cooling by longwave radiation exchange; ƒ moisture-related heat losses by transmission and moisture evaporation. The factors relevant to hygrothermal building component simulation are summarised below. The standard starts with the description of the physical model on which hygrothermal simulation tools are based. Then the necessary input parameters and their procurement are dealt with. A benchmark case with an analytical solution is given for the assessment of numerical simulation tools. The evaluation, interpretation and documentation of the output form the last part.
Inputs
• Assembly, orientation and inclination of building components
• Hygrothermal material parameters and functions • Boundary conditions, surface transfer for internal and external climate
• Initial condition, calculation period, numerical control parameters Outputs
• Temperature and heat flux distributions and temporal variations • Water content, relative humidity and moisture flux distributions and temporal variations Post processing • Energy use, economy & ecology • Biological growth, rot and corrosion • Moisture related damage and degradation The post processing tools are not part of this standard. As far as possible references to publications dealing with these tools is given. SIST EN 15026:2007

It also provides a benchmark example intended to be used for validating a simulation method claiming conformity with this standard, together with the allowed tolerances. The equations in this standard take account of the following storage and one-dimensional transport phenomena: • heat storage in dry building materials and absorbed water; • heat transport by moisture-dependent thermal conduction; • latent heat transfer by vapour diffusion; • moisture storage by vapour sorption and capillary forces; • moisture transport by vapour diffusion;
• moisture transport by liquid transport (surface diffusion and capillary flow). The equations described in this standard account for the following climatic variables: • internal and external temperature; • internal and external humidity; • solar and longwave radiation; • precipitation (normal and driving rain); • wind speed and direction. The hygrothermal equations described in this standard shall not be applied in cases where: • convection takes place through holes and cracks; • two-dimensional effects play an important part (e.g. rising damp, conditions around thermal bridges, effect of gravitational forces); • hydraulic, osmotic, electrophoretic forces are present; • daily mean temperatures in the component exceed 50 °C.
kg/(m²⋅s) h surface heat transfer coefficient W/(m2⋅K) hc convective heat transfer coefficient W/(m2⋅K) he specific latent enthalpy of evaporation or condensation J/kg hr radiative heat transfer coefficient W/(m2⋅K) K liquid conductivity s/m pa ambient atmospheric pressure Pa psuc suction pressure Pa pv partial water vapour pressure Pa pv,a partial water vapour pressure in the air Pa pv,s partial water vapour pressure at a surface Pa pv,sat saturated water vapour pressure Pa pw water pressure inside pores
Pa q density of heat flow rate W/m2 qlat density of latent heat flow rate W/m2 qsens density of sensible heat flow rate W/m2 Rw liquid moisture flow resistance of interface m/s RH2O gas constant of water vapour J/(kg⋅K) sd,s equivalent vapour diffusion thickness of a surface layer m T thermodynamic temperature K Ta air temperature of the surrounding environment K Teq equivalent temperature of the surrounding environment K SIST EN 15026:2007

W/(m⋅K) ϕ relative humidity - µ diffusion resistance factor - ρa density of air kg/m³ ρm density of solid matrix kg/m³ ρw density of liquid water kg/m³ σs Stefan-Boltzmann constant W/(m2⋅K4)
4 Hygrothermal equations and material properties 4.1 Assumptions The hygrothermal equations specified in the following clauses contain the following assumptions: • constant geometry, no swelling and shrinkage; • no chemical reactions are occurring;
• latent heat of sorption is equal to latent heat of condensation/evaporation;
• no change in material properties by damage or ageing; • local equilibrium between liquid and vapour without hysteresis;
• moisture storage function is not dependent on temperature; • temperature and barometric pressure gradients do not affect vapour diffusion. The development of the equations is based on the conservation of energy and moisture. The mathematical expression of the conservation laws are the balance equations. The conserved quantity changes in time, only if it is transported between neighbouring control volumes.
()()xqqtTwcc∂+∂−=∂∂⋅⋅+⋅latsenswmmρ (1) The increase of the moisture content of a control volume shall be determined by the net inflow of moisture. The moisture flow rate equals the sum of the vapour flow rate and the flow rate of liquid water. xgtw∂∂−=∂∂ (2) lvggg+= (3) The relative humidity shall be defined by the following equation:
()Tppsatv,v=ϕ (4) The pressure acting on the water inside a building material due to the capillary forces is different from the pressure of the surrounding air. The difference is called suction. psuc = pa - pw
(5) The suction of the pore water is related to the relative humidity of the surrounding air by the Kelvin equation: psuc = -ρw RH2O T lnϕ (6) The relation between the state variables ϕ, pv, psuc, T and the moisture content of a building material is defined by the moisture storage function. The moisture storage function of a building material shall be expressed either as the moisture content as a function of suction (suction curve), w(psuc), or as the moisture content as a function of the relative humidity (sorption curve), w(ϕ).
4.2 Transport of heat and moisture 4.2.1 Heat transport 4.2.1.1 Heat transport inside materials Heat transport shall be composed of sensible and latent components. Sensible heat transport shall be calculated with Fourier’s law with a thermal conductivity which depends on moisture content.
xTwq∂∂⋅−=)(sensλ (7) Latent heat transport shall be calculated by the following equation: velatghq= (8) 4.2.1.2 Heat transport across boundaries The heat flow from the surrounding environment into the construction consists of convection, shortwave radiation from the sun and longwave radiation exchange with sky and surrounding surfaces.
Sensible heat flow from each surrounding environment to the building envelope shall be given by: ()surfeqsensTThq−= (9) The heat transfer coefficient and the equivalent temperature are: rchhh+= (10) ()()rarsolsolaeq1hTTEhTT−++=α (11) The radiative and convective heat exchanges are represented by an equivalent temperature. Other means of accounting for these effects may be used.
If the surface temperature is known it can be used as a boundary condition.
Latent heat flow to and from the boundaries is proportional to the vapour flow rate at the surfaces (see 4.2.2). 4.2.2 Moisture transport 4.2.2.1 Moisture transport inside materials Moisture is transported by capillary forces and diffusion. The transport equations shall be formulated using the partial vapour pressure and the suction as the driving potentials. wvggg+= (12) ()xpg∂∂=v0v1δϕµ (13) ()xppKg∂∂=sucsucw (14) The temperature dependence of the liquid conductivity may be neglected.
NOTE For the liquid transport alternative potentials such as relative humidity, moisture content and temperature may be used, if the transport coefficients are transformed and the interfaces between two materials are handled in such a way that the suction and the partial vapour pressure are still continuous functions across the interface. 4.2.2.2 Moisture transport across material interfaces
Internal interfaces The details of the contact between two layers of building materials can have a large influence on the liquid moisture transport. Additional coatings, such as adhesives, can also modify the diffusive moisture transport.
Small air gaps between materials and the modification of pore structure at material interfaces, because of chemical reaction products, reduce the capillary water transport across the interface. The influence of the interface on the liquid moisture flow may be described by a moisture resistance, Rw, which is defined by: wsucwûRpg= (15) SIST EN 15026:2007

()sv,av,sd,0vppsg−=δ (16) where sd,s is the equivalent vapour diffusion thickness of the interface, in m. The uptake of driving rain is limited by the amount of water which can be absorbed by the material at the surface: ∂∂=xpKgsucmaxw, (17) so that: gw = min(gp, gw,max) (18) where gp is the water available for absorption from precipitation. 4.3 Material properties 4.3.1
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