Moisture transfer General principles Moisture transfer Water and

Moisture transfer General principles

Moisture transfer Water and moisture in buildings: - atmospheric (rain, air) - (initial) built-in moisture - elevating - condensated most common task Exceptions exist: condensated moisture can be the most important!

Moisture transfer Water in constructions: - in all 3 phases: - water vapor - water - ice

Moisture transfer Water in constructions: - in all 3 phases: - water vapor - water - ice - it can cause failures (mould, corrosion, destruction of materials, conditions for decaying fungi)

Moisture transfer Water in constructions: - in all 3 phases: - water vapor - water - ice - it can cause failures (mould, corrosion, destruction of materials, conditions for decaying fungi) it decreases insulating properties

Moisture transfer Water in constructions: - in all 3 phases: - water vapor - water - ice part of gas mixture called „air“: - nitrogen, oxygen, argon, CO 2, neon, helium, methane, krypton, hydrogen, xenon solid aerosols water vapor and other gases mixture has in certain altitude certain atmospheric pressure Dalton law John Dalton (1766 – 1844) - total pressure of gas mixture is sum of partial pressures: partial parts: partial pressures in mixture in BP: partial pressure of water vapor (in air)

Moisture transfer Water vapor in air: - amount of vapor in air is expressed as: - specific (absolute) humidity - partial water vapor pressure - relative humidity pressure of vapor in air it expresses how close is air to saturation by water vapor typically approx. 85% in winter and 50% in summer (ext. air) real vapor content of air in kg/kg (symbol x) or in kg/m 3 (symbol v – also called vapor concentration) typically approx. 1 g/kg in winter and 10 g/kg in summer (ext. air)

Definitions Specific humidity [kg/kg] Water vapor content of air. It expresses how much water vapor in kg is included in 1 kg of dry air. It is often presented in g/kg. Typical values for external air: approx. 1 g/kg in winter, approx. 10 g/kg in summer Water vapor concentration [kg/m 3] Water vapor content of air. It expresses how much water vapor in kg is included in 1 m 3 of dry air.

Definitions Specific humidity [kg/kg] Water vapor content in air. It expresses how much water vapor in kg is included in 1 kg of dry air. It is often presented in g/kg. Typical values for external air: approx. 1 g/kg in winter, approx. 10 g/kg in summer Water vapor concentration [kg/m 3] Water vapor content in air. It expresses how much water vapor in kg is included in 1 m 3 of dry air. Typical values : for θ = -15 C …. 1, 4 g/m 3 for θ = 20 C …. 17, 3 g/m 3

Definitions Partial water vapor pressure [Pa] Water vapor pressure in air (or generally in gas mixture). It can be derived from ideal gas law: water vapor gas constant [J/(kg. K)] air temperature [ C] vapor concentration [kg/m 3]

Definitions Partial water vapor pressure [Pa] Water vapor pressure in air (or generally in gas mixture). It can be derived from ideal gas law: water vapor gas constant [J/(kg. K)] air temperature [ C] vapor concentration [kg/m 3] Saturated partial water vapor pressure [Pa] Maximum possible water vapor pressure in air with given temperature. It is partial vapor pressure in air in conditions of total saturation of air by water vapor. It is derived from measurements, it depends on air temperature.

Definitions Relative humidity [%] Ratio between actual water vapor content and maximum possible water vapor content in air with given temperature. It expresses how close is air to saturation by water vapor concentration saturated partial vapor pressure Typical value for external air: approx. 85 % in winter approx. 50 % in summer Typical design value for internal air: 50 %

Moisture transfer Water vapor in constructions: For better image: - - for the moisture transfer, relation between size of pores in material and mean free path of vapor molecules is crucial macrocapillary: H 2 O molecule: - distance between consecutive crashes - diameter 10 -6 m -8 -2 diameter 3. 10 -10 m - for vapor l=4. 10 m - length 10 mm - mean free path 400. 10 -10 m building materials have in general microstructure with pores common pore system: x 1 000 -7 m) - macrocapillaries (diameter >H 10 macrocapillary : O molecule: 2 - microcapillaries 10 -7 m) - diameter 0, 3 mm - diameter (< 1 m length size larger-than mean 10 freekm path, i. e. vapor molecule more likely hits another molecule than capillary wall its size can be smaller than vapor mean free path wood - mean free path 40 mm model

Moisture transfer Impact of environment: - air humidity affects humidity of material (water molecules stick to surface of pores: ADSORPTION) - equilibrium is created for every humidity of ambient air Water content of material is characterized by: - volumetric water content (based on volume) gravimetric water content (based on mass) water volume material volume weight in moist state weight in dry state

Moisture transfer Dependence of material water content on ambient humidity: - sorption isotherm (curve) different for individual materials difference between sorption x desorption (hysteresis)

Moisture transfer Vapor transfer in air

Moisture transfer Vapor transfer in air: - diffusion: - movement of particles in environment - molecules move incidentally from regions of high concentration to regions of low concentration - diffusion flux: 1 st Fick law generally: Analogy to Fourier law (heat flux). For water vapor: Adolf E. Fick (1828– 1901) vapor diffusion coefficient in air (material) [s] partial vapor pressure in air (in pores) [Pa]

Moisture transfer Vapor transfer in air: - diffusion: - movement of particles in environment - molecules move incidentally from regions of high concentration to regions of low concentration - diffusion flux: 1 st Fick law generally: Analogy to Fourier law (heat flux). For water vapor: Adolf E. Fick (1828– 1901) Flow is often approx. 1 D, then: It can be expressed also in another way.

Moisture transfer Vapor transfer in air: - diffusion: - movement of particles in environment - molecules move incidentally from regions of high concentration to regions of low concentration - spatial and time distribution of partial vapor pressures: 2 nd Fick law Analogy to heat conduction equation. Adolf E. Fick (1828– 1901)

Moisture transfer Vapor transfer in air: - convection: - vapor is transferred by moving air - considerably more intensive than diffusion (10 x-10000 x) - it can be oriented in the same or opposite direction than diffusion - difficult modeling (CFD)

Moisture transfer Moisture processes in constructions

Moisture transfer through construction: - complex complicated process still not theoretically finalized „Moisture transfer is a very complex process and the knowledge of moisture transfer mechanisms, material properties, initial conditions and boundary conditions is often limited. Therefore this International Standard lays down simplified calculation methods…“ (preface from EN ISO 13788) - modes of vapor transfer through constructions depend on: - size of capillaries moisture content in capillaries boundary conditions tightness of construction

Moisture transfer Modes of vapor transfer: Processes: - diffusion (macrocapillaries) - effusion (microcapillaries) movement of molecules without reciprocal hits - thermodiffusion (usually negligible) temperature thermo diffusion coefficient increasing moisture ciontent I. low moisture content i e

Moisture transfer Modes of vapor transfer: Together with diffusion+effusion: - adsorption on walls of pores - molecullar moisture (attached to walls of pores) Driving forces: - part. vap. pressure difference (diffusion, effusion) - temperature difference (thermodiffusion) increasing moisture ciontent I. low moisture content i e

Moisture transfer Modes of vapor transfer: Processes: - diffusion (macrocapillaries) - surface diffusion (surface of macrocapillaries) - capillary conduction (microcapillaries) they can be (mainly in winter) oriented in opposite way than diffusion (different driving forces) increasing moisture ciontent II. average moisture content i e i e

Moisture transfer Modes of vapor transfer: Processes: - diffusion (macrocapillaries) - surface diffusion (surface of macrocapillaries) - capillary conduction (microcapillaries) Driving forces: - part. vap. press. difference (diffusion) - rel. hum. difference (surface diffusion) - capillary pressure difference (cap. conduction) increasing moisture ciontent II. average moisture content i e i e

Moisture transfer Modes of vapor transfer: Processes: - capillary conduction Driving forces: - capillary pressure difference increasing moisture ciontent III. high moisture content i e i e

Moisture transfer All transport mechanisms presented so far take place in air-tight construction. In construction with leakages, there is also: Vapor transfer by convection Effects: - considerably higher transport of water vapor - significant moisture impacts increasing moisture ciontent Modes of vapor transfer: i e i e

Moisture transfer Modes of vapor transfer: Effects of w. v. convection depend on its orientation: i e - exfiltration - infiltration - more risky moist air penetrating construction local increase of moisture content in materials fast and fatal deffects! pay attention to constr. with mineral wool and to ventil. constr. guarantee air-tightnes!!! else:

Moisture transfer Modes of vapor transfer: Effects of w. v. convection depend on its orientation: - exfiltration leakages i e temperature field for exfiltration - infiltration rel. humidity field for exfiltration - temperature field for infiltration less risky cold dry air penetrating construction local drying appears rel. humidity field for infiltration usually without moisture deffects convection can be reversed, air-tightness is still crucial!

Moisture transfer Modes of vapor transfer: - diffusion effusion thermodiffusion surface diffusion capillary conduction convection usual technical approach: - only diffusion - verified as fast method for safe evaluation of condensation risk in constructions increasing moisture ciontent List of transport processes: i e i e

Moisture transfer Vapor diffusion

Vapor diffusion through construction Diffusion is always oriented againts gradient of partial vapor pressures, i. e. from regions with high partial vapor pressure to regions with low partial vapor pressure diffusion flux (1 st Fick law) vapor diffusion coefficient in material [s] Result of measurement, usually not used in calculations. Instead: vapor resistance factor

Vapor diffusion through construction Vapor diffusion coefficient in air diffusion flux (1 st Fick law) Result of measurement, usually not used in calculations. Instead: vapor resistance factor

Definitions Water vapor resistance factor [-] Ratio between vapor diffusion coefficient in air and vapor diffusion coefficient in material. It expresses how much less the material is permeable for water vapor than still air with the same thickness. vapor diffusion coefficient in air vapor diffusion coefficient in material

Vapor diffusion through construction Vapor resistance factor Types of vapor resistance factor: - dry - - wet - - measured for low air humidities (dry cup method) used for evaluations of constructions with ambient RH < 60 % measured for high air humidities (wet cup method) used for evaluations of constructions with ambient RH > 60 % according to temperature during measurement - 10 C (in past) 23 C (today)

Vapor diffusion through construction Vapor resistance factor Typical values of vapor resistance factor: - air - - up to 10 mm. . . μ = 1 more than 10 mm … μ = 0, 01/d (approx. model of convection according to EN ISO 13788) building materials μ-value depends on microstructure of material connected pores closed pores

Vapor diffusion through construction Vapor resistance factor Typical values of vapor resistance factor: - air - - up to 10 mm. . . μ = 1 more than 10 mm … μ = 0, 01/d (approx. model of convection according to EN ISO 13788) building materials - mineral wool. . . μ = 2 -5 EPS. . . μ = 30 -70 XPS. . . μ = 80 -150 foam glass. . . μ = 700 000 concrete. . . μ = 30 -150 bitumen (waterproofing). . . μ = 20 000 – 50 000 PVC membranes (waterproofing). . . μ = 7 000 – 20 000 vapor barriers. . . μ = 50 000 – 1 000 difficult measurement, often poor quality of data or completely unavailable

Vapor diffusion through construction Vapor resistance factor Typical values of vapor resistance factor: - air - - up to 10 mm. . . μ = 1 more than 10 mm … μ = 0, 01/d (approx. model of convection according to EN ISO 13788) building materials Connections are the most important for many materials (mainly with high μ-value).

Vapor diffusion through construction Vapor resistance factor Typical values of vapor resistance factor: - air - - up to 10 mm. . . μ = 1 more than 10 mm … μ = 0, 01/d (approx. model of convection according to EN ISO 13788) building materials Leakage area (mainly over 1 % Connections are the most important for many materials from total area: with high μ-value). Influence of leakages is usually taken as a guess. max. μ = 0, 27/d E. g. for mechanically fixed vapor barriers: (i. e. μ. d = max. 0, 27 m, - reduction of μ 10 x for standard realisation measurement by Mrlík) - reduction of μ 100 x for low quality realisation Always to increase the safety of calculation!

Vapor diffusion through construction Vapor resistance factor Typical values of vapor resistance factor: - air - - up to 10 mm. . . μ = 1 more than 10 mm … μ = 0, 01/d (approx. model of convection according to EN ISO 13788) building materials special case: impermeable materials with joints (e. g. steel sheets) vapor diffusion through joints (leakage diffusion) Final eqv. vapor resistance factor is calculated from characteristic section with area A, including effects of length of joints (l), their measured leakage diffusion coefficient (Λ), thickness of material d and its vapor resistance factor μ

Vapor diffusion through construction Other diffusion parameters: - equivalent diffusion thickness more clear for many materials: - foil μ=600 000, d=0, 1 mm - bitumen μ=150 000, d=4 mm - ? sd=60 m sd=600 m diffusion resistance thermo-diffusion function, dependent on atmosph. pressure and temperature, usually 5, 312. 109 s-1

Vapor diffusion through construction Non-homogeneous constructions: - calculation for characteristic section …or more exactly from 2 D or 3 D vapor transfer calculation: partial vapor pressures difference diffusion flux

Moisture transfer Requirements of ČSN 730540 -2 and Glaser method

Vapor diffusion through construction Requirements of ČSN 730540 -2: – vapor condensation must be eliminated if it is dangerous for construction Condensation is dangerous if it leads to: - considerable decrease of lifecycle of construction - mould growth - changes of volume - considerable increase of weight - degradation of materials

Vapor diffusion through construction Requirements of ČSN 730540 -2: – vapor condensation must be eliminated if it is dangerous – condensate be able to evaporate totally - podstatnémust zkrácení životnosti - plísně – total annual vapor condensate must be lower than: změny • - objemové for unventilated flat roofs, - výrazné zvýšení constructions withhmotnosti timber elements, - degradace materiálu ETICS and other constructions with impermeable external layers: 0, 1 kg/m 2 or 3 % (resp. 6 %) 0, 5 kg/m 2 or 5 % (resp. 10 %) • for other constructions: Ventilated constructions: l requirements are valid for internal deck l in ventilated layer:

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation – for lowest external temperatures – necessary for constructions with unacceptable condensation • annual cycle calculation – for changing external (and internal) conditions – annual vapor condensate amount – possibility of evaporation

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation – for lowest external temperatures – necessary for constructions with inadmissible Glaser method condensation (H. Glaser, 1958: problems of cooling chambers) • annual cycle calculation – for changing external (and internal) conditions Assumptions: – annual amount of condensated water vapor - vapor condensate amounts are relatively small – possibility of evaporation - only (or prevailing) mechanism is vapor diffusion - latent heat and hygroscopic (ability of materials to absorb water) can be neglected Boundary conditions: - design external temperature θe + design rel. humidity φe - design temperature of indoor air θai + design rel. humidity φi

Definitions Design outdoor air relative humidity [%] Relative humidity of outdoor air derived from long-term measurements for climate conditions in Czechia. Empirical dependence on external temperature is used:

Definitions sat. part. vapor pressure in exterior air [Pa] rel. humidity of interior air [%] Design outdoor spec. gas constant of water vapor [J/(kg. K)] air relative humidityvapor [%]production [kg/h] abs. temperatures of int. and ext. air [K] Relative humidity of outdoor air derived from long-term measurements for climate conditions in Czechia. Empirical dependence on external air volume in room [m 3] temperaturesat. is used: part. vapor pressure in interior air [Pa] air change rate [1/h] Design indoor air relative humidity [%] Relative humidity of internal air used for purposes of evaluation of building constructions. • standard value for buildings with normal humidity: φi = 50 % • values for buildings with high (or low) humidity from: • tables in ČSN 730540 -3 • HVAC project (controlled RH adjustment) • calculation

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation – for lowest external temperatures – necessary for constructions with inadmissible Glaser method: condensation • • graphical-numerical θai • annual cyclemethod calculation θ partial steps: – for changing external (and internal) conditions 1. temperature distribution – annual amount of condensated water vapor si – possibility of evaporation all layers are included in calculation! Surface resiatance Rsi: same value as for roof assembly U-value calculation (exlud. layers above waterproofing) (i. e. 0, 13/0, 10/0, 17 W/(m 2 K)) θse Rsi thermal resistances of layers (from interior) θe Rse R

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation – for lowest external temperatures – necessary for constructions with inadmissible Glaser method: condensation • • graphical-numerical • annual cyclemethod calculation partial steps: – for changing external (and internal) conditions 1. temperature distribution – annual amount of condensated water vapor 2. saturated partial vapor – possibility of evaporation pressure distribution psat = f(θ) Eqv. diff. thicknesses for surface transfer: very small, therefore neglected sd sdi eqv. diff. thicknesses of layers (from interior) sde

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation – for lowest external temperatures – necessary for constructions with inadmissible Glaser method: condensation • graphical-numerical method psat, si • annual cycle calculation • partial steps: – for changing external (and internal) conditions 1. temperature distribution – annual amount of condensated water vapor psat curve is derived 2. saturated partial vapor – possibility of evaporation from temperature curve: pressure distribution psat = f(θ) Sat. part. vapor pressure on internal surface. Derived from internal surface temperature: psat, si = f(θsi) psat, se the same for external surface eqv. diff. thicknesses of layers (from interior) sd

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation – for lowest external temperatures – necessary for constructions with inadmissible Glaser method: Maximum possible part. condensation vapor pressure • graphical-numerical method • annual cycle calculation • partial steps: – for changing external (and internal) conditions pi 1. temperature distribution – annual amount of condensated water vapor 2. saturated partial vapor – possibility of evaporation pressure distribution critical region 3. part. vapor pressure distrib. Assumed part. vapor pressure pe eqv. diff. thicknesses of layers (from interior) sd

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation – for lowest external temperatures – necessary for constructions with inadmissible Glaser method: condensation • graphical-numerical method • annual cycle calculation • partial steps: – for changing external (and internal) conditions pi 1. temperature distribution – annual amount of condensated water vapor 2. saturated partial vapor p ≥ psat : condensation – possibility of evaporation pressure distribution p < psat : diffusion only 3. part. vapor pressure distrib. pe eqv. diff. thicknesses of layers (from interior) sd

Vapor diffusion through construction condensation on Calculation: interface of materials – two basic tasks: • condensation risk calculation typical for unventilated roofs – for lowest external temperatures – necessary for constructions with inadmissible Glaser method: condensation • graphical-numerical method • annual cycle calculation • partial steps: – for changing external (and internal) conditions pi 1. temperature distribution – annual amount of condensated water vapor 2. saturated partial vapor – possibility of evaporation pressure distribution 3. part. vapor pressure distrib. Condensation Oblast kondenzace: area: tečny z bodů tangents frompp to i a i +pp e eke křivce p psat course eqv. diff. thicknesses of layers (from interior) pe sd

Vapor diffusion through construction condensation on Calculation: interface of materials – two basic tasks: • condensation risk calculation typical for unventilated roofs – for lowest external temperatures – necessary for constructions with inadmissible Glaser method: condensation • graphical-numerical method • annual cycle calculation • partial steps: – for changing external (and internal) conditions pi 1. temperature distribution – annual amount of condensated water vapor 2. saturated partial vapor – possibility of evaporation pressure distribution 3. part. vapor pressure distrib. real distribution of part. vapor pressure: eqv. diff. thicknesses of layers (from interior) pe sd

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation – for lowest external temperatures – necessary for constructions with inadmissible Glaser method: condensation • calculation of condensation rate • annual cycle calculation in kg/(m 2 s): – for changing external (and internal) conditions pi – annual amount of condensated water vapor – possibility of evaporation rozdíl mezi hustotou dif. toku v. p. z interiéru k oblasti kondenzace (gd. A) a hustotou dif. toku z oblasti kondenzace do exteriéru (gd. B) Teplotní difuzní funkce, závisí na atmosférickém tlaku a teplotě. Obvykle se uvažuje 5, 1 až 5, 3. 109 s-1. psat, A = = psat, B sd. A pe eqv. diff. thicknesses of layers (from interior) sd

Vapor diffusion through construction Calculation: condensation area – two basic tasks: (wider zone) • condensation risk calculation – for lowest external temperatures – necessary for constructions with inadmissible Other typicalcondensation cases: B A - brickwork (1 layer) cycle • annual calculation sd. A – for changing external (and internal) conditions pi – annual amount of condensated water vapor – possibility of evaporation sd. B psat, A psat, B eqv. diff. thicknesses of layers (from interior) pe sd

Vapor diffusion through construction Calculation: condensation area – two basic tasks: • condensation risk calculation (interface insulationbrickwork) – for lowest external temperatures – necessary for constructions with inadmissible Other typicalcondensation cases: - int. insulation without vap. calculation barrier s • annual cycle d. A (plasterboard, insulation, brickwork) – for changing external (and internal) conditions pi – annual amount of condensated water vapor – possibility of evaporation sd. B psat, A psat, B pe eqv. diff. thicknesses of layers (from interior) sd

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation – for lowest external temperatures – necessary for constructions with inadmissible Other typicalcondensation cases: - ventilated constructions • annual cycle calculation (concrete, insulation, ventilated layer, cladding) – for changing external (and internal) conditions pi sd, totvapor – annual amount of condensated water – possibility of evaporation No condensation occurs! Diffusion flow rate (diffusion flux) pe eqv. diff. thicknesses of layers (from interior) sd

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation • annual cycle calculation – for changing external (and internal) conditions – annual amount of condensated water vapor Aim of calculation: – possibility of evaporation - how large could be annual amount of condensate? - when condensation occurs? - is evaporation sufficient? Two basic methods: ČSN 730540 - from design external temperature up to 25 C - annual amount of condensate + evaporation capacity EN ISO 13788 repeating Glaser method - month after month (for mean temperatures and humidities) - condensate in individual months

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation • annual cycle calculation – for changing external (and internal) conditions ČSN 730540 – annual amount of condensated water vapor Boundary conditions: – possibility of evaporation - external air temperatures and their frequency (array with 5 C step) - rel. humidities of external air (see formula earlier) - internal parameters constant (θai + φi)

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation • annual cycle calculation – for changing external (and internal) conditions ČSN 730540 – annual amount of condensated water vapor Boundary conditions: – possibility of evaporation - external air temperatures and their frequency (array with 5 C step) - rel. humidities of external air (see formula earlier) - internal parameters constant (θai + φi) θ = (θ +5) to 25 e Procedure: start: θ e + condensation? condensation rate + - OK, end e condensation? condensation rate - evaporation rate

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation • annual cycle calculation – for changing external (and internal) conditions ČSN 730540 – annual amount of condensated water vapor annual amount of condensate – capacity possibility of evaporation and of evaporation θe = (θe+5) to 25 Procedure: start: θ e + condensation? condensation rate + - OK, end condensation? condensation rate - evaporation rate

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation • annual cycle calculation – for changing external (and internal)EN conditions ISO 13788 – annual amount of condensated water vapor Boundary conditions: – possibility of evaporation - mean monthly temperatures and rel. humidities of external air (according to location and latitude) - design temperature of internal air θai (usually constant, except unheated spaces) - rel. humidity of internal air: - generally variable (higher in summer)

Definiční přestávka Monthly mean indoor air relative humidity [%] Monthly mean value of internal air relative humidity derived from mean daily values. Generally variable through the year, usually higher in summer and lower in winter. It is derived according to EN ISO 13788 in dependence on type of ventilation: • taken from HVAC projects for air-conditioned buildings (i. e. for buildings with adjustment of internal air relative humidity where φi is known) • calculated from known internal moisture production for buildings with forced ventilation description of quantities can be found at definition of design indoor air rel. humidity earlier

Definitions Monthly mean indoor air relative humidity [%] Monthly mean value of internal air relative humidity derived from mean daily values. Generally variable through the year, usually higher in summer and lower in winter. It is derived according to EN ISO 13788 in dependence on type of ventilation: • taken from HVAC projects for air-conditioned buildings (i. e. for buildings with adjustment of internal air relative humidity where φi is known) • calculated from known internal moisture production for buildings with forced ventilation • calculated from assessed moisture production for buildings with natural ventilation rel. humidity of external air saturat. part. vapor pressure in external air sat. part. vapor pressure in internal air

Definitions Monthly mean indoor air relative humidity [%] Monthly mean value of internal air relative humidity derived from mean daily values. Generally variable through the year, usually higher in summer and lower in winter. It is derived according to EN ISO 13788 in dependence on type of ventilation: • taken from HVAC projects for air-conditioned buildings (i. e. for buildings with adjustment of internal air relative humidity where φi is known) • calculated from known internal moisture production for buildings with forced ventilation • calculated from assessed moisture production for buildings with natural ventilation increase of partial water vapor pressure due to internal activity (internal vapor pressure excess)

Definitions Increase of partial water vapor pressure due to internal activity (internal partial vapor pressure excess) [Pa] Difference between partial vapor pressure in internal and external air caused by production of water vapor by internal sources. If internal vapor production and air change rate are known, it can be calculated as: specific gas constant for water vapor [J/(kg. K)] vapor production [kg/h] abs. temperature of internal air [K] air change rate [1/h] air volume of a room [m 3] Naturally, the air change rate cannot be reliably specified for naturally ventilated rooms. Pressure excess Δp is therefore derived by guess on basis of internal humidity classes.

Definitions Increase of partial water vapor pressure due to internal activity (internal partial vapor pressure excess) [Pa] Difference between partial vapor pressure in internal and external air caused by production of water vapor by internal sources. Internal humidity classes: měrná plynová konstanta vodní páry [J/(kg. K)] 1. unoccupied buildings, stores… and other buidlings with very dry micro-climate According to 2. offices, dwellings with normal occupancy… and produkce other buildings with dry micro-climate v. p. EN[kg/h] ISO 13788 (2012) taken as standard abs. teplota vnitřního for 3. buildings with unknown occupancy most [K] calculations. vzduchu Former standard: 4. sports halls, kitchens, canteens… and other buildings with moist micro-climate th 4 class. 5. swimming pools, laundries… and other buildings with very moist micro-climate intenzita větrání [1/h] objem vzduchu v místnosti [m 3] Naturally, the air change rate cannot be reliably specified for naturally ventilated rooms. Pressure excess Δp is therefore derived by guess on basis of internal humidity classes.

Definitions Increase of partial water vapor pressure due to internal activity (internal partial vapor pressure excess) [Pa] Internal partial vapor pressure excess Δp is dependent on assumed vapor production in interior (humidity class) and on external air temperature. The lower is the external temperature, the higher is the Δp excess – it is assumed that air change rate is small during low external temperatures and therefore the influence of internal vapor sources is higher.

Vapor diffusion through construction Calculation: – two basic tasks: • condensation risk calculation • annual cycle calculation – for changing external (and internal)EN conditions ISO 13788 – annual amount of condensated water vapor Determination Procedure: of 1 st month with – possibility condensationof evaporation exists? - + from starting month to last Moisture content in construction at the end of each month (with respect to previous state) OK, end Annual changes in accumulated moisture content

Vapor diffusion through construction Comparison of both methods: EN ISO 13788 ČSN 730540 - (interior without changes, cannot calculate condensation in summer, relatively rough data for exterior) + (evaluation for design outdoor air temperature θe) model of reality condensation risk in extreme conditions ? (more safe for 1 -layered constructions, overestimates evaporation to interior) + (variable φi + θai, condensation in any month, possible selection of 1 st month, better model of exterior, more calculation years) - (evaluation only for mean monthly temperatures) ? safety of calculation (usually more optimistic results, but sometimes not)

Vapor diffusion through construction Comparison of both methods: EN ISO 13788 ČSN 730540 - (it cannot be evaluated) built-in moisture critical moiscontent + (it can be evaluated in simplified way) ture content - (it cannot be evaluated) + accumulated moisture redistribution content in dependency on time of moisture (it can be evaluated in simplified way) evaporation assumed from centre of condens. area without redistribution condensation area i e with redistribution evaporation from edges of increased condensation area (it is increased by capillary conduction)

Vapor diffusion through construction Ventilated constructions: - evaluation of: - internal deck (in standard way: U-value, diffusion) - ventilated air layer - external deck (internal surface temperature – see previous lectures) Method from ČSN 730540 -4: - simplified 2 D model - calc. procedure: - air velocity in layer distribution of temperature + sat. part. vapor pressure distribution relative humidity distribution evaluation of requirements CFD analysis: not always possible, complicated modeling of diffusion

Moisture transfer Principles of hygro-safe design

Design principles Goal: - design of construction without or with low risk of vapor condensation (fullfilment of technical requirements) low built-in moisture content after realisation fast drying after beginning of operation moisture equilibrium during operation: wetting safe hygroaccumulating capacity drying Analogy of moisture equilibrium (Straube & Burnett, 2005)

Design principles Basic rule: construction has no condensation risk if: - thermal resistance of layers increases to exterior diffusion resistance of layers decreases to exterior usually valid for ventilated constructions, partly for ETICS Rule is valid in our climatic conditions and for normal buildings in winter! Pay attention to cooling chambers.

Design principles Basic rule: construction has no condensation risk if: - thermal resistance of layers increases to exterior diffusion resistance of layers decreases to exterior usually valid for ventilated constructions, partly for ETICS The rule usually cannot be guaranteed, design is therefore traditionally based on limitation of diffusion (from the side with higher partial vapor pressure): - by less permeable layer (sandwich constr. ) - by vapor barrier

Design principles The most suitable materials: • foils from PE, m. PVC, polyamides • bitumen membranes (preferably with Al sheet) Tightness is crucial (joints, connections, penetrations) ! Problematic solution: • steel sheets, glass, ceramic tiles: joints !? • paints: realisation ? ! The rule usually cannot be guaranteed, design is therefore traditionally based on limitation of diffusion (from the side with higher partial vapor pressure): - by less permeable layer (sandwich constr. ) - by vapor barrier

Design principles For vapor barriers, it is always necessary to ensure: • wholeness of barrier (seal up all joints) • long-time functionality • protection against mechanical damage • coordination of building processes (installations of HVAC) The rule usually cannot be guaranteed, design is therefore traditionally based on limitation of diffusion (from the side with higher partial vapor pressure): - by less permeable layer (sandwich constr. ) - by vapor barrier

Design principles Nejvhodnější materiály: Beware of confusion of materials! • folie PE, m. PVC, polyamidy asfaltové pásy (nejlépe s kovovou vložkou) Vapor barrier is not any membrane. It should not be confused with e. g. diffusion foils (and otherwise). Problematičtější řešení: • plechy, sklo, keramické obklady: spáry !? Materials must be used according to • nátěry: provádění ? ! their purpose! • The rule usually cannot be guaranteed, design is therefore traditionally based on limitation of diffusion (from the side with higher partial vapor pressure): - by less permeable layer (sandwich constr. ) - by vapor barrier

Design principles Alternative to membranes in timber buildings: • boards from wood (mainly OSB) • consequences: • often higher impermeability (solid base) • it is necessary to adapt assembly: • ventilated constructions • or “diffusion-opened” constructions The rule usually cannot be guaranteed, design is therefore traditionally based on limitation of diffusion (from the side with higher partial vapor pressure): - by less permeable layer (sandwich constr. ) - by vapor barrier

Design principles Basic rule: construction has no condensation risk if: thermal resistance of layers increases to exterior diffusion resistance of layers decreases to exterior - If the rule cannot be fulfilled, new capillary active materials are also used instead of vapor barriers: - relatively new solution promising approach, still not fully verified usually materials based on calcium-sillicate or wood opened for diffusion highly porous

Design principles Basic rule: construction has no condensation if: insulations: Principle of capillary risk active thermal resistance of layers increases to exterior - resistance applied from internal side diffusion of layers decreases to exterior - condensation is not restricted, it is taken into account - e - condensate is se created in inconvenient Nelze-li dodržet, používají kromě parozábrany i kapilárně aktivní conditions at wall-insulation interface materiály: - relatively new solution - immediate redistribution of condensate to whole i promisingth. approach, not insulation still by capillary conduction e fully verified - successive easy evaporation after usually materials based on change of conditions calcium-sillicate or wood i opened for diffusion Proper function requires: highly porous - interior with low or normal humidity - not suitable for humid interiors! e i

Design principles Other chosen problems: - floors on ground with thick thermal insulation: - condensation on waterproofing! - it is necessary to protect organic materials in assembly or better use hygro-resistant materials

Design principles Other chosen problems: - internal insulation: - without problems in dry interiors, otherwise vapor condensation risk - traditionally solved using vapor barrier (problems with tightness) - newly also capillary active insulations - pay attention to wooden ceilings: internal insulation inappropriate due to risk of rot creation at the end of wooden beams !