CONDENSATION Predicting Interstitial Condensation Welcome to Neath Port Talbot College! Predicting Interstitial Condensation

Interstitial Condensation This is condensation that occurs within the fabric of a composite construction such as walls and roofs. Interstitial condensation risk can be estimated from a knowledge of the thermal and vapour characteristics of the building fabric and the environment. Names of who is presenting and positions What we are here to do today NB: you can also copy and use this slide as a template for further slides required with writing

How? By plotting the temperature profile and the dew-point profile as they pass through the element of the building Names of who is presenting and positions What we are here to do today NB: you can also copy and use this slide as a template for further slides required with writing

How? Dewpoint This is the critical point where the air is saturated. Dependent on the amount of water vapour present in the air. Names of who is presenting and positions What we are here to do today NB: you can also copy and use this slide as a template for further slides required with writing

Why? To determine the likelihood of interstitial condensation occurring within the fabric To be able to design against this likelihood and eliminate possible risk Names of who is presenting and positions What we are here to do today NB: you can also copy and use this slide as a template for further slides required with writing

Method By: Calculation Use of psychometric chart Use of manufacturers’ literature Graphically Names of who is presenting and positions What we are here to do today NB: you can also copy and use this slide as a template for further slides required with writing

6 Step process Calculate overall temperature drop Calculate Thermal Resistance (if not given) Calculate temperature drop across elements Plot temperatures Calculate Moisture conditions of external & internal environment Find Vapour Resistance using Psychometric Charts Calculate vapour pressure drop across layers Determine dewpoint temperature at boundary of each element Plot dew-point Analyse & conclude Names of who is presenting and positions What we are here to do today NB: you can also copy and use this slide as a template for further slides required with writing

Example

STEP 1 Calculate overall temperature drop External Temperature = 00C Internal Temperature = 200C Total Temperature drop = 200C

STEP 1 Calculate total resistance Internal Surface = 0.123 Plasterboard = 0.06 EPS = 0.75 Concrete = 0.105 External Surface = 0.055 Total = 1.093

STEP 2 Calculate Thermal Resistance 1.81 Element Thickness Thermal Conductivity (λ) Resistance Internal Sur 0.123 Plaster 0.010 0.06 0.17 EPS 0.025 0.75 0.03 Blockwork 0.150 0.105 1.43 External Su 0.055 1.81 Thermal Resistance = Thickness/Thermal Resistance

STEP 3 Calculate temperature drop across layers Layer Inside air 200C Thermal Resistance Temp Drop across each element Boundary Temp Inside air 200C Int: surface 0.123 (0.123/1.093)*20 = 2.26 17.740C Plaster 0.06 (0.06/1.093)*20 = 1.10 16.640C Blockwork 0.105 (0.105/1.093)*20 = 1.92 14.720C EPS 0.75 (0.75/1.093)*20 = 13.72 1.000C Ext: Surface 0.055 (0.055/1.093)*20 = 1.00 0.000C

STEP 4 Draw a scaled section of the construction Plot the boundary temperatures from step 2 on the section Join the temperatures together to create a profile

STEP 5 Find internal vapour pressure. Internal temp = 20oC Humidity = 59% External temp = 00C Humidity = 100%

STEP 5 Internal 20 oC 59% Vapour Pressure = 1400mb

STEP 5 External 0 oC 100% Vapour Pressure = 600mb

STEP 5 Vapour Pressures Internal 1400mb External 600mb Difference

STEP 4 Vapour Pressures drop by layer Total = 7.15 MNs/g Thickness Vapour Resistivity Vapour Resistance Int: surface negligible Plaster 0.010 50 0.5 Blockwork 0.105 30 3.15 EPS 0.025 100 2.50 Ext: surface Total = 7.15 MNs/g Vapour Resistance = Vapour Resistivity x thickness

STEP 4 Vapour Pressures drop by layer Layer 1400 Boundary Plaster 0.5 Vapour Resistance Vapour Pressure drop Vapour Pressure Int: surface 1400 Boundary Plaster 0.5 (0.5/7.15)*800 = 55.94 1344 Blockwork 0.105 (3.15/7.15)*800 = 352.45 992 EPS 0.025 (2.50/7.15)*800 = 279.72 Ext: surface 712

STEP 5 Using Psychometric Chart find the Dewpoint Temperature for each vapour pressure.

STEP 4

STEP 5 Vapour Pressure Dewpoint Temperature 1400 120C 1344 11.50C

STEP 5 Plot the Dew-point temperatures on section and join temperatures to create profile

STEP 5 Plot the Dew-point temperatures on section and join temperatures to create profile

STEP 6 Analyse & conclude Is there a risk of interstitial condensation? If so, what can be done about it? Is there a risk of surface condensation?

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