Automated Internal Condensation Prediction Using the VE Scripting Tool

This session will cover:
Structural vs. dewpoint temperatures – background
Scripting structure and required edits/setup
Condensation risk index, window & wall surfaces hours of occurrence
Low/Medium and High-risk testing
Dynamic simulation on exterior surfaces of rooms check - results and reporting
Exterior surfaces temperatures notes
NCC 2025 – Public Draft Comment (PDC 2025) – condensation mitigation

1. Automated Internal Condensation Prediction Using the VE Scripting Tool Roger Cladingboel – Vice President ANZ 31 st July 2024

2. Welcome   Structural vs. dewpoint temperatures – background Scripting structure and required edits/setup Condensation risk index, window & wall surfaces hours of occurrence Low/Medium and High-risk testing Dynamic simulation on exterior surfaces of rooms check - results and reporting Exterior surfaces temperatures notes NCC 2025 – Public Draft Comment (PDC 2025) – condensation mitigation www.iesve.com

3. Structural vs. dewpoint temps – background   Predicting surface condensation in buildings involves understanding the interactions between temperature, humidity, and building materials. Essentials: Dew Point : The temperature at which air becomes saturated with moisture and water vapor starts to condense. Surface Temperature : The temperature of the building material surface. Relative Humidity (RH) : The amount of moisture in the air compared to the maximum amount of moisture the air can hold at that temperature. www.iesve.com Wall Temp Profile:

4. Dew point temps   IESVE Model Data outputs: Indoor and Outdoor Temperature : Indoor and Outdoor Relative Humidity Surface Temperature : Every surface inside and outside. Calculated Dew Point temps Compare Surface Temperature to Dew Point: Determine the surface temperature of the building material. Compare the surface temperature with the calculated dew point temperature. If the surface temperature is below the dew point temperature, condensation is likely to occur. Psychrometric Charts These charts help visualize the relationship between air temperature, dew point, and relative humidity. www.iesve.com Psychrometric Profile:

5. Vista-pro (manual check)   Manual Procedure – Chart or table of data: Plot room dew points and selection of surfaces window and wall to compare and spot crossovers for occurrence of condensation. For example 1 week in Winter shown across for Cairns. Consider Material Properties Thermal Conductivity : Materials with low thermal conductivity are less likely to have cold surfaces. Vapor Permeability/Resistivity : Materials with high vapor permeability allow moisture to pass through, reducing condensation risk. Insulation : Proper insulation can help maintain surface temperatures above the dew point. Software Tools : Unlike tools like WUFI, esp -r etc , IES is not a full dynamic hygrometric model or mould simulation at the moment, request if you would like this ([email protected]) www.iesve.com

6. Scripting structure and required edits/setup   Room internal surface dewpoint check description Gets rooms with external surfaces and sub-surfaces. Looks up room air & dewpoint temperatures Looks up construction internal surface temperature data. Tests per time-step if lowest room internal surface temperature is less than room dewpoint temperature. Totals instances when this occurs. Exports the data to an xlsx; one tab per room. Script requires the vistaset.ies file to be edited: Open Program Files>IES>VE 2023>apps>units> vistaset.ies ; Search for the string Ext surface temperature Delete 'HIDE' in Apache|HIDE Ext surface temperature|Ext surface temperature|Temperature|u|t|s|u|maroon|0|5|1|-|-30|70|-22|150| So it looks like this ... Apache|Ext surface temperature|Ext surface temperature|Temperature|u|t|s|u|maroon|0|5|1|-|-30|70|-22|150| Once set run model thermal simulation to generate aps file. Ext surface temperature will also be visible in VistaPro . Make sure surf temps are active on all zones in output options for any apache runs to be tested. www.iesve.com

7. Condensation risk index, window & wall surfaces hours of occurrence   The Condensation Risk Index (CRI) is a measure used to evaluate the likelihood of condensation forming on surfaces within a building. Condensation can lead to issues such as mold growth, structural damage, and poor indoor air quality. Some general guidelines can be provided: Low CRI Value : A lower CRI value typically indicates a lower risk of condensation. This means the conditions are less likely to reach the dew point, where condensation occurs. Scale-Specific Values : If a particular scale is used, such as a 0-100 scale where 0 represents no risk and 100 represents high risk, a good value might be below 30, suggesting a low probability of condensation. Manufacturer Guidelines : For specific products or building materials, manufacturers may provide recommended CRI ranges to avoid condensation. www.iesve.com Source: abcb.gov.au condensation guide

8. Window & wall surfaces hours of occurrence   www.iesve.com Source: abcb.gov.au condensation guide

9. Low/medium/high risk   www.iesve.com Output sheet from VE Script Remember conduction is 1D in IESVE, so there is no current complexity around thermal bridging and edge effects on wall & glazing. Simple test: Low within 0.5-1C of Tdew Medium within 0.25-0.5C of Tdew High risk range within 0-0.25C of Tdew VE Script risk code snip

10. Residential moisture inputs:   www.iesve.com Some typical water vapour residential inputs that should be included in any domestic building simulation test. Domestic test simulation results – Launceston with/without 3xloads of washing dried internally. Source: BRANZ 2012

11. Dynamic simulation on exterior surfaces   www.iesve.com Exterior surface temps vs Ambient dew point Same approach with internal with some caveats, remember to switch exterior temperatures on. Complications with predictions arise due to: Exterior convection model (wind/rain treatment) Surface treatments / hydrophobics etc Rain data generally not provided with climate files. Exterior surface temps vs Ambient dew points manual process Currently not in the script, due to prediction complications.

12. Weather files with rain data.   www.iesve.com Source: Trevor Lee Exemplary Energy [email protected] Traditional simulation weather files in Australia (CSIRO) don’t contain rain data but epw format allows for it. Others sources or commercial companies can provide. Rain data may be actual recorded or synthetic. SY_SMY-with-ACTUAL-and-synthetic-precip-JFMAMJJASOND-beta_20240729_(C)_ Exemplary.epw typical week shown on rhs . Other sources maybe available online with stochastic generating tools for rain predictions

13. NCC 2025 – Public Draft Comment (PDC 2025) – condensation mitigation   www.iesve.com The NCC are proposing further changes to NCC Volume One and the Housing Provisions Standard1 (Housing Provisions) to better manage the risk of condensation in residential and residential-type buildings. These include changes to 4 main areas: External walls in climate zones 1 to 5 External walls in climate zones 6 to 8 Roof ventilation openings Application of the requirements to hotels, hostels etc. (Class 3 buildings) and aged-care buildings (Class 9c buildings). DTS solutions to include vapour barriers, drained and vented cavities as well as appropriate roof ventilation openings Don ’t be like Egon!

14. Further reading..   www.iesve.com Handbook-condensation-in-buildings-2019 NCC Condensation mitigation modelling: final report ABCB/SBRC & Uni of Wollongong

15. IESVE is industry standard software which enables users to quickly consider many aspects of design (using a single model) Loads, BR Compliance, HVAC system sizing, Building Operation, Daylighting, Energy and Carbon 3D geometry, building activity library, construction database Performs quick, informative, loads analysis on any building type IESVE   www.iesve.com

16. Applications ModelIT The single central 3D data model at the heart of the VE provides geometry and data shared by all applications. APACHE Originally dubbed AP plication for A ir- C onditioning and H eating E ngineers, the user interface, rules processor and the best whole-building energy simulation engine in the world SunCast Calculate the position of the sun in the sky, track solar penetration throughout the building interior and calculate shadows. CIBSE/ASHRAE Loads Calculate heat loss and gain calculations based on the CIBSE/ASHRAE Guides. www.iesve.com

17. Thank you Any Questions? [email protected]