Our Moisture Assessments estimate aims to specify design criteria for predicting, mitigating, or reducing moisture damage to wall materials, components, and systems, depending on climate, construction type, and HVAC system operation.
Superseding our Condensation Assessment based on the outdated Glaser Method (based on ISO 13788), our Moisture Assessments are undertaken using the EnergyPlus 9.5 and the combined heat and moisture transfer finite (HAMT) solution algorithm.
HAMT is a completely coupled, one-dimensional, finite element, heat and moisture transfer model simulating the movement and storage of heat and moisture in surfaces simultaneously from and to internal and external environments.
As well as simulating the effects of moisture buffering, HAMT can also provide temperature and moisture profiles through composite building walls and help identify surfaces with high surface humidity.
Setting up a Moisture Assessment
To undertake Moisture Assessment, select ‘Moisture’ in the results area. Next, the following inputs are required to identify the study period, assessment method, model inputs and Internal Conditions.
- Run Period - The period in which you would like to assess the performance of a wall. 3 years is as minimum default recommendation. If any results appear to be increasing over time, 5 or 10-year studies are then recommended.
- Include Reports – Reports are available for Dew Point, Water Content and Mould Growth. All reports are post-processed with results available for either the entire wall make-up or individual layers within a wall.
- Orientation – The selection of orientation will impact the ability of a wall system to wet and dry over time. Typically, a non-equatorial facing wall will have a lower drying potential and thus represent a worst-case orientation.
- Cavity Ventilation Rate – Sets the ventilation rate in air changes per hour, impacting the ability of a wall cavity to wetting and drying. Cavity ventilation rates are highly variable and are impacted by openings, cavity geometry, depth and cladding type.
- Floor Area – Typically the combined floor area (m²) of all zones in which moisture may occur.
- Floor to Ceiling Height – Typically the average height (mm) or all zones in which moisture may occur.
- Surface Resistances – External and internal surface resistance values are taken from either HAMT modelling defaults or as per the System R-value requirements from the local building code.
- Specify Temperature – The ‘Indoor Temperature (°C)’ setpoint for the entire Moisture Assessment. 21 °C is typically adopted.
- Specify Relative Humidity – The ‘Indoor Relative Humidity (%)’ setpoint for the entire Moisture Assessment. Relative Humidity is typically uncontrolled and therefore not set by default.
- Air Changes per Hour – The number of air changes per hour (ACH) is set for the entire Moisture Assessment. It is a measure of how quickly the air in an interior space is replaced by outside (or conditioned) air by ventilation and infiltration. An ACH of 0.35 is typical, 0.2 is normal, and 0.1 is airtight.
- Relative Humidity Mode – The relative humidity simulation method is chosen. ‘Simplified’ nominates moisture as a function of average daily outdoor temperature. In most cases, ‘Intermediate’ should be adopted. ‘Intermediate’ requires the ‘Indoor Typology’ to be determined, either ‘Residential’ or ‘Commercial’ and the resultant ‘Moisture Generation Mode’. ‘Moisture Generation Mode’ enables the rate of moisture (kg/s) to be determined for the entire Moisture Assessment based on ‘Number of People’, ‘Number of Bedrooms’ or ‘Custom’.
Once complete, click ‘Create’ and then ‘Run 1 Calculation’. Once your Moisture Assessment has been reviewed, click ‘Begin Study’, update the Title and Subtitle and click ‘Begin’. Once your simulation is complete, an automated email will be issued or your can view and wait for your Study to complete under ‘View Studies’.