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  • HAM: computer models
  • computer codes for heat-air-moisture transfer



    • Related References
  • report on EMPTIED
    CHIC , (1999), Envelope Moisture Performance Through Infiltration, Exfiltration And Diffusion - EMPTIED
  • Straube, J.F. and Burnett, E.F.P, (2001), Overview of hygrothermal (HAM) analysis methods




    		• Essay:

    HAM: EMPTIED

    Moisture Transfer - About EMPTIED, CMHC software that models the infiltration, exfiltration and diffusion of moisture in a wall.

    Acronym: Envelope Moisture Performance Through Infiltration Exfiltration and Diffusion

    Developer (Name/Institue): CMHC

    Date: 1985 - present

    Main Feature: CMHC software that models the infiltration, exfiltration and diffusion of moisture in a wall.

    schl.gc.ca/publications/en/rh-pr/tech/1999-123e.html (April/2002)

    Description:

    EMPTIED uses monthly bin temperature data and outputs plots of the monthly amount of condensation, drainage, and evaporation. It is very easy to operate and provides fast, generally conservative results. It is recommended for simple analysis of air leakage.

    EMPTIED was developed to take the following factors into account:

    ? The level of absolute humidity in the interior is relevant to moisture performance of walls.

    ? As moisture enters a wall, either by air leakage or diffusion, if there are water absorptive materials in the wall that are at or below the dew point temperature of the indoor air, there will be condensation that will be stored until conditions change to favor drying.

    ? If materials below dew point temperature are non-absorptive or saturated, condensation will occur on the surfaces as ice or water, and may be removed (to the exterior, one hopes) or redistributed by downward flow.

    ? Conditions in the wall are not constant¡ªeach month is different, with different numbers of hours when the exterior conditions are within any particular range of temperature and humidity.

    ? Air leakage usually transports far more moisture into a wall than vapour diffusion. Most air-transported moisture is carried by air moving under relatively low pressure differences that occur most of the time, such as stack effect and superimposed fan pressures.

    ? Absolute prevention of condensation is not possible. However, if condensation is stored or removed without harm and does not accumulate from year to year, then performance is satisfactory.

    EMPTIED takes the following information as inputs:

    ? Month-by-month indoor temperature and humidity conditions.The user can specify them or EMPTIED

    ? can calculate them assuming that humidity on the interior comes from ventilation air and normal occupancy, excluding mechanical humidification and unusual occupancies.

    ? Hourly bin data (counts of the number of hours in an average year that exterior conditions fall into particular combinations of temperature and humidity ranges) for exterior conditions. EMPTIED includes data for several North American cities so the user can select a city.

    ? Superimposed mechanical pressure or suction, if any (zero is the default).

    ? Equivalent leakage area per unit area of wall.

    ? Specifications for layers in the wall, including vapour resistance, maximum capacity for storage of moisture, thermal resistance, and thickness. EMPTIED supplies a menu of common materials with properties already specified, but the user can edit them and add new materials to the list.

    ? Identification of two layers in the wall where condensation is expected to occur.

    ? How many years to run the simulation, and what month to start with.

    ? The data entry screens (but not the menus for selection of materials or other pre-defined data) are shown in Figure 1.

    EMPTIED

    ? predicts condensation amounts using one-dimensional models for flows of air, moisture, and heat. Calculations are done month-by-month and bin-by-bin, and results are reported for each month.

    ? EMPTIED calculates temperatures, assuming steady state conditions for the duration of each bin, neglecting latent heat and heat transported by moving air. Air flows are calculated assuming that the driving force is superimposed pressure plus stack effect pressure over a one storey height (of 2.4 m¡ª7 ft. 10 1/2 ft.) due to the temperature difference between interior and exterior for each bin.



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