Overview of AWDABPT-UG

The program calculates the average enclosure (room) and entrance tower air temperatures under the given climatic and room thermal load conditions. A heat transfer analysis is performed dynamically over the required time period of up to a year (if you have the computer capability available). Finite difference numerical methods are used so that the thermal storage effect of the enclosure structure and the surrounding soil is properly modelled.

The ground thermal properties together with the long term average air temperatures at the enclosure's location are used to estimate ground temperatures over a twelve month period. Actual ground temperatures for a given day at given depths may also be used to help shape the ground temperature model. That is, you can adjust the soil thermal properties to gain a better fit of the temperature curves.

A proper solar radiation generator, based on the model for the equation of time and the solar declination, is used. The solar radiation received on a surface can be varied by selection of its solar absorptance (absorption factor), the turbidity factor (haze) of the air and the cloud cover. Re-radiation from external surfaces to the sky is also modelled.

Convection and radiation heat transfer coefficients are calculated during the running of the program at each time increment. The convection coefficients are determined depending on temperatures as well as whether still conditions apply or air movement due to wind (external surfaces) and fans (internal surfaces) occurs.

The average room air temperature is determined from a heat flow balance of heat source and sinks such as the equipment, the walls, roof and floor and consequently the surrounding soil, the room air itself, thermal stores in the room, heat exchangers (room air conditioners, chilled water storage fan-coil units, etc.) and outside air used for room ventilation or entering as infiltration.

The relevance of the predictions provided by AWDABPT-UG can be no better than the extent to which the user's input data correctly models the subject enclosure. Further, the accurate modelling of the outside weather conditions may not be fully achievable by this program due to the rapid changes which weather can undergo.

Whenever possible, testing of the program's results against measured underground enclosure temperatures should be done.

The following is a brief summary of input data for and functionality of AWDABPT-UG:

Input Data Required

Some or all of the following information is required in the data file before running the program. Items preceded by “” comprise the minimum data required to ensure a reasonable run. Other data will either be the default values or zero.

 Enclosure type - rectangular or cylindrical.

 Enclosure and entrance tower internal dimensions.

 Thickness of walls, roof/ceiling, floor and entrance door.

   Surface area multipliers, internal and external, for walls and roof.

 Transmission coefficients (U-values) for walls, roof, floor and entrance door.

    (Values must exclude the air surface film conductance and radiation components since they are calculated by the program).

 Thermal capacity and the density of the walls, roof, floor and entrance door.

   Solar shading of roof and entrance door - insulated panels or sheet metal screens.

   Equipment heat dissipation, constant or by hourly variations over 24 hours.

   Equipment thermal capacitance and initial temperature estimate.

   Equipment thermal conductance to the room.

   Emissivity of internal and external surfaces.

   Solar absorptivity of door surface and roof surface when at ground level.

   Room view factors for radiation heat exchange.

 Outside shade temperature profile:

      Your hourly data, or,

      Daily maximums and diurnal swings for:

         A profile supplied by AWDABPT-UG,

         A harsher profile built up from DEF(Aust) 5168 / STANAG 2895 A1 & A2 profiles.

   Wind speed and wind multiplier factors for walls, roof and floor where appropriate. Daily or hourly averages can be used for wind speed.

   Relative humidity at time of maximum outside temperature on day 1, or daily or hourly RH levels.

   Atmospheric turbidity (haze).

   Cloud cover, fixed, daily or hourly.

   Albedo (ground solar reflectance).

   The vegetation coefficient is a factor that can be used to take into account the difference in ground cover between the chamber site and cover at the location at which ground temperatures have been measured.

 The average ground and air temperatures for the selected year:

      Average annual ground temperature at a depth of 10 m. When local ground temperature data is unavailable, the average annual ground temperature at a depth of 10 m may be said to be the average annual air temperature at the location.

      Average annual maximum air temperature. This is the highest of the long-term mean daily maximum temperatures on a monthly basis.

      Average annual minimum air temperature. This is the lowest of the long-term mean daily minimum temperatures on a monthly basis.

      Air temperature phase. It is the day of the year, from 1 January, of the maximum ground surface temperature, usually indicated by the time period of the maximum outside air temperatures. One way to estimate this is to use a graph of the daily mean maximum, or the 86 percentile, temperatures and interpolate the peak day.

   Your ground temperatures at 10 m or more from the chamber for a particular day of the year can be used.

     Any or all of the following depths are available for your data:

       ground surface, 50 mm, 100 mm, 500 mm, 1 m, 2 m, 3 m, 4 m, 5 m and 6 m.

     In addition, you can enter your own depths and temperatures for two additional depths.

 The soil properties:

   The soil thermal conductivity.

   The soil thermal capacity and the density.

   The ground thermal diffusivity is calculated from your ground thermal conductance, capacity and density values or can be entered to overwrite the calculated value.

   If the soil infill option is used, then the properties of that infill soil and the distance from the enclosure floor and walls are required.

 Day and month for start of the simulation.

 Latitude, longitude and reference longitude.

   Height above sea level of the site.

   Daylight saving.

   Internal loads including latent loads.

   Room thermal store -

     Thermal capacitance, initial temperature,

     Thermal conductance to room air,

     Phase change material latent heat of fusion and transition temperature.

   Outside air cooling system flow rate and setpoint temperature.

   Use of variable air flow controller and its lower outside air temperature setpoint.

   Air to air heat exchanger conductance (internal air to external air).

   Thermostat settings for inside and outside air circuit fans.

   Refrigerated cooling using domestic or industrial type air conditioners

    (designed to AS 1861 operating condition A [35 °C outside] or B [46 °C outside]).

   Cooling capacity and setpoint temperature.

   Refrigeration system thermal store -

      Thermal capacitance, initial temperature,

      Thermal conductance to room air,

      Phase change material latent heat of fusion and transition temperature.

   Heating using natural convection or forced convection, with or without thermal storage.

   Water storage cooling system -

      Volume of water, initial water temperature,

      Average capacity of outside fan coil unit,

      Average capacity of room heat exchanger:

         room fan off, water pump on (natural convection),

         room fan and pump on (forced convection).

      Room temperature when water pump turns on and when room fan turns on.

   Time of cooling / heating plant or a.c. mains power failure.

   Restoration time delay of:

      outside air ventilation system,

      refrigerated cooling system,

      air to air heat exchanger,

      heating system.

Computer Requirements

This program runs on a Windows 32 bit platform such as Microsoft Windows® 7 to 10, Vista and Microsoft Windows® XP SP3. A 2 GHz processor would provide a satisfactory computation speed and for jobs with a period of analysis over fifteen days, the highest speed systems are suggested. As an example, a job running on a 3 GHz single CPU system takes about eight minutes to complete fifteen days of simulated run time, as well as ten days prior to day one to settle the day one initial temperatures due to the long soil time constants.

The ability to export and import some data to and from a spreadsheet is provided. A computer that can run a Windows spreadsheet version should be able to run AWDABPT. Supported spreadsheets for exporting data from AWDABPT tables are Microsoft® Excel, Open Office Calc and Corel® Quattro Pro (WordPerfect® Office X4).