Overview of AWDABPT Buildings

The program calculates the average room air temperature under the given climatic and room thermal load conditions. A heat transfer analysis is performed dynamically over the required time period of up to twenty days. Finite difference numerical methods are used so that the thermal storage effect of the building structure is properly modelled.

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 equipment building or shelter can be a single zone or comprise up to twenty-five rooms. 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, 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 option to include a space that is not an actual room is provided. A space will adjoin one or more rooms and will have a predetermined temperature profile that may be constant or may vary with the attenuated outside shade temperature and/or the adjacent room temperatures.

The option to test the influence of variance in selected input data is provided. Only one type of property, but more than one value, at a time can be selected. The analysis assumes that the range over which a value is to be varied will approximate the normal probability distribution (the bell curve) for the likelihood of its occurrence. The Monte-Carlo method is used.

The relevance of the predictions provided by AWDABPT can be no better than the extent to which the user's input data correctly models the subject building. 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 building or shelter temperatures should be done. Some validation of AWDABPT has been done on:

- concrete buildings,

- insulated steel stud and sheet steel clad air conditioned shelters with phase change material standby cooling,

- naturally cooled thermally transparent and shaded shelters,

- telecommunications equipment cabinets with and without the assistance of an air-to-air heat exchanger.

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

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.

 Number of rooms up to a total of twenty-five.

 Building internal dimensions per room and orientation.

 Thickness of solid portions of walls, roof/ceiling and floor.

 Roof pitch.

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

 Transmission coefficients (U-Values) for walls, roof and floor.

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

    (As you are probably aware, CFD programs often only model convective air temperature and air velocity and can neglect radiant

    temperatures that impact surface temperatures and thus room air temperature.  Radiant heat transfer amounts to

    around half of the total heat transfer, particularly when dealing with thermal comfort).

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

   Door and window dimensions, U-value and solar absorptivity. Two per wall.

   Solar shading of roof and each wall - insulated panels or sheet metal screens.

   Use of ridge vent on roof solar shade.

   Eaves width for each wall and height of eaves above/below top of wall.

   Shading of doors.

   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 external surfaces.

   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,

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

      An external bush/forest fire mode temperature profile can be superimposed on the outside shade profile supplied by AWDABPT

      to gain some assessment of the impact on the building internal temperatures, for example, inside a fire bunker.

   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).

   Ground thermal conductivity.

 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.

   Evaporative cooling, direct or indirect.

   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,

      heating system,

      air to air heat exchanger.

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 1 GHz processor would provide a satisfactory computation speed and for jobs with the maximum of 15 rooms, the highest speed systems are suggested. As an example, a 15 room job running on a 3 GHz single CPU system takes about ten minutes to complete the maximum of 20 days of simulated run time.

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).