Design Weather Data Tab

 

This section of the dialog contains the information about how the weather data has been chosen using the Selection Wizard. The Selection Wizard… button will take the user directly to the design weather data section (Pages 2-3) of the wizard if selected here. The Add to custom database button allows the user to save the current design weather data.

 

This is the outside air dry-bulb design temperature applicable to the building location. This number is only used in ApacheLoads and ApacheCalc calculations. This value can be either manually entered or derived by the Weather Selection Wizard.

 

Cooling loads weather data describes the summer time external design weather data. This data is used for both CIBSE and ASHRAE cooling loads calculations. The different parameters that are used for both types of analysis can be viewed by selecting either the ASHRAE analysis or CIBSE analysis radio button.

 

 

To globally adjust the cooling loads weather data enter values into the following:

·       Dry-Bulb (representing Maximum Outside Dry Bulb Temperature)              

·       Wet-Bulb (representing Maximum Outside Wet Bulb Temperature)                   

When these figures are entered, select Apply and ApLocate will use the selected pattern and shift the data to be based on the maxima as given. This allows you to use an appropriate pattern but provides flexibility in design temperatures. To review the detail of the pattern, press the Apply button. To return to the original values use the selection wizard.

 

Custom weather files can be created by modifying the individual values of existing files. Once modified the data values turn a green colour to indicate that a change has been made. To do this, for the parameters common to both CIBSE and ASHRAE for each month from January to December inclusive, the following data are required:

·       Min Tdb - Minimum Daily Dry-Bulb Temperature.

·       Max Tdb - Maximum Daily Dry-Bulb Temperature.

·       Tdb lag - Dry-Bulb Time Lag – enter the lag in hours with respect to 12 noon (excluding any local time correction) at the standard time meridian. For example, if you type in 3, here, the dry bulb temperature will peak at 15:00 GMT (or at 16:00 if 1 hour summertime correction is in operation).

·       Twb at Max Tdb - Daily Wet-Bulb Temperature at Maximum Dry-Bulb Temperature.

 

For a CIBSE analysis, the following additional parameter is required:

·       Linke Turbidity Factor - describes the combined impacts of various atmospheric factors on the solar beam transmittance – refer to CIBSE Guide Part J Weather, solar and illuminance data for a complete description of this factor.

For an ASHRAE analysis, the following additional parameters are required

·       Solar radiation parameter A

·       Solar radiation parameter B

·       Solar radiation parameter C (ratio of diffuse horizontal to direct normal irradiation):

 

Parameters A and B are used in the following expression to determine direct normal irradiance:

direct normal irradiance = A *  exp( - B / sin (solar altitude))

Please refer to the Climate Design Information section of ASHRAE Fundamentals for a detailed description of these solar radiation parameters.

This data must be entered for 12 months of the year (if you are only interested in summer conditions, leave the winter data in its default state). ApLocate uses this data to generate sinusoidally varying weather data for input to the CIBSE and ASHRAE Heat Gain calculations.

 

The Sinusoidal and ASHRAE standard profile options dictate the way in which the daily cooling loads weather data is generated from the maxima and minima parameters. By choosing the Design Day Graphs or Design Day Tables the effect of either the sinusoidal (to be used in CIBSE Heat Gain calculation) or the ASHRAE standard profile (to be used in ASHRAE Heat Balance cooling load calculation) can be viewed. Either method can be used whether CIBSE or ASHRAE calculations are performed.

 

Once a new weather data set has been created, this can be entered into the database using Add to custom database button. A dialogue box will appear into which the name of the new data set should be entered:

 

Any stored custom data set can later be retrieved by selecting the appropriate option on Page 2 of the Selection Wizard (Source of Design Weather).