Edit / translate hourly weather data

The Edit/Translate Hourly Weather Data dialog can be accessed from the Tools menu and can be used to process hourly weather data.  You may wish to do this for various reasons:

• Convert EnergyPlus epw data to be compatible with DesignBuilder day of week results for daily, hourly and sub-hourly output (set the year to 2002).
• Translate weather data in other formats to the epw format so that it can be used in DesignBuilder.
• Generating modified weather data sets for investigating climate change scenarios.

Note: The Rocky Mountain Institute now provides a free .epw hourly weather data editing and translation tool called Elements. Users may find this to be a more convenient way to edit epw files than the processor built into DesignBuilder. It provides a spreadsheet environment and allows individual values to be edited or ranges of data can be pasted in from an external spreadsheet program. For more information see the Big Ladder downloads page

Translation Overview

Use this dialog to convert weather data to and from a range of file formats.

To edit/convert a file or files:

1. Select the folder containing the file(s) using the browse box at the top of the left-hand side of the screen.  All relevant weather data files are then loaded into the table on the left.
2. Check the check box next to each file that is to be converted.
3. Ensure that the correct options have been set on the Options tab.
4. Press the Convert button to start the process.

Converted files are stored in the Weather data folder. You can access these files by clicking on the Edit/Review tab.

Input Data

On Input data tab you can select the name(s) of the source file (s) to be converted by checking in the checkboxes.

Use the Select all and Select none buttons for widespread changes.

Click on the Convert button to start the conversion.

Options

On the Options tab you can select various options to be used during the conversion.

Output file format

Supported formats are:

•     EnergyPlus data files (.epw)
•     EnergyPlus 'comma separated values' files (.csv)
•     TMY2 data files (.tmy2 or tm2)
•     TMY data files (.tmy)
•     IWEC data files (.iwec or iwc)
•     Samson data files (.samson or dat)
•     WYEC2 data files (.wyec2 or wy2)
•     DOE-2 formatted data files (.fmt or txt)
•     ESP-r formatted data files (.esp-r or clm)
•     BLAST ASCII formatted data files (.blast or asc)

Required extensions are shown in brackets.  

Error Correction - Fix out of range data

You can automatically correct any values that are outside the typical range for the EnergyPlus converter by checking the Fix out of range data checkbox.

Error reporting

Change filename

You can apply the standard convention used by DesignBuilder to rename the output file. If you select this option the output file will be named using the Country_Location_Source convention.

Modify

You can make some changes in the weather data as follows.

Fix year

You can fix the year to 2002. This is a recommended step for cases where you would like to view daily, hourly or sub-hourly EnergyPlus results within DesignBuilder or within the Results Viewer. The reasons for this are explained on the Add new hourly weather data page.

Modify climate

You can set the number of heating and/or cooling degree days or add a fixed delta to the dry-bulb outdoor air temperature values in the weather data. If you select the degree day option DesignBuilder adds or subtracts the same temperature difference to/from all dry-bulb outdoor air temperature values in the weather data so as to give the requested heating and cooling degree day values based on the supplied base temperature. The algorithm used is as follows:

For Each Hour in the weather file:

If Tdb < TDDBaseHeat Then

Tdb = Tdb - HeatAdj

Else If Tdb > TDDBaseCool Then

Tdb = Tdb - CoolAdj

where:

Tdb is the Outdoor air dry bulb temperature

TDDBaseHeat is Heating base degree day temperature

TDDBaseCool is Cooling base degree day temperature

HeatAdj is the delta T required to be subtracted to give the correct overall number of heating degree days

CoolAdj is the delta T required to be subtracted to give the correct overall number of cooling degree days

HeatAdj = 24 * (HeatDD - OldHeatDD) / HeatDDCount

CoolAdj = 24 * (CoolDD - OldCoolDD) / CoolDDCount

HeatDDCount is the number of hours in the year where Tdb < TDDBaseHeat

HeatDD is the user defined required heating degree days

OldHeatDD is the number of heating degree days in the source data

CoolDDCount is the number of hours in the year where Tdb > TDDBaseCool

CoolDD is the user defined required cooling degree days

OldCoolDD is the number of cooling degree days in the source data

Edit/Review

You can view all files in the current hourly weather data folder on this tab. You can open any of the files for viewing/editing by clicking on the Open selected file link on the info panel or by double-clicking on it.

Converting from Other Formats

If you have data in a format that is not supported by the DesignBuilder weather data translator there are 2 ways this can be used to generate an equivalent weather file in epw format.

1. Use the EnergyPlus custom weather data translation tool. Detailed descriptions on its use are provided in the Auxiliary Programs Guide (which is an essential guide for all epw weather data conversion/analysis. The EnergyPlus weather converter tool can be obtained by downloading the EnergyPlus software and is not supported by DesignBuilder support desk. However if you run into problems with it, you should be able to get help from the EnergyPlus support desk or forum.
   
   
2. The second option is to use an existing epw file as a template and copy columns of data across from your weather data source file using the csv spreadsheet format.

The rest of this section provides details on the second of these methods.

To translate weather data from any format follow these instructions. Note that as a starting point you will need to have the main data required by EnergyPlus stored in a csv format file or spreadsheet. The data required is:

• Air temperature
• Dew point temperature
• Relative Humidity
• Atmospheric pressure
• Global horizontal solar radiation
• Diffuse Horizontal solar radiation

• Direct normal radiation

• Wind Speed
• Wind Direction
• Cloud cover

If any of the above parameters are missing and you are unsure about how to derive them, you may wish to consider using the EnergyPlus custom weather translator instead which has built-functions to derive some missing parameters based on other equivalent data. e.g. Direct normal radiation can be derived based on known solar position and global and diffuse horizontal radiation.

If you do have all the required data in columns of a csv file then you are ready. The process is as follows:

1. To start the process, generate a template for a similar location in csv format. To do this use the weather data translation tool, selecting the 'EnergyPlus 'comma separated values' files' output option on the Options tab.
2. Load the csv file created in step 1 into a spreadsheet to use as the template.
3. In a separate spreadsheet load the new data.
4. Copy and paste the data column by column from the new data spreadsheet into the equivalent columns in template spreadsheet. A 'missing value indicator' value can be entered in any of the places EnergyPlus doesn't use the data. The 'missing value indicator' value is different for each field and details can be found in the Auxiliary Programs Guide.
5. Check that the header data at the top of the template spreadsheet is correct.
6. Ensure the year is set to 2002 in all rows.
7. Save the template as a csv file.
8. Use the weather file translator to translate the template csv file to epw format.
9. Rename the epw file as required.
10. Check that the data has been copied correctly by loading the file into DesignBuilder and clicking on the Simulation tab when at site level. You'll need to set up a new Hourly weather data component referencing the new epw file and select this first.
11. Check carefully that data output from simulations that use the new weather file makes sense. Pay particular attention to solar radiation. To do this you could check hourly incident solar radiation on a few surfaces in a model.

Note 1: If your regional settings aren't like UK/US, you could run into a couple of problems, such as the spreadsheet program changing the DataPeriods line from 1/1, 12/31 to 01-Jan -- you'd need to hand edit that before step 7

Note 2: Be aware that specific year data is not usually deemed appropriate for Energy Analysis. See this document for more information on selecting weather data:

Drury B. Crawley. 1998. "Which Weather Data Should You Use for Energy Simulations of Commercial Buildings?" in ASHRAE Transactions, pp. 498-515, Vol. 104, Pt. 2. Atlanta: ASHRAE. (PDF 197 KB) PDF: http://energyplus.gov/pdfs/bibliography/whichweatherdatashouldyouuseforenergysimulations.pdf