Frequently Asked Questions

The following are common questions asked about our software products:

  1. I have just installed Winsteam (or @Air or @Gas or XLInterp).  Why aren't any of the functions  available in Excel?
  2. The Add-in Manager in Excel does not list "WinSteam for Excel" (or @Air or @Gas or XLInterp).  What should I do?
  3. I have just upgraded WinSteam and an old spreadsheet is returning errors.  What is wrong?
  4. Why are the values of enthalpy that I get from @Gas so different from the values I am used to from published tables?

I have just installed Winsteam (or @Air or @Gas or XLInterp).  Why aren't any of the functions  available in Excel?

Before you can use the functions in Excel, you have to tell Excel's Add-in Manager to make the functions available.  To do this, select the Add-ins command on Excel's Tool menu. (For Office 2007, Press the Office button then the Excel Options button.  Select Add-Ins from the menu then press the Go button.)  This brings up a dialog box listing various add-ins.  Towards the bottom of the list, you should find and entry, "WinSteam for Excel".  Check the box next to it and press OK.  The WinSteam functions will now be available in Excel every time you start Excel.  The same procedure must be done for @Air, @Gas and XLInterp as well.

The Add-in Manager in Excel does not list "WinSteam for Excel" (or @Air or @Gas or XLInterp).  What should I do?

Excel's Add-in Manager will usually look in the Office/Library or Excel/Library folder for add-ins.  The installation program usually copies the Add-in file to the proper folder but sometime it cannot.  You should search you disk drive for the file "xlstm32.xll" and move it to the appropriate Library folder.  If you do not wish to move the add-in file, you may open the add-in Manager (see above) and press the "Browse" button.   Then locate the add-in file and press OK.  Then check the "WinSteam for Excel" check box and press OK.

I have just upgraded WinSteam and an old spreadsheet is returning errors in Excel.  What is wrong?

First make sure that the Excel Add-in Manager has loaded "WinSteam for Excel".  See the two topics above for more details.

If this does not solve your problem, check the unit set argument.  In older versions of Excel. the unit set argument was optional.  If you omitted the unit set argument, WinSteam assumed you wanted "English" units.  In newer versions of WinSteam, the unit set argument includes more options and we recommend that you always include the unit set argument with each function call.  When you installed WinSteam you were asked whether to make the unit set argument optional or mandatory.  If you accepted the default, it made the unit set argument mandatory.  If your old spreadsheet omitted the unit set argument, this would cause an error.

To remedy this, Download this small file that allows you to make the unit set argument optional.  When you run this file it allows you to choose whether you want the unit set argument in Excel to be optional or mandatory.  We still recommend that you explicitly enter the unit set argument in all new spreadsheet. 

Please note, if you are running Windows 2000, NT, XP or Vista, you  must install WinSteam as an Administrator or else the selection of optional unit set argument will not take effect.

Why are the values of enthalpy that I get from @Gas so different from the values I am used to from published tables?

There are a few reasons.  First, with the default units sets, all specific properties are presented on a dry basis just like the ASHRAE air property tables.  You can change this to a wet basis by adding a "W" to the unit set argument (for example, "ENGW".) 

Second, some tables reference the enthalpy of the gases to absolute zero while others choose different temperatures.  @Gas, by default, uses the same reference conditions as the ASHRAE air tables.  This is zero deg F when using English unit sets and zero deg C when using SI or metric unit sets.  You can choose to use a reference temperature of absolute zero by adding an "A" to the unit set argument (for example, "ENGA".)  Recognize that enthalpies are meaningful only when taken as a difference between two conditions.  You will see that the enthalpy differences will be the same regardless of the choice of reference temperature.

Third, regardless of what reference temperature is selected for the gas components, @Gas always uses the reference condition for the water component as liquid water at the triple point.  This is done to be consistent with the ASME steam tables and is also consistent with the way ASHRAE handles moist air properties.  Many references treat the water vapor component as a perfect gas and reference the enthalpy to absolute zero or some other temperature.  With our method, water either added or removed from the process can be treated using the standard ASME steam tables or Techware's WinSteam product.  This makes it easy to handle situations where evaporation or condensation occur.  Since the water component is referenced to liquid water, you should use higher heating values when adding heat from the combustion of fuels in the gas stream.

Finally, the enthalpies and other properties calculated by the @Gas functions take into account the compressibility effects of the gas and therefore are not perfect gas approximations.