Library for TAPPS2 by Austrian PLC manufacturer Technische Alternative making HVAC calculations easier. Made and maintained by Schwab Technik GmbH the company behind Xerovent energy efficient dehumidification.
This .bib library can be added to TAPPS2. It's content then appears in the program window left bottom section.
Currently the library contains:
- a function template for calculating saturation vapour pressure of water vapour over water — over supercooled water at sub-zero temperatures.
- an identical function template as above but in units of hPa (mbar) with two decimal places
- a set of blocks to calculate basic properties of humid air such as
- partial pressures of steam and dry air
- absolute humidity
- mixing ratio
- density of dry air
- specific humidity
- a set of blocks to calculate mixing ratio alone
- a set of blocks to calculate enthalpy
$h_{1+x}$ out of a temperature and a mixing ratio - a set of blocks to calculate surface humidity (activity of water) out of a mixing ratio and a surface temperature
- a set of blocks to calculate surface humidity out of specific humidity and a surface temperature
- save the .lib-File on your local hard drive
- open TAPPS2 and within TAPPS2 open a .tdw file or create a new one
- on the bottom left part right-click ''own libraries''. Or click on the
Add Libraryicon on the top left window corner. - in the dialog that appears, choose the .lib file from the location you saved it.
Just drag the desired function block set from the library in the bottom left corner to your programming area. Depending on the hardware version, MTx2 displays have a built-in air pressure sensor whose signal can be used to calculate the mixing ratio. Alternatively, a fixed value adjusted to the sea level of the location can be used; the resulting error is negligible for most building technology applications.
TA specifies the absolute humidity and dew point directly with its humidity sensors (MTx2, RAS-CT4 RAS, RFS). However, both values change when air flows through a heat exchanger. Therefore, when comparing air of different temperatures, the mixing ratio should generally be used.
The saturation vapour pressure over water is calculated with the exact formula of Dietrich Sonntag from 1990. It is more accurate than VDI/VDE 3514 Sheet 1; over the temperature range used here, its own deviation is orders of magnitude smaller than the error of the curve interpolation and therefore negligible. This accuracy is helpful when working with small temperature differences.
The possible maximum of 120 support points is used for the interpolation, covering the range from -30.0 °C to 69.0 °C without a gap. The pressure values and reference points were selected to minimise the interpolation error. This means that the pressure values at a reference point may differ slightly from the true value if this improves the interpolated values. At low temperatures, the relative error is greatest, but it stays below ±0.35 %. At higher temperatures, the absolute error is greatest, but does not exceed ±1.5 Pa. Since TA does not process values above 30000 Pa, the maximum application temperature is 69.0 °C. There is no longer a range with reduced accuracy; the curve is equally accurate throughout.
- At sub-zero temperatures the saturation vapour pressure is now calculated over supercooled water instead of over ice, matching how the sensors report their relative humidity. Only temperatures below 0 °C are affected; there the results are higher: about +5 % at -5 °C, +10 % at -10 °C, +22 % at -20 °C and +34 % at -30 °C. From 0 °C upwards nothing changes.
- The enhancement factor of 1.0047 is gone. All values drop by 0.47 % as a result.
- A faulty support point at 30.5 °C was corrected; it was about 22 % too low.
- The curve now extends to 69.0 °C instead of 68.9 °C and is equally accurate throughout. The reduced-accuracy section between -30 °C and -20 °C is gone.
If you have parametrised limits or setpoints based on the previous blocks, review them after updating — especially for applications below 0 °C.
- Sonntag, Dietrich: Important New Values of the Physical Constants of 1986, Vapor Pressure Formulations based on the ITS-90 and Psychrometer Formulae. In: Zeitschrift für Meteorologie 70 (1990) 5, pp. 340–344
- World Meteorological Organization: Guide to Instruments and Methods of Observation (WMO-No. 8), Volume I, Annex 4.B: Formulae for the computation of measures of humidity.