HX_TPHI: Enthalpy & absolute humidity to temperature & relative humidity
The HX_TPHI (FB422) block calculates the enthalpy and absolute humidity to form temperature and relative humidity (as per the h,x diagram). HX_TPHI_SiUn (FB422), HX_TPHI_UsUn (FB795), HX_TPHI_CaUn (FB790)
The following functions are integrated in the block:
- Calculation of the condensed amount of water and the effective enthalpy (without condensate) if the air state is within the fog area.
- Air pressure connection (optional).
Inputs
Pin | E | Description |
E | pa | Enthalpy |
HuAbs | pa | Absolute humidity |
AP | pa | Air pressure Measured value for air pressure or constant value. See Engineering. |
Outputs
Pin | E | Description |
T | a | Temperature. The temperature is calculated from the input variables. |
HuRel | a | Relative humidity. |
HuCod | a | Condensed water portion in saturated air. If the air state is within the fog area of the h,x diagram (below saturation curve), the condensed amount of water is determined. |
EEf | a | Enthalpy effective (without condensate). The amount of energy of the amount of water is deducted from the enthalpy [E] measured. |
Input values
Pin | Description | Data Type | Default value | E.g. Engineering unit or Text group | Min. | Max. |
E | Enthalpy | Real | 40.0 | kJ/kg | 0.0 | 100.0 |
17.2 | Btu/lb | 0.0 | 43.0 | |||
HuAbs | Absolute humidity | Real | 7.8 | g/kg | 0.0 | 50.0 |
0.008 | lb/lbda | 0.0 | 0.05 | |||
AP | Air pressure | Real | 0.96 | bar | 0.0 | 4.0 |
28.35 | inHg | 0.0 | 118.1 |
Output values
Pin | Description | Data Type | Default value | E.g. Engineering unit or Text group | Min. | Max. |
T | Temperature | Real | 20.0 | °C | -50.0 | 150.0 |
68.0 | °F | -58.0 | 302.0 | |||
HuRel | Relative humidity | Real | 50.0 | %RH | 0.0 | 100.0 |
HuCod | Cndnsd.water in sat.air | Real | 2.0 | g/kg | 0.0 | 20.0 |
0.002 | lb/lbda | 0.0 | 0.02 | |||
EEf | Enth.eff.(no condensate) | Real | 40.0 | kJ/kg | -20.0 | 100.0 |
17.2 | Btu/lb | -8.6 | 43.0 |
Engineering
Parameterizing the air pressure [AP]
If the air pressure is not available as a measured variable, it can be defined as a constant. Air pressure decreases at increasing altitude above sea level; the constant thus needs to be defined in dependence of the altitude above sea level:
Altitude (m) | AP (bar) |
| Altitude (ft) | AP (inHg) |
0 | 1.013 | 0 | 29.91 | |
300 | 0.978 | 1000 | 29.34 | |
600 | 0.943 | 2000 | 28.29 | |
900 | 0.910 | 3000 | 27.30 | |
1200 | 0.877 | 4000 | 26.31 | |
1500 | 0.846 | 5000 | 25.38 | |
1800 | 0.815 | 6000 | 24.45 | |
2100 | 0.785 | 7000 | 23.52 |
Process response
Standard (see General rules and information).
Troubleshooting
Standard (see General rules and information).