Psychrometric Function Block

This function block calculates different values from the temperature and relative humidity like the enthalpy, dewpoint or absolute humidity.

Figure 1: Psychrometric - Wire Sheet

Figure 2: Psychrometric - Property Sheet

Figure 3: Psychrometric - Logic Diagram

Input

Input Name

Description

Temperature

This is 32-bit floating point input slot. It depends on the global setting for the controller.

Rel Humidity

This is 32-bit floating point input slot. It is measured in percentage (%).

Table 1:Inputs of Psychrometric Function

Output

Output Name

Description

Out

Output = Enthalpy (kJ/kg or BTU/LB), Dewpoint, or Absolute humidity (g/kg, kg/m3, g/m3) (Depends on the selected operation).

Table 2:Outputs of Psychrometric Function
Parameter

Parameter Name

Description

Operation

There are three operations: Enthalpy, Dewpoint, and AbsHumidity.

  • Enthalpy: This function computes the enthalpy (kJ/kg or BTU/LB) based on the temperature (°C or °F) and relative humidity (%) inputs. Enthalpy is a measure of the energy contained in the air. The warmer and more humid the air, the higher the enthalpy. Enthalpy is important for heat recovery
  • Dewpoint: The dew point is the temperature at which air begins to form dew, for example, on a cold-water pipe. A cooling ceiling should not be supplied with colder water than the calculated dew point of the air in the room, otherwise drops can form on the ceiling and drip down.
  • AbsHumidity: The absHumidity indicates the humidity in relation to the volume. The value is measured in the supply air and is used to control the humidification of the supply air.

Out Save

Master Sync Enabled: If you set it to "true" the last output will be set as output for one cycle after the controller restarts. The application can use it to return to the same state before the controller restart.

Out: To enable or disable the Out feature.

Table 3:Parameters of Psychrometric Function

Example

1.       Operation is Enthalpy (Enthalpy = 42.3 kJ/kg)

Figure 4: Psychrometric Example with Enthalpy


2.       Operation is Dewpoint (Dewpoint = 7.03°C)

Figure 5: Psychrometric Example with Dewpoint

3.       Operation is Absolute Humidity (Absolute Humidity = 6.23 kg/m3)

Figure 6:Psychrometric Example with Absolute Humidity

Refer to General Description for general information about IRMN4 Function Blocks.