Issue
Customers have requested clarification on how Enthalpy is calculated within a Sigma Programmable Object.
Product Line
Satchwell BAS & SigmaEnvironment
Satchwell Sigma
Cause
Need for transparency and understanding of the internal formula used for Enthalpy calculations in Sigma.
Resolution
The Sigma Programmable Object calculates Enthalpy (I) using the following formula:
I = 1.006 * t + x * (2501 + 1.8 * t)
Where:
t= temperature in °Cx= humidity ratio, calculated as:
x = 0.62198 * (í * pdm) / (p - í * pdm)
Assuming standard atmospheric pressure p = 101.325 kPa, the formula simplifies to:
x = 0.62198 * (í * pdm) / (101.325 - í * pdm)
Where:
í= relative humidity (as a decimal)pdm= saturation vapor pressure, calculated as:
pdm = p' = 101325 * 10^A
With:
A = A0 - (A1 / T) - A2 * log10(T) - A3 * 10^(-T / A4) + A5 * 10^(A6 / T)
Constants:
- A0 = 20.82648355
- A1 = 2948.997118
- A2 = 5.02808
- A3 = 29811.33781
- A4 = 32.923061
- A5 = 25.21934913
- A6 = 1302.8503
Temperature in Kelvin:
T = 273.15 + tAdditional Notes
- This formula is based on psychrometric principles and is used to calculate the total heat content of moist air.
- Ensure temperature and humidity inputs are accurate for reliable results.
