Enthalpy Calculations

If you are using any of our HUM series and basically any of our products with a humidity sensor on it has the enthalpy and dew point temeprature calculations built in. And on checking with the team here I see that we have not yet added it to the Tstat10 with humidity option, we’ll tend to this asap.

That said, Wikipedia shows a formula for a quick approximation of the dew point using this formula in DegC. You can get the formula for DegF on wikipedia.


And to calculate enthalpy, the formula is found on calculatoratoz.com
Again this is in metric and you can find the formula for imperial units on the calculator website.

h = 1.005tdb+(ω(2500+(1.9*tdb)))

h is the enthalpy of moist air in kj/kg, this is the sum of the enthalpy of the dry air and the enthalpy of the water vapour.

tdb is the dry bulb temperature which is the temperautre measured in °C from a typical thermistor or RTD freely exposed to the air but shielded from radiation and moisture.

w is the specific humidity in percent, this is the humidity measured by a typical humidity sensor element located in the same shielded air as the dry bulb temperature sensor.

The above formulas are approximations at 1 atmosphere pressure.

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Hey Maurice

Thx for the reply. We do have the formulas from ASHRAE, however formulas involves a natural logarithm of Relative humidity / 100 which is a value between 0 and 1. Usually the logarithm is negative, however the LN functions of T3 is giving a positive value.

TD: =243.04*(LN(RH/100)+((17.625T)/(243.04+T)))/(17.625-LN(RH/100)-((17.625T)/(243.04+T)))

I guess there is a problem with the logarithm function in T3. The simplified linear formulas is accurate only for relative humidities above 50%

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Chelsea will check the log function. I like your formula better and will change my post. Thanks.


Hey Chelsea, did u have the chance to check the logarithm formulas for value between 0 and 1