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.

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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.

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