Modeling HVAC System with Direct Free cooling

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That is exactley What I am doing @Petros Dalavouras . The only difference is that I plotted the 23ºC and 80% relative humidity in a Psychrometric Chart (@ 420 meter above sea level which gives me 96.403 kPa) and for that data I got values of 23 ºC Dry-bulb Temperature, 61142 J/Kg Enthalpy and 19.46 ºC Dewpoint Temperature.

From my understanding, defining the parameters OS requires will not limit the maximum Relative Humidity.

For example, picture 1 show wheater data points where economizer will be active but should be inactive.

Picture 1

This is true. A fixed Dew point cannot give a variable RH since DB is also a variable. That being said, what is your application that requires a RH limit since cold air, even with high 100% RH, has low humidity ratio. That is what I was mentioning to my answer. Despite that, an "ElectronicEnthalpy" economizer probably can solve this problem. Keep in mind that OS does not have a field for the ElectronicEnthalpy's curve so you'll have to insert one manually for example with a text editor. Check this post

Thank you for your answer. I am modeling a computer room (not a Data Center) but close to it. It has only 6000W of internal equipment. It does already exist, and the way the HVAC equipment work is using 100% outdoor air when both outdoor air DBT is below 18ºC and RH is below 80%. I would like to improve energy eficiency (and evaluate that) by using 100% outdoor air when both outdoor air DBT is below 23ºC and RH is below 80%. I will try to use an "Eletronic Enthalpy" economizer. Not sure if I will be able to do that because I have almost no experience using the text editor for cases like this.