what is Enable Ideal Air Loads?

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I am assuming that you are talking about the Ideal Load Air System in EnergyPlus. You can find more information about it in the EnergyPlus documentation:

The input object ZoneHVAC:IdealLoadsAirSystem provides a model for an ideal HVAC system. It occupies a place in the program hierarchy corresponding to a zone HVAC unit. It is not connected to a central air system - instead each ZoneHVAC:IdealLoadsAirSystem object supplies cooling or heating air to a zone in sufficient quantity to meet the zone load or up to its limits, if specified. The supply air conditions are controlled based on specifications in the ZoneHVAC:IdealLoadsAirSystem input. The system has options for humidity control, outdoor air, economizer, demand controlled ventilation, and heat recovery.

This description is from the Engineering Reference Guide. You can access it online here. You can also download the entire documentation here. If you are new to EnergyPlus, it might be good to take a closer look at the Input Output Reference Guide as well.