First, I would double-check that your zone's thermostat is set up correctly. You can refer to this post for details.

If your thermostat is set up correctly, then check your ZoneHVAC:IdealLoadsAirSystem object. Some input fields that could be causing this unmet hours issue are:

• Availability Schedule Name: Check if there are schedule values of 0
• Minimum Cooling Supply Air Temperature: Check if the minimum supply air temperature is too high
• Cooling Limit: Check this and it's related input fields if maximum supply air flow is too low
• Cooling Availability Schedule Name: Check if there are schedule values of 0