Keep in mind that 5.456 tons is cooling required for the lighting only. You still need to factor in the building location, building construction type, factor in other equipment that produces heat in the space such as fan motors, pumps, chillers, etc. I would also suspect you will require a dehumidifier as well unless you get A/C equipment that can run as a dehumidifier for when lights are off. Running a sealed room with CO2 is going to be a different beast than having to condition the air if you are ventilating it, and local weather is obviously going to factor very differently if you ventilating the room as the fresh air will need to be conditioned as well.
I would suggest looking at commercial HVAC equipment, and contacting manufacturers to get further guidance if you can't reach any consultants. There are consultants that would be able to assist you online, and ASHRAE.org would be a good resource.