From the given simple question, I guess you want to know the approach on how to design/select a pre-cooled coil unit that takes 100% outdoor air at 4500 cfm (one-pass system).
To start off, you need to make a couple of decisions in your system design:
1) Is the conditioned air (after the pre-cooled coil unit) delivered to Air Handling Unit or direct into the room?
2) Is the pre-cooled coil unit designed to handle all the outdoor air load (sensible and latent)?
You can then work out the cooling load requirements, desired supply air conditions and plot it on the psychrometric chart for a better understanding of the process.
For selecting a 100 % fresh air unit, you can plot entering and leaving conditions of fresh air directly on the psychrometric chart and find the total sensible and latent load of the coil. If you want to calculate the sensible and latent load of the unit through manual calculations with psychrometric chart, you need to know the following information and few of these to be obtained directly from psychrometric chart.
Total amount of fresh air to be cooled in CFM
Entering dry bulb temperature of fresh air into the unit and humidity ratio in terms of grains of moisture per pound of dry air.
Desired leaving dry bulb temperature of fresh air from the unit and humidity ratio in terms of grains of moisture per pound of dry air.
You would calculate 100% OA unit requirements same as you would a non-100% OA unit; difference being entering air temperature. Leaving air temperature may or may not be the usual 55°F depending on what you want to do with it.
As for selecting a unit, the process is the same. Open a catalogue, search the web, and (most useful) talk to a sales rep.
