Well, the best way to model UFAD system that I know is using the EnergyPlus. The two main differences between conventional systems and UFAD systems, are plenum thermal decay and the room air stratification. The thermal decay in the plenum or the difference between discharge air temperature after the cooling coil and the temperature of air leaving the diffuser can be as high as 10F depending on the construction and operational parameters.

Simply increasing the supply temperature will not model many actual system behaviors that are present. First the peak load will be underestimated since portion of the heat gain in the plenum goes into the slab below the raised floor instead of the zone. Some of the cooling from plenum decay that does make it into the zone will not contribute to cooling the zone, but will exchange heat with the ceiling via radiation. Both of those behaviors can be beneficial or harmful to energy consumption depending on operational parameters of the system, such as minimum flow rate.

I'd encourage you to submit your question to support@iesve.com or visit the user forums over at iesve.com

There you'll find the best answers to your questions - and many FAQ's about how to model certain system types.

You'll note that the VE currently has several UFAD and displacement ventilation prototypes in it that you can start with and modify as needed. All the prototypes include the necessary components for accurate UFAD/DV modeling including stratification of the zones, variation of where the load is, detailed solar load assignment at each time step, etc.