The purpose of this paper is to compare energy consumption with under floor air distribution systems for office buildings, specifically a call center application.;The building being modeled will have an HVAC system that utilizes an underfloor air distribution system (UFAD). This type of system allows air to be introduced into the plenum space under the floor. The air comes up through the floor into the space through plenum space pressurization. The air is then taken out of the space up high and returned back to the air handling unit.;The three systems reviewed for delivery of the air to the underfloor system (comparing energy consumption on the UFAD systems) are roof top units (RTU) with full economizers, boilers and chillers and a ground source heat pump (GSHP). These systems are being modeled as a heating and cooling plant for the UFAD system. The first costs as well as the energy consumption have been analyzed to determine simple paybacks from system to system listed above.;It was calculated that the RTU has the lowest initial cost at {dollar}1,492,049, the boiler/chiller was next at {dollar}1,769,069 and the highest cost system was the GSHP at {dollar}2,700,002. The systems energy cost per year were calculated to be; RTU - {dollar}77,440, boiler/chiller - {dollar}46,782 and GSHP - {dollar}8,557. The system paybacks from the RTU versus the boiler/chiller were 9 years, the RTU versus the GSHP was 17.4 years and the boiler/chiller versus the GSHP was 24 years.