The influence of three ventilation systems, namely, the displacement ventilation system, the stratum ventilation system, and the underfloor air distribution system, on human thermal comfort was investigated at different supply air temperatures. We compared the air velocity, CO2 concentration, temperature, human thermal comfort, and energy utilization coefficient of the three systems at a supply air temperature range of 18–24 °C. The results showed that the underfloor air distribution system provided the best performances for CO2 dispersion and cooling at a supply air temperature of 18 °C. For optimal human thermal comfort, the underfloor air distribution should be chosen at a supply air temperature of 18 °C, the displacement ventilation system is suggested at a supply air temperature of 19 °C, 20 °C, and 24 °C, and the stratum ventilation system would be most suitable at a supply air temperature of 21 °C, 22 °C, and 23 °C.