Previous studies on high pressure fogging have shown their capability for maintaining temperature and humidity in acceptable ranges most of the year in greenhouses located in semiarid regions. The heat load, and therefore cooling demand, inside the greenhouse vary during the day and throughout the seasons. Thus, it may be advantageous to use a variable pressure fogging (VPF) system, where specific fog rates can be supplied based on the cooling demand. However, the absence of effective cooling strategies is one of the drawbacks limiting the extensive use of these systems. A well defined control strategy should account for plant's contribution on cooling and humidification in the control algorithm. This study compared the accuracy of three evapotranspiration models using measured values from greenhouse grown pepper plants. The results showed that Stanghellini model (R2=0.93) predicted measured evapotranspiration rates slightly better than Penman-Monteith (R2=0.84) and Takakura models (R2=0.79). Furthermore, a computer simulation was developed to compare a proposed control algorithm for VPF to a typical on/off fixed pressure fogging system based on vapor pressure deficit (VPD). Results showed that VPD based fixed pressure fogging strategy consumed more water and energy compared to the VPF system. Cycling of the pump was smaller and higher stability of temperature and relative humidity were achieved by the operation of the VPF system.