Protected horticulture using greenhouses and also recently plant factories is becoming more popular, especially for high-value crops such as paprika, tomato, strawberry, due to year-round production of high yield and better quality crops under controlled environment. Temperature and humidity are most important ambient environmental factors for not only optimum crop growth but also disease control. This study was conducted to analyze vertical and spatial variability of temperature and humidity in test greenhouses for control optimization of a hybrid dehumidifier with a heating module. In the study, a 600-W dehumidifier with a 3.5-kW heating module, developed for 200 m2 area for Korean plastic greenhouses The unit was developed to prevent crops from freezing or abnormal growth at temperatures of 0~5∞C using the heating module, simultaneously with the dehumidification. Temperature and humidity would be different from those at the equipment location, and vary vertically and spatially in greenhouses. Control strategies such as sensor location and equipment operation duration need to be developed considering the variability. First, tests were conducted in a closed chamber so that temperature and humidity not be affected by outside conditions. Next, 34 m2 small-sized plastic greenhouse was used. Temperature-humidity sensor nodes were located at 3 heights (i.e., equipment height, 0.5 and 1 m from the ground), and 9 sensor nodes were uniformly located at each of those heights. Additional nodes were located around the equipment. Sensor nodes were fabricated using ATmega128 main board and ZigBee communication module. Sensor measurements were obtained for 2 hours after the equipment operation start at a 10-Hz sampling speed. In the closed chamber, the average times required to change the initial conditions (i.e., -5∞C,  90% RH) to the target conditions(i.e., 10∞C, 70% RH) were 58, 66 and 75 minutes for the heights, respectively. When the initial conditions were varied, the required control time changed, but the pattern by height was similar. Greenhouse tests showed considerable vertical and spatial variability, and the pattern also changed by time. Differences by heights were 3~6∞C and 10~20% RH, and those by spatial location were 2~4∞C and 7~15% RH. Results of the study confirmed considerable vertical and spatial variability of temperature and humidity in greenhouses. Further study would be necessary under plant growing conditions, for reliable control strategies of the dehumidifier with a heating module.