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This is a study of using a sensor in the water temperature control system for hydroponics. The purposes of the study were (1) to design and construct a water temperature control system using thermoelectric peltries for the NFT (Nutrient Film Technique) hydroponic vegetable growing and (2) to study the efficiency of the hydroponic vegetable growing using the constructed water temperature control system. The designed hydroponic greenhouse had a measurement of 0.8 m (W) ´ 2.5 m (L) ´ 1.8 m (H). It was made of 16 white-painted plastic pipes each of which had 14 plant holes. The watering system was controlled by a low pressure water pump, and the water temperature was controlled by an RTD (Resistance Temperature Detection) sensor specifically designed for the NFT hydroponic greenhouse. A power supply was used to give electric current to the water temperature control system and the three thermoelectric peltries each of which needed a 6 watt and 12 volt dc power supply. To study the efficiency of the hydroponic growing, two different types of nutrient solution were prepared 50 ml of each type of the nutrient solution was mixed with 20 l of water to plant celery sprouts afterwards. The results of the study unveiled that the plastic covers and shading nets helped reduce the temperature inside the greenhouse by 3 °C. According to the plant growth against the nutrient solution constant coolant can produce an average water temperature at 27.37 °C. This is because waveform waveforms the dc power supply can be supplied with constant voltage. When experimenting with thermoelectric plates and a cooling fan measuring 15.4 amperes. The test of growth of celery at the rate of nutrient suitable for celery in 5 weeks.