Microclimate and energy consumption in commercial, hot-water and steam heated greenhouses for tomato production

Steam and hot-water heating systems are the two most widely used systems in Canadian greenhouse vegetable production. To improve greenhouse climate management and energy use efficiency, their effects on energy consumption and microclimate in a hot-water and a steam heated commercial greenhouses with tomato crops were quantified. Both greenhouses were gutter-vented, double-polyethylene greenhouses with a gutter height of 4.26 meters. For the hot-water heated greenhouse, a steel hot-water pipe (51 mm inner diameter) loop (45 cm between the two pipes) was placed at 10 cm above the ground and between the double-rows of tomato plants. One steam steel pipe (38 mm inner diameter) was hung 30 cm high inside each double-row of tomato plants in the steam heated greenhouse. Solar radiation, air temperature and humidity, leaf wetness and temperature were monitored at 4 heights. We found that there was a larger vertical variation in air temperature and relative humidity in the steam than the hot-water heated greenhouse. The air temperature below 1.5 meters was about 0.5 degrees C higher in the steam heated greenhouse than in the hot-water heated greenhouse, while the air temperature above the crop canopy was the same. In winter when the greenhouses were intensively heated, leaf wetness duration was shorter and relative humidity was lower in the steam heated greenhouse.