Performance experiment and design of simply assembled Chinese solar greenhouse equipped with heating and dehumidification system

Traditional Chinese solar greenhouse has thick north wall and its structure is non-standard, in which crop yield is lower because of the lack of automatic equipment for controlling the inside temperature and humidity. In order to solve this problem, we designed a simply assembled Chinese solar greenhouse that was equipped with heating and dehumidification system. In this study we presented 2 simply assembled Chinese solar greenhouses with active heat storage-release systems as the experiment greenhouses. One of them was also equipped with dehumidification system. Each greenhouse was 33 m long and 8 m wide with 3.8 m ridge height, 3.2 m height and 0.166 m thickness of the north wall. The wall of simply assembled greenhouse was composed of 2 fiber cement boards and a polystyrene board in between. A traditional solar greenhouse with brick wall using active heat storage-release system was chosen to be a reference greenhouse. It was 60 m long and 8 m wide with 3.8 m ridge height, 2.3 m height and 0.58 m thickness of the north wall. Compared with the brick wall, simply assembled Chinese solar greenhouse could save 72% of land resources. Steel frames of the experiment greenhouse were assembled together. It saved much more time to build a simply assembled Chinese solar greenhouse. All greenhouse crops were tomatoes planted on October 20th, 2014. Active heat storage-release system and dehumidification system were active automatically at night during the experiment. Active heat storage-release system was a heat-energy storage and release system by using water as the medium. During the day time (from 09:00 to 16:00) this system was used to store solar energy. During the nighttime (from 00:00 to 08:00), it released the energy into greenhouse for increasing the indoor temperature. In the experiment the system increased the indoor temperature by 4.5 ℃ at night compared with the traditional solar greenhouse. And the average air temperature was 1.3℃ higher in the simply assembled Chinese solar greenhouse than that in the traditional solar greenhouse combined with active heat storage-release system, which was because of higher insulation of the wall material. On cloudy day, the active heat-release system also improved the indoor temperature by 1.1 ℃. The dehumidification system had an air duct on the floor along the south-facing roof that distributed the outside air from a ventilator installed in the system box. This box contained the water-to-air heat exchanger, and 2 electrical heaters. The cold, dry air outside was heated by warm water from the water tank through a heat exchanger. Heat energy got from the warm water was supplied by the active heat storage-release system. A manual valve was used to control the air speed and 2 automatic valves were used to control the inlet of outside air. The dehumidification system could be activated from 18:00 to 08:30 in the next morning. When the inside relative humidity was higher than 85%, water went through the heat exchanger while the ventilator was switched on. When the indoor air temperature would drop below 8 ℃, the dehumidification system would switch off for preventing further cooling of the greenhouse by the cold air outdoor. During dehumidifying process, the first electric heater would be switched on when the water temperature was below 25 ℃. The second would work when the water temperature was below 20℃. During the experiment, the dehumidification system reduced the indoor relative humidity by 14% compared with the traditional solar greenhouse. During the dehumidification process, the energy consumption of the water pump and ventilator was 218.3 kJ/m2 per day. The energy supplied by the electric heaters was 643.6 kJ/m2 per day assuming that the energy conversion efficiency was 100%. The heat energy supplied by the active heat storage-release system was 639.4 kJ/m2 and its consumption was 153.4 kJ/m2 per day on average. It was expected that the electric heaters could be eliminated if the active heat storage-release system could be scaled up to provide an additional heat energy of 643.6 kJ/m2 per day. For a commercial greenhouse, it was important to improve the performance of the active heat storage-release system to get more solar energy and reduce the additional energy input. A more energy-efficient way of auxiliary heating was necessary in case of continuous cloudy days. By the financial analyses, the cost of brick wall greenhouse was 491.7 yuan/m2, and the simply assembled greenhouse was 334.5 yuan/m2. The biggest difference was from the charge of north wall. In conclusion, the simply assembled greenhouse with heating and dehumidification equipment saves much land resource, and has better indoor environment and less cost.