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Sun W.,Beijing Academy of Agriculture and Forestry Sciences | Sun W.,Key Laboratory of Agri informatics | Chen X.,Beijing Academy of Agriculture and Forestry Sciences | Chen X.,Key Laboratory of Agri informatics | And 10 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2016

The closed greenhouse is a light-permeable greenhouse type, with totally-enclosed architectural structure. Cooling by ventilation is replaced completely by mechanical cooling. Excess solar energy is collected and stored to be reused to heat the greenhouse or other buildings. The closed greenhouse can achieve energy conservation and emission reduction, recycling water of evapotranspiration, maintaining a high level of CO2 concentration, as well as isolating the bacteria spores from external environment, etc. However, high air temperature inside the closed greenhouse is difficult to control effectively in summer, or a great deal of energy is needed to consume, resulting in a restriction of the closed greenhouse when used in actual production. In order to decrease air temperature inside the closed greenhouse, taking low carbon emission and energy-saving into consideration, a closed greenhouse with water-walls (CGWW) was designed and built in Changping District of Beijing, China. With an indoor ground surface of about 7.6 m2, it was supported by a steel skeleton and assembled from some glass tanks filled with water. And for suppressing the growth of green algae, pH value of the water was adjusted to 9.5. Water layer thickness of side walls and roof were 30 and 13 cm, respectively. Cooling characteristics of the CGWW in summer was tested from 26 Jul. to 10 Sep. 2015. During the test, cucumbers and rapes were cultivated inside the CGWW. The results showed that, average air temperature inside the CGWW was 29.4-34.3℃ around noon (10:00-16:00), decreased by 0.8-6.8℃ compared with ambient. Meanwhile, the air temperature drop range inside the CGWW got bigger with the increase of solar radiation or ambient air temperature (P<0.01). In 94.6% of the photosynthesis period (06:00-18:00), air temperature inside the CGWW was controlled within 35℃, which could avoid the high temperature stress effectively. So the CGWW had remarkable effect for cooling in summer. During the nighttime, relative humidity inside the CGWW was controlled within 80%, and the average value was 54.7%-73.7%, decreased by 7.2%-17.5% compared with ambient. Meanwhile, there was a negative linear correlation between humidity difference and temperature difference, inside and outside the CGWW (P<0.01). During the daytime, solar radiation in horizontal direction inside the CGWW was 31.5-67.4 W/m2, and accounted for 11.9%-17.8% of that outside the CGWW. As solar radiation transmitted into the CGWW from outside, ratio of far-red light decreased from 41.9% to 9.2%, with a transmittance of 6.0%, which was conducive to the suppression of high temperature inside the CGWW. Red and blue light had the most ratios and accounted for 23.9% and 27.1% of the spectrum distribution inside the CGWW, respectively, and both of them had an increase compared with outside. And red and blue light had transmittances of 32.4% and 37.5%, respectively, which were far higher than both UV-A and far-red light. Due to the selective permeability of the water-walls for solar spectrum, obviously, high temperature inside the CGWW could be controlled while adequate photosynthetically active radiation could be ensured. In addition, the CGWW showed some of regularity in distributions and daily variation of water-walls temperature and air temperature inside the CGWW. In summary, the CGWW which can obtain an ideal cooling effect, suitable humidity and illumination conditions via its own structure, has been proved to be a feasible, low carbon and energy saving greenhouse type, and will provide a reference and technical supports for the development of closed greenhouses. © 2016, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved. Source


Zhou B.,Chinese Academy of Agricultural Sciences | Zhou B.,Key Laboratory of Energy Conservation and Waster Treatment of Agricultural Structures | Zhang Y.,Chinese Academy of Agricultural Sciences | Zhang Y.,Key Laboratory of Energy Conservation and Waster Treatment of Agricultural Structures | And 5 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2016

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. © 2016, Chinese Society of Agricultural Engineering. All right reserved. Source


Sun W.,Chinese Academy of Agricultural Sciences | Sun W.,Key Laboratory of Energy Conservation and Waster Treatment of Agricultural Structures | Zhang Y.,Chinese Academy of Agricultural Sciences | Zhang Y.,Key Laboratory of Energy Conservation and Waster Treatment of Agricultural Structures | And 7 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2014

Active heat storage-release associated with heat pump heating system (AHSRHPS) has remarkable heating and energy-saving effects, which use the same principle as an indirect-expansion solar heat pump, while allowing the technical parameters and processes to continue to improve. The system in this study was designed and constructed in the experimental glass greenhouse at the Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences. The main objective was to investigate performance evaluation and thermoeconomic analysis of AHSRHPS for greenhouse heating in the winter. This included the exergy loss of the system and components, defining the specific locations and primary causes of exergy loss, finding methods and technical routes used to reduce exergy loss by exergy analysis based on the second law of thermodynamics, and lastly, optimizing the system further. The heat collecting efficiency of the system ranged from 89.0% to 100.5% during the test and was much higher than the common solar water heating systems. Increasing the heat convection area between an active heat storage-release device and heated indoor air contributed to promoting the heat collecting efficiency. The coil heat exchanger of the heat pump equipment integrated with the heat storage water tank avoided power consumption of circulating water pumps at the heat source and load sides. In doing so, the water temperature of the heat source side had a relatively high temperature, causing the coefficient of performance (COPHp) of the heat pump equipment to range from 5.48 to 6.08, a much higher result than traditional water and ground source heat pumps. However, the discharge pressure and temperature had a tendency of increasing, which resulted in a reduction on COPHp, as the water temperature at load side increased. Over-high temperature requirements went against the system operations of reliability and economy. The exergy loss and efficiency of the overall system was obtained to be 9.77×104 kJ and 48.7% per day. The component which had the largest exergy loss and the lowest exergy efficiency was the active heat storage-release device, followed by heat pump equipment, circulating water pump and heat storage water tank. Exergy loss ratios in this order were 78.7%, 8.3%, 7.7%, and 5.3%. The exergy efficiencies in this order were 25.6%, 38.3%, 75.0%, 88.2%. Among them, the heat transfer between solar radiation and circulating water mostly caused the exergy loss of the active heat storage-release device. Improving production processes could help to decrease the exergy loss to some extent. The exergy losses from the heat pump equipment were mainly caused by the heat exchange losses of the heat exchangers and power consumption by the compressor. Controlling to get the proper evaporating and condensing temperature was the emphasis in optimization. The primary cause of circulating water pump exergy loss was mechanical friction, most likely caused by pump selection. The exergy loss of the heat storage water tank was mainly caused by heat loss during nighttime, making an enhancement in heat-retaining capacity desirable. In the view of the overall system, the components that needed technique optimization most were active when using the heat storage-release device and heat pump equipment. The majority of exergy loss was caused by heat exchange with finite temperature difference, decreasing the temperature difference of heat transfer, reducing the quantity of heat transfer process, and improving production technology. In addition, enhancement of greenhouse insulation could promote exergy efficiency of the system during the heat release period at night. Economy, reliability and thermodynamic properties should be considered synthetically to select the best balance during the optimization of the system and its components. Greenhouse warming is the most important part in greenhouse production in the winter, having various heating methods and uneven performance, and rational use of energy and power savings as imperatives. This study will provide a new thinking for performance evaluation and optimization of systems for greenhouse heating. Source


Zhang Y.,Chinese Academy of Agricultural Sciences | Zhang Y.,Key Laboratory of Energy Conservation and Waster Treatment of Agricultural Structures | Yang Q.,Chinese Academy of Agricultural Sciences | Yang Q.,Key Laboratory of Energy Conservation and Waster Treatment of Agricultural Structures | And 2 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2012

In order to increasing air temperature at night in Chinese solar greenhouse which meet the need of crop growth, a water curtain system was designed to increase the air temperature in Chinese solar greenhouse at night. In this system north wall of Chinese solar greenhouse was regarded as a support, and water was used as media to store and release heat. In the day, when water circuited and passed water curtain, the solar radiation was absorbed in the system and stored the heat in a water tank simultaneously. At night, when water circuited and passed water curtain, the heat was released to the greenhouse and then the air temperature was increased in the Chinese solar greenhouse. The experiments had in last winter showed that the air temperature at night in greenhouse was increased by over 5.4°C and the soil temperature at crop rhizosphere was increased by over 1.6°C, the heat release from water curtain at night in this system was 4.9-5.6 MJ/m 2, the increasing of the thermal storage and heat release of water curtain system in greenhouse made the tomatoes safely grow in winter and the time that cherry tomatoes was came into the market was put ahead by 20 days. It is significant to structure improvement and temperature control in Chinese solar greenhouse. Source


Fang H.,Chinese Academy of Agricultural Sciences | Fang H.,Key Laboratory of Energy Conservation and Waster Treatment of Agricultural Structures | Yang Q.,Chinese Academy of Agricultural Sciences | Yang Q.,Key Laboratory of Energy Conservation and Waster Treatment of Agricultural Structures | And 9 more authors.
Applied Engineering in Agriculture | Year: 2015

To increase the year-round greenhouse production in North China, a sustainable heating method should be developed to increase the night air temperature during the winter in Chinese Solar Greenhouses (CSGs). Solar heating is an inexpensive and effective way to heat greenhouses, and has been investigated by several previous studies. For the present study, a heat collection-heat release (HCHR) system that was attached to the north wall was developed for CSG night temperature improvement. Two experimental greenhouses were located in Beijing, China, with a floor area of 392 m2 each. Environmental parameters (temperature, humidity, heat flux) inside and outside the greenhouse were investigated, including the average solar collection efficiency of the heating system and the pump energy consumption rates. The results showed that the average solar collection efficiency of the system was 52%, which was 1.3 times greater than the reported value of a HCHR system installed in a small CSG. The effective collector absorptivity was 0.59 and heat transfer proved to be by natural convection. The night air temperature in the experimental CSG was increased by 5 ° C on average compared to the reference CSG. To meet the heating demand of the CSG during cold winter nights the release capacity must be increased by 40%. Pump capacity to circulate the water proved to be crucial for energy efficiency. © 2015 American Society of Agricultural and Biological Engineers. Source

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