Thermal Environment Of Greenhouse Research Articles

Heat storage and release performance of solar greenhouses made of composite phase change material comprising methyl palmitate and hexadecanol in cold climate

Solar greenhouses play a crucial role in winter crop cultivation in the cold regions of China. However, adverse weather conditions such as low temperatures can negatively affect their production. Therefore, improving the greenhouse thermal environment and energy utilisation is crucial for optimising greenhouse productivity. One effective method of storing energy is phase change technology. In this study, melt blending was used to prepare composite phase change materials (CPCMs), with methyl palmitate and hexadecanol as raw materials. In addition, ceramsite was encapsulated with a styrene-acrylic emulsion to form a shape composite phase change material (SCPCM). The results showed that the latent heat of phase change of the CPCMs was 221 J/g, with an initial phase change temperature of 23.48 ℃. The encapsulation of the SCPCM with a styrene-acrylic emulsion significantly reduced leakage. Phase-change ceramsite concrete slabs were developed by integrating the SCPCM into concrete. These slabs were used to construct phase-change and non-phase-change greenhouses. A temperature-testing system was installed in the greenhouses to examine the temperature variations and distributions under typical sunny and cloudy conditions. Results revealed that compared with the control greenhouse, the phase-change greenhouse exhibited a decrease of 3.0 ℃ in the maximum indoor temperature during sunny days and an increase of 3.2 ℃ in the minimum indoor temperature at night. This study highlights the effective temperature control capabilities of phase-change ceramsite concrete slabs for improving energy utilisation and provides valuable theoretical and technical insights for the future utilisation and widespread adoption of phase-change greenhouses.

Optimized model predictive control for solar assisted earth air heat exchanger system in greenhouse

Agricultural greenhouses play a crucial role in addressing the threat of climate change to agricultural systems. The greenhouse systems control exhibits nonlinear characteristics and large lag, both affecting the regulation of the greenhouse thermal environment. In this paper, a control strategy was designed to set the dynamic reference value of the control objective of the greenhouse model, considering factors such as solar radiation and the heating capacity of water body. A complete greenhouse model was developed using TRNSYS, and then the model predictive control building and optimization were implemented through MATLAB. The control effects of traditional proportional-integral-differentiation control, initial model predictive control, and optimized model predictive control were compared. The results showed that the regulation of greenhouse temperature was improved by 10.6 % in the coldest mouth compared to the conventional proportional-integral-differentiation control by the optimized model predictive control. During a typical cold month, the violation of constraints was reduced by 29.7 % by dynamically setting the target of the greenhouse with the optimized model predictive control. The performance of greenhouse climate control is enhanced by the proposed optimized model predictive control method, ensuring a stable regulation of the crop growth environment.

Comparative Analysis of the Filling Mass of Vertical Heat Exchanger Tubes on the Thermal Environment of Arched Greenhouses

The greenhouse’s energy consumption is a major limiting factor for output and development. To address this, it is necessary to adopt green and low-carbon heating technologies to replace traditional fuels. This will not only help conserve energy but will also reduce emissions, thereby improving the thermal environmental conditions for agriculture. This paper aims to research and develop a vertical heat exchange tube array device specifically designed for greenhouses. The focus is on enhancing the passive heat absorption and heat storage efficiency of the device and its influence on the thermal environment of the greenhouse. In order to improve the heat absorption and storage efficiency of the heat exchanger device and its impact on the greenhouse thermal environment, experimental comparative analysis was conducted using air, water, and phase-change materials as working fluids inside the pipes. Through a combination of experiments and simulations, it was verified that the heat exchanger device is capable of actively regulating the greenhouse thermal environment. The results show that heat exchangers of all three types of working fluids can effectively improve the stability of soil temperature and play a “shifting the peak and filling the valley” role in regulating the indoor air temperature while positively regulating the relative humidity of the air. Notably, when the working fluid is a phase-change material, it has the most significant impact on the thermal environment of the greenhouse.

CFD Analysis of Solar Greenhouse Thermal and Humidity Environment Considering Soil–Crop–Back Wall Interactions

In the study of solar greenhouses, microclimate, soil, and back walls have an important influence on the greenhouse thermal environment because of their good heat storage and release characteristics. The transpiration of crops makes indoor humidity increase sharply, which is the main factor affecting indoor humidity distribution. Therefore, it is of great significance to grasp the microclimate change law of solar greenhouses and study the coupling effect of thermal and humidity environment. In this paper, based on computational fluid dynamics (CFD), a three-dimensional model of the thermal and humidity environment of a solar greenhouse is established, and the indoor temperature and humidity distribution under the influence of soil, crops, and back walls are considered. The CFD model initialization uses binary fitting functions to fit the temperature distribution of soil, back wall, and air. The distribution law of the temperature field and relative humidity field of the solar greenhouse under three different working conditions is simulated, that is, the insulation is uncovered and the ventilation window is closed during the day (G1), the insulation is uncovered and the ventilation window is opened during the day (G2), and the insulation is put down and the ventilation window is closed at night. (G3). The results show that the simulation results are in good agreement with the actual results under the three working conditions, and this paper can provide a reference for the improvement of the greenhouse structure and environmental regulation.

Study on the Influence of Solar Array Tube on Thermal Environment of Greenhouse

The stratum and microenvironment temperatures in a greenhouse are important factors that affect crop yield. In order to solve the problem of temperature imbalance caused by solar radiation in greenhouses, this paper proposes the application of a solar radiation array tube in a greenhouse. By adding water or phase change materials to the array tube, the influence of the array tube on the formation and microenvironment temperature changes was studied, and a 10-day test was carried out. A test group and control group were set up to monitor test results, and the ground was divided into six areas. The depths of each area were 10 cm, 30 cm, and 50 cm, and the heights of the greenhouse centers were 0 cm, 30 cm, 60 cm, 90 cm, 120 cm, 150 cm, and 180 cm. Via an analysis of the test results obtained for the formation and microenvironment temperature, the arrangement of the array tube was found to exert a constant temperature regulation effect on the microenvironment of the greenhouse at a formation depth of 10 cm and was able to improve this formation depth to a certain extent. The temperature at 30 cm and 50 cm plays a positive role in building a good vegetation growth environment.

Performance study of an active solar water curtain heating system for Chinese solar greenhouse heating in high latitudes regions

Thermal preservation and heat storage performance cannot be fully realized in the traditional design of the Chinese solar greenhouse (CSG) north wall. To increase greenhouse thermal efficiency and maximize solar energy utilization, researchers have divided greenhouse into the independent solar heating system as well as the independent north wall heat preservation system. The wall-mounted solar heating system used water as a medium with the characteristics of chemical stability, liquidity preference and high specific heat capacity for heat transport and storage have been developed. To explore and create a better suitable greenhouse thermal environment, we proposed an active solar water curtain heating system with a non-woven fabric liner between the two-layer polyethylene film coated with black water-based paint. The greenhouse heating load was estimated based on energy balance theories during the nighttime and the water mass for heat transfer was calculated. Field tests were carried out to verify theories and investigate the thermal performance of the system. The average heat collection ratio was about 80.1 % and 63 % of the stored heat was released at night with the 3.6 °C improvement in interior air temperature and 6.6 % reduction in interior air relative humidity. The heating COP of the system was 12.5 on average and the energy saving rate was 92 %. Besides, the greenhouse with the solar heating system can save energy consumption cost about 348 USD yr−1 as the cost of solar heating system can be repaid in 1.4 years. The system combined the energy balance method to design with more efficient thermal performance, energy conservation, utilization of solar energy and affordable payback period thereby creating a suitable thermal environment in the Chinese solar greenhouse, which is recommended for practical application.

Study on the thermal performance of a new type of latent heat storage unit (LHSU)

In order to improve the utilization rate of solar energy, accelerate the heat storage rate. A new type of shell-and-tube latent heat storage unit is proposed, which is mainly composed of high endothermic film, eccentric shell-and-tube heat storage unit, fan and PCM. The unit and two greenhouses were built to study their thermal performance under four cases. The experimental results show that under the passive case (fan not run), and the maximum temperature and heat flux of LHSU sunny surface can reach 52.4 °C and −302.5 W/m2. Compared with ordinary greenhouse, the average indoor air temperature at night in the PCM greenhouse can be increased by 1–1.4 °C, and the indoor air temperature fluctuation can be reduced by 0.5–2 °C. Under the three active cases, the average indoor air temperature at night in the PCM greenhouse can be increased by 1.3–2.1 °C, 1.6–2.6 °C and 0.8–1.2 °C, respectively, the indoor air temperature fluctuation can be reduced by 1.5–2.7 °C, 1–2.6 °C and 0.7–1.9 °C, respectively. When the fan runs only at night, the unit can save 33.3% of the electric energy as compared with all-day operation, which is a better choice for further energy saving. The LHSU shows excellent energy saving performance and can effectively improve the thermal environment in greenhouse. It can also be used for energy storage in buildings.

Thermal environment model construction of Chinese solar greenhouse based on temperature–wave interaction theory

Chinese solar greenhouse (CSG) is an important energy-saving building to ensure the winter production of crops, but it still faces the problem of unbalanced supply and demand between actual thermal performance and crop temperature demand. The purpose of this study is to establish the relationship between greenhouse thermal environment simulation and thermal performance design and to put forward specific thermal performance requirements for the main heat storage components (walls) in the greenhouse design stage. Therefore, this study proposed a method to construct the thermal environment fluctuation model of Chinese solar greenhouse based on temperature-wave interaction theory. The method used dimensional analysis method to comprehensively analyze the related physical quantities of greenhouse thermal environment, explored the temperature fluctuation interaction among indoor air, energy storage wall and outdoor air, and constructed the thermal environment fluctuation model of Chinese solar greenhouse. Finally, the thermal environment fluctuation equation of Chinese solar greenhouse was established under the external climatic conditions in Xi'an, Shaanxi Province, and verified by the measured data of the experimental greenhouse. The experimental results show that the mean absolute error (MAE) between the predicted and measured indoor air temperature is 0.66 °C, the root mean square error (RMSE) is 1.04 °C, and the determination coefficient (R2) is 0.9956 (n = 2822). The model and equation accurately described the interaction between greenhouse internal components and the external greenhouse environment. The study put forward specific thermal performance design requirements for the main heat storage components (walls) in greenhouse, and also provided a new research method for the thermal environment model of Chinese solar greenhouse.

Design and experiment of Internet-of-Things cooling system in glass greenhouse based on computational fluid dynamics simulation

In the summer heat season, the performance of the greenhouse cooling system is the key factor in greenhouse crop pollination and fruit formation. Scientific design of greenhouse cooling systems and intelligent control of cooling equipment can ensure the normal growth of greenhouse crops and save energy. In this paper, the thermal equilibrium theory of the greenhouse is analysed, and the glass greenhouse thermal environment model is established based on the theory of engineering thermophysics combined with greenhouse environmental regulation. This study uses computational fluid dynamics simulation technology to simulate the change of the greenhouse temperature field, perform experimental analysis, and scientifically design an intelligent greenhouse temperature control cooling system. It provides a reference for designing an internet of things cooling system in a glass greenhouse in theoretical analysis and engineering practice.

Thermal Environment Regulating Effects of Phase Change Material in Chinese Style Solar Greenhouse

Phase change material (PCM) can store and release heat within a certain temperature range during the phase transitions. Compared with sensible heat material, latent heat phase change material (PCM) is very attractive, because of its high-energy storage density and isothermal behavior during the phase change process. This paper attempts to research the application of PCM in Chinese style solar greenhouse. The PCM we used is butyl stearate with the phase change temperature about 18°C, and spinach of F1 from Italy is chosen to be the test plant. The research is a contrast test with the same two greenhouse models, one is installed with PCM and the other is not. By recording the temperature with T type thermocouples on the different set-points and observing the growth situation of the plants in two greenhouses, we can recognize the effect of the PCM on the thermal environment of greenhouse.

Modeling of Diurnal Change of Greenhouse Thermal Environment and its Hand Calculation

Modeling of Diurnal Change of Greenhouse Thermal Environment and its Hand Calculation

Temperature Effects of Passive Greenhouse Apparatus in High-Latitude Climate Change Experiments

1. Passive greenhouse apparatus is commonly used to investigate the in situ biological response of terrestrial communities to global warming. 2. Although close conformity of greenhouse treatment effects to general circulation model (GCM) scenarios is widely claimed, no proof of such a relationship has yet been published. 3. Here, the relationship between passive greenhouse thermal environment and future climate conditions is considered using temperature data collected from within and without greenhouses deployed in the maritime Antarctic. It is revealed that in terms of thermal extremes, diel and annual variation, and overall distribution across the temperature spectrum, such apparatus achieves only poor simulation of GCM forecasts. 4. During summer, greenhouses induce an amplified daily range of temperatures, elevated maxima and accelerated rates of change. 5. During spring and autumn, diel temperature variation continues inside the green-houses while snow cover protects the controls. 6. During winter, an inverse treatment effect occurs, in which the relative depth of snow cover causes lower temperatures in greenhouses than in controls. 7. These treatment effects differ significantly from GCM climate predictions. Changes recorded in the composition, structure and function of greenhouse biota may thus be artefacts of the methodology. 8. Thorough a priori testing of greenhouse treatment effects is recommended for future climate change studies that are to be conducted in environments subject to seasonal snowfall, solar elevation and day length

A design procedure for an air-type solar heating system for greenhouses

System performance, crop yield and cost are the major criteria for design optimization of a greenhouse solar heating system. While experimental study and evaluation of each plausible design are cost-prohibitive, resorting to detailed computer simulations would enable the prediction of system performance at specified locations. This paper discusses the development of a design procedure for greenhouse space heating. A simulation model that describes the greenhouse thermal environment and thermal storage, is verified by short-term actual data. Monthly average meteorological data were then used as inputs to the computer program for predicting long-term system performance, as indicated by the fraction of annual heating load supplied by solar energy. Results from simulation runs suggested that monthly solar heating fraction may be correlated with a dimensionless variable that involved mean daily solar radiation on an outside horizontal surface, total capture factor of the greenhouse cover, and night-time heat load. Such correlation was presented as a preliminary guidline for designers. Crop yield and economic analyses have to be carried out before selecting an optimum design for a particular location.

A Dynamic Thermal Performance Simulation Model of an Energy Conserving Greenhouse With Thermal Storage

ABSTRACT A transient rather than steady-state analysis is required for accurate prediction, modification and control of a greenhouse thermal environment. In this study a dynamic mathematical model for predicting temperatures and moisture levels in a solar-assisted energy conserving circular (hoop) type greenhouse was developed. The greenhouse used in the development and testing of the model had added thermal mass in the form of water located under plant benches. Active and passive forms of thermal storage were investigated. Other energy conservation features incorporated in the test greenhouse included arch shutter thermal insulation applied in-between the double-layered inflated transparent plastic covers at night to reduce heat losses or heat gain. The greenhouse thermal model was programmed on a digital computer and comparisons of the greenhouse measured variables with model predictions showed a high degree of correlation.

A Time Dependent Analysis of Greenhouse Thermal Environment

ABSTRACT RISING fuel prices are having a significant effect on further development of the greenhouse industry. This has directed research efforts along two paths: (a) improving the greenhouse structure to reduce energy losses, while maintaining a desirable growth environ-ment; and (b) developing alternate energy sources such as solar, wind, waste heat from power plants, and geo-thermal energy to meet greenhouse heating demand. Although a number of greenhouse thermal environ-ment models (analytical and numerical) are available at present, each model is restrictive in its applicability. A more general time-dependent analysis of greenhouse thermal environment is desirable to detect and control thermal stress on plants, to design so as to reduce heat-ing and cooling requirements, and to consider intermit-tent sources of heating and cooling such as solar and wind.