Greenhouse Air Temperature Research Articles

Grapes (Vitis vinifera) drying by semitransparent photovoltaic module (SPVM) integrated solar dryer: an experimental study

In present research paper, semi-transparent photovoltaic module (SPVM) integrated greenhouse solar drying system has been used for grapes (Vitis vinifera) drying. Based on hourly experimental information namely solar intensity, moisture evaporated, ambient air temperature, grape surface temperatures, relative humidity and greenhouse air temperature etc. heat and mass transfer coefficient for the SPVM drying system have been evaluated. It has been seen that the convective heat transfer coefficients for grapes found between 3.1–0.84 W/m2 K. Also, there is a fair agreement between theoretical and practical mass transfer (moisture evaporated) during drying of grapes with a correlation coefficient (r) and root mean square percentage deviation (e) of 0.88 and 11.56 respectively. Further, nonlinear regression procedure has been used to fit various drying models namely Henderson and Pabis model, Newton’s model, and Page’s model. From the analysis, it was found that Page’s model is best fitted for grapes drying in SPV greenhouse as well as open sun drying. Further, net electrical energy, thermal energy and equivalent thermal energy were found to be 3.61, 17.66 and 27.15 kWh during six days of drying respectively.

Ventilation optimization of solar greenhouse with removable back walls based on CFD

Ventilation is important for crop production and quality in greenhouse cultivation, and vent dimension and position are the basis of greenhouse design. In this study, the effect of the back wall vent dimension on solar greenhouse cooling was investigated by CFD (Computer Fluid Dynamics). The results showed that the average air temperature in a solar greenhouse with removable back walls (RG) was reduced by approximately 1.7°C and the highest temperature dropped by approximately 5.8°C compared with the traditional solar greenhouse with a brick back wall (TG). A 2-D CFD transient simulation model was developed to simulate the indoor temperature and airflow distributions in RGs with different back wall vent sizes. The results suggest that a back wall vent of 1.4m increased inside the ventilation efficiency in a solar greenhouse with removable back walls.

Performance analysis of a partially closed solar regenerated desiccant assisted cooling system for greenhouse lettuce cultivation

In this paper, a novel scheme of a partially closed solar regenerated liquid desiccant assisted evaporative cooling system has been proposed. The objective of the system is to provide suitable conditions inside greenhouses for cultivation of high value temperate crops like lettuce throughout the year in hot and humid climates of tropics and subtropics. The partially closed system re-circulated a fraction of return air from the greenhouse and ventilated a certain amount of ambient air. A forced parallel flow solar regenerator has been used to re-concentrate the weak desiccant solution. A thermal model has been developed to predict the greenhouse air temperature, vapour pressure deficit and the coefficient of performance of the system. The predicted greenhouse temperature has been compared with that of a reference model study available in literature. A very good agreement is established on comparing the temperatures predicted by the two models with a root mean square error of 0.82 °C and average percentage difference being 2.4%. The COP of the cooling system varied between 0.64 and 0.74 for daylong operation in the most humid month of the year (July). The maximum greenhouse temperature predicted using our proposed model was about 27 °C for year round system operation for the place under consideration (Kolkata). The predicted vapour pressure deficits were also in the optimum range. Thus, optimum or viable lettuce growing conditions were predicted by our model all year around. The study consequently reinforces the viability of cultivation of target plantation (lettuce) in hot and humid climates prevailing in the tropical or subtropical countries like India with our model.

Microclimate and agronomical effects of internal impermeable screens in an unheated Mediterranean greenhouse

In unheated greenhouses in mild-winter areas, low-cost, fixed, water-impermeable plastic screens are frequently installed in winter cycles of the vegetable crops more sensitive to fungal diseases. They are used to prevent rain and condensation falling on the crop and to improve the greenhouse air temperature. Two experiments were carried out to quantify how fixed and movable impermeable screens affect microclimate and crop behaviour in an unheated greenhouse in a mild-winter area. The fixed screen improved the night-time temperature and humidity of the air below the screen, and reduced the water condensation on its inner plastic surface or the proliferation of fungal diseases, but did not completely prevent it. Compared to the greenhouse without screen, the movable screen, usually unfolded at night, increased the night-time temperature of the air and the crop, reduced the night-time relative humidity of the air below the screen, prevented the water condensation on the screen or the crop, accelerated melon crop development, and significantly increased early marketable yield of melon fruits and their quality, but it did not substantially affect the substrate temperature, or the total marketable yield of melon fruits. In the comparison of the greenhouse with fixed versus movable screen, no substantial differences were found for a winter cucumber cycle in night-time temperature and relative humidity of the air below the screens, in shoot biomass or in fresh weight of total and marketable cucumber fruits. This can be mainly attributed to the small differences between both treatments in the shortwave radiation reaching the crop.

Influence of light and temperature on flower development in gerbera

Higher intensities artificial lighting are currently being installed for gerbera crops, mainly because of the relatively low costs of high-capacity HPS lamps with a higher light output. In addition, LED lighting systems are becoming even more efficient. In order to gain insight on increasing production with various high-capacity lighting systems, an experiment was performed with three lighting systems. Gerbera, cv. Kimsey was grown under HPS, hybrid (combination of HPS and LED) and under a LED lighting system in three greenhouses of 144 m2. Different light and temperature set points were used to investigate the effects of the light sum and light spectrum in combination with greenhouse air temperature and plant temperature on growth, development and production. A lower plant temperature under HPS lighting with lower air temperatures was expected to result in more generative growth, but this did not appear to be the case. Even though, gerbera under HPS during the winter months produced more flowers, but overall the differences in production under HPS and LED lighting were small. Although growers suspected that under LED-lighting, either a hybrid or LED-only lighting system, botrytis infection might increase due to the lack of radiative heat for the crop, no increase in botrytis infection was observed. Additional measurements of air and plant temperature under HPS and LED lighting were performed to investigate the influence of both factors on the initiation and development rate of gerbera flowers. These results are presented and discussed in the light of optimizing cultivation conditions for gerbera.

Performance Study of a Floricultural Greenhouse Surrounded by Shallow Water Ponds

In the present paper, an innovative low energy-intensive evaporative cooling system has been proposed for greenhouse application in near-tropical regions dominated by hot climate. The system can operate under dual- ventilation mode to maintain a favourable microclimate inside the greenhouse. A single ridge type un-even span greenhouse has been considered, targeting a few species of Indian tropical flowers. The greenhouse has a continuous roof vent as well as adjustable side vents and is equipped with exhaust fans on top and roll-up curtains on the sides. The greenhouse is surrounded by shallow water ponds outside its longitudinal walls and evaporative surfaces partially cover the free water surface. Inside the pond, low cost evaporative surfaces are so placed that they form air channels. Thus, outside air flows through the channels formed by the wetted surfaces over the water surface and undergoes evaporative cooling before entering the greenhouse. A simplified theoretical model has been presented in this paper to predict the inside greenhouse air temperature while ambient weather data are used as model inputs. The study reveals that during average radiation periods, the greenhouse can depends solely on natural ventilation and during peak radiation hours fan-induced ventilation is needed to maintain the required level of temperature. It is seen that under dual-ventilation mode greenhouse, temperature can be kept 3-6 oC lower than ambient temperature when saturation effectiveness is 0.7 and with 75% shading.Article History: Received February 25th 2017; Received in revised form April 14th 2017; Accepted May 4th 2017; Available onlineHow to Cite This Article: Misra, D. and Ghosh, S. (2017) Performance Study of a Floricultural Greenhouse Surrounded by Shallow Water Ponds. International Journal of Renewable Energy Development, 6(2), 137-144.https://doi.org/10.14710/ijred.6.2.137-144

Modelling and experimental verification of the thermal performance of an active solar heat storage-release system in a Chinese solar greenhouse

An active solar heat storage-release (AHS) system that stores solar energy in a water storage tank can supplement heat to raise the air temperature in Chinese solar greenhouses (CSGs) during cold winter nights. To quantify such heat transfer processes and to improve the performance of AHS systems, a tank temperature model was developed. The model was calibrated and validated, and it can predict water temperatures in the storage tank with an average accuracy of 0.4 °C. The model was used to determine the required solar collector area and storage tank volume under various desired air temperatures in different greenhouses. In two cases, greenhouses with a ground area of 272 m2 and roughly 62 m2 of solar collectors were installed to maintain temperatures above 12 °C under Beijing climate conditions. To facilitate a 1 °C increase in the air temperature set-point, approximately 2 m2 of additional solar collectors and 0.1 m3 of additional storage tanks are needed.

Evaluation of optimal water flow and temperature in response to outdoor air temperature in plastic greenhouse with recirculated water curtain system

This study evaluated the optimal supply water temperature and flow rate in response to the outdoor air temperature in order to maintain a target indoor air temperature and minimize the amount of energy required to reheat a recirculated water curtain in a plastic greenhouse. This paper proposed a multiple regression model that estimated the indoor air temperature using the outdoor air and the inlet water temperatures, as well as the water flow rate, as independent variables. We also established a multiple regression model that estimated the average amount of energy required to reheat the recirculated water curtain. To this end, the study analyzed and quantified a reasonable inlet water temperature and water flow rate in response to the outside air temperature using isothermal and iso-energy curves. The results indicated that maintaining a higher water flow rate was preferable to maintaining a higher inlet water temperature for cultivation purposes.

COMPUTATIONAL STUDY OF CANARY GREENHOUSE SIDE WALL AND ROOF VENTS OPENING EFFECT ON NOCTURNAL AIRFLOW AND CLIMATE PATTERNS

The following paper presents a Computational Fluid Dynamic (CFD) comparative study ofthe effect of side wall and roofs vents openings on canary greenhouse airflow circulation andclimate distribution under different ventilation processes. The investigation was conducted ina one hectare canary greenhouse type, which is the most widespread type in the wholeMediterranean and along the Atlantic coast area of Morocco, especially in souss vally region.The simulations were performed with the commercial code CFD2000 based on the solution ofthe partial differential equations, which describe the flows, and was obtained by discretizingthe space and time and solving the transport equations on the spatial grid as differenceequations, used a finite volume discretization. The standard two equations k-ε model wasused to describe the turbulent transport. The influence of external factors such the covertemperature, the wind speed, on the flow was simulated by boundary conditions, these valueswere obtained from experimental results. Simulations were conducted with a fixed windspeed equal 1.05 m/sec, tomato crop rows oriented north-south and the ventilation openingsare continuous and equipped with insects screen type 20/10. Results reveal that ventilationopening arrangements strongly affects the greenhouse wind speed, which can generate aheterogeneous climate, especially during daytime. But in the other hand, results confirm thatthere is no significant effect of the side wall vents opening on canary greenhouse airtemperature and humidity fields.

Membership function model for defining optimality of vapor pressure deficit in closed-field cultivation of tomato

Estimation of plant’s evapotranspiration (ET) or water loss to the atmosphere depends on the vapor pressure deficit (VPD) of the closed-field environment (greenhouse). The objective of this work was to develop a membership function model for defining optimal VPD of greenhouse air for tomato cultivation (Lycopersicon esculentum) at different growth stages (GS) and light conditions (sun, cloud, night). Mathematical descriptions of a peer-reviewed published growth response (GR) model for optimal greenhouse air temperature (T) and relative humidity (rH) were derived and implemented in a computer program. An incremental algorithm was written in MATLAB© based on definitive concepts in VPD equations and the GR model. Non-linear regression was applied to describe mathematical relationship between the incremented outputs of the model and the calculated VPD values (R2=0.999 to 1). Results were validated with three published literatures and were shown to be capable of exploring optimal levels of VPD by means of real numbers between 0 and 1. This study can contribute to knowledge-based information and decision support systems in greenhouse climate control and management by quantifying comfort level of microclimate.

Measuring optimality degrees of microclimate parameters in protected cultivation of tomato under tropical climate condition

The objective of this work was to integrate a membership function growth response model for measuring optimality degrees of air temperature (T) and relative humidity (RH) in a tropical greenhouse planted with tomato (Lycopersicon esculentum). Experiment was carried out during spring growing season of 2015, for a total of 147days, in an insect-proof net-screen covered greenhouse in tropical lowlands of Malaysia. An analysis framework with a custom-designed hardware/software was developed for interfacing with the model and data processing. Raw data were separated into three groups of growth stages according to the original model, as early growth, vegetative growth, and flowering to mature fruiting growth stages. For each collected T and RH, an optimality degree denoted by Opt(T) and Opt(rH) with value between 0 and 1 was calculated. Preliminary results showed that maximum T and RH belong to the mature fruiting stage (39.7°C and 98.9%), and were recorded respectively at sun and cloud light conditions. The minimum and maximum values of Opt(T) were equal to 0.16 and 0.95 at the early growth stage, 0.42 and 0.92 at the vegetative stage, and 0.27 and 0.75 at the flowering to mature fruiting stage. These values for Opt(RH) were 0.62 and 1, 0.31 and 0.9, and 0.46 and 1, respectively. Further analysis of results showed that comparison between averaged optimality degrees in different light conditions (night, sun, cloud) depends on the specific growth stage. For example, during early growth stage, night hours had the highest Opt(T) and Opt(RH), while at the vegetative growth stage, Opt(T) did not vary significantly with light conditions. The presented framework contributes to knowledge-based information in greenhouse climate control and management by measuring optimality degrees for addressing specific hours, light conditions and growth stages associated with maximum and minimum cooling requirements.

Improvement of greenhouse microenvironment and sweetness of melon (Cucumis melo L.) fruits by greenhouse shading with a new kind of near-infrared ray-cutting net in mid-summer

In melon (Cucumis melo L.), low soluble solids content (SSC, °Brix) of midsummer-harvested fruits represents a problem for growers. We developed two new near infrared ray (NIR)-cutting nets that combine high visible light (VL) transmittance and strong absorption in the NIR region (700–2500nm) to improve the sweetness of melon fruits harvested in mid-summer. The first type, NIR-cut net A, had a VL transmittance of 69.2% and a NIR absorbance of approximately 45%. The other type, NIR-cut net B, had a VL transmittance of 61.6% and a NIR absorbance of 55%. These NIR-cut nets decreased the temperature by approximately 9°C compared to the control when using a metal halide lamp for artificial lightning in laboratory experiments. In greenhouse experiments, the air temperature of the control greenhouse reached 38°C at noon on a sunny day in midsummer, while the temperature was 34°C in the greenhouses shaded with NIR-cut nets in the same conditions. Thermal imaging indicated that our NIR-cut nets also reduced the leaf temperature of greenhouse-grown plants by approximately 5°C on a sunny day in midsummer. The use of the NIR-cut nets during the fruit maturation period did not affect the size of fruits, while still increasing their sugar accumulation. The Brix values of fruits grown in greenhouses covered with NIR-cut net A or B were 13.8 and 14.0°, respectively, higher than that of control (13.4°). Sucrose concentration of fruits shaded with NIR-cut net A or was 81.3mgl−1, significantly higher than that of the control (68.5mgl−1), while it was 71.4mgl−1 for fruits grown in the greenhouse shaded with NIR-cut net B. These results demonstrate that NIR-cut net A is a valuable tool for improving the sugar content of greenhouse-grown melon fruits in midsummer.

棟傾斜の異なる農業用ハウスにおける気温分布

棟傾斜の異なる農業用ハウスにおける気温分布

Study on heat transfer characteristics of straw block wall in solar greenhouse

A new type of solar greenhouse with straw block north wall was developed. The heat transfer characteristics, temperature, heat absorption, release and loss of its north wall were investigated by theoretical and experimental analyses and the economic and environmental evaluations of north walls were carried out. The thermal storage coefficient of heat storage layer, the total thermal inertia index and the total thermal resistance of the new type straw block north wall (ST) were 38.5%, 13.9% and 25.4% higher than that of porous clay block north wall (CL), respectively and the average air temperature of Chinese solar greenhouse with ST was 0.7°C higher than that of Chinese solar greenhouse with CL on cloudy day. The temperature of heat storage layer as well as the heat absorption and release of ST were higher than that of CL. The heat loss of ST was less than that of CL. Compared to CL, the cost, energy consumption and CO2 emissions of ST were reduced 26.3%, 81.7% and 29.4%, respectively. ST had better thermal properties and could improve thermal environment of greenhouse. Besides, it was low-cost and environmentally friendly.

Performance of Active Heat Storage-Release Unit Assisted with a Heat Pump in a New Type of Chinese Solar Greenhouse

Abstract. Chinese Solar Greenhouses (CSG) rely solely on solar radiation for heating to achieve energy savings. However their land utilization efficiency is only 30% to 48%. A new type of solar greenhouse was designed where an active heat storage-release system (AHS) was added to replace the north wall and the greenhouse ridge was north-south oriented. In this way, the spacing between greenhouses can be shortened and the land utilization efficiency can be increased up to 91%. To further improve the thermal performance of the new type of greenhouse, a heat pump (HP) was incorporated in the AHS system to form a new design defined as AHS-HP. The HP was used to regulate the water temperature in three storage tanks that served as the heat reservoir for the AHS system. By regulating the water temperatures, the heat collection and releasing can be done more efficiently than without HP. Two new types of greenhouses located in Beijing, one with AHS-HP (experimental greenhouse) and one without (reference greenhouse), were compared in terms of indoor air temperature, relative humidity (RH), and electricity consumption. Nighttime air temperature in the experimental greenhouse was increased from 2°C to 4.5°C, on average, compared with the reference greenhouse. The coefficient of performance (COP) of the HP was 4.8 to 6.3 during the daytime and 3.1 to 4.9 at night. The COP of the AHS-HP system was 3.2. The average daily electricity consumption of the AHS-HP is 0.04 kWh m-2 day-1. The low cost AHS-HP has the potential to be applied in solar greenhouses if it is properly designed and operated.

Heliogreenhouse Ground Temperature Forecasting Technology Research

Based on the comparison and observations of the internal and external meteorological conditions of the heliogreenhouse, BP neural network, stepwise regression and energy balance principle were used, respectively, to construct the greenhouse air temperature prediction model. The results showed that although the BP neural network- based prediction model had a high forecasting accuracy, due to the comparatively different growth characteristics of cultivated crops, there was a lack of wide adaptability of services; the mechanism of the prediction model constructed by the energy balance principle was strong, but it was difficult to obtain the relevant parameters and had a poor prediction accuracy and a short effective service period; the greenhouse temperature prediction model constructed by the stepwise regression had a comparative advantage over the previous two models and the forecasting effectiveness can be for the next 1-7 days.

Incremental Auto Regressive Prediction Models with External Variables of Greenhouse Air Temperature for Control Purposes

The impact of actuators should be considered in the prediction modeling of greenhouse air temperature. In this paper, the operating state of a greenhouse was divided into five sub-states based on the on-off characteristic of actuators. A group of novel incremental auto regressive models with external variables (IARX models) suitable for the five operat-ing sub-states were deduced from the mechanistic modeling of greenhouse air tempera-ture. The new IARX models have fewer coefficients than other known ARX models. In or-der to validate the IARX prediction models, the related environmental factors of a glass greenhouse were measured. The prediction results of the IARX models were compared with two typical ARX models. The maximum prediction errors and the mean square errors of the IARX models, under the three operating sub-states of passive state(all actuators are not working), mechanical ventilation and fan-pad cooling, are 0.1°C, 0.14°C, 0.7°C, and 0°C, 0.3°C, 0.4°C, respectively. The prediction results are much better than those of one compared model, while similar with the other.

Dynamic Mechanistic Modeling of Air Temperature and Humidity in the Greenhouses with on-off Actuators

The mechanistic models of greenhouse microclimate can be used as the simulators for designing new control strategies. According to the on-off characteristics of the actuators in greenhouse in China, the operating state of a greenhouse was divided into several sub-states, and new mechanistic models of greenhouse air temperature and humidity were built. In order to validate the new models, the relevant environmental factors under three sub-states were measured in a glass greenhouse. The mean square error of greenhouse air temperature and relative humidity are 0.57°C and 2.8% respectively. These results indicate that the new models are suitable for the development of energy-saving control strategies of greenhouse microclimate in future.

Thermal model development and performance analysis of a solar photovoltaic supported greenhouse dryer

In this paper, a novel scheme of a standalone grid independent solar greenhouse dryer has been proposed. A thermal model for forced convection solar greenhouse drying of Peas has been developed. The model takes hourly values of climate data for the chosen location along with certain other data related to the product and the greenhouse as input and predicts the hourly values of product temperature, greenhouse air temperature, convective heat transfer coefficient and the amount of moisture evaporated from the product. The performance of the dryer has been analysed for a representative day in the month of December for the climatic condition of Kolkata, India (22.32°N, 88.20°E). To make the system grid independent, a photovoltaic-based power system with battery backup has been designed. The performance of the integrated power system has been analysed for all the seasons of a climatic cycle. Finally, an economic analysis has been included to calculate the payback period of the proposed dryer.

Thermal model development and performance analysis of a solar photovoltaic supported greenhouse dryer

In this paper, a novel scheme of a standalone grid independent solar greenhouse dryer has been proposed. A thermal model for forced convection solar greenhouse drying of Peas has been developed. The model takes hourly values of climate data for the chosen location along with certain other data related to the product and the greenhouse as input and predicts the hourly values of product temperature, greenhouse air temperature, convective heat transfer coefficient and the amount of moisture evaporated from the product. The performance of the dryer has been analysed for a representative day in the month of December for the climatic condition of Kolkata, India (22.32°N, 88.20°E). To make the system grid independent, a photovoltaic-based power system with battery backup has been designed. The performance of the integrated power system has been analysed for all the seasons of a climatic cycle. Finally, an economic analysis has been included to calculate the payback period of the proposed dryer.