Effect of Greenhouse Cladding Materials and Thermal Screen Configuration on Heating Energy and Strawberry (Fragaria ananassa var. “Seolhyang”) Yield in Winter

Strawberry cultivation depends on environmental factors, making its cultivation in the greenhouse a challenge in the winter. This study investigated the most appropriate greenhouse cladding material and thermal screen configuration for strawberry production in the winter by considering greenhouse air temperature, relative humidity (RH, vapor pressure deficit (VPD, and solar radiation (SR). Two gothic greenhouses with different cladding materials and thermal screen configurations, namely, the single-layer greenhouse and double-layer greenhouse, were used for strawberry cultivation. The greenhouse microclimate was controlled by natural ventilation aided with circulating fans and boilers. Strawberries were planted on 5 greenhouse benches, 660 stands per greenhouse. Daily environmental parameters were recorded and processed into daytime and nighttime. The impacts of cladding material-thermal screen configurations on temperature, RH, VPD, and SR, and the subsequent effect on strawberry yield in both greenhouse systems, were evaluated. Comparing the environmental parameters recorded in the single-layer and double-layer greenhouse showed that VPD and SR were significantly different in the daytime, whereas RH and VPD were significantly different in the nighttime. The post hoc test further showed that RH, VPD, and SR in both greenhouses were significantly different. The significant difference in RH and VPD can be attributed to the inner layer of polyethene in the double-layer greenhouse, which sealed up the pores of the thermal screen, resulting in humidity buildup, causing a lower VPD than in the single-layer greenhouse. The single-layer greenhouse yield was 14% greater than the double-layer greenhouse yield and can be attributed to the higher daytime VPD and lower RH achieved in the single-layer greenhouse at night. The study established that though the single-layer greenhouse system was cost-effective regarding construction, the operating cost of the single-layer greenhouse was higher than that of the double-layer greenhouse.

Effect of glazing configuration as an energy-saving strategy in naturally ventilated greenhouses for strawberry (Seolhyang sp.) cultivation

Strawberry cultivation is highly dependent on environmental parameters and energy during the winter. Two gothic greenhouses with different glazing material combinations, polyolefin–thermal screen (PoTS) and polyolefin–thermal screen–polyethylene (PoTSPe), were used for strawberry cultivation. The energy-saving capabilities of the two configurations and their impact on the microclimates of the greenhouses were investigated. The temperature, relative humidity, vapor pressure deficit, leaf temperature, carbon dioxide concentration and solar radiation over the experimental period in the PoTS greenhouse were 13.0 ± 2.3°C, 75.8 ± 6.5%, 0.4 ± 0.1 kPa, 13.6 ± 1.7 °C, and 168.8 ± 82.3W/m2, respectively, whereas those of the PoTSPe condition were 13.1 ± 2.3 °C, 80.0 ± 5.7%, 0.3 ± 0.1 kPa, 13.5 ± 1.6 °C, and 183.1 ± 90.5 W/m2. The mean fuel consumption by the PoTS and PoTSPe greenhouses were 5.5 and 3.5 L, respectively. The performance analysis shows that both greenhouses were able to maintain the environmental parameters and leaf temperature within the recommended ranges, although more energy was consumed in the PoTS. More yield was obtained in the PoTS greenhouse, however, not significantly different from PoTSPe yield.

Numerical evaluation of passive strategies for nocturnal climate optimization in a greenhouse designed for rose production (Rosa spp.)

In passive plastic greenhouses that do not have heating systems, the phenomenon of thermal inversion occurs, which means that the temperature inside the greenhouse is lower than the outdoor environment; therefore, the plants are exposed to thermal conditions that are unsuitable for production. The aim of this work was to evaluate passive air climatization alternatives seeking to optimize the nocturnal microclimate of a multi-tunnel Gothic greenhouse projected for rose production in Bogota savannah. The experimental approach included the use of a CFD-2D simulation model successfully validated by recording and archive of temperature data in a greenhouse. A total of 24 steady-state simulations were developed that included 3 nighttime temperature values, 2 sky conditions and 4 greenhouse configurations. The results showed that under the clear sky condition there was a thermal inversion with a value of −0.53 and −1.11 °C for the standard night-time greenhouse configuration. The installation of a thermal screen and porous mesh in the fixed roof vents allowed to control the presence of thermal inversion under clear sky conditions and optimizing the indoor temperature value in the greenhouse under cloudy sky conditions.

Optimization of Greenhouse Thermal Screens for Maximized Energy Conservation

In this work, we proposed a Building Energy Simulation (BES) dynamic climatic model of greenhouses by utilizing Transient System Simulation (TRNSYS 18) software to study the effect of use of different thermal screen materials and control strategies of thermal screens on heat energy requirement of greenhouses. Thermal properties of the most common greenhouse thermal screens were measured and used in the BES model. Nash-Sutcliffe efficiency coefficients of 0.84 and 0.78 showed good agreement between the computed and experimental results, thus the proposed model appears to be appropriate for performing greenhouse thermal simulations. The proposed model was used to evaluate the effects of different thermal screens including; Polyester, Luxous, Tempa, and Multi-layers, as well as to evaluate control strategies of greenhouse thermal screens, subjected to Daegu city, (latitude 35.53 °N, longitude 128.36 °E) South Korea winter season weather conditions. Obtained results show that the heating requirement of greenhouses with multi-layer night thermal screens was 20%, 5.4%, and 13.5%, less than the Polyester, Luxous, and Tempa screens respectively. Thus, our experiments confirm that the use of multi-layered thermal screen can reduce greenhouse heat energy requirement. Furthermore, screen-control with outside solar radiation at an optimum setpoint of 60 W·m−2 significantly influences the greenhouse’s energy conservation capacity, as it exhibited 699.5 MJ · m−2, the least energy demand of all strategies tested. Moreover, the proposed model allows dynamic simulation of greenhouse systems and enables researchers and farmers to evaluate different screens and screen control strategies that suit their investment capabilities and local weather conditions.

Movable Thermal Screen For Saving Energy Inside The Greenhouse

In this work, a movable thermal screens was designed and examined for the purpose of decreasing greenhouse heating loss in Baghdad during winter nights. Three types of automatic movable thermal screens were tested to decrease the heat loss inside a greenhouse. The transparent cover area was 29.2 with 4 mm glass cover thickness. The mathematical model was formulated in four parts which are the inside air, transparent cover, soil surface, and subsoil layer. The results of the thermal curtains showed that the average temperature of the inside air during the night for the polyethylene, polypropylene, and bubble films was 8.1 ̊C, 10.3 ̊C, and 12.5 ̊C respectively and greenhouse without screens was 5.9 ̊C. These results showed that the bubble film was more effective in a saving energy than polypropylene and polyethylene films. Good agreement was obtained between the mathematical model and the measured values (with relative root mean square errors below 5%). It was shown that the suggested different types of movable thermal curtains were powerful in decreasing heating losses, which is reached about 21.7 % compared with a greenhouse without curtains.

Peculiarities of development and extinguishing fires at the objects where liquified petroleum gas is stored

The possibility of using sprayed water jets is established, primarily radial air jets, in vertical and horizontal planes in order to reduce the temperature of the burning Liquefied Petroleum Gas, starting from the cut-off of its expiration into free space. Various technical means of supplying water in a spray and spray nozzles for their creation, which are used in solving the problem of reducing the temperature of the burning Liquefied Petroleum Gas are viewed. It has been established that the active phase of the sprayed water jet is most effective (0,5-0,75 of the lengths), which, acting under the cut of the flame is crushed to a finely dispersed phase under the influence of a high-speed gas jet. As can be seen from the above, the heating rate of the finely dispersed water phase is increased up to the gaseous state, which leads to a decrease of the temperature of the flame in its middle combustion zone. Consequently, in the flame temperature will be much lower than the temperature of the flame cone, and, as a result, close to the extinction temperature. The authors recommend the use of modern jet-forming devices to realize this goal – nozzles NRT-5, NRT-10, NRT-20, NRS, as well as hand nozzles of the kind RSK-50, RS-А, RS-B, PROTEK. In order to cool, for example, one horizontal ground steel tank on both sides, it is necessary to use at least two hydraulic guns, which will act as maneuvering. In this case, the flow of water from the hydraulic gun with a diameter of the nozzle 25 mm will be from 16 to 18 liters per second. Therefore, the task is to find, calculate and experimentally prove the efficiency of the thermal screen, which is created in the form of a moving water surface that can effectively protect a particular physical object from the thermal impact of the heat zone. In order to reduce the flow of water to cool the tanks, the authors suggest using the NRS to create radial (flat) water jets. Application of such a nozzle allows to increase the area of simultaneous cooling of the maximum surface area per unit time due to the expansion of the angle of the spray jet spark. The water consumption does not exceed 13 liters per second.

Analysis of the influence of selected factors on natural greenhouse ventilation

In greenhouses, in order to maintain proper indoor air temperature, during the period of high values of solar radiation intensity, shading treatments using thermal screens and ventilation are applied. The research was carried out in a mono-span greenhouse in order to determine the effectiveness of natural ventilation. The object of analysis is a greenhouse with a thermal screen installed inside. The tests were carried out during the summer days. The effect of the research was to determine the ventilation air flow through the vents of the greenhouse on the basis of measurements and calculation analyzes. The dependence of the air flow on the windward and leeward side was determined from the wind speed and the temperature difference between the indoor and outdoor air. On the basis of calculations made from observation during shading of the cultivated area and with open ventilators, the coefficients of air exchange per unit floor area of the greenhouse were determined. It was established that at a wind speed exceeding 0.8 m/s, the air exchange rate in the tested greenhouse exceeds the value recommended by the American Society of Agricultural Engineers of 0.04 m3/(s.m2).

Modeling of heat consumption in a greenhouse using experimental data

The use of experimental research results to teach artificial neural networks was aimed at determining the relationship between heat consumption and measured variables. The mechanism of changes in heat consumption was determined by changes in external climate parameters, microclimate conditions in the greenhouse and parameters describing the functioning of the technical equipment of the facility. The accuracy of modeling the heat consumption in the case of changes in the properties of the building's external partitions has been determined. In a greenhouse, this is related to the functioning of an additional movable curtain - a thermal screen. MLP networks - multilayer perceptrons with hidden layers proved to be particularly useful for predicting changes in heat consumption. In the analysis attention was paid to the accuracy of modeling depending on the size of the measurement data set. The sources of information are collections with different intervals between registered measurement records, which were collected during the tests carried out during the full calendar year.

METHOD OF CALCULATION OF THERMAL PROPERTIES FOR BUILDING ENVELOPES WITH SCREEN INSULATION

The present research is performed in the framework of energy and resources conservation measures promotion in civil engineering. It introduces the perspectives of using thermal isolation in outer building envelopes and in air ventilation and conditioning systems insulation. The paper analyses the use of thermal screen isolation in building envelopes and air ventilation systems and proves that at the moment there is no methodology able to calculate these constructions in the existing engineering practice. The authors conducted a physical experiment to get reliable data on thermal screen isolation properties taking expanded polyethylene as a sample material. The results of the experiment as well as the obtained thermal conduction coefficient are presented in the paper. On the basis of the numerical data the authors introduce a verified methodology of calculation of thermal properties for building envelopes with screen insulation.