Greenhouse Heating Research Articles

An integrated dynamic model for evaluating the influence of ground to air heat transfer system on heating, cooling and CO2 supply in Greenhouses: Considering crop transpiration

Nowadays, one of the most important challenges in developing greenhouses is meeting their energy demand. The other challenge is the high water consumption of evaporative-cooling systems in arid and semi-arid regions. In this study, a integrated dynamic model is developed to determine the greenhouse relative humidity, carbon dioxide, and temperature, considering transpiration. The model is applied to a greenhouse utilizing a ground to air heat transfer system, located in the Alborz province of Iran and the results are validated with experimental data. Energy and water performance of the greenhouse are evaluated for the case study greenhouse. Then, the model is applied to a greenhouse (similar to the case study) in different climate zones of Iran to study the impact of climatic conditions on greenhouse performance. The results are presented for both cases of presence and absence of plant in greenhouses. Transpiration causes the heating/cooling demand of the greenhouse to increases/decreases by 17–40%/63–71% from climate 1 (cold and dry-humid climatic conditions) to climate 4 (mild and hot-humid climate regions). The water consumption of the evaporative-cooling system decreases by 17–49% from climate 1 to 4 when transpiration is taken into consideration.

Multi-layer hierarchical optimisation of greenhouse climate setpoints for energy conservation and improvement of crop yield

Energy conservation is an increasingly important issue in greenhouse production. Since higher energy input usually produces higher crop yields, crop yield and energy consumption must be carefully traded off. Generally, at any instant, the heating energy demand and crop yield depend on an interior temperature setpoint. Good, dynamically determined greenhouse climate setpoints not only improve crop yield, but also reduce the total energy consumption of the greenhouse. The greatest uncertainty in determining setpoints is the long-term weather. To deal with this uncertainty, this paper presents a multi-layer hierarchical optimisation framework for greenhouse climate setpoints. This framework has two optimisation layers with different timescales, and the whole production cycle is divided into several crop development stages, with each stage including several days. In the first layer, off-line multi-objective optimisation is carried out using historical weather data to maximise the crop yield and minimise the total energy consumption of the greenhouse heating. The aim is to optimise the mean temperature for each crop development stage. Based on the constraint of the optimal mean temperatures of the development stages, this work used a surrogate-assisted constrained single-objective method for online optimisation of the daily temperature using current short-term weather forecasts. Since the proposed method does not directly optimise the greenhouse climate setpoint, but instead optimises the mean temperature of the stages and the daily mean temperature, this work develops an effective indoor daily mean temperature serialisation method to generate the temperature setpoint series. The simulation results show that, compared to a widely used commercial system, the energy efficiency can be improved by 24.9%, 16.8% and 14.6% under real weather conditions of three example years. • Energy saving problem of greenhouse production is discussed. • A setpoint optimisation strategy of greenhouse climate is proposed. • A way to solve multi-timescale optimisation problem is presented. • Surrogate-assisted optimisation is used to optimise the daily mean temperature. • A comparison study of energy-saving performance is presented.

Coupling ecological wastewater treatment with the production of livestock feed and irrigation water provides net benefits to human health and the environment: A life cycle assessment

Ecologically designed wastewater treatment systems (ex., Eco-Machines™) utilize a diverse ecosystem to treat wastewater to the same extent as conventional treatment, but require less energy and chemical inputs. The environmental benefits of Eco-Machines™ can be theoretically maximized by incorporating hyperaccumulating aquatic plants (ex., duckweed) to facilitate nutrient recovery and conversion into protein-rich biomass, which can then be harvested for a range of agricultural and bioenergy applications. Although it has been established that ecological wastewater treatment systems are more cost- and energy-efficient than conventional wastewater treatment systems, a systematic life cycle assessment (LCA) of an Eco-Machine™ coupled with its beneficial by-products has not been conducted. In this study, a series of LCAs were performed on different operational scenarios for a 1000 gallon per day, pilot-scale Eco-Machine™ that, in addition to producing irrigation-quality water, also produces duckweed biomass for aquaculture. The analysis revealed that Eco-Machines™ located in warm climates, which do not require a greenhouse or supplemental heating, use approximately a third of the energy and produce half of the greenhouse gas emissions compared to conventional wastewater treatment systems in similar locations, while also providing benefits to human health, ecosystem quality, climate change, and resources. In addition, increasing the growth area for duckweed using vertical farming techniques improves the overall impact of the system. This study suggests that with proper management, ecological wastewater treatment systems that upcycle nutrients and water into beneficial products can provide a net benefit to human health and the environment.

Review of geothermal conditions of Hungary

The heat flow map of Hungary was presented in the Atlas of Geothermal Resources in Europe in 2002 and was last updated in 2005. Since that time several geothermal projects, e.g. TransEnergy (2010-13), assessment of the geothermal potential of the Drava basin (2013) Paks-II, NPP (2016) and continuous drilling activity in the country have been in progress. Large amount of temperature data became available, which allowed the update of the Geothermal Database of Hungary and the compilation of an updated heat flow map and temperature maps.
 The heat flow is determined based on the Fourier law using the thermal conductivities of rocks and temperature gradient calculated from temperature observations in boreholes and wells. The thermal conductivity is known from laboratory measurements made on core samples. The thermal conductivities and the temperature data are stored in the Geothermal Database of Hungary.
 The heat flow is calculated in 2001 boreholes and wells using the Bullard-plot technique. The mean heat flow in Hungary is 90 mW/m2, varying between 30 mW/m2 and 120 mW/m2. The high values are found over buried basement highs in the eastern and southern part of the country, while the low values are located in the recharge areas of karstic flow systems. In the sedimentary basins, where the thickness of the Neogene and Quaternary sediments reaches 5-7 km, the heat flow is slightly below the mean value (80-90 mW/m2) due to the cooling effect of sedimentation. These basins contain the main thermal water aquifer in Hungary utilized for district heating and green house heating. The buried basement highs characterized by high heat flow (100-120 mW/m2) are potential sites to create artificial geothermal reservoirs by hydraulic fracturing (EGS).
 Temperature maps at 500 m, 1 km, 2 km and 3 km depths were also compiled. Similarly to the heat flow, the temperature anomalies strongly reflect the local and regional groundwater flow systems.

Thermal Energy Storage in Phase Change Material Integrated Solar Collectors for Air Heating Application

Solar energy is an abundant source of renewable energy which can able to support the expansion of energy demand. This review paper represents a complete literature review on recent developments in the phase change material (PCM) based solar collectors for air heating applications such as building heating, greenhouse heating, etc. In this paper thermal efficiency of various types of storage based collector and their performance for air heating (SAH) applications have been discussed. Based on the literature, it has been found that compared to basic solar air heating (SAH) systems, the collector-storage based air heating systems are able to provide higher efficiency with their capacity to recover and utilize the stored heat at night or cold weather conditions. These storage based collectors can be efficiently utilized for applications requiring medium operating temperature range during daytime as well as night times.

Performance monitoring and verification of a groundwater source heat pump heating system in a greenhouse

The traditional heating of greenhouse is mainly by burning coal and fuel; this has some disadvantages such as low energy efficiency and high carbon dioxide emissions. As a renewable energy, groundwater source heat pump (GWSHP) has been widely concerned, and its heating application in greenhouse has a significant impact on energy saving and emission reduction. This paper introduces the GWSHP, and establishes a heating system combined with an existing fuel oil heater (FOH) in a horticultural greenhouse in Gunma Prefecture, Japan. The GWSHP bore most of the heat load, and the FOH was only used as an auxiliary heat source at low temperature. A heating cycle operation monitoring was carried out from November to May of the following year, and the fuel oil saving rate and energy saving rate of the system were calculated to be 74.4% and 22.3% respectively. The results show that the combined heating of GWSHP and FOH is energy-saving and environmentally friendly, and can be widely used in areas rich in groundwater.

Impact of the Heating Greenhouse and Root-Zone prior to Sunrise on Water Uptake, Photosynthesis, Plant Growth and Yield for Tomato Rockwool Hydroponics

Impact of the Heating Greenhouse and Root-Zone prior to Sunrise on Water Uptake, Photosynthesis, Plant Growth and Yield for Tomato Rockwool Hydroponics

Combustion of olive tree pruning pellets versus sunflower husk pellets at industrial boiler. Monitoring of emissions and combustion efficiency

The aim of the present paper is to compare the combustion results of two solid biofuels suitable for industrial applications: olive tree pruning (OTP) pellets and sunflower husk (SH) pellets. The former derives from the thin prunings, along with the leaves, whereas the latter derives as a byproduct from the sunflower oil extraction industries. The combustion was performed in operating conditions at two industrial fixed bed biomass boilers (1.16 MWth capacity each) with a common flue gas stack used for greenhouse heating. Combustion tests were performed at the industrial boiler for two consecutive days. During the first day, the OTP pellets were combusted and monitored for emissions, whereas in the second day the reference fuel that is normally used in the plant (SH pellets) was monitored. While combusting OTP pellets, the boiler’s performance was found to exhibit a slightly worse, leading to a decrease of 3.5% points of the boiler efficiency compared to SH pellets. Lower emissions of CO and NOx were also observed for OTP pellets, while the ash formation exhibited signs of reduced slagging. Dust emissions were high for both fuels, indicating that particle emission abatement equipment should be installed at the facility.

UTILIZATION OF SOLAR ENERGY IN GREENHOUSE HEATING DURING WINTER SEASON IN EGYPT

The main aim of this study is to investigate the utilization of solar energy as a renewable energy source and compared to the traditional energy in greenhouses heating during winter season. To achieve that study, the effect of two different heating systems (Traditional heating (G1) and solar heating (G2)) on the cucumber growth parameters during growth period and cucumber fruit characteristics and total yield were investigated. Temperature and relative humidity during the growth season were recorded. The obtained results indicated that the indoor air temperatures ranged from 18.78 to 25.29 and 18.00 to 25.15 ᵒC for G1 and G2, respectively, whereas the outdoor air temperature ranged from 11.00 to 21.66 ᵒC. The temperatures were added by using electrical (G1) and solar energy (G2) for greenhouse heating ranged from 1.5 to 9.3 and 0.85 to 7.78 ᵒC, respectively, during experimental period. The indoor relative humidity ranged from 63.33 to 88.67 and 70.93 to 93.94 % for G1 and G2, respectively, whereas the outdoor air relative humidity ranged from 45.93 to 92.73 %. The plant length, stem diameter and total leaf area values for cucumber grown in G1 were higher than those of the plant growth in G2. The fruit length was 24.79 and 19.44 cm for G1 and G2, respectively. The fruit diameters were 3.36 and 3.19 cm for G1 and G2, respectively. The results also indicate that the fruit weight and number of fruits per plant were 115.07 and 108.73 g and 19 and 17 for G1 and G2, respectively. The total yield values of cucumber were 182.09 and 152.92 kg for G1 and G2, respectively, during growth period.

Comparison of Energy Needed to Heat Greenhouses and Insulated Frame Buildings Used in Aquaculture

The document discusses the comparison of energy requirements for heating greenhouses and insulated frame buildings used in aquaculture. This work highlights the challenges of overheating in unventilated greenhouses during summer and the high heating costs due to low insulation values. It emphasizes the importance of ventilation and cooling systems to maintain optimal temperatures for aquaculture operations. The document also explores the differences in initial costs, energy efficiency, and expected lifetimes between greenhouse structures and frame buildings. Recommendations for improving energy efficiency, reducing heating costs, and enhancing overall operational effectiveness in aquaculture facilities are provided.

Model and simulation of temperature changes in the buffer tank cooperating with the greenhouse heating system

The paper presents a mathematical model describing the water temperature change in a buffer tank. The buffer tank is an integral part of modern greenhouse heating systems. The model includes heat fluxes from the heating boiler, heat fluxes transferred to the greenhouse interior and heat losses from the system (tank, pipes connecting the tank with the heating system). The differential method was used to determine the temperature value in the tank. Verification tests carried out in a real facility showed that the mean square error is 0.14K.

A Research on Sustainability of a Geothermal Energy Resource in Kırklareli City

Geothermal energy is one of the most important renewable energy sources which provides a massive contribution to the existing region. Low-enthalpy resources are convenient, especially for direct usage applications such as household and greenhouse heating and thermal tourism with today's technology. Direct usage applications have social and economic positive effects via supplying the primary demand of the local communities, such as heating and nourishment. Although geothermal energy is clean and renewable, that causes adverse environmental impacts during drilling or usage stages. Therefore, some criteria should be taken into consideration for the sustainable evaluation of the source. These criteria can be identified within the determined framework of sustainable development goals for each project. In this study, a newly discovered geothermal energy resource at Kırklareli- Asılbeyli Region is investigated for potential applications according to the UN Sustainable Development Goals. It is pointed out the precautions should be taken into consideration from the discovery phase until the end of life for sustainable use of the source.

Energy cost and efficiency analysis of greenhouse heating system enhancement using phase change material: An experimental study

The growing production of greenhouse gases and fossil fuels price obligated decision-makers in communications to implement energy sources more efficiently. The greenhouses have been developed through the years for the safe production of food sources. Thermal energy devotes a large portion of energy need in greenhouses. In developing countries, the rate of fuel consumption in the greenhouse is high, and there is an urgent need for improving heating systems. Here the possibility of reusing and storing the waste heat by phase change material (PCM) in a sample greenhouse studied experimentally. The PCM heat recovery system (PCM HRS) is a20cm×50cm×140cm plate type heat exchanger where the plates are replaced with PCM plate containers. The charge and discharge of the system are performed in two separate sections. The discharge stage organized in two separate schemes: delivering the stored heat directly inside the greenhouse space and using stored heat to preheat the combustion air of the burner. The heating system analyzed from the viewpoint of energy and the results show that the effect of preheating the heater air gives rise to a 23.7% reduction of gas consumption and the effect is much more pronounced compared to the direct using of the stored heat. Also, the resulted energy saving obtained by using the PCM HRS returns the initial investment within four months.

Passive Heating and Cooling of Photovoltaic Greenhouses Including Thermochromic Materials

The integration of photovoltaic technologies into greenhouse envelopes appears to be an innovative and environmentally-friendly way to supply their various energy demands. However, the effect on the inner growing conditions, especially on the temperature, must be assessed in order to effectively implement this solution. In this study, experimental temperature data were obtained over two years for four structures built with different photovoltaic technologies (mono-crystalline silicon, amorphous silicon, cadmium telluride, and an organic polymeric technology) and fitted to a thermal model in order to provide a comprehensive analysis of their potential utilization as a cover material in greenhouses. Additionally, the thermal effect of color in structures composed of several common construction materials (brick, wood, plasterboard and glass) was quantified and modelled, supplementing the thermal analysis of passive solutions for this application. In all cases, inner and ambient temperature differences of up to +20 °C, created by a passive heating effect during the day, and −5 °C, created by a passive cooling effect during the night, have been observed, suggesting the use of the photovoltaic modules with different degrees of structure coverage, complemented with the color tuning of the modules themselves as passive methods to control the temperature and light spectrum of greenhouses.

Environmental Analysis of Sustainable Production Practices Applied to Cyclamen and Zonal Geranium

Italian floriculture is facing structural changes. Possible options to maintain competitiveness of the involved companies include promotion of added values, from local production to environmental sustainability. To quantify value and benefits of cleaner production processes and choices, a holistic view is necessary and could be provided by life cycle assessment (LCA) methodology. Previous studies on ornamental products generally focused on data from one company or a small sample. The aim of this study was a gate-to-gate life cycle assessment of two ornamental species, cyclamen (Cyclamen persicum Mill.) and zonal geranium (Pelargonium × hortorum Bailey), using data from a sample of 20 companies belonging to a floriculture district in the Treviso, Veneto region. We also assessed the potential benefits of the environmental impact of alternative management choices regarding plant protection and reuse of composted waste biomass. Life cycle impact assessment showed higher impact scores for the zonal geranium, mainly as a consequence of greenhouse heating with fossil fuels. This factor, along with higher uniformity of production practices and technological levels of equipment, translated to a lower variability in comparison with cyclamen production, which showed a wider results range, in particular for eutrophication, acidification and human toxicity potential. The application of integrated pest management with cyclamen had significant benefits by reducing acidification and human toxicity, while reducing use of mineral nutrients through amending growing media with compost resulted in a reduction in eutrophication potential. Similar achievable benefits for zonal geranium were not observed because of the dominant contribution of energy inputs.

Research on the issue of using the heat of combustion products for heat supply of greenhouses

Cultivation of agricultural crops in winter season is carried out in special greenhouses. For heating greenhouses, a huge amount of heat energy is consumed. In the conditions of Turkmenistan, up to 1500 tons of standard fuel per year is consumed to heat the greenhouse with an area 1 hectare. The increase in heating costs leads to an increase in the prices of grown products. Therefore, saving fuel energy in the greenhouses is one of the most important economic factors. Possibilities of using the heat of the combustion products of steam boilers at the Mary State Electric Power Station (Turkmenistan) for heating greenhouses are discussed in the article. For this purpose, a special contact heat exchanger is installed on the line of the outgoing combustion products of steam boilers. In the experimental facilities, water is injected from top to bottom, and combustion products move in the opposite direction. In this case, the temperature of the combustion products decreases from 120-150 °C to 30-40 °C. The temperature of the cooling water of the combustion products rises from 10-20 °C to 40-45 °C. To increase the contact surface of water and gas in a contact heat exchanger, spray-type layer conductor is used. A distinctive feature of the experimental facility is the use of local materials as a spray-type layer with a conductor. For subsoil heating of greenhouses, water is supplied with the temperature of 40 °C, and for the raise of the vegetables grown in them water is supplied with the temperature of 22-25 °C. The use of the heat of combustion products to heat greenhouses is of great importance both for saving fuel and for purifying the environment from harmful emissions.

Development of a sun tracking algorithm for solar panels for agricultural enterprises

In agriculture, use of solar energy is of crucial importance for water heating and functioning of greenhouses. It becomes even more important in agricultural enterprises which are located far from electric energy transmission lines. Furthermore, in Russia the importance of solar energy for agricultural enterprises can be motivated by deterioration of electric energy transmission lines. The article is devoted to the development of a sun tracking algorithm for solar panels without using GPS or sensors. The tracking algorithm has been created on the basis of well-known astronomic methods for calculation of the Sun’s position in azimuth coordinates. The control diagram using the Arduino platform is presented. The authors’ program works for the calculation of the Sun’s position complete with evaluation of error. It also works well with servo drive units. The hardware and software bundle have shown acceptable error values which did not exceed 2 % while aligning the panels with the sun.

Exploitation assessment of geothermal energy from African Great Rift Valley

Countries that are in the Great Rift Valley have one of the lowest average annual electricity consumption per capita in Africa with a value of 164 kWh per inhabitant. Furthermore, the electrification rate is 34% that is more than fifty percentage points below the world average, which is around 86%. One possible solution to improve the electrification rate is to properly exploit the energy resources present in the territory. One of the most significant energy sources of this region is certainly geothermal energy which has a potential of about 15 GWe, mostly concentrated in Ethiopia. Furthermore, it is possible to find the resource in a wide temperature range, not only to produce electricity, which, nonetheless, has a very limited exploitation rate, as only 900 MWe are installed between Kenya and Ethiopia, but also for direct use. In this study, two geothermal power plants for two different geothermal sites, Corbetti and Arus-Bogoria, respectively in Ethiopia and Kenya, have been hypothesized after analyzing the resource potential. For the first, which has been estimated to be of high enthalpy (~300°C), a flash plant configuration was assumed, and the estimated energy production potential was found to be around 50-100 MWe. While for the second, at medium enthalpy (T<200°C), the use of a binary cycle plant was assumed with an obtained production of about 20 MW of electricity. Finally, the possibility of geothermal water exploitation for greenhouse heating, drying of agricultural products, civil sanitary uses, recreational uses (spa), or for industrial purposes has been assessed.

Parametric study on a simplified model for the estimation of the heating and the cooling loads of a closed-span greenhouse: a case study in Korea

The modeling of greenhouse heating and cooling loads at the required operating conditions is important for greenhouse managers or planners. However, the conventional model for the greenhouse thermal load prediction is complex for staff without sufficient academic background. Therefore, a steady-state simplified model based on the estimation of related heat transfer parameters was developed to predict the hourly heating and cooling requirements of the closed greenhouses in Korea and the Northeastern Asian region. In the suggested approach, the thermal load was simplified as a function of greenhouse size, the temperature difference between the setting indoor temperature and the ambient temperature, total horizontal solar radiation, overall heat transfer coefficient, and the fraction factor of solar conversion. Except the designed parameters and the climatic variables, the overall heat transfer coefficient and the fraction factor of the solar conversion were restored using an inverse procedure based on a linear regression approach, which was assessed with synthetic data calculated using the TRNSYS software. The climatic data from meteonorm assisted the simulations for six Northeastern Asian locations. The short-term load profiles and the monthly thermal energy consumptions from eight case studies with different greenhouse sizes and locations were validated with the TRNSYS solutions. The mean bias error and the coefficient of variation of the root-mean-square-error of annual loads were controlled within 5% and 11%, respectively. Satisfactory results suggested that the simplified model could be used for the greenhouse thermal load estimation especially in Korea and the Northeastern Asian region. However, the model should be tested with more regions in future work for extensive applications.

Performance evaluation of hybrid photovoltaic/thermal solar system combined with greenhouse for drying of rose flower

A study was conducted to evaluate the performance of Hybrid Photovoltaic/Thermal (HPV/T) solar system combined with a greenhouse dryer and air cooling arrangements. The experiments were carried out in warm and humid climatic condition of Odisha, India for the winter and summer months during the year 2020. The enhancement in the electrical efficiency of the solar panel was studied by lowering its temperature during the operating period with the help of extracting absorbed heat energy from its back surface through an air cooling arrangement. The extracted heat energy in this study, was utilized in a low thermal energy consuming application such as greenhouse heating for drying of rose flower. It was observed that the temperatures of solar panel were decreased in the range of 9-12 ˚C and its efficiencies were increased in the range of 8-14% respectively in forced air cooling system compared to without cooling in clear sunny days. The reduction in moisture contents of the rose flower compared to fresh flower was about 67-73% in HPV/T greenhouse drying, 54-61% in greenhouse drying alone and 32-41% in open sun drying in 3 days’ duration of drying. The colour, appearance and texture of the flower were also maintained in HPV/T greenhouse drying for its marketability in International market.