Greenhouse Heating Research Articles

Study on the double-coil heat exchanger for dehumidification and heating in greenhouses: Modeling, analysis, and optimization

Heat exchangers are widely used in dehumidification and heating technologies owing to their excellent heat transfer performance, however, their dehumidification capability is limited for greenhouse applications. This study evaluates a double-coil heat exchanger (DC-HE) for dehumidification and heating in greenhouses. Humid air undergoes condensation dehumidification through the dehumidifying coil and is then reheated by the heating coil before being released. Using double coils allows for the separate circulation of cold and warm water in their respective paths, handling the latent and sensible heat of the air. In this study, predictive methods for air treatment in a heat exchanger are combined, and theoretical calculations are performed on the DC-HE and validated through experimental investigations. Furthermore, the impact of variables such as air temperature, relative humidity, water temperature and flow rate, and air flow rate on the moisture removal rate (MRR), latent heat ratio (LHR), and heating capacity (qheat) of the DC-HE is analyzed, the effects of these variables on the sensible and latent heat transfer rates are discussed. Finally, the optimal variables for maximizing MRR and LHR are determined using the response surface method and multi-objective genetic algorithm. When the inlet air temperature, relative humidity, cooling-side water temperature, heating-side water temperature, cooling-side water flow rate, heating-side water flow rate, and air flow rate are 11.8 ℃, 95 %, 3 ℃, 30 ℃, 2 m/s, 2 m/s, and 2 m/s, respectively, the DC-HE achieves an MRR of 1.58 g/s, an LHR of 62.2 % and a qheat of 9.99 kW. Compared with other finned tube heat exchangers, the DC-HE enhances the moisture removal capacity and significantly reduces the temperature requirement for the heat source, offering a promising dehumidification and heating technology for greenhouse applications.

Geoenergy in the Styrian Basin

The Styrian Basin (SB) is the westernmost basin within the Pannonian Basin Complex and is located in SE Austria, where the crustal thickness decreases from more than 40 km to less than 30 km. It can be divided into the West and East Styrian Basin. The pre-Neogene basement includes Penninic and crystalline rocks overlain by Paleozoic rocks. The age of the basin fill ranges from the early to late Miocene. Despite a long hydrocarbon exploration history, only a single sub-economic gas field has been discovered. The lack of commercial deposits is probably due to limited source-rock quality and an unfavourable heat-flow history. In contrast, a significant number of geothermal wells with a cumulative length of >54 km have been drilled in the East SB. The main geothermal reservoirs are fractured Paleozoic carbonates and Miocene (Badenian) sandstones. Geothermal gradients in the SB are typically above 4°C/100 m. The hottest geothermal well (Frutura GT1) produces water with a temperature of 125°C (bottom hole temperature 138°C) from a depth of ∼3.3 km. Utilization of geothermal energy in the SB includes balneology, district and greenhouse heating, production of medical salt, CO 2 and electricity.

Performance study of solar air collector-air source heat pump system inside the greenhouse

During the process of heating greenhouses, the phenomenon of inadequate heating installations is widespread. To address this issue, this paper proposed a solar air collector-air source heat pump (SAC-ASHP) system for greenhouses, combining solar technology with heat pump (HP) technology to provide sufficient heat during continuous cloudy days and winter. The heating capacities of the system on sunny, cloudy, and overcast days were 100.2 kWh, 112.3 kWh, and 157.8 kWh, respectively. The corresponding power was 30.1 kWh, 36.1 kWh, and 53.6 kWh. The coefficient of performance (COP) of the single air source heat pump (ASHP) for these days was 3.4, 3.2, and 3.0, respectively, while the COP of the solar heat pump (SHP) was 4.0, 3.5, and 3.1. Additionally, greenhouse employed heat and moisture recovery for humid air, aiming to provide a suitable environment for plant growth around the clock while conserving energy. The heat collection in the heat and moisture recovery combined HP mode was 66.7 % higher than in the heat exchanger (HE)-fan mode. This experimental study investigated the operational performance of the system in dynamic environments, revealing the stability of the system for greenhouse heating in cold regions, and providing new research ideas for greenhouse heating.

Decarbonising primary industries with geothermal heat – a pathway to greater direct use

ABSTRACT This paper discusses the opportunities and policy levers to increase the use of low-temperature geothermal resources in New Zealand for decarbonising primary industries, in particular, covered crops. Geothermal heat (geoheat) is a local, reliable, resilient and sustainable energy source. Low-temperature geothermal energy (220°C) is available in the Taupō Volcanic Zone with low awareness of the nationwide availability of lower temperature resources. Covered crop growers in New Zealand, needing to decarbonise their operations, are investigating the potential of utilising geoheat, following the example of the Netherlands. The Netherlands has strategically invested in low-temperature geothermal energy, utilising 80 °C water resources, from ∼ 2 to 3 km below the surface to heat greenhouses. Internationally, risk mitigation schemes and insurance programmes have proven pivotal policy instruments for fostering geothermal adoption. This paper discusses the opportunities that the adoption of using low-temperature geothermal provides to New Zealand drawing upon successful models from other countries.

An Analytical Approach for Sustainable Greenhouse Heating in Lebanon: A Focus on Air Source Heat Pumps

Abstract In Lebanon, where economic challenges and Mediterranean climate dominate, protected cultivation methods, such as greenhouses, are widely used for sustainable agriculture. Tomatoes, with an annual production of around 250,000 tons in Lebanon, are the focus of this study. Tomato leaves require a temperature range of (18-25ºC) for optimal growth. The present study explores the potential of air-source heat pumps as a sustainable heating method. It includes a comprehensive literature review and discusses alternative heating methods. A dynamic energy model was developed after using statistical models to plot the temperature and solar radiation profiles for the worst-case scenario for heating. This energy model sizes the heat pump to maintain 18 ºC in a standard 332 m2 Quonset greenhouse with thermal polyethylene covering. The model’s validity was demonstrated by comparing its temperature profiles with a study conducted in West Bengal, India. The results indicate the adequate size for the studied case is 16 kW. Sensitivity analysis showed the required power for different temperature settings (12-18ºC) and the effect of wind speed by analyzing the heat transfer coefficient of the cover, which doubled the power when the heat transfer coefficient increased from 4 to 10 W/m2.K.

Exploration of new function for thermal energy storage: Temperature stabilizer

Thermal energy storage (TES) is a technology that stores thermal energy by heating or cooling a storage medium so that the stored energy can be used when needed. TES is usually used in greenhouse heating, centralized solar power, and industrial waste heat recovery to improve the efficiency of energy utilization. This article explores a new application of TES, which relies on its constant outlet temperature to provide stable working conditions for other components. A simulation consisting of 10 cycles with a total length of 100 h is designed. Each cycle contains 5 h of discharge and 5 h of charge, achieved by adjusting the inlet temperature. Rock and NaNO3 are selected as materials for sensible and latent heat storage. This paper discusses the temperature distribution and thermal storage capacity of TES under alternating inlet temperature. The results indicate that the outlet temperature of sensible heat storage will fluctuate and the maximum amplitude is 4.56 K. For latent heat storage, the outlet temperature is constant, and fluid temperature and liquid phase ratio distribution do not change with the number of cycles. There is a significant temperature difference between fluid and solid in phase transition stage, with a maximum value of 10.72 K. Mathematical relationship between latent heat storage parameters and the minimum length of TES is obtained.

Experimental investigation on heating performance of long- and short-term PCM storage in Chinese solar greenhouse

Phase change material (PCM) board on north wall of the greenhouses can absorb and store solar heat during the daytime, then releases it at night to provide the thermal environment for crop growth. However, its capability to regulate the greenhouse temperatures in severe winter is limited, necessitating an additional heat source. The heat gap within the greenhouse can be replenished flexibly and promptly by controllable triggering of supercooled salt hydrate for long-term heat storage. This study proposed a synergetic energy storage and release system, combining the short-term storage and passive release of the PCM wallboard with the long-term storage and active triggering solidification of the supercooled salt hydrate in separate storage unit. The temperature regulation effect of this synergetic system was experimentally investigated in a test Chinese greenhouse. The results showed that the combination of the PCM north wallboard with the supercooled salt hydrate storage unit reduced the daytime average temperature by 2.0 °C ~ 3.8 °C compared with the control greenhouse. In sunny days, the PCM north wallboard could meet the nighttime heat demand of the greenhouse with the average temperature rise of 5.2 °C ~ 6.7 °C. In severe weather, by triggering supercooled sodium acetate trihydrate (SAT, CH3COONa·3H2O, Tm = 58.0 °C) at late night, the temperature rose by 5.3 °C in 1 h, effectively heating for 5 h. While supercooled sodium thiosulfate pentahydrate (STP, Na2S2O3·5H2O, Tm = 48.5 °C) was triggered, the temperature rose by 3.3 °C in 1 h, effectively heating for 4 h. Furthermore, the synergetic system was still effective for greenhouses under ventilation and irrigation conditions during the day. This study provides guidance for the development of synergetic PCM systems with long- and short-term solar thermal storage and release for greenhouse heating.

Enhancing nocturnal microclimate in Tunisian greenhouses: Experimental study on integrating an innovative conic helicoidal heat exchanger with a geothermal heat pump system

Ensuring an optimal nocturnal microclimate within greenhouses is essential for successful crop cultivation. In regions like Tunisia, characterized by arid and semi-arid climates, managing temperature and humidity during the night, particularly in cold winter months, is challenging and often requires external heating sources. This study aims to investigate the use of geothermal energy as a sustainable solution for greenhouse heating, focusing on an innovative helicoidal geothermal system to maintain ideal nocturnal conditions.The primary objective of this research is to evaluate the effectiveness of the helicoidal geothermal system in achieving optimal temperature and humidity levels for plant growth during the night. Conducted at the Research and Technology Centre of Energy in Tunisia, the experimental investigation involved a new ground heat exchanger coupled with a heat pump system.The experimental setup consisted of two greenhouses: one serving as a control and the other equipped with two Conic Helicoidal Ground Heat Exchangers (CHGHE) and a Ground-Source Heat Pump (GSHP) system, which includes both underground and suspended heat exchangers. The results demonstrated that the geothermal system, operating at an optimal flow rate of 0.6 kg/s, successfully maintained the nocturnal comfort temperature required for plant growth. The coefficients of performance for the geothermal heat pump (COPhp) and the overall system (COPsys) were calculated to be 3.12 and 2.7, respectively.These findings underscore the potential of near-surface geothermal energy, utilizing a geothermal heat pump, to efficiently heat greenhouses under the climatic conditions of Tunisia. This approach not only supports sustainable agricultural practices but also offers significant energy efficiency and cost-saving benefits.

Research on waste heat utilization potential of data centers for agricultural greenhouse heating

Research on waste heat utilization potential of data centers for agricultural greenhouse heating

Use of Dielectric Heating in Greenhouses

Use of Dielectric Heating in Greenhouses

Implementation of solar system for electricity generation for rural farmers: A review

Solar energy offers a promising renewable alternative to traditional fossil fuel-based electricity generation for powering agricultural activities in remote rural areas. Several studies have demonstrated the technical and economic feasibility of photovoltaic, solar thermal, and hybrid solar systems for various on-farm applications such as water pumping, crop drying, greenhouse heating. These systems provide clean energy for irrigation, milling, cooling, and mechanical operations to improve productivity. When integrated with battery storage, solar also enables electrification and lighting in off-grid farms. The upfront capital cost of solar installations has been reducing significantly, and various incentive programs have enhanced the affordability for smallholder farmers. However, adoption of solar energy in the agriculture sector still faces certain challenges. Lack of adequate financing options and initial higher costs compared to conventional fuels limit widespread deployment. Technical skills are required for installation, operation and maintenance of these systems. Seasonal variations and uncertainty of solar resources necessitate proper system sizing and integration with demand patterns. Policy support through subsidies, tax benefits and financing schemes can help address these barriers. With the declining price trends and increasing reliability of solar technologies, the potential for energy access and economic gains from solar power in rural agriculture appears promising.

Integrated approach for geothermal exploration: Case study from Salar area (Afyonkarahisar, Turkey)

The intense investment demand in the geothermal sector in Afyonkarahisar province in recent years has enabled the utilization of geothermal waters such as district heating and greenhouse heating, electricity generation, and spa facilities and accelerated the exploration of new geothermal areas in the region. In this study, the Salar (Afyonkarahisar) region's geothermal potential was investigated using the mineralogy and geochemistry of hydrothermal alteration, hydrogeochemistry, and resistivity models obtained from magnetotelluric data. The Salar region is located within the Afyon-Akşehir Graben (AAG) and 10 km south of Afyonkarahisar province. The most important manifestations of the geothermal system are the geothermal water at temperatures of 25 °C and 31 °C obtained from the boreholes and hydrothermal alteration in Salar. Afyon volcanoclastics are reservoir rocks. Smectite and illite are the most important clay minerals in the hydrothermal alteration zones. The transformation from volcanic glass and alkali feldspar to smectite and illite reflects neutral-alkaline alteration conditions in felsic rocks. The clay minerals' stable isotopes (δD and δ18O) indicate hypogene conditions. Discharge temperature, electrical conductivity and pH of Salar region geothermal waters vary from 25 to 31 °C, 320–357 µs/cm, and 6.8, respectively. The Salar geothermal waters are Ca-(Na)-HCO3 type chemically. The electric resistivity models reveal shallow low resistivity (10 < ρ < 80 Ωm) layer related to the alluvium, Gebeceler formation, and Afyon volcanoclastics and deeper high resistivity (80 <ρ < 200 Ωm and ρ > 200 Ωm) layer based on Deresinek and Değirmendere formation respectively. The difference in electrical resistivity arises from the geothermal waters and hydrothermal alteration zones, influenced by the AAG tectonics.The stable isotopes (δD and δ18O) and alpha cristobalite geothermometer calculations indicate that the condition of the temperature in the active and fossil geothermal systems in the Salar does not change, and the condition of the temperature is between 44 °C and 112 °C.

Thermoeconomic analysis and environmental impact assessment of the Akkuyu nuclear power plant

Within the scope of this study, a thermoeconomic analysis was carried out for Akkuyu Nuclear Power Plant (ANPP), the first nuclear power plant of Türkiye. As a result of the analysis, it is aimed to reduce the cost of energy production and prevent thermal pollution at the same time by converting the heat discharged into the environment into useful heat due to the working principle of NPP. Thermodynamic analysis was performed in the Engineering Equation Solver (EES) program using equipment values equivalent to ANPP. Cost analysis was performed using the specific exergy costing (SPECO) method, which is based on the second law of thermodynamics and is the most widely used cost analysis method. The study concludes that the energy efficiency is 35%, while the economic analysis shows that the best case has an exergy efficiency of 68% with a payback period of 7–8 years, and an electricity cost of $0.0196 per kWh. It is possible to use the heat discharged from the plant indirectly in district heating (heating, hot water needs of the lodgings, guesthouses in the facility), greenhouse heating, agricultural drying and heating, considering the geographical conditions and livelihood of the region. Thus, 68% of the waste heat was utilized, the unit cost of the energy produced was reduced and at the same time thermal pollution was reduced at the same rate. The results of the study can contribute to the efforts preventing energy waste, thermal environmental pollution, and reducing greenhouse gas emissions. Additionally, it could aid in the development of more energy-efficient and environmentally friendly power generation systems, including pioneering nuclear power plants in developing countries.

Coupled system for underground heating exchange and solar heat-humidity regulation in greenhouse: Experimental study and simulation analysis

In winter, greenhouses located in mid to high latitudes are required a function of dehumidification and warming due to the low outdoor temperature. Focusing on small spires greenhouses, this study regulates the low temperature and high humidity environment inside the greenhouse and proposes a new-type of greenhouse heat and humidity regulation system by combining composite solid desiccant dehumidification with ground heat exchange system. The greenhouse internal environment is warmed and dehumidified at night by utilizing the adsorption effect of the compound dehumidifier and the sensible heat exchange between the heat exchange system in the ground and the greenhouse. Solar thermal energy is collected during the day using multi-curved tank collector (MTC) for thermal storage in the geothermal system and desiccant desorption. The rationality of pipeline layout is verified through CFD simulation, and the indoor temperature and humidity distribution during the system operation is explored. The experimental results show that the moisture adsorption capacity of the composite desiccant SG-CaCl2 for 10h is 0.511 g/g. The optimal regeneration temperature is 80–100 °C. This system can reduce the nighttime relative humidity of the greenhouse in winter from 96.5 % to 83.6 %, and the average indoor air temperature after warming is 12.8 °C. The heat exchange efficiency of the underground heating exchange system is 0.38. During the desorption phase on daytime, the maximum outlet temperature of MTC is 103.8 °C, and the average heat collection efficiency is 0.42. The system can effectively regulate the air environment in the greenhouse to the appropriate zone for crop growth by combining solar thermal collector technology with recyclable solid dehumidification technology.

Case study: reducing heating energy consumption in a high tunnel greenhouse with renewable energy and microclimate control by bench-top root-zone heating, bench covers, and under-bench insulation

Appalachian State University's Nexus project designed an efficient greenhouse heating system that integrated renewable energy and root zone heating technology to reduce the greenhouse heating energy burden on local farmers and installed it at local cooperative farms. This study analyzed 5 years of data from 2018 to 2022 to investigate the energy savings and microclimate control effectiveness of the Nexus heating system installed at Springhouse Farm in North Carolina, USA. By varying bench cover materials, bottom insulation, and the number of loops of root zone tubing, the different soil temperatures required for plant types and growth stages were achieved with a single temperature controller. A root zone heating fluid of 32.2 ℃ satisfactorily maintained the germination soil between 20 and 25 ℃ in March 2019 with an average outside temperature of 4.8 ℃ and an average low temperature of − 0.4 ℃. Growing soil maintained an average temperature of 15 ℃ with bottom insulation and an average of 11–12 ℃ without bottom insulation. Compared to the conventional heating system (a forced-air propane unit heater alone), weather-adjusted propane consumption (propane usage divided by heating degree days) was reduced by 65% with the Nexus system alone and 45% with the Nexus system and unit heater together. It shows that the Nexus system has significantly reduced greenhouse heating energy consumption and maintained productive conditions. The renewable energy fraction ranged only 9–13% of the total thermal energy used due to the high inlet temperature entering the solar thermal collector. This can be improved by separating the heat storage and backup heat source.

Solar Energy's Role in Achieving Sustainable Development Goals in Agriculture

The adoption of solar energy in agriculture has the potential to significantly contribute to achieving multiple Sustainable Development Goals (SDGs), particularly those related to clean energy access (SDG 7), sustainable economic growth (SDG 8), responsible consumption and production (SDG 12), and climate action (SDG 13). This review article examines the various applications of solar energy in agricultural practices, including irrigation, crop drying, greenhouse heating, and powering farm machinery. It analyzes the economic, environmental, and social benefits of transitioning to solar-powered agriculture, such as reduced reliance on fossil fuels, lower greenhouse gas emissions, improved energy security, and increased income for farmers. The article also discusses the challenges and barriers to widespread adoption, including high upfront costs, lack of awareness and technical expertise among farmers, and inadequate policy support. Through a comprehensive review of existing literature and case studies, this article highlights the immense potential of solar energy in transforming the agricultural sector and contributing to sustainable development. It concludes by emphasizing the need for concerted efforts from governments, international organizations, and the private sector to promote and facilitate the integration of solar energy in agriculture, particularly in developing countries where access to clean energy and sustainable farming practices are most crucial for achieving the SDGs.

Life Cycle CO2 Emissions Analysis of a High-Tech Greenhouse Horticulture Utilizing Wood Chips for Heating in Japan

High-tech greenhouse horticulture offers efficient crop cultivation that is unaffected by outdoor climate. However, compared to conventional cultivation systems, energy requirements, such as greenhouse heating and control, are larger, and concerns about the associated increase in CO2 emissions exist. Although several previous studies have analyzed CO2 emissions from high-tech greenhouse horticulture, few have covered the entire life cycle. This study aimed to analyze CO2 emissions from high-tech greenhouse horticulture for tomatoes in Japan across the entire life cycle. A hybrid method combining process and input–output analyses was used to estimate life cycle CO2 (LC-CO2) emissions. The emission reduction potential of replacing liquefied petroleum gas (LPG) for greenhouse heating with wood chips was also examined. The results show that LC-CO2 emissions were estimated to be 3.67 kg-CO2 per 1 kg of tomato, 55.6% of which came from the production and combustion of LPG for greenhouse heating. The substitution of LPG with wood chips has the potential to reduce LC-CO2 emissions by up to 49.1%. However, the improved LC-CO2 emissions are still higher than those of conventional cultivation systems; thus, implementing additional measures to reduce LC-CO2 emissions is crucial.

Sustainable Heat Supply for Greenhouses with Heatpumps

The heating of greenhouses in Germany is yearly responsible for the emission of about 3 million tCO2eq. In the small horticultural city of Straelen in North-west Germany, the possibility to partially replace the heat supply of greenhouses with heat pumps instead of CO2-intensive coal and oil boilers has been investigated. Different scenarios based on the power of the heat pump and the type of source (air or ground) have been simulated and compared economically and ecologically. Over the lifetime of the whole system, the levelized cost of heat for a combined heat pump &amp; gas boiler heating system is lower than the reference case (coal &amp; gas boilers). The installation of a heatpump covering at least 70% of the yearly heat demand would reduce the CO2-emission from minimum 70%.

SWOT analysis of a liquid-dominated active geothermal system for non-electrical uses of geothermal energy: A case study, Seferihisar-İzmir

There are numerous natural outflows, 3 thermal baths, 9 disused geothermal wells, and 3 private companies operating in the Seferihisar geothermal system, including a power plant generating electricity. The potential of these resources is suitable for non-electrical use of geothermal energy, such as greenhouse heating and thermal tourism. SWOT analysis method has been used to assess the pros and cons of the geothermal resource in Seferihisar, aiding the identification of suitable applications and investments for both present and future projects. The region is rich in terms of geothermal resources and has convenient access to both public and ware transport, which are described as strengths of the resource. However, poor management and an excess of licensed geothermal fields weaken the effective consumption of the system. A huge number of projects have led to opposition from environmentalist groups. The proven technology of geothermal energy has resulted in an increase in incentives and investment consolidations with governmental support. In the light of SWOT analysis, considering SO, ST, WO, and WT strategies, the untapped geothermal resources present in the Seferihisar geothermal system, combined with the natural attractions and cultural richness of the county, will contribute significantly to non-electrical/direct uses of the geothermal energy in the near future

Effect of root zone heating on cold tolerance of papaya (Carica papaya L.)

ABSTRACT Low-temperatures during winter are a serious problem in the cultivation of tropical fruit trees in temperate regions. The study investigated whether root zone heating treatments could improve cold injury tolerance in papaya. Leaf water potential was −2.22MPa and leaves wilted in the Control, where the root zone was not heated. However, where the root zone was heated to 20°C or only during the daytime, leaf water potentials were −1.31MPa and −1.41MPa, respectively, and no signs of leaf wilting were observed, suggesting that cold wind damage was suppressed unless temperatures fell below freezing. In contrast, where the root zone was heated, leaves wilted rapidly as temperature fell below the freezing point, and all trees had died by 12 January 2018 (72 days of experiment), suggesting that freezing injury could not be controlled by heating the root zone. It is therefore suggested that in addition to root zone heating, heating the greenhouse only on days when the temperature is below the freezing point would also prevent freezing injury. This has the potential to reduce the total greenhouse heating time by 97%. It also has the potential to reduce fuel costs for overwintering papaya, a tropical fruit tree cultivated in a temperate region.