Greenhouse Heating System Research Articles

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.

Energizing Sustainable Agriculture: Advances in Greenhouse Heating through Microwave-Based Technologies

For the agricultural sector to develop sustainably in the future, progress toward more environmentally friendly technologies and methods is crucial. It is necessary to increase output while reducing the demand for energy, agrochemicals, and water resources. Although greenhouses can be utilized successfully for this purpose, significant technical advancements are required, especially when it comes to heating, to lower the use of fossil fuels and boost energy efficiency. Microwaves can warm plants without heating the entire greenhouse volume, which takes a significant amount of energy to compensate for heat loss in the outdoor environment. In this paper, through a thorough examination of the state of the art, a general overview of novel greenhouse heating systems based on radiation is reported. First, the strengths and weaknesses of microwave heating are discussed, and finally, the use of microwaves for soil sterilization is examined. All outcomes suggest these irradiation-based technologies can contribute significantly to energetically sustainable agriculture; moreover, they can be used to increase plant comfort.

Study of Solar Combined Air Energy Greenhouse Heating System Model

At present, it is difficult to bring centralized heating to rural areas owing to factors such as scattered distribution, distance from towns and cities, and difficulty in laying public pipes. According to research, most rural residents use inefficient household heating facilities, thereby resulting in serious environmental pollution and a decline in the quality of life of residents. In order to alleviate environmental pollution, the use of solar energy, air energy, and other renewable energy for rural heating of such decentralized buildings is of profound significance. This study analyzed the distribution characteristics of solar energy resources and solar combined air energy greenhouse heating system, established and solved a mathematical model of the solar combined air energy greenhouse heating system, calculated solar heat collection and solar heating energy consumption. From the data analysis, the relationship among heat gain power, heating power, and the water temperature of the water storage tank of the heat pump system was obtained. The mathematical model of the storage tank of the solar combined air energy greenhouse heating system was solved, and the operating conditions and volume of the storage tank of the solar combined air energy greenhouse heating system were determined. The study also analyzed the solar heat collection and solar heating energy consumption in Qingdao, thereby pointing out the advantages of the solar combined air energy greenhouse heating system, and finally obtained the best heating scheme.

Thermal performance of greenhouse heating with loop heat pipe solar collector and ground source heat pump

The hybrid heating system consisting of loop heat pipe solar collector (LHPSC) and ground source heat pump (GSHP) is proposed to control greenhouse temperature in Harbin (the coldest provincial capital of China) in this paper. The combined thermal resistance network and energy balance model is developed to predict transient greenhouse temperature corresponding to the energy supplied by GSHP. The influence of ambient temperature on the thermal performance of greenhouse heating system is analyzed. The results show that the greenhouse temperature fluctuates in the range of 17–24 °C corresponding to the energy of 200 kW intermittently supplied by GSHP, which is reasonable for predicting greenhouse temperature in severely cold regions. As ambient temperature varies from −24 °C to −13 °C, heat loss of maintenance structure, ground, ventilation and water storage tank change in the range of 51.9–73.2 kW, 2.45–3.45 kW, 11.1–15.5 kW and 5.87–6.91 kW, respectively. The maximum thermal efficiency of loop heat pipe solar collector is higher (76.38%) than that of evacuated tube solar collectors (45%–50%), which will be promising for greenhouse heating due to higher thermal efficiency and better environmental adaptability. The results presented in this study will provide further valuable guidelines for designing greenhouse heating system.

Greenhouse heating by energy transfer between greenhouses: System design and implementation

Multi-span greenhouses consume enormous amounts of energy for heating in northern China, resulting in poor profitability and unsustainability. A greenhouse heating system, utilizing energy transfer between greenhouses based on a dual source heat pump, was designed to remedy this issue. The system collects surplus air heat inside Chinese solar greenhouses (CSGs) for heating multi-span greenhouses. Through enabling a greenhouse energy transfer in time and space, improved utilization efficiency of surplus air heat in CSGs is achievable, resulting in an overall reduction of heating costs. This study defines the heating approach and describes the overall system design. The dual source heat pump acts as the core component, with two separate evaporators placed in the CSG and ambient air. Calculations for system sizing are then presented, including a heating load model of multi-span greenhouses, a surplus air heat model of CSGs, the selection of required equipment (dual source heat pump, heat storage tank, and surface air cooler of the combined air conditioning unit), and the area matching. Finally, a case study illustrates the implementation processes of the heating system. The available CSG surplus air heat ranged 100.8–112.6 W m−2 for system sizing, and the minimum area of CSGs was suggested to be twice the multi-span greenhouse area. The pilot test showed that the running status and heating effect of the system was stable. The coefficient of performance (COP) of the heat pump reached 4.3–4.8 when using CSG surplus air heat as the heat source, performing 23–26 % higher than when using ambient air over the same periods. Throughout the entire course of heat collection, dual source heat pumps, switching sources based on their setting, achieved a total COP of 3.4–4.2, increased by 6–11 % compared with air source heat pumps. This study provides a novel heating approach and an energy-saving system for multi-span greenhouses.

Simulation research on airflow distribution performance of solar greenhouse heating system in northwest China

Combined with the structure of the solar greenhouse, this paper proposed a new type of solar greenhouse heating and ventilation system with the framework of the solar greenhouse as the carrier of heating and ventilation. The system’s return air mode, tuyere type, tuyere installation position and aperture ratio were determined by computational fluid dynamics (CFD). The results showed that: 1) When the inlet wind speed was 10m/s and the temperature was 37°C, using the upper return air method, the average temperature of the greenhouse crop area increases by 14.7°C, which was greater than 1.3°C of the lower return air and 2.3°C of the middle return air, the heating effect was the best. 2) Based on the nozzle and slot-type tuyere, five kinds of air outlets were designed. It was found that the use of the nozzle-type air outlet could promote the circulation effect of the airflow in the greenhouse and send more heat to the crop area. 3) When the aperture ratio was controlled at 1.5, the number of air outlets has little effect on the greenhouse heating effect.

Development of an HTR-Type nuclear and bifacial PV solar based integrated system to meet the needs of energy, food and fuel for sustainable indigenous cities

In this study, a unique integrated system is developed to produce multiple useful outputs, including energy, fuel, and food, for indigenous communities to achieve sustainable development and address some of the sustainability goals developed by the United Nations in this regard. The Nunavut Territory is identified with the highest food and energy insecurity across Canada for the present study. A pilot project is, in this regard, developed under a case study and thermodynamically analyzed for Iqaluit, Nunavut as an Indigenous City. The high-temperature reactor (HTR)-type pebble bed nuclear reactors are considered to be used with the copper chlorine Cu-Cl hydrogen production cycle, bifacial photovoltaic (PV) plant, gas and steam turbines, greenhouse, fish farm and residential heating systems, and multi-effect water desalination in the integrated multigenerational system. The proposed system primarily produces electricity, district heating, fresh water, domestic hot water, and hydrogen fuel. The simulations are carried out on the PVsyst and Aspen Plus. The renewable and nuclear energy systems, as well as other subsystems, are assessed via the engineering equation solver (EES) software package. The proposed integrated system has achieved a 62.64% overall energy efficiency and a 68.91% overall exergy efficiency at the average ambient conditions. Moreover, the present system is designed in different capacities for eleven indigenous communities in Nunavut Territory by considering the energy resources and local demand.

Integrated Building Energy Simulation–Life Cycle Assessment (BES–LCA) Approach for Environmental Assessment of Agricultural Building: A Review and Application to Greenhouse Heating Systems

A substantial reduction in the environmental impacts related to the construction and operation of agricultural buildings is needed to adapt to the continuing development of agriculture. The life cycle assessment (LCA) is a methodology used to quantify the environmental impact of different processes involved in the production and therefore has been increasingly applied to assess the environmental burden. However, most LCA-related research studies have focused on the overall environmental impact of the entire system without considering the energy load of the agricultural buildings. By integrating the LCA tool with other design tools such as the building energy simulation (BES), the identification of environmental hotspots and the mitigation options become possible during the design process. Thus, the objective of the paper was to identify the current integration approaches used to combine BES and LCA results to assess the environmental impact of different heating systems such as absorption heat pump (AHP) using energy from thermal effluent, electricity-powered heat pump and kerosene-powered boilers used in a conventional multi-span Korean greenhouse. The assessment result revealed that the environmental impact caused using a kerosene-powered boiler is largest in terms of the acidification potential (AP), global warming potential (GWP) and Eutrophication Potential (EP) of 1.15 × 100 kg SO2-eq, 1.13 × 102 kg CO2-eq and 1.62 × 10−1 kg PO4-eq, respectively. Detailed analysis of the result showed that the main contributor for greenhouse gas emission was caused by the type, amount and source of energy used to heat the greenhouse, which contributed to a maximum of 86.59% for case 1, 96.69% for case 2 and a maximum of 96.47% for case 3, depending on the type of greenhouse gas being considered.

BASIC PRINCIPLES OF AUTOMATION CONTROL OF HEATING OF PROTECTED GROUND STRUCTURES

This article describes how to control the operating modes of greenhouse heating systems, how to control the heating process in the daytime and in the evening, the temperature of heating furnaces using automatic regulators and relays. The effectiveness of manual and automatic control is also noted.

Development of a Low-Cost Biomass Furnace for Greenhouse Heating

The energy crisis and increasing fossil fuel prices due to increasing demands, controlled supplies, and global political unrest have adversely affected agricultural productivity and farm profitability across the globe and Pakistan is not an exception. To cope with this issue of energy deficiency in agriculture, the best alternate strategy is to take advantage of biomass and solid waste potential. In low-income countries such as Pakistan, the greenhouse heating system mostly relies on fossil fuels such as diesel, gasoline, and LPG. Farmers are reluctant to adopt greenhouse farming due to the continuously rising prices of the fossil fuels. To reduce reliance on fossil fuel energy, the objective of this study was to utilize biomass from crop residues to develop an efficient and economical biomass furnace that could heat greenhouses to protect the crop from seasonal temperature effects. Modifications made to the biomass furnace, such as the incorporation of insulation around the walls of the furnace, providing turbulators in fire tubes, and a secondary heat exchanger (heat recovery system) in the chimney, have increased the thermal efficiency of the biomass furnace by about 21.7%. A drastic reduction in hazardous elements of flue gases was observed due to the addition of a water scrubber smoke filter in the exit line of the flue. The efficiency of the biomass furnace ranged from 50.42% to 54.18%, whereas the heating efficiency of the diesel-fired heater was 71.19%. On the basis of the equal heating value of the fuels, the unit material and operating costs of the biomass furnace for wood, cotton stalks, corn cobs, and cow dung were USD 2.04, 1.86, 1.78, and 2.00 respectively against USD 4.67/h for the diesel heater. The capital and operating costs of the biomass furnace were about 50% and 43.7% of the diesel heater respectively, resulting in a seasonal saving of about 1573 USD. The produced smoke was tested as environmental friendly under the prescribed limits of the National Environmental Quality Standards (NEQS), which shows potential for its large-scale adoption and wider applications.

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.

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.

Energy savings in greenhouses by transition from high-pressure sodium to LED lighting

Greenhouses in high latitudes consume vast amounts of energy for heating and supplemental lighting. Light emitting diodes (LEDs) have been suggested as having great potential for reducing greenhouse energy use, as they are extremely efficient at converting electricity to light. However, LEDs emit very little heat, which must be compensated by the greenhouse heating system. Thus, it is unclear how much energy can be saved by LEDs when the need for extra heating is taken into account. This study presents a first analysis of the energy demands for greenhouses transitioning from high-pressure sodium (HPS) to LED lighting, providing a quantification of the total energy savings achieved by LEDs. Model simulations using GreenLight, an open source greenhouse model, were used to examine a wide range of climates, from subtropical China to arctic Sweden, and multiple settings for indoor temperature, lamp intensity, lighting duration, and insulation. In most cases, the total energy saving by transition to LEDs was 10–25%. This value was linearly correlated with the fraction of energy used for lighting before the transition, which was 40–80%. In all scenarios, LEDs reduced the energy demand for lighting but increased the demand for heating. Since energy for lighting and heating is often derived from different origins, the benefits of a transition to LEDs depend on the environmental and financial costs of the available energy sources. The framework provided here can be used to select lighting installations that make optimal use of available energy resources in the most efficient and sustainable manner.

Accumulation of solar energy to heat greenhouses

The primary task of a greenhouse is to create optimal microclimate, which doesn’t depend on external climatic conditions, to grow plants. We can observe significant air temperature and humidity difference in a traditional greenhouse during 24 hours. The stable microclimate in greenhouses is provided by different engineering systems such as heating, ventilation, lighting, etc. These systems require a lot of energy. Saving energy and reducing the mode of temperature amplitude inside the operating greenhouse during exploitation period can be achieved by using solar energy in the greenhouse heating system, namely, by using heat accumulators. However, the test method of optimal heat accumulator to equalize the temperature amplitude inside the greenhouse wasn’t described in any research. The purpose of this research is to determine the optimal heat accumulator for equalizing temperature amplitude inside the greenhouse under atmospheric effects in spring. The experimental research of the heat-humid regime was carried out for the greenhouse without any heat accumulation. Relationship between the volume and the surface area of the accumulator and its efficiency was identified.

Performance of a passive solar heating system in multi-span Moroccan greenhouse

Performance of a passive solar heating system in multi-span Moroccan greenhouse

Modelling of Ventilation Rate and Heating Rate using Multi-Module Fuzzy Control System for A Greenhouse

The implementation of Ventilation rate and Heating rate can save energy and reduce cost of production. In previous studies, ventilation rates and heating rates were calculated based on mass and energy balance but they are mainly influenced by several factors. In order to check for the effectiveness and applicability of greenhouse ventilation rate and heating rate, we study a multi-module fuzzy control method and use fuzzy logic controllers to control the coordination of a greenhouse heating and ventilation systems. The complexity is reduced by using fuzzy tool in matlab-simulink environment which enables a quick design. The experimental data showed that the new multi-module fuzzy control reduced temperature and humidity fluctuations and maintained temperature and humidity closer to the desired temperature and humidity; this method can be easily used to control other equipment in the greenhouse.

Modelling of Ventilation Rate and Heating Rate using Multi-Module Fuzzy Control System for A Greenhouse

The implementation of Ventilation rate and Heating rate can save energy and reduce cost of production. In previous studies, ventilation rates and heating rates were calculated based on mass and energy balance but they are mainly influenced by several factors. In order to check for the effectiveness and applicability of greenhouse ventilation rate and heating rate, we study a multi-module fuzzy control method and use fuzzy logic controllers to control the coordination of a greenhouse heating and ventilation systems. The complexity is reduced by using fuzzy tool in matlab-simulink environment which enables a quick design. The experimental data showed that the new multi-module fuzzy control reduced temperature and humidity fluctuations and maintained temperature and humidity closer to the desired temperature and humidity; this method can be easily used to control other equipment in the greenhouse.

GreenLight – An open source model for greenhouses with supplemental lighting: Evaluation of heat requirements under LED and HPS lamps

Greenhouse models are important tools for the analysis and design of greenhouse systems and for offering decision support to growers. While many models are available, relatively few include the influence of supplementary lighting on the greenhouse climate and crop. This study presents GreenLight, a model for greenhouses with supplemental lighting. GreenLight extends state of the art models by describing the qualitative difference between the common lighting system of high-pressure sodium (HPS) lamps, and the newest technology for horticultural lighting - the light-emitting diodes (LEDs). LEDs differ from HPS lamps in that they operate at lower temperatures, emit mostly convective heat and relatively little radiative heat, and can be more efficient in converting electricity to photosynthetically active radiation (PAR). These differences can have major implications on the greenhouse climate and operation, and on the amount of heat that must be supplied from the greenhouse heating system. Model predictions have been evaluated against data collected in greenhouse compartments equipped with HPS and LED lamps. The model predicted the greenhouse's heating needs with an error of 8–51 W m −2 , representing 1–12% of the measured values; the RMSE for indoor temperature was 1.74–2.04 °C; and the RMSE for relative humidity was 5.52–8.5%. The model is freely available as open source MATLAB software at https://github.com/davkat1/GreenLight . It is hoped that it may be further evaluated and used by researchers worldwide to analyse the influence of the most recent lighting technologies on greenhouse climate control. • Model for lighting in greenhouses, including HPS and LED lamps, was developed. • Model was evaluated using data from a greenhouse with HPS and LED top-lights. • Model evaluates energy requirements of the greenhouse with an accuracy of 1–12%. • Model predicts indoor temperature and humidity with an RRMSE of 6–11%. • Model is publicly available in free open source format.

Numerical and experimental study of laboratory and full-scale prototypes of the novel solar multi-surface air collector with double-receiver tubes integrated into a greenhouse heating system

The application of greenhouse technologies is rapidly expanding in China and other regions of the world with the continental climate. Such technologies are characterized by a considerable consumption of fossil fuels, especially in winter periods. Various renewable energy technologies are used to reduce the energy demand in greenhouses, including solar heating. Simpler designs of water or air solar collectors are preferred without sun-tracking devices and reduced dimensions and weight. In this work, a novel solar multi-surface air collector with double-receiver tubes, which does not require a sun-tracking device is proposed and has increased concentration ratio and sun rays convergence and reduced thermal losses. The laboratory and full-scale prototypes of the proposed novel collector were manufactured and tested in laboratory conditions during the December-January period as a part of the greenhouse with the active-passive ventilation wall and latent thermal storage, located in the Beijing Region. Results of experiments demonstrate that the solar collector increases the average temperatures of the greenhouse north wall inner surface by 7.5 °C, indoor air during the night-time by 1.8 °C and indoor soil by 1.5 °C. The novel collector provided active heat gains of 11.831 GJ during the December-January period and satisfied from 11% to 81% of the heat load. A lumped parameter mathematical model of the proposed collector was developed, and the comparison of simulation results and experimental data demonstrate its high accuracy in prediction of the collector performance. The model was used to study the influences of outdoor meteorological parameters, air velocity in the receiver tubes and their length on the performance of the collector. This data was used to determine the rational design parameters and air velocity of the full-scale collector. The model was also used to rationalize the variation of air velocity in the receiver tube during the day.

Novel composite phase change materials with enhancement of light-thermal conversion, thermal conductivity and thermal storage capacity

Composite phase change materials (CPCMs) play a key role in solar energy conversion and storage. However, it is difficult to efficiently utilize solar energy due to their inherent low thermal conductivity, low light absorption and the usual competitive nature between thermal conductivity and latent heat. In this work, novel CPCMs were developed by using TiO2-TiC-C loaded expanded vermiculite (EVT) as a supporting matrix and lauric-myristic-stearic eutectic mixture (LA-MA-SA) as a PCM. The EVT was further acidized (EVTa) to enhance its PCM absorbability. Owing to the high thermal conductive and light absorption nature of TiO2-TiC-C nanocomposite, the prepared CPCMs exhibit efficient light-thermal energy conversion. The thermal conductivities of LA-MA-SA/EVT and LA-MA-SA/EVTa were 0.694 and 0.676 W/(m K), respectively. And the PCM content in LA-MA-SA/EVT and LA-MA-SA/EVTa were 64.5 and 70.6 wt%, respectively. Moreover, the feasibility of CPCM being a water heating source was experimentally confirmed. These novel CPCMs have good application prospect in low temperature solar-thermal installations, such as temperature adaptable greenhouse and water heating system.