Soil Warming System Research Articles

Investigation of photo-thermal performance of compound parabolic concentrator system for soil heating in facility agriculture

Aiming at the large carbon emissions of facility agricultural heating in severe cold regions in winter, a compound parabolic concentrator based soil heating system was presented. The system integrated with novel trough compound parabolic concentrator and was used for soil heating in facility agriculture. Following the structure of the compound parabolic concentrator, TracePro software was selected to trace the light in the compound parabolic concentrator. The variation trend of the light escape rate of the compound parabolic concentrator with the different incident angles was analyzed. Based on the calculation results, the performance of the solar collector system was investigated, and the impact of circulating air velocity on the photo-thermal performance of the solar collector system was explored. Research results indicate that when the circulating air velocity is 1.4 m/s and the average ambient temperature is about 28.9?, the temperature of the system outlet is up to 90.9?. The average instantaneous heat collection, maximum photo-thermal conversion efficiency, and unit area heat collection of the system are 740.6 W, 27.83%, and 0.8 MJ/m2, respectively. This research can effectively promote the efficient integration of the solar collector system in facility agriculture.

Experimental and Numerical Study of an Active Solar Heating System with Soil Heat Storage for Greenhouses in Cold Climate Zones

Root temperature is an important ecological factor affecting plant growth. A solar greenhouse with an active solar heating system was built in Jinan, in the cold climate zone of northern China. Experiments encompassing the complete cycle of heat collection, heat storage, and heat release were carried out. Using the experimental data, the numerical simulation of soil heat storage with a variable heat flow was executed using the ANSYS (ANSYS Inc., Pittsburgh, PA, USA) Fluent software. Soil temperature fields were studied on typical sunny days and typical cloudy days in the transition season and winter. The solar collector efficiency and coefficient of performance of the system were investigated. The applicability of this active solar soil heating system with soil heat storage for cold areas was evaluated. The results showed that the system effectively maintained suitable ground temperatures to prevent plant growth inhibition caused by low ground temperatures in winter. During the experimental period, the solar collector efficiency was 47% and the system’s coefficient of performance was 67.70. The thermal performance of the system was much better than a traditional energy system. This study showed that this active solar heating system with soil heat storage is an economic and feasible way to increase soil temperatures in solar greenhouses in cold areas.

Performance Analysis of Compound Parabolic Concentration Photothermal and Photoelectricity Device for Soil Heating in Facility Agriculture

It is difficult for solanum crops to grow continuously during winter in severe cold regions. Thus, a soil heating system for facility agriculture based on solar concentration technology was proposed, and a novel compound parabolic concentration photothermal and photoelectricity device (CTPV) equipped in the system was designed to address this problem. In accordance with the structure of the device, LightTools optical software was selected to analyze the variation trend of the light escape rate of the device with the different incident angles. On the basis of the calculation results, an experimental test system was used to investigate the relationship of the air temperature of the inlet and the outlet, total output power of the solar cells, and photothermal and photoelectricity efficiency of the device with the operation time during a sunny day. Research results reveal that the light escape rate of the device is 5.36% at an incidence angle of 12°. At a velocity of 1.5 m/s, the maximum air temperature of the outlet can reach 55.6 °C, and the total output power of the solar cells is 474.4 W. The variation of the total power of the solar cells is consistent with the simulation results. The maximum instantaneous heat collection and the maximum photothermal and photoelectricity efficiency of the device are 306 W and 60.4%, respectively, and the average efficiency is 44.9%. This study can serve as a reference for compound parabolic concentration technology applied for soil heating in facility agricultural soil heating systems.

Mathematical modelling of heat transfer in a greenhouse with surface soil heating system

The use of low-temperature heat of industrial and natural origin for heating the soil in greenhouses allows practitioners to get very early vegetable and berry crops. The paper suggests a mathematical model of greenhouse heat exchange with a system of soil surface heating for substantiating the system structure and its efficiency in different conditions. The solution of the mathematical model was performed using the method of least squares in COMSOL Multiphysics software. The comparison of the results of experimental studies with the results of mathematical modelling revealed that the proposed mathematical model with a high degree of reliability allows predicting the thermal regime in greenhouses with surface soil heating using cover sleeves.

Experimental study of the burning-cave hot water soil heating system in solar greenhouse

In the northern China areas, the traditional heating methods are widely used in solar greenhouse, for example: electric heating, hot air heating, hot water heating, burning-cave heating etc. If copying the assuring building indoor environment of constant heating ways into solar greenhouse, it will further increase building energy consumption, thus improving the efficiency of energy utilization, establishing appropriate growing environment, and realizing the agricultural waste recycling are important ways of consistent with the Chinese conditions, construction of sustainable development, improving the efficiency of the greenhouse production. To solve the problem of traditional heating method for high heating energy consumption, the inharmonious between greenhouse air temperature and soil temperature, uneven soil temperature, the research build the burning cave hot water soil heating system of solar greenhouse experimental platform in accordance with principle of energy cascade utilization. This experiment platform will transfer burning cave internal heat into soil heating system. The soil is evenly heated by system. Through testing the actual operation effect of the burning cave hot water soil heating system of new solar greenhouse, electric heating system, no taking any heating measures system, burning cave hot water soil heating system of solar greenhouse can improve the soil average temperature 5 ∼ 6 °C. This research provides experimental basis for practical applications and promotion.

Heat transfer analysis of soil heating systems

Heat transfer from a pipe in a soil heating system has been numerically examined in this study. The Brinkman-extended Darcy equations are used to model the flow in the soil while Navier--Stokes equations are used for that above the soil. A parametric study has been performed to investigate the effects of Rayleigh number, Darcy number, and air layer thickness on the flow patterns and heat transfer rates. The results show that heat transfer increases with the Rayleigh number, but the convective strength decreases with a reduction in the Darcy number. The present results confirm the existence of a critical fluid layer thickness that leads to a minimum heat transfer from the pipe. However, the critical layer thickness is a more complicated function of Rayleigh number and Darcy number than that reported in the previous studies.

ESTIMATION OF THE ENERGY CONSUMPTION OF ELECTRICAL WIRE HEATING IN SAND SUBSTRATES ACCORDING TO THE TARGET ROOT ZONE TEMPERATURE

Heat transfer processes occurring in greenhouse cultivation substrates are very complex due to the high number of environmental and soil factors involved. Few estimation methods allow establishing the energy consumption of the heating elements as a function of the design parameters (depth and spacing) and of environmental and cultivation criteria, such as the ambient temperature and the target root zone temperature suitable for plant development. The objctive of this work is to analyze the influence of the target root temperature on the energy consumption of six configurations of soil heating system: 150, 225 and 300 mm depth with 100 and 150 mm spacings. An experimental test was arranged to measure ambient and root temperatures and operation times of the electrical heating cables. Dimensional analysis was applied to data obtained experimentally to relate all the involved variables: thermal properties of the substrates, depth, spacing, power and operation time of the heating cable, daily mean values of the measured temperatures. The obtained expressions permitted to quantify the energy consumption. An increase in target temperature in the root zone brings about increases in daily energy demand. An increase in air temperature brings about a decrease in energy requirements, but the slope of the curves increases as a function of target temperature. At a fixed heating cable depth, energy consumption is always higher for 100 mm cable spacing than for 150 mm spacing, and the differences become larger for shallower heating cable installation depths. The heating system with the cable installed at 150 mm spacing and 150 mm depth obtains the lowest energy consumption value, while the configuration with the cable installed at 100 mm spacing and 150 mm depth, and the configurations with the cable buried at 225 mm depth require the highest consumption.

Financial Assessment of a new Soil Heating Technology for Off-season Asparagus Production

The financial effectiveness of a soil heating system placed under the crowns in each raised bed (UCR) of Asparagus plants (Asparagus officinalis L.) was evaluated and then compared with a traditional greenhouse production system (TPS), a plastic greenhouse without any heating system, in northern Greece. Several appraisal approaches, such as net present value, net present value adjusted for inflation and benefit/cost ratio, were used to evaluate the effectiveness of UCR system for off-season Asparagus production. Results demonstrate the importance of UCR system in terms of volume of production, gross returns and overall effectiveness. Finally, the performed sensitivity analysis indicates that product price variations alter the accrued benefits.

Root production is determined by radiation flux in a temperate grassland community

AbstractAccurate knowledge of the response of root turnover to a changing climate is needed to predict growth and produce carbon cycle models. A soil warming system and shading were used to vary soil temperature and received radiation independently in a temperate grassland dominated by Holcus lanatus L. Minirhizotrons allowed root growth and turnover to be examined non‐destructively. In two short‐term (8 week) experiments, root responses to temperature were seasonally distinct. Root number increased when heating was applied during spring, but root death increased during autumnal heating. An experiment lasting 12 months demonstrated that any positive response to temperature was short‐lived and that over a full growing season, soil warming led to a reduction in root number and mass due to increased root death during autumn and winter. Root respiration was also insensitive to soil temperature over much of the year. In contrast, root growth was strongly affected by incident radiation. Root biomass, length, birth rate, number and turnover were all reduced by shading. Photosynthesis in H. lanatus exhibited some acclimation to shading, but assimilation rates at growth irradiance were still lower in shaded plants. The negative effects of shading and soil warming on roots were additive. Comparison of root data with environmental measurements demonstrated a number of positive relationships with photosynthetically active radiation, but not with soil temperature. This was true both across the entire data set and within a shade treatment. These results demonstrate that root growth is unlikely to be directly affected by increased soil temperatures as a result of global warming, at least in temperate areas, and that predictions of net primary productivity should not be based on a positive root growth response to temperature.

Heat and moisture transfer in soil warming by circulating warm water in a buried pipe line.

In warming the soil bed for the protected cultivation of a typical water retentivity by circulating warm water, changes of temperature and moisture content distributions of the soil with time were predicted theoretically by applying Philip and deVries' model. Heat and moisture transport properties were estimated systematically, on the basis of the matric potential of soil water expressed by an approximate function of temperature and moisture content, and of the several empirical constants. Temperature and moisture content distributions were calculated by finite difference technique for the cases of 30°C, 40°C and 50°C of water temperature Tl, assuming the bare soil. It was shown that the drying rate of the soil around the warm water pipe becomes larger as Tl becomes higher, and that the dry out would be limited within an extremely narrow region around the pipe. The calculated results shown here would become useful information on planning the soil warming system in a greenhouse.

An investigation of practical process design and control of a soil warming system with heat generated in compost.

An optimum design and a control method of a soil warming system with heat generated in compost were investigated, following a concept of process design. Provided that many of the input data such as thermal physical properties of compost bed, the amount of heat required to soil warming, and the micrometeorological condition in a greenhouse are given and that the dimensions of the tube for heat extraction is premised, there are only two decision variables to be optimized. One is the space of arrangement of the tubes for heat extraction and the other is the flow rate of medium fluid in the tubes. Optimum numerical values of the decision variables were obtained, taking account of stability in operation, increase in heat efficiency and reduction of the cost of equipments of heat source. Assuming that the system is applied to the protected cultivation in a small scale, a representative example of the flow sheet of the system was proposed, and operation manuals of the system were described. Optimum numerical values of the decision variables, operation manuals and the flow sheet proposed here would become the basis of the detailed design of equipments and devices of the system.

Application of heat generated in compost to soil warming.

A simulation model of a soil warming system with a compost heat extractor was proposed. The soil warming system for the model simulation was constituted by some compost beds for heat extraction, pipe lines for circulation of the medium water and water reservoirs. The application of the simulation model to the practical example for warming the soil bed was investigated by the analysis of the heat balance of the system, using some actual operating conditions. The heat balance in the soil warming was treated analytically and systematically, taking account of the process control of the system. The concept of the model simulation and procedure for the systematical analysis of the heat balance in the soil warming may be of use for the planning, design and operations of the actual soil warming system.

The use of soil warming to protect sports fixtures

This paper discusses the heating of soil in sports grounds to reduce cancellations in poor weather conditions. The correct type of drainage is vital to a pitch but it is even more important if the owner is considering installing a soil-warming system. Various designs of system are investigated from the original research through to installation, while considering their running costs and effect on turf. The alternatives to undersoil heating are examined as well as new systems which have yet to appear in major sports grounds. The fundamental approach to heat transfer is applied to the heating of buried pipes. Conclusions reached include the fact that soil warming of some kind makes economic sense.

Design procedures for subsurface soil-warming pipe systems

Soil warming has the potential to be an alternative to conventional heating methods in agriculture. It has been proven that crop yield is enhanced and growing periods are shortened with relatively little energy input. A subsurface soil-warming system consists of a network of parallel horizontal hot-water pipes buried at an appropriate depth in the soil to maintain a favourable temperature field throughout the root zone. Theoretical steady-state, constant property soil-warming models for four pipe configurations are presented in dimensionless form. Experimental verification of one of the configurations is presented. A procedure for establishing optimal pipe depth and spacing according to root-zone heating requirements is described and an example is illustrated. Effects of diurnal temperature fluctuations are also considered. Applications for these models include greenhouse crops and small unprotected crops of several hectares.

Soil Warming with Power Plant Waste Heat in Greenhouses1

Abstract A subsurface soil warming system consisting of parallel line heat sources, buried 52 cm deep and 122 cm apart, simulating a proposed arrangement for the use of power plant waste heat, was installed in a plastic covered greenhouse. Soil warming with a heat source temperature of about 36°C increased soil temperatures substantialy but had little effect on the air temperature.

Insulated soil-heating system to prevent frost-heaving of field instrumentation

Insulated soil-heating system to prevent frost-heaving of field instrumentation