Estimation of Thermal Diffusivity for Greenhouse Soil Temperature Simulation

Jizhang Wang,Peter P Ling,Wee Fong Lee

doi:10.3390/app10020653

Jizhang Wang, Peter P Ling + Show 1 more

Open Access

https://doi.org/10.3390/app10020653

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Journal: Applied sciences	Publication Date: Jan 16, 2020
Citations: 9	License type: CC BY 4.0

Affiliation: Jiangsu University, The Ohio State University

Abstract

In greenhouse energy balance models, the soil thermal parameters are important for evaluating the heat transfer between the greenhouse air and the soil. In this study, the soil thermal diffusivity was estimated from greenhouse soil temperature data using the amplitude, phase-shift, arctangent, logarithmic, and min-max methods. The results showed that the amplitude method and the min-max method performed well in estimating the soil thermal diffusivity. The obtained soil thermal diffusivity was input into a sinusoidal model to determine the greenhouse soil temperature at different soil depths. For greenhouse applications, the daily average soil temperature at different depths was predicted according to the temperature at the surface and the annual mean soil temperature. The model was validated using soil temperature data from summer and winter, when the greenhouse was cooled and heated, respectively.

Highlights

Collecting excess daytime solar energy to heat a greenhouse at night is an economic approach to conserve greenhouse energy consumption
Greenhouse conditions are often maintained at constant temperatures that are controlled by active cooling and heating systems, the greenhouse soil temperature is affected by the greenhouse air and by the change in solar radiation [19], such as the outdoor conditions
Our results showed that in the greenhouse, the diurnal soil temperatures at different depths have a steady sinusoidal behavior

Summary

Introduction

Collecting excess daytime solar energy to heat a greenhouse at night is an economic approach to conserve greenhouse energy consumption. Solar radiation is captured by the soil during the daytime and released at nighttime to warm the greenhouse air. To better understand the heat transfer mechanisms between the soil and the greenhouse air, studying the thermal transfer capacity of the greenhouse soil is desirable [1,2]. The two most important soil thermal properties are the heat transfer coefficients between the floor and the greenhouse air, as well as between the floor surface and the greater ground depths [3,4,5,6]. To study the time delay, researchers have often used soil temperature data to estimate the thermal diffusivity. Horton and Wierenga (1983) estimated soil thermal diffusivities based on measured soil temperature data using six different methods (the amplitude, phase-shift, arctangent, logarithmic, numerical, and harmonic methods). The calculated apparent thermal diffusivities were used to predict the soil temperatures before they were compared to another set of measured temperatures [7]

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Conclusion