modelSolar_model

Global, PAR and NIR heat fluxes
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Information

The solar radiation incident in a greenhouse can be split in three spectral parts: ultra violet (UV, from 0.3 to 0.4 μm), visible light (from 0.4 to 0.7 μm) and near infrared light (NIR, from 0.7 to 3 μm). The visible light has an interest for biological growth and is referred as photosynthetically active radiation (PAR) in greenhouse modeling. The fraction of UV is 6- 10% and of PAR is 45-60% of the global radiation. However, for plant growth it is common to assign 50% to PAR, neglect the UV and assign the other 50% to NIR. Besides the spectral division, the solar radiation can be divided in direct and diffuse radiation. The solar model of this work is simplified by making no distinction between diffuse and direct solar radiation and by assuming that the transmission coefficient of the greenhouse cover does not depend on the solar angle.

This model computes the short-wave radiation originated from the sun absorbed by the different components of a greenhouse. Therefore, the optical properties of the greenhouse components are parameters of the model. The user can set the parameters according to their case study. In case the user does not have this data, the default values, which are related to typical materials, can be used. Default values of the parameters are given for tomato crop, single-glass cover, concrete floor and aluminised screen.

A detailed description of the model equations can be found in the online documentation of the library https://greenhouses-library.readthedocs.io/en/latest

The solar model icon has one input connector, for the global irradiation, and four output connectors, whose output values are equal to the absorbed global radiation by (from top to bottom): the cover, the air, the canopy and the floor. Each output connector must be connected to the short-wave input connector of its corresponding component. The model outputs the radiation values in Wm⁻². However, the PAR absorbed values are also available in the model in μmol{photons}m⁻²s⁻¹, for which a conversion factor from global radiation to PAR equal to 2.3 μmol{photons} J⁻¹ is used.

Parameters

TypeNameDefaultDescription
Modelica.Units.SI.AreaAfloor surface
Realeta_glob_air0.1Ratio of global radiation absorbed by greenhouse construction elements
Canopy
RealK1_PAR0.7
RealK2_PAR0.7
RealK_NIR0.27
Realrho_CanPAR0.07
Realrho_CanNIR0.35
Floor
Realrho_FlrPAR0.07
Realrho_FlrNIR0.07
Roof
Realtau_RfPAR0.85
Realrho_RfPAR0.13
Realtau_RfNIR0.85
Realrho_RfNIR0.13
Thermal Screen
Realtau_thScrPAR0.6
Realrho_thScrPAR0.35
Realtau_thScrNIR0.6
Realrho_thScrNIR0.35

Connectors

TypeNameDefaultDescription
Interfaces.Heat.HeatFluxInputI_glob
Interfaces.Heat.HeatFluxOutputR_SunCov_Glob
Interfaces.Heat.HeatFluxOutputR_SunAir_Glob
Interfaces.Heat.HeatFluxOutputR_SunCan_Glob
Interfaces.Heat.HeatFluxOutputR_SunFlr_Glob

Components

TypeNameDefaultDescription
RealLAI1Leaf Area Index
RealSC0Thermal screen closure
Modelica.Units.SI.HeatFluxR_t_PARTransmited flux of the cover
Modelica.Units.SI.HeatFluxR_NIRIncident flux on the cover
Modelica.Units.SI.HeatFluxR_t_GlobTotal transmitted flux, radiation above the canopy
Modelica.Units.SI.HeatFluxR_SunCan_PAR
Modelica.Units.SI.HeatFluxR_FlrCan_PAR
Modelica.Units.SI.HeatFluxR_SunCan_NIR
Modelica.Units.SI.HeatFluxR_PAR_CanTotal PAR absorbed by the canopy
RealR_PAR_Can_umolTotal PAR absorbed by the canopy
Modelica.Units.SI.HeatFluxR_SunFlr_PAR
Modelica.Units.SI.HeatFluxR_SunFlr_NIR
Modelica.Units.SI.PowerP_SunCov_Glob
Modelica.Units.SI.PowerP_SunCan_Glob
Modelica.Units.SI.PowerP_SunAir_Glob
Modelica.Units.SI.PowerP_SunFlr_Glob
Realtau_CF_NIR
Realrho_CF_NIR
Realtau_CCF_NIR
Realrho_CCF_NIR
Realalpha_CanNIR
Realalpha_FlrNIR
Realtau_ML_covNIR
Realrho_ML_covNIR
Realtau_covNIR
Realrho_covNIR
Realalpha_covNIR
Realtau_ML_covPAR
Realrho_ML_covPAR
Realtau_covPAR
Realrho_covPAR
Realalpha_covPAR
Realeta_glob_PAR0.5
Realeta_glob_NIR0.5
Realeta_GlobPAR2.3Conversion factor from global radiation to PAR, umol photols/J