ESTIMATIVA DA RADIAÇÃO SOLAR GLOBAL EM ESTUFA DE POLIETILENO A PARTIR DO BRILHO SOLAR

Resumo

O trabalho descreve uma analise da transmissividade da radiação global, o brilho solar em estufa de polietileno, e a obtenção da equação de estimativa da radiação global ( H_G^IN ) em função da  razão da insolação  interna (n / N)^IN  e  externa ( n / N )^EX. As bases de dados da  radiação global e número de horas de brilho solar nos dois meios, foram medidas no período de março de 2008 e fevereiro de 2009 em Botucatu/SP/Brasil. A  correlação (tipo Y = aX) obtida para  a radiação global foi H_G^IN = 0,762 H_G^EX , com coeficiente de determinação de R²= 0,9948,   enquanto  o brilho solar  (n )^IN = 0,768 ( n  )^EX   com R²= 0,9384. As equações de Ångström-Prescott tipo Y = a + b X obtidas por regressão linear em função da razão de insolação interna e externa foram:

                                                   H_G^IN / H₀ = 0,23 + 0,35 ( n / N )^IN 

                                                   H_G^IN / H₀ = 0,23 + 0,28 ( n / N )^EX 

com coeficientes de determinação R²= 0,9104  e  R² = 0,8543    respectivamente.

Palavras-chave: Ambiente protegido, equação de Ångström- Prescott, razão de insolação.

GLOBAL SOLAR RADIATION ESTIMATION INSIDE POLYETHYLENE GREENHOUSES FROM THE SUNSHINE DURATION

SUMMARY: This paper describes the study of the hours of bright sunshine (n ^IN) inside a polyethylene tunnel type greenhouse, and their relations to the hours of bright sunshine outside (n ^EX), astronomic day duration (N), global radiation inside (H_G^IN) and global outside (H_G^EX) for a database of measurement in the period from March 2008 to February 2009 in Botucatu. It was calculated the annual evolution of the mean monthly clearness index Kt atmosphere of that ranged from 39.6% to 62.7%, with an annual average of 50.0%; the transmissivity of global radiation in polyethylene cover (τ_G = G^IN / G^EX), which ranged from 79.4% to 71.2%, with an annual average of 75.6%; the ratio of the number of hours of bright sunshine inside and outside the greenhouse of polyethylene (N^IN / N^EX), which ranged from 65.0% to 82.0% with an annual average of 76.0%; and the relationship between relative sunshine inside and outside the greenhouse of polyethylene (n / N) ^IN / (n / N) ^EX, which ranged from 65.0% to 82.0% with an annual average of 75.0%. For the annual collation of data per day, was determined to estimate a linear equation between the relative sunshine inside and outside the greenhouse as polyethylene (n / N) ^IN = 0.768 (n / N) ^EX, with a high degree of correlation R² = 0.9384. It was also obtained by linear regression equation for Ångström H_G^IN depending on the ratio relative sunshine inside (n / N) ^IN and outside (n / N) ^EX as: H_G^IN / H₀ = 0.23 + 0.35 (n / N ) ^IN and H_G^IN / H₀ = 0.23 + 0.28 (n / N) ^EX with a coefficient of determination R² = 0.9104  and R² = 0.8543 respectively.

Keywords: Greenhouse; Ångström equation; relative sunshine.