Numerical Experiments on Light Transmission in Greenhouses (2)

Abstract

In the preceding paper (Kozai 1973), an analytical method has been developed for calculating the distribution of direct solar irradiation in an isolated single-span greenhouse glazed with flat glass as a function of house dimensions, house orientation, latitude of greenhouse site, time of year, and the mean radiation characteristics of the greenhouse site. In this paper, it is clearly shown that the proportion of the area of a greenhouse surface that may be regarded as freely transmitting sunlight varies widely with the shape of a structural frame and geometrical position of the sun relative to the frame.
Applications of the model to various greenhouses are described in this paper. In this analysis no consideration was given to internal reflection. The model considered the effect has already been described in the other paper (Kozai 1972b).
Some of the results computed for the winter months for the greenhouses whose shapes and dimensions are given in Fig. 1 and Table 1 are as follows:
1. The transmissivity of the greenhouse covered with only horizontal structural elements for direct solar light is not largely decreased with the increase of the depth of the structural elements. However, the horizontal structural elements running E-W directionin the south roof and wall cause a nonuniform space distribution of the daily integrated direct solar light in a greenhouse.
2. The transmissivity of a N-S house for direct solar light is sharply decreased with the increase of the depth of the glazing bars.
3. The space average transmissivity of the NW-SE house for direct solar light is decreased to about 42% at around 9:30 in winter.