The mathematical model of the longwave optical properties for a curved venetian blind is developed in this study.
The venetian blind is treated as an effective layer.
A six surface enclosure is created from the two adjacent consecutive curved slats.
The overlap length of the slat when closed is defined as part of the surfaces in the enclosure.
The radiosity method is used to determine the longwave optical properties of the effective layer.
The developed longwave optical properties are transmittance,reflectance, absorptance and emittance.
The longwave optical properties are found to vary strongly with the slat angle.
The longwave optical properties are also dependent on other parameters, such as slat emittance,slat width, distance between two consecutive slats and on the longwave optical properties and the position of the slat which getting zero transmittance value.
The slat width and the distance between adjacent slats also have strong effect on the longwave optical properties.
The discrepancy between the longwave optical properties calculated from the curved slat model and from the flat slat
model can be significant when the slat curvature is increasing.
The steady state energy balance method which accounted for the existing of the diathermanous layer along with the developed longwave optical properties is used to determine the surface temperature of the effective layer.
The empirical expression for the total heat flux from the indoor glass window and the adjacent venetian blind is adopted in the developed model to determine the surface temperature of the venetian blind.
The validation of the developed model for calculating the longwave optical properties is performed by comparing the predicted surface temperature of the venetian blind with the measured surface temperature.
The agreement of the predicted and measured result is good within the accuracy of the measurement method and measurement instruments.
Better measurement methods and measurement instruments are needed for better validation.
With the mathematical models for calculating the longwave optical properties and surface temperature of the curved venetian blind, one is able to determine the thermal performance of the glass windows installed with venetian blinds with
respect to thermal comfort.
Using the developed longwave optical properties along with the shortwave optical properties of the venetian blind, one can determine the thermal performance of the system of glass windows and venetian blinds in terms of heat transmission and
thermal comfort.