Numerical and experimental validation for the thermal transmittance of windows with cellular shades

Abstract

Some highly energy efficient window attachment products are available today, but more rapid market adoption would be facilitated by fair performance metrics. It is important to have validated simulation tools to provide a basis for this analysis. This paper outlines a review and validation of the ISO 15099 center-of-glass zero-solar-load heat transfer correlations for windows with cellular shades. Thermal transmittance was measured experimentally, simulated using computational fluid dynamics (CFD) analysis, and simulated utilizing correlations from ISO 15099 as implemented in Berkeley Lab WINDOW and THERM software. CFD analysis showed ISO 15099 underestimates heat flux of rectangular cavities by up to 60% when aspect ratio (AR) = 1 and overestimates heat flux up to 20% when AR = 0.5. CFD analysis also showed that wave-type surfaces of cellular shades have less than 2% impact on heat flux through the cavities and less than 5% for natural convection of room-side surface. WINDOW was shown to accurately represent heat flux of the measured configurations to a mean relative error of 0.5% and standard deviation of 3.8%. Several shade parameters showed significant influence on correlation accuracy, including distance between shade and glass, inconsistency in cell stretch, size of perimeter gaps, and the mounting hardware.

Parametric analysis on the heat transfer, daylight and thermal comfort for a sustainable roof window with triple glazing and external shutter

“…experimental validation has been conducted to evaluate thermal transmittance of windows with cellular shades [10]. An experimental study by E.M. Alawadhi et al [11] has compared heat flux from indoor surface of the window to room depending on the opening of the shutter in a hot climate.…”

Cellular Shade Energy Savings in a Commercial Setting

“…The number of studies on cellular shades is also limited compared with other shading devices. Hart performed experimental testing of cellular shades in a laboratory environment using 13 cellular shades [4]. Hart's study validated the heat flux simulated by WINDOW [5] against measured data but did not measure or validate the solar heat gain.…”