A suspended particle device (SPD) switchable glazing changes its state from opaque to transparent in the presence of a power supply. SPD glazing’s near normal transmission varies with incident angle and clearness index.
Due to a lower diffuse component, higher glazing transmission ensues at higher clearness indices. Transmittance values for different azimuthal incident angle for a SPD glazing for its “transparent ” and “opaque” states have been determined.
In Dublin, be low 0.5 clearness index, isotropic diffuse transmittance was prevailed while transmission of direct insolation was dominant above 0.5 clearness index. For south facing vertical plane SPD glazing transmittance in its transparent and opaque states are 0.25 and 0.025 respectively while clearness index is below 0.5.
Solar Energy Material for Glazing Technology:
A wide variety of different advanced glazing technologies are available that (i) control heat and/or light gain, (ii) provide low heat loss (iii) control air-flow, (iv) deflect day light deep into a room and/or (v) provide reduced noise transmission.
A switch able transparency glazing can be actuated electrically or non-electrically. Electrically actuated glazings include AC-powered suspended particle devices (SPD) and DC powered electrochromic (EC) devices. Electrically-actuated SPD glazing can provide control of solar heat gain and glare in building fenestration applications.
MEASUREMENTS AND RESULTS
The variation of spectral transmission with wave length of an SPD glazing in transparent and opaque states, measured in a laboratory using AvaSpec-UL S2048L Star Line Versatile Fiber optic spectrometer. Solar spectral irradiance at AM 1.5 is for comparison. As can be seen, an opaque SPD glazing would be able to control visible solar radiation, transmitting only a relatively small portion of solar radiation below 820 nm.
COMPARISON AND INTERPRETATION OF RESULTS
The transmission of SPD glazing in transparent and opaque state using different model described in Table 1. It was found that the model described by Montecchi & Polato gave best fit for x=3. Karlsson & Ross gave best fit for A=8 p=2 q=2, beta =2. At higher incident angle, little variation was observed for Karlsson & Ross model from those of Waide & Norton and Montecchi & Polato. Incident angle between 35–60, the measured transmittance deviates from other three models.
Correlation between clearness index and glazing transmittance, transmitted solar energy and solar heat gain coefficients has been evaluated for SPD glazing in its “transparent” and “opaque” state.
For clearness index be low 0.5, isotropic diffuse transmittance was dominant whereas after 0.5 clearness index, transmission of direct in solation was dominant. However, vertical plane glazing transmittance changes with season, day and time, single value glazing transmittance of 0.25 and 0.025 for transparent and opaque south facing SPD glazing can be chosen through out the year while clearness index is less than 0.5.
Present study of fers a yearly usable single glazing transmittance, transmitted solar energy, solar heat gain coefficient for SPD glazing in transparent and opaque state, which is advantageous for the building designers in northern latitude areas.
Source: Dublin Institute of Technology
Authors: Aritra Ghosh | Brian Norton | Aidan Duffy