Double glazings combined with phase change materials (PCM) result in daylighting elements with promising properties. Light transmittances in the range of 0.4 can be achieved with such facade panels. Compared to a double glazing without PCM, a facade panel with PCM shows about 30% less heat losses in south oriented facades. Solar heat gains are also reduced by about 50%. This results in calculated U-eff-values of -0.3 to -0.5 W m(-2) K-1, depending on PCM used. For an optimised panel, we calculated an U-eff-value of -0.6 W m(-2) K-1. Although the U-eff-value of a double glazing is -0.8 W m(-2) K-1, the PCM-systems may prove advantageous in lightweight constructed buildings due to their equalised energy balance during the course of day. Facade panels with PCM improve thermal comfort considerably in winter, especially during evenings. In summer, such systems show low heat gains, which reduces peak cooling loads during the day. Additional heat gains in the evening can be drawn off by night-time ventilation. If a PCM with a low melting temperature of up to 30 degreesC is used, thermal comfort in summer will also improve during the day, compared to a double glazing without or with inner sun protection. A homogeneous appearance of the PCM-systems is achievable by use of a concealment, like a screen-print glazing. (C) 2004 Elsevier Ltd. All rights reserved.