For decades, various technologies have been developed aiming to enhance the energy efficiency of buildings. As a recent example, fluidic windows have been reported which literally enable to wrap buildings into a liquid layer and to transform the building envelope into a thermally active system for energy harvesting, distribution and storage. Elaborating on this concept, we now consider the performance of insulation glass units (IGU) which implement glass-glass capillary panels for liquid circulation. Such devices contain a scalable heat pump that can reversely be operated in active cooling or heating modes. By bridging the insulation panel inside the window, also passive cooling functionality is achieved. Long-term computational performance analysis shows that adequate thermal comfort can be ensured with different window-to-floor size ratios, and for different internal heat gain, for example, caused by differences in room occupation. For a size ratio of 0.4, we demonstrate a competitive seasonal performance factor, i.e., ∼6.5 for heating and ∼10.9 for cooling. On-device photovoltaic power can cover more than four fifths or the annual electricity consumption of all auxiliary components. For the size ratio of 0.4 in a highly-occupied office room, the device specific primary energy consumption ensuring year-over thermal comfort is as low as ∼2.9 kWh/(m 2 a).

There has been a growing trend for buildings with large glazing size. As a trade‐off, this comes with enhanced solar heat input and/or reduced thermal insulation. Several approaches are being followed to reduce the energy consumption in these buildings, including the prolific field of smart windows. In a previous report, a fluidic window device for thermal harvesting and air‐conditioning was introduced. Using this example, the impact of a building's window‐to‐wall ratio on the triple glazed fluidic window's energy consumption and user thermal comfort is evaluated, providing design guidelines for large‐scale implementation of such smart windows with real‐world buildings. The analysis shows that the proposed window design reduces the primary energy demand as compared to using a conventional air‐conditioning system. Building simulation results indicate that the system enables satisfying thermal comfort for buildings with different window‐to‐wall ratios. Although a higher window‐to‐wall ratio improves the heat pump efficiency, it requires more heating and cooling energy. On‐device photovoltaic modules may be used for changing this relationship. In this case, the proposed device may become self‐sufficient once the transfer efficiency is high enough. It is argued that similar considerations should be applied to other types of smart window technologies.

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Recently, we introduced a transparent capillary glass panel fabricated by lamination of a structured glass sheet and a thin glass cover used for liquid circulation. Major applications of such device are room heating and cooling and energy harvesting for heat pumps. In order to model a façade of a building, a story of a building or even the entire building, simplified but accurate models for the temperature and the fluid flow distribution within the capillary panel as well as a device optical and thermal model are necessary. In this paper, our simplified models are introduced.

Erfahrungen mit hohen Heizenergieeinsparungen nach verbesserten Anlageneinstellungen haben in der Praxis auf den Begriff des Verschwendungspotenzials geführt. In dieser Arbeit wird mit Blick auf den Gebäudebestand gezeigt, wie es sich berechnen lässt und welchen Einflüssen es unterliegt. Nachdem im ersten Teil bereits darauf eingegangen wurde, wie sich der Abbau des Verschwendungspotenzials auswirkt, widmet sich Teil 2 dieses Fachaufsatzes nun der Frage, wie sich hohe überkritische Werte einstellen können.