The energy and Comfort Performance of a Lightweight Translucent Adaptable Trombe Wall in Different Buildings and Climates

Abstract

A traditional Trombe wall is known as a high thermal-mass wall, situated behind a window of a room and separated by an air cavity. The idea behind using a Trombe wall is that heat, ventilation and comfort can be passively generated by using the ‘free’ energy of the sun. The surface of the wall absorbs solar radiation when the sun shines, stores the energy and releases the heat at night to the room, when the occupants need it (Saadatian, Lim, Sopian, & Salleh, 2013). In addition, a Trombe wall can be used as natural ventilation system, of which its power is generated by the buoyancy effect in the cavity. Because a traditional Trombe wall is heavy, blocks daylight and cannot be adjusted to changing environmental conditions and seasonal differences, a new and innovative version was devised by the Double Face research team (4TU). The innovative version is called a lightweight translucent adaptable Trombe wall (LTATW) and is about five times lighter than a traditional Trombe wall. In addition, the wall is translucent and can rotate around its axes. The lower weight and translucent character are achieved by applying a phase change material in combination with aerogel, instead of stone or bricks. Phase change materials can store a large amount of (latent) heat during the change from solid to liquid state and thus, increase the thermal inertia of the system. The translucent elements are located in front of a glass façade and act as a thermal buffer in both winter and summer by rotating the elements towards the source of incoming heat or towards the sink for heat release (4TU.Bouw, 2014). In the winter, the layer of PCM is oriented towards the outdoor environment at daytime and is thermally charged by the low winter sun. At night, the system rotates and releases the accumulated heat to the interior. In the summer, the LTATW is oriented towards the interior at daytime to store the interior heat loads and during the night, it rotates again and releases the heat to the outside environment by means of (passive) night ventilation (4TU.Bouw, 2014).In this thesis, the results of a numerical spin-off study of the Double Face research project are shown, in which the influence of eight parameters (climate, building function, orientation, age, building method, room size, window size and type of glazing) on the energy and comfort performance of the innovative Trombe wall has been studied. First, an initial simulation model was developed in Matlab/Simulink, which was subsequently validated using a cross-comparison with results from DesignBuilder. After validation, the initial model has been extended to a suitable and reliable final version, with which more than 6000 different situations were simulated. The results of the simulations are values for the reduction or increase in energy demand for heating and cooling, expressed in percentages or in kWh. All results are processed in multiple designer tables, which interested designers can consult to assess whether installing the Trombe wall is useful for his or her situation, or not. In addition to the development of designer tables, the influence of each individual parameter on the performance of the Trombe wall was investigated using modeFRONTIER. It was found that in case of heating only a cold and temperate climate support a proper operation of the Trombe wall, since no heating is required in the other climate types. From the analysis, it was concluded that in relative sense (%), the Trombe wall performs best in a temperate climate, and that in absolute sense (kWh), the Trombe wall performs best in a cold climate. In case of cooling, the system performs best in a temperate climate and in a dry climate. Because the LTATW is designed to be both a passive cooling system in the summer and passive heating system in the winter, it has clearly been proven that only the temperate climate is the most logical choice. The average reduction of the heating energy demand in a temperate climate equals 36.1% (or 181.3 kWh per year) and the average reduction of the cooling energy demand equals 49.9% (or 115.0 kWh per year). Analysis of the second parameter, building function, has shown that in case of heating the function is not of great influence. The system performs well in both an office and a residence. In case of cooling, higher reductions of the energy demand are achieved in residences. Thirdly, the influence of the orientation of the Trombe wall was investigated and it was found that the best performance in case of heating occurs on a southern orientation. In case of cooling, the orientation is of less importance. The study shows that the age of a building does not have a major influence on the performance of the Trombe wall. Only in case of cooling, a slight preference can be expressed for new buildings. Studying the influence of the construction method on the performance of the wall has shown that this parameter has the least influence of all studied parameters. In both light-weight, medium-weight and heavy-weight buildings, a good performance can be achieved. For the size of the room, it was found that both room sizes perform equally well. It could be concluded that a Trombe wall can be installed in both small rooms and big rooms, but that when a room is too big, the capacity of the Trombe wall will no longer be useful to reduce a large amount of the initial energy demand. The same applies to cooling. Research has shown that for heating purposes, a room with a smaller window is more often preferred and for cooling purposes, a large window. Because the innovative Trombe wall will have to serve as both a passive heating and cooling device, an average size window will therefore probably be the most suitable. Finally, the influence of type of glazing was studied. It became clear that in relative terms the largest reductions of the heating energy demand are achieved with clear glazing. In case of cooling, the type of glazing is of less influence. Multiple sensitivity analyses were carried out to study the influence on the results of conditions that are easily affected by building occupants, and finally, a side-study was carried out into the influence of the Trombe wall on the energy demand for artificial lighting. It was found that even under slightly different circumstances the same conclusions can be drawn with regard to the influence of the parameters. The influence of the Trombe wall on the energy demand for artificial lighting is not negligible and should be carefully considered too.