3.1. Active building wall
Active building walls are kind of walls which can actively control the heat flux of the walls with solar energy [21] and [22]. Fig. 2 depicts the sketch diagram of an active building wall, which is integrated with a photovoltaic (PV) unit and a thermoelectric (TE) unit. The PV forms the external surface of the wall with an airflow channel between it and the inside thermoelectric panel. In the active building wall, the PV unit changes the solar radiation energy into electrical energy while the TE unit changes the electrical energy into thermal energy, as shown in Fig. 3. The TE unit can operate in a heating or a cooling mode, depending on the direction of the current supplied by the PV unit. This feature allows for the active building envelope to be used for heating as well as cooling applications. Compared with conventional thermal technologies, the active building walls have advantages as follows: (1) operating with solar energy, (2) consisting of solid state devices and operating silently with no moving parts, (3) using little or no fossil energy sources, and (4) beneficial to environment in the long term.
Recently researchers have created lots of novel solar thermoelectric cooling systems and improved the systems’ performances. In this paper, applications of solar thermoelectric cooling technologies are reviewed and the possibility of their application in ZEBs is discussed. In details, in Section 2, solar thermoelectric cooling system is introduced. In Section 3, technologies of thermoelectric active building envelope including active wall and window system, which both use solar energy active control the thermal flux of building envelope, are introduced. In Section 4, the researches on applications of thermoelectric technologies in waste heat and cold recovery are reviewed, including heat recovery in mechanical ventilation system, thermoelectric air conditioner condense heat recovery, waste water heat recovery, kitchen exhaust heat recovery. In Section 5, solar thermoelectric air conditioners such as thermoelectric radiant air conditioner and solar thermoelectric energy storage air conditioner are presented. In Section 6, summary of solar thermoelectric cooling theologies for use in ZEBs are conducted. Finally, conclusions are drawn in Section 7.
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