Schematic diagram and photograph of the thermoelectric cooling unit. 

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... an operating voltage of 16 V and an exhaust temperature of 36 ◦ C, the coefficient of performance decreases from 1.66 to 1.22 when the temperature of water increases from 28 ◦ C to 46 ◦ C. In comparison with the conventional electric water heater, thermoelectric heat pump water heater with kitchen exhausts heat recovery is more efficient. Besides, its performance can be further improved by optimizing the design and fabrication on the basis of experiment data. It also has other advantages, such as facility, reliability, no pollution, etc. [41]. The air conditioners and refrigerators have become common household appliances around the world. More and more people will need air conditioners as the quality of life that people demand improves. However, the refrigerant of traditional air conditioner, Freon, once leaked, will do irreversibly damage to the ozone sphere and thus cause stronger ultraviolet radiation. Moreover, electric- driven air-conditioning system consumes too much energy. To meet their demands, fossil fuels are burned to generate electricity, which causes greenhouse effect and continuously worsen global warming, and in turn the demand of air-conditioning would further increases. These facts are encouraging manufacturers to seek alternatives to conventional refrigeration technology. One of the alternative refrigeration systems is thermoelectric cooling technology [42,43]. A solar thermoelectric cooled ceiling combined with displacement ventilation system has been developed for space climate control, as presented in Fig. 12 [44]. The solar thermoelectric cooled ceiling (STCC) adopts thermoelectric cooler instead of hydronic panels as radiant panels. The solar thermoelectric cooled ceiling (STCC) is burdened with removal of a large fraction of sensible cooling load. The TE modules are connected in series and sandwiched between the aluminum radiant panel and heat pipe sinks in STCC. The heat sinks are used for dissipating heat of TE modules. The fan can provide forced air convection to help the TE modules to release heat more efficiently into the atmosphere. By controlling the direction of the current, the functions of cooling and heating can be both achieved. The combined system dehumidifies the supply fresh air using a thermoelectric dehumidified ventilation system, as shown in Fig. 8 [35]. The thermoelectric dehumidified ventilation system is responsible for removal of a small fraction of sensible cooling load and all latent cooling loads. A 1.8 m × 0.6 m aluminum cooling panel with ten TE modules was tested in an experiment room, and the TE modules were uniformly distributed in the aluminum panel. The size of the TE module is 39 mm × 39 mm × 3.8 mm, with 127 thermoelectric couples of bismuth telluride and ceramic surface, type of 9500/127/060B. The performance of the thermoelectric cooled ceiling was investigated under cooling mode and heating mode. Results indicated that increasing the operating voltage increased the total heat flux. The decreasing the temperature difference between ambient temperature and indoor temperature significantly increased the total heat flux and slightly increased the system COP in both cooling and heating mode. The total heat flux of the STCC system in cooling mode was higher than 60 W/m 2 and the system COP could reach 0.9 under operating voltage of 5 V. In the heating mode, the total heat flux of the STCC system under operating voltage of 4 V was over 110 W/m 2 and the COP of the system could reach 1.9 [44]. Thermoelectric air conditioner with heat storage system has been developed as shown in Fig. 13. The thermoelectric cooling system primarily consists of a thermoelectric cooling unit, a shell-and-tube PCM heat storage unit, an air-water heat exchanger and a piping system. Heat absorbed from the indoor environment through the thermoelectric cooling unit can be released through the air-water heat exchanger with water as the heat transfer fluid (HTF). The system can realize two operating modes, which are dissipating generated heat to outdoor air through the air-water heat exchanger (mode 1) and releasing heat to the shell-and-tube PCM heat storage unit (mode 2). The two modes can be easily switched over through manually controlling valves [45]. The work principle is as follows: if outdoor air temperature is relatively low, such as in the early morning or late afternoon, the working mode 1 will be in operation and heat generated by space cooling will be dissipated to the outdoor environment. When outdoor air temperature is high, the PCM heat storage unit will be activated and the system will convert to mode 2. At night, the PCM heat storage unit will be discharged by using relatively cool outdoor air. Therefore, PCM with appropriate melting temperature suitable for local weather conditions would be preferred for its advantage of using “free cooling” at night to “regenerate” the PCM. The schematic diagram and photograph of the thermoelectric cooling unit are shown in Fig. 14. It is depicted that the thermoelectric module is sandwiched between the conductive fin and the water tank. Two axial fans are installed at the fin side to enhance convective heat transfer. A finned coil is employed in the water tank to achieve better heat exchanges. The thermoelectric module used in this study was RC12-8. PCM was RT22, which had a melting temperature of 19–23 ◦ C (with main peak at 22 ◦ C and heat storage capacity of 200 kJ/kg). The experiment results showed that the average COP of the thermoelectric air conditioners was 0.8, and the maximum COP value was 1.22. The maximum cooling capacity achieved 210 W at present. Comparison experimental study showed that 35.3% electrical energy could been saved in the prototype thermoelectric cooling system by using PCM heat storage on the condition that outdoor air temperature was in the range of 30–33 ◦ C and temperature of the conditioned space was set at 24 ◦ C. In order to build cost-effective ZEBs, the energy demand should be a minimized, which can be provided only by renewable energy. Therefore, measures that can minimize the building energy demand should be fully considered when design buildings. Fig. 15 shows the technical route of solar thermoelectric cooling technologies for use in zero energy buildings. Active solar thermoelectric building envelopes and thermoelectric low-grade energy recoveries are used to restrain the heat losses or gains of buildings and improve energy efficiency and therefore to reduce the building energy demand to a minimum, the small amount of energy need then could be satisfied just by solar thermoelectric air conditioner. In this way only renewable energy is consumed in buildings, which fully meets the demand of ZEBs. Due to the advantage of inherently reliable, low maintenance, silent, clean, and distributed nature, the solar thermoelectric cooling technologies can be easily integrated with buildings. Besides, the distributed nature of the thermoelectric (TE) heat pumps minimizes overall energy consumption by providing local temperature control and eliminating the energy costs associated with air circula- tion fans and duct losses. Therefore, applications of active building envelope, energy recovery and solar thermoelectric air conditioner in zero energy buildings are promising. Even though the performances of solar thermoelectric cooling technologies and relevant applications cannot compete with vapor compression technologies at present, the performance of solar thermoelectric cooling system can be enhanced by improving and optimizing the heat exchanger structure and the operating parameters, because those aspects significantly affect the efficiency of the whole system. Moreover, the performance of solar thermoelectric cooling system can be improved by selecting TE and PV system with higher performances. As the efficiency of commercial available PV is about 15–20%, and the products still have a large space to improve compared with the maximum PV efficiency of 39% [46]. Meanwhile, the TE performance is closely related to the figure of merit of thermoelectric materials, ZT, the TE modules used in the present researches have a ZT of about 0.6–0.7, which is not high considering the progress of TE technology. It is achievable since the latest quantum well materials have a ZT as high as 2.4 at 300 K [47], and when TE materials have a ZT = 2, the COP of TE coolers can reach to the COP of vapor-compression coolers in climate-control applications [48]. In current studies, the solar thermoelectric cooling technologies were established by bulk components, such as commercially available TE and PV systems. Thermoelectric and PV industry develop rapidly along with the advent of new materials. Recent advances in thin-film TE and PV systems, and emerging researches in the area of organic TE and PV materials, offer opportunities to yield extremely thin, efficient, and low-cost thermoelectric systems. For example, when PV and TE modules are collapsed to very thin sections, the solar thermoelectric technologies might be applied in transparent building materials, such as glass. In order to minimize the energy demands in buildings, increase energy effectiveness and reduce fossil energy consumption, the solar thermoelectric cooling technologies such as active building envelope, thermoelectric energy recovery systems and solar thermoelectric air conditioners are recommended to be used in zero energy buildings. Active building envelope is a new thermal control technology which integrates TE modules and PV units within building envelope. It can actively control heat flux in wall and compensate for passive heat losses or gains in building envelope by using solar energy. However, it has not been actually used in buildings so far, only theoretical researches and experiment tests of a single system were made, more work should be done for its application in buildings. Thermoelectric waste heat recovery devices have a high ...