1. Introduction

Thermoelectric module is a sold-state energy conversion device made up of thermocouples, which are wired in series electrical circuit and parallel thermal junctions. A thermocouple consists of N-type and P-type semi-conductor elements, so as to generate thermoelectric cooling (viz., Peltier-Seebeck effect) when a voltage difference in appropriate direction is applied through the connected circuit. Thermoelectric cooling has benefits of high reliability, no moving parts, compact size, no requirement of thermo-fluid and light weight of thermoelectric modules. The direct current (DC) required to power thermoelectric cooling (TEC) modules can be easily fed by solar powered photovoltaic (PV) devices. In this way energy conservation is achieved through utilization of available solar energy. With application of low

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voltage DC power source in a TEC module, heat transfer takes place from one side to the other side. In this way, TEC module's one side is cooled and other side is heated. In a TEC module, electric current drifts from N-type element to P-type element [1]. The temperature of the cold junction gradually decreases with heat transfer mechanism from environment to cold junction at a lower temperature. This heat transfer mechanism takes place with passing of transport electrons from a low energy level inside the P-type thermocouple element to a high energy level inside the N-type thermocouple element through the cold junction. Simultaneously, transport electrons transmit absorbed heat to hot junction at a higher temperature. This extra generated heat is dissipated to heat sink, whereas transport electrons return to a lower energy level in the P-type semiconductor element, viz., the Peltier effect takes place (see Figure 1).

results have shown that TEC system was able to produce 16.2C temperature difference between the ambient and building zone. However, the TEC COP was relatively low, varying

Building-Integrated Thermoelectric Cooling-Photovoltaic (TEC-PV) Devices

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Gillott et al. [5] investigated TEC devices for small-scale space's air conditioning building application. A thermoelectric cooling unit was built for 220 W cooling capacity with a maximum COP of 0.46 with input electrical current of 4.8 A for each TEC module. Arenas et al. [6] and Vázquez et al. [7] developed an active thermal window (ATW) and transparent active thermoelectric wall (PTA) for room cooling application for building retrofit applications. In these devices, thermoelements embedded on window glass transfer heat through the glass in order to cool the room. A full-size prototype ATW was installed in a window frame (100 100 cm), which was able to generate up to 150 W of cooling power while glass transparency decreased by about 20%. Their work was patented [8]. Most of TEC devices directly cool down the indoor air. Shen et al. [9] investigated a novel thermoelectric radiant air-conditioning system (TE-RAC). The TE-RAC system employs thermoelectric modules as radiant panels for indoor cooling, as well as for space heating by easily reversing the input current. Their analysis of a commercial thermoelectric module, TEC1-12706 with a ZT value of 0.765, have obtained a maximum cooling COP of 1.77

The cooling effect in the TEC module is dependent on parameters such as electric current, the hot and cold side temperatures, the electrical contact resistance between the cold side and the surface of TEC device, thermal and electrical conductivities of thermoelement and thermal resistance of the heat sink on the hot side of TEC module. The required cooling capacity with maximum electric current determines the number of thermoelements in a TEC module. The main disadvantage of thermoelectric cooling module is its poor coefficient of performance (COP), predominantly in large capacity applications [10]. The COP and the cooling capacity of the TEC module can be predicted using the standard module theory based on one dimensional (1-D) heat balance equations, with the assumptions of negligible thermal and electrical contact resistances. The COP estimated from the standard module theory is determined from the hot and cold side temperatures of TEC module and figure of merit, ZT of the thermoelectric material. The design of thermoelectric cooling system is based on temperature difference

with an electric current of 1.2 A while maintaining cold side temperature at 20C.

across the hot and cold sides of the TEC module and the required cooling capacity.

In this chapter, one dimensional (1-D) energy balance model is presented for evaluating system design of a prototype thermoelectric cooling – photovoltaic (TEC-PV) device. The prototype consists of an integrated design with ceiling suspended, wall mounted, rooftop and active

The total energy efficiency of photovoltaic driven thermoelectric cooling devices can be increased with enhancement of photovoltaic system efficiency and with the use of thermoelectric materials with better performance. The COP of thermoelectric air conditioning devices powered through photovoltaic modules is typically not higher than 0.6 [10]. With consideration of photovoltaic

from 0.2 to 1.2 in this study.

façade TEC-PV devices.

2. Energy balance model

There is constant development and efforts made for making thermoelectric air-conditioning systems in technical competence with vapor-compression technology. The performances of thermoelectric and conventional vapor compression air-conditioners have been compared by Riffat and Qiu [2]. Results have shown that the COPs of vapor compression and thermoelectric air-conditioners are in between 2.6–3.0 and 0.38–0.45, respectively. However, thermoelectric air conditioners have several other capabilities compared to vapor-compression technology. TEC modules can be built into a planar structure on walls and false ceiling and are quiet in operation especially suitable for small offices and mini apartments. Cosnier et al. [3] have presented numerical and experimental results of a thermoelectric air-cooling and air-heating system. The maximum cooling power of 50 W per module, with a COP varying between 1.5 and 2 was reached with electrical current of 4 A and maintaining 5C temperature difference between the hot and cold sides. Cheng et al. [4] have investigated a solar-driven thermoelectric cooling module with a waste heat regeneration unit for green building applications. Their

Figure 1. Principle of thermoelectric cooling.

results have shown that TEC system was able to produce 16.2C temperature difference between the ambient and building zone. However, the TEC COP was relatively low, varying from 0.2 to 1.2 in this study.

Gillott et al. [5] investigated TEC devices for small-scale space's air conditioning building application. A thermoelectric cooling unit was built for 220 W cooling capacity with a maximum COP of 0.46 with input electrical current of 4.8 A for each TEC module. Arenas et al. [6] and Vázquez et al. [7] developed an active thermal window (ATW) and transparent active thermoelectric wall (PTA) for room cooling application for building retrofit applications. In these devices, thermoelements embedded on window glass transfer heat through the glass in order to cool the room. A full-size prototype ATW was installed in a window frame (100 100 cm), which was able to generate up to 150 W of cooling power while glass transparency decreased by about 20%. Their work was patented [8]. Most of TEC devices directly cool down the indoor air. Shen et al. [9] investigated a novel thermoelectric radiant air-conditioning system (TE-RAC). The TE-RAC system employs thermoelectric modules as radiant panels for indoor cooling, as well as for space heating by easily reversing the input current. Their analysis of a commercial thermoelectric module, TEC1-12706 with a ZT value of 0.765, have obtained a maximum cooling COP of 1.77 with an electric current of 1.2 A while maintaining cold side temperature at 20C.

The cooling effect in the TEC module is dependent on parameters such as electric current, the hot and cold side temperatures, the electrical contact resistance between the cold side and the surface of TEC device, thermal and electrical conductivities of thermoelement and thermal resistance of the heat sink on the hot side of TEC module. The required cooling capacity with maximum electric current determines the number of thermoelements in a TEC module. The main disadvantage of thermoelectric cooling module is its poor coefficient of performance (COP), predominantly in large capacity applications [10]. The COP and the cooling capacity of the TEC module can be predicted using the standard module theory based on one dimensional (1-D) heat balance equations, with the assumptions of negligible thermal and electrical contact resistances. The COP estimated from the standard module theory is determined from the hot and cold side temperatures of TEC module and figure of merit, ZT of the thermoelectric material. The design of thermoelectric cooling system is based on temperature difference across the hot and cold sides of the TEC module and the required cooling capacity.

In this chapter, one dimensional (1-D) energy balance model is presented for evaluating system design of a prototype thermoelectric cooling – photovoltaic (TEC-PV) device. The prototype consists of an integrated design with ceiling suspended, wall mounted, rooftop and active façade TEC-PV devices.
