4.1. Importance of outdoor air ventilation

Indoor air quality improvement is achieved by bringing in outdoor air into the building environment. Introduction of outdoor air increases energy consumption of the conventional air conditioning system. In the conventional air conditioning system, limited energy conservation is achieved through heat recovery ventilators, such as fixed-plate, run-round coil and rotary wheel. In these heat recovery ventilators, passive means are employed through temperature and humidity difference between fresh outdoor air and return air, which are dependent on outdoor weather conditions. However in a thermoelectric cooling-photovoltaic (TEC-PV) device, dedicated outdoor air is cooled and dehumidified by active means through input of solar power. The design is assessed by estimating the cooling capacity for selection of a TEC module according to the temperature difference between the hot and cold side. The current required to operate the TEC module can be obtained from trials and also checked from manufacturer data curve to meet the actual cooling capacity. Energy efficiency of a thermoelectric cooling (TEC) device is defined as the ratio of the cooling capacity to the electrical energy consumed. Exergy analysis is based on quality of energy, used for evaluating energy process with respect to ideal thermodynamic equality. Exergy analysis is used for identifying exergy losses, which is used for understanding of irreversible losses of energy conversion in its system design.

The system design consists of: (i) outdoor fresh air ventilation; (ii) thermoelectric cooling (TEC); (iii) building integration; (iv) photovoltaic power generation; and (v) exhaust air ventilation.

#### 4.2. Operation

The outdoor fresh air is cooled down and dehumidified as it flows over a heat sink/exchanger attached to thermoelectric cooling (TEC) module. The cool air enters the indoor environment which is to be maintained at 23C and 55% RH. The stale air is taken out through ducted exhaust air ventilation system. The exhaust air also cools down the heat sink/exchanger attached to hot side of thermoelectric module (TEM). The outdoor fresh air is introduced into the single zone building air volume at varying rates as mentioned in Table 2. Four DC fans are used to provide power for forced airflow. Two of them are installed on supply fresh air side and other two are installed on exhaust air side. The input power for each fan is 1.5 W with airflow rate at 60 m3 h<sup>1</sup> . The maximum fresh air supply in the room is 120 m3 h<sup>1</sup> at full capacity. The outside fresh air is at 33C and 75% RH. Eight solar PV modules of 300 W each are used to power thirty TEC modules of 60 W each and four DC fans of 1.5 W each. Four solar PV modules are placed on south façade while other four are fixed on roof top. The maximum sensible cooling load in the building zone is 1 kW while maximum latent load varies up to 0.48 kW.

#### Principle:

Two-stage Dehumidification (Condensation): Depending on dew point of the air, cooling dehumidification and iso-thermal dehumidification can take place on fins inside cooling duct and on wall with TEC modules.

Heat transfer process: A steady state is reached when temperature of air remains constant with heat transfer from the cold side fins. Cold side fins are placed both on supply duct and inside room. Hot side fins are placed on exhaust duct and exterior of room wall surface. The height of heat transfer surface inside the duct is 0.5 m and height of heat transfer surface inside the room is 2.5 m. The condensation phenomenon at initial dehumidification will result in rapid temperature drop of cold side fins. The dehumidification will continue further at steady temperature of cold side fins. In order to improve the performance of fins for dehumidification, rapid elimination of condensed water is necessary. This is achieved by specially treated heat transfer surfaces (fins) with superhydrophilic or super water repellant surfaces [13].

4. System design of thermoelectric cooling-photovoltaic (TEC-PV) device

Indoor air quality improvement is achieved by bringing in outdoor air into the building environment. Introduction of outdoor air increases energy consumption of the conventional air conditioning system. In the conventional air conditioning system, limited energy conservation is achieved through heat recovery ventilators, such as fixed-plate, run-round coil and rotary wheel. In these heat recovery ventilators, passive means are employed through temperature and humidity difference between fresh outdoor air and return air, which are dependent on outdoor weather conditions. However in a thermoelectric cooling-photovoltaic (TEC-PV) device, dedicated outdoor air is cooled and dehumidified by active means through input of solar power. The design is assessed by estimating the cooling capacity for selection of a TEC module according to the temperature difference between the hot and cold side. The current required to operate the TEC module can be obtained from trials and also checked from manufacturer data curve to meet the actual cooling capacity. Energy efficiency of a thermoelectric cooling (TEC) device is defined as the ratio of the cooling capacity to the electrical energy consumed. Exergy analysis is based on quality of energy, used for evaluating energy process with respect to ideal thermodynamic equality. Exergy analysis is used for identifying exergy losses, which is used for understanding

The system design consists of: (i) outdoor fresh air ventilation; (ii) thermoelectric cooling (TEC); (iii) building integration; (iv) photovoltaic power generation; and (v) exhaust air ventilation.

The outdoor fresh air is cooled down and dehumidified as it flows over a heat sink/exchanger attached to thermoelectric cooling (TEC) module. The cool air enters the indoor environment which is to be maintained at 23C and 55% RH. The stale air is taken out through ducted exhaust air ventilation system. The exhaust air also cools down the heat sink/exchanger attached to hot side of thermoelectric module (TEM). The outdoor fresh air is introduced into the single zone building air volume at varying rates as mentioned in Table 2. Four DC fans are used to provide power for forced airflow. Two of them are installed on supply fresh air side and other two are installed on exhaust air side. The input power for each fan is 1.5 W with airflow rate at

. The maximum fresh air supply in the room is 120 m3 h<sup>1</sup> at full capacity. The outside

fresh air is at 33C and 75% RH. Eight solar PV modules of 300 W each are used to power thirty TEC modules of 60 W each and four DC fans of 1.5 W each. Four solar PV modules are placed on south façade while other four are fixed on roof top. The maximum sensible cooling load in the

Two-stage Dehumidification (Condensation): Depending on dew point of the air, cooling dehumidification and iso-thermal dehumidification can take place on fins inside cooling duct

building zone is 1 kW while maximum latent load varies up to 0.48 kW.

4.1. Importance of outdoor air ventilation

322 Bringing Thermoelectricity into Reality

of irreversible losses of energy conversion in its system design.

4.2. Operation

60 m3 h<sup>1</sup>

Principle:

and on wall with TEC modules.

The schematic of a building zone with two stage cooling through TEC modules by means of supply duct and wall mounted TEC modules with solar PV façade exhaust duct is illustrated in Figure 2. The performance characteristics with voltage variation of analyzed TEC1-12710 modules in TEC calculator is provided in Figure 3. The variation in theoretical values of COP (cooling) and temperature (cold) for ZTm = 1 is provided in Figure 4. The variation in theoretical values of cooling capacity with temperature difference is provided in Figure 5. The variation of theoretical heat transfer coefficient with height of heat transfer surface (fins) is provided in Figure 6. The theoretical variation of cooling capacity load served inside room with height of heat transfer surface (fins) is provided in Figure 7. The variation of theoretical exergy of air cooled inside the room with cold side temperature and Tout at 306 K is illustrated in Figure 8. All the results are based on theoretical values irrespective of actual performance values of the prototype TEC-PV device.

Figure 2. Schematic of a building room zone with TEC modules and PV ventilated façade.

Figure 3. Performance characteristics of TEC1-12710 module with voltage variation analyzed in TEC calculator.

Figure 5. Variation in theoretical values of cooling capacity with temperature difference.

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Figure 6. Variation of heat transfer coefficient with height of heat transfer surface (fins).

Figure 4. Variation in theoretical values of COP (cooling) and temperature (cold) for ZTm = 1.

Figure 5. Variation in theoretical values of cooling capacity with temperature difference.

Figure 3. Performance characteristics of TEC1-12710 module with voltage variation analyzed in TEC calculator.

324 Bringing Thermoelectricity into Reality

Figure 4. Variation in theoretical values of COP (cooling) and temperature (cold) for ZTm = 1.

Figure 6. Variation of heat transfer coefficient with height of heat transfer surface (fins).

5. Conclusion

devices powered by photovoltaic modules.

ηpv photovoltaic system efficiency

ZTm figure-of-merit for thermoelectric material

COP coefficient of performance

α Seebeck coefficient, Volts/K

R electric resistance, Ohms

Qc absorbed heat flux, W Qh released heat flux, W

P electric power, W

Nomenclature

Thermoelectric cooling (TEC) is one of the specialized areas in "Thermoelectrics." This chapter has presented the summary of energy balance model parameters representing various performance characteristics of building-integrated thermoelectric cooling-photovoltaic (TEC-PV) devices. The cooling performance of thermoelectric modules for air-conditioning applications is a sustainable technology though not competitive with conventional vapor compression technology. There is significant growing interest level in thermoelectric cooling (TEC) because of their useful control aspects. This is because TEC modules are readily operated at partial load by changing the electric current. Moreover, there is increase in cooling COP with reduction of cooling power. Modular capability is the key merit of thermoelectric cooling (TEC) devices. These devices do not generate noise, thus are of considerable interest in many building applications in which noise is a significant factor. Furthermore, key advantage is the operation

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of thermoelectric cooling (TEC) devices without requirement of polluting refrigerants.

Air-conditioning of fresh outdoor air for direct indoor use through proper system design of supply air ventilation system and exhaust air ventilation system is another key benefit of thermoelectric cooling (TEC). In addition, photovoltaic (PV) roof-top power generation and photovoltaic (PV) ventilated façade are integrated into the system design, thus making it further sustainably sound in terms of input electricity requirements through green power and active ventilation system for supply and exhaust air. Finally, thermoelectric modules (TEM) offer air-conditioning solutions with flexible electrical loads in contemporary context of smart energy systems for buildings. Thermoelectric modules (TEM) have best advantage of their reversible operation as heating and cooling devices obtained by changing the direction of electric current. The future work comprises of advanced modeling and simulation of the presented prototype through thermoelectric modules (TEMs) operation as heating and cooling

Figure 7. Variation of cooling capacity load served inside room with height of heat transfer surface (fins).

Figure 8. Variation of theoretical exergy of air inside room with cold side temperature and Tout = 306 K.
