**2.2. Thermoelectric system of THU version 1.2**

Recently, an improved prototype of the THU v1.1 was designed, named THU v1.2. This second version mainly consists of three subsystems: a heating system, a ventilation system and a control system. The heating system is composed of 20 Peltier modules (Marlow Industries, Inc.) with a heat dissipation system. All Peltier modules are connected in parallel, require a voltage of 20 volts and have a heating capacity of 1 kW (1/4TR heating tonnage). The elements of heat dissipation system are composed of 20 finned heat sinks and four tangential fans. This second version has more insulation, better heat dissipation and lower power consumption. **Figure 2** shows the outside and inside views of THU v1.2 prototype.

In order to know the economical and thermal viability of the THU v1.2 prototype, an identical test room was built for a conventional air-conditioning system, as shown in **Figure 3**. The conventional air-conditioning system uses inverter technology to regulate the voltage, current and frequency of an air conditioner so that it consumes only the necessary energy. The used model in this work is the air-conditioning split (1X1 MSZ-HJ35VA Mitsubishi Split) with a heating capacity of 3.6 kW (1TR heating tonnage).

To provide a consistent baseline for comparative analysis, the authors show the technical information for the THU prototype and conventional air-conditioning system (**Table 1**).

#### **2.3. Design and operating principle**

The exterior image in this project is based on an opaque ventilated façade with an active mechanism (air grilles) that adapts to different environmental conditions and seeks maximum efficiency at all times. The activation mechanism adjusts the air chamber ventilation of the façade and the heating system. This means that during winter months, the grilles are shut to enhance the accumulation of heat inside a room. However, in the summer months, the grilles are opened to extract the excess heat from the system. It is relevant to mention that the initial configuration of the active ventilated façade is in accordance with the requirements under the regulation of the ventilation of the cavity of the ventilated façade. As is shown in **Table 2**, an enclosure of a light sheet metal, as a light element with low thermal inertia that allows an immediate response to external environmental conditions and a ventilation capacity of 50CFM in the room was selected.

The internal concept of the THU prototype consists of three layers, two air chamber and a HVAC system (thermoelectric system), as is shown in **Figure 4**. The first layer (external view) is composed of the metallic frame with two fans and a heat dissipation system. The fans allow the entrance of air to the external chamber (chamber connected to the outside environment), it passes through of the heat pipes and leaves external chamber eliminating the excess heat

**K/W)**

**Material Thicknesses (mm) Λ (W/mK) R (m2**

Sheet metal 0.8 — — Ventilated air chamber/sealed 100 — 0.18 Inner sheet 177.5 0.163 4.62 Semi-rigid rockwool panel 80 0.034 1.91 Sandwich panel 35 0.028 1.25 Rockwool panel 50 0.035 1.40 Plasterboard 12.5 0.25 0.05

**Table 2.** Technical parameters of the active ventilated façade THU v1.2.

**Figure 3.** Schematic diagram of conventional system v2.0: (a) top view, (b) inside view and (c) outside view.

Internal dimension (m) 4.0 × 2.4 × 2.5 3.75 × 2.10 × 2.0 3.75 × 2.1 × 2.0

Façade thickness (mm) 35 160 160 Dimension of chambers (cm) 100 × 10 100 × 10 No U of the façade (W/m2 K) 0.52 0.21 2.21 Double height No Yes Yes Roof thickness (mm) 35 127 127 U of the roof (W/m2 K) 0.52 0.21 0.21 Floor thickness (mm) 19 195 195 U of the floor (W/m2 K) 5.26 0.29 0.29

**Table 1.** Technical parameters of the prototypes.

**Parameter/component THU v1.0 THU v1.2 Conventional system V2.0**

Techno-Economic Analysis of a Peltier Heating Unit System Integrated into Ventilated Façade

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127

**Figure 2.** Integration of the thermoelectric system in THU v1.2: (a) top view, (b) inside view (air inlet and outlet and ceramic surface) and (c) outside view of the prototype with the grills to dissipate the heated/cooled air.

Techno-Economic Analysis of a Peltier Heating Unit System Integrated into Ventilated Façade http://dx.doi.org/10.5772/intechopen.76642 127

**Figure 3.** Schematic diagram of conventional system v2.0: (a) top view, (b) inside view and (c) outside view.


**Table 1.** Technical parameters of the prototypes.

**2.2. Thermoelectric system of THU version 1.2**

126 HVAC System

heating capacity of 3.6 kW (1TR heating tonnage).

**2.3. Design and operating principle**

ity of 50CFM in the room was selected.

**Figure 2** shows the outside and inside views of THU v1.2 prototype.

Recently, an improved prototype of the THU v1.1 was designed, named THU v1.2. This second version mainly consists of three subsystems: a heating system, a ventilation system and a control system. The heating system is composed of 20 Peltier modules (Marlow Industries, Inc.) with a heat dissipation system. All Peltier modules are connected in parallel, require a voltage of 20 volts and have a heating capacity of 1 kW (1/4TR heating tonnage). The elements of heat dissipation system are composed of 20 finned heat sinks and four tangential fans. This second version has more insulation, better heat dissipation and lower power consumption.

In order to know the economical and thermal viability of the THU v1.2 prototype, an identical test room was built for a conventional air-conditioning system, as shown in **Figure 3**. The conventional air-conditioning system uses inverter technology to regulate the voltage, current and frequency of an air conditioner so that it consumes only the necessary energy. The used model in this work is the air-conditioning split (1X1 MSZ-HJ35VA Mitsubishi Split) with a

To provide a consistent baseline for comparative analysis, the authors show the technical information for the THU prototype and conventional air-conditioning system (**Table 1**).

The exterior image in this project is based on an opaque ventilated façade with an active mechanism (air grilles) that adapts to different environmental conditions and seeks maximum efficiency at all times. The activation mechanism adjusts the air chamber ventilation of the façade and the heating system. This means that during winter months, the grilles are shut to enhance the accumulation of heat inside a room. However, in the summer months, the grilles are opened to extract the excess heat from the system. It is relevant to mention that the initial configuration of the active ventilated façade is in accordance with the requirements under the regulation of the ventilation of the cavity of the ventilated façade. As is shown in **Table 2**, an enclosure of a light sheet metal, as a light element with low thermal inertia that allows an immediate response to external environmental conditions and a ventilation capac-

**Figure 2.** Integration of the thermoelectric system in THU v1.2: (a) top view, (b) inside view (air inlet and outlet and

ceramic surface) and (c) outside view of the prototype with the grills to dissipate the heated/cooled air.

The internal concept of the THU prototype consists of three layers, two air chamber and a HVAC system (thermoelectric system), as is shown in **Figure 4**. The first layer (external view) is composed of the metallic frame with two fans and a heat dissipation system. The fans allow the entrance of air to the external chamber (chamber connected to the outside environment), it passes through of the heat pipes and leaves external chamber eliminating the excess heat


**Table 2.** Technical parameters of the active ventilated façade THU v1.2.

mainly govern the thermoelectric effect are the electric power and the heat flow. The electric power shows the difference between the heat dissipated on the hot side and the heat absorbed

Techno-Economic Analysis of a Peltier Heating Unit System Integrated into Ventilated Façade

*Pelect* = *qhot* − *qcold* = *V* ∙ *I* (1)

*qe*,*com* = *K*(*T* − *To*) (2)

*<sup>g</sup> <sup>T</sup>* <sup>−</sup> \_\_1 2 *I g*

*<sup>g</sup> <sup>T</sup>* <sup>+</sup> \_\_1 2 *I g*

where α is the total Seebeck coefficient (V/K), <sup>α</sup> <sup>=</sup> m(α<sup>p</sup> <sup>−</sup> <sup>α</sup>n), the subscripts p and n stand for p-type and n-type semiconductors, m is the number of Peltier cells, R is the total electrical resistance

S is the cross-sectional area of semiconductor arms, S is the cross-sectional area of semiconduc-

A key parameter used to measure the performance of any air-conditioning system is the COP, defined as the useful thermal power output per unit of heat power. Its mathematical expres-

The air-conditioned systems can be used in heating and cooling modes. In this work, the heating cycle is only considered, so the COP in heating mode for conventional system is given by [43]

*Ta* ′ − Δ *Tevap* ′ \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ *Troom*

′ Δ *Tcond* ′ + *Tevap*

′ − *Ta*

is the ambient temperature outside the evaporator in the heating mode (° K), Troom

room air temperature outside the condenser in the heating mode (° K), Tcond

/Sn), ρ is the electrical resistivity, l is the length of the semiconductor arms,

is the operational electrical current of a multi-couple Peltier cell.

/l <sup>p</sup> + κ<sup>n</sup> Sn /l n

is the heat absorbed at the cold side of the Peltier modules (W). The heat conduction

is the heat dissipated on the hot side (W)

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129

<sup>2</sup> *R* + *K*(*T* − *To*) (3)

<sup>2</sup> *R* + *K*(*T* − *To*) (4)

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ *Input Power* (*kW*) (5)

, κ is the thermal conductivity of

′ (6)

′ is the

′ is the temperature

at the cold side of the Peltier modules, and this is given by

where I is the load current, V is the output voltage, qh

from the hot side to the cold side is given by

*q*<sup>1</sup> = *I*

*q*<sup>1</sup> = *I*

tor arms, K is the total thermal conductance, R <sup>=</sup> <sup>κ</sup><sup>p</sup> Sp

g

*COP*(*thermal*) <sup>=</sup> *Useful Power* (*kW*)

The heat flow is given by

and qc

and

(Ω), <sup>R</sup> <sup>=</sup> <sup>m</sup>(ρ<sup>p</sup> <sup>I</sup>

where Ta ′ p /Sp + ρ<sup>n</sup> I n

the semiconductor materials,I

sion can be given as follows [42]:

*COP*(*heat*) = 1 +

**Figure 4.** Schematic diagram of the design: (a) THU v1.1 prototype and (b) THU v1.2 prototype.

from the thermoelectric system. A relevant detail in the external view is that for THU v1.1, two axial fans were used, which were placed on the façade, while the second version THU v1.2 used two tangential fans, which were fixed in the lower part of the external chamber. This difference improves aesthetics and heat dissipation in the thermoelectric system.

The thermoelectric system is fixed in the second layer and its function is to separate the two chambers and supply heat to the room. Finally, the third layer connects the internal chamber with the room. This is composed of a group of heat sinks and two tangential fans (fixed in the lower part of the internal chamber). They allow the passage of air into the inner chamber for supplying hot air in the room. In this model, an air exit grill on the top of the wall was placed for extracting the cold air of the room.

#### **2.4. Mathematical model**

The Peltier modules consist of two or more elements of n-type- and p-type-doped semiconductor material that are electrically connected in series and thermally connected in parallel. These thermoelectric elements and their electrical interconnects are typically mounted between two ceramic substrates. Applying a voltage to a thermoelectric module creates a temperature difference. This temperature difference can be used to transfer heat from a cold side to a hot side and vice versa. Therefore, Peltier modules can be used to control the climate in rooms: to heat in winter and to cool in summer. In this regard, it is necessary to obtain a better heat transfer between the Peltier cells and the room air for increasing the heat transfer area of the ceramic plates with heat sinks [39, 40]. In this section, a brief overview of the basic equations that influence the functioning of a THU system is presented. The equations that mainly govern the thermoelectric effect are the electric power and the heat flow. The electric power shows the difference between the heat dissipated on the hot side and the heat absorbed at the cold side of the Peltier modules, and this is given by

$$P\_{\text{dett}} = q\_{\text{hot}} - q\_{\text{cold}} = V \cdot I \tag{1}$$

where I is the load current, V is the output voltage, qh is the heat dissipated on the hot side (W) and qc is the heat absorbed at the cold side of the Peltier modules (W). The heat conduction from the hot side to the cold side is given by

$$q\_{e,con} = \text{K}(T - T\_o) \tag{2}$$

The heat flow is given by

$$q\_1 = \ \text{al}\_g \ T - \frac{1}{2} I\_g^2 \ R + \text{K}(T - T\_o) \tag{3}$$

and

from the thermoelectric system. A relevant detail in the external view is that for THU v1.1, two axial fans were used, which were placed on the façade, while the second version THU v1.2 used two tangential fans, which were fixed in the lower part of the external chamber. This

The thermoelectric system is fixed in the second layer and its function is to separate the two chambers and supply heat to the room. Finally, the third layer connects the internal chamber with the room. This is composed of a group of heat sinks and two tangential fans (fixed in the lower part of the internal chamber). They allow the passage of air into the inner chamber for supplying hot air in the room. In this model, an air exit grill on the top of the wall was placed

The Peltier modules consist of two or more elements of n-type- and p-type-doped semiconductor material that are electrically connected in series and thermally connected in parallel. These thermoelectric elements and their electrical interconnects are typically mounted between two ceramic substrates. Applying a voltage to a thermoelectric module creates a temperature difference. This temperature difference can be used to transfer heat from a cold side to a hot side and vice versa. Therefore, Peltier modules can be used to control the climate in rooms: to heat in winter and to cool in summer. In this regard, it is necessary to obtain a better heat transfer between the Peltier cells and the room air for increasing the heat transfer area of the ceramic plates with heat sinks [39, 40]. In this section, a brief overview of the basic equations that influence the functioning of a THU system is presented. The equations that

difference improves aesthetics and heat dissipation in the thermoelectric system.

**Figure 4.** Schematic diagram of the design: (a) THU v1.1 prototype and (b) THU v1.2 prototype.

for extracting the cold air of the room.

**2.4. Mathematical model**

128 HVAC System

$$q\_1 = \ \text{aI}\_g \ T + \frac{1}{2} \text{I}\_g^{\text{-}} \text{R} + \text{K}(T - T\_o) \tag{4}$$

where α is the total Seebeck coefficient (V/K), <sup>α</sup> <sup>=</sup> m(α<sup>p</sup> <sup>−</sup> <sup>α</sup>n), the subscripts p and n stand for p-type and n-type semiconductors, m is the number of Peltier cells, R is the total electrical resistance (Ω), <sup>R</sup> <sup>=</sup> <sup>m</sup>(ρ<sup>p</sup> <sup>I</sup> p /Sp + ρ<sup>n</sup> I n /Sn), ρ is the electrical resistivity, l is the length of the semiconductor arms, S is the cross-sectional area of semiconductor arms, S is the cross-sectional area of semiconductor arms, K is the total thermal conductance, R <sup>=</sup> <sup>κ</sup><sup>p</sup> Sp /l <sup>p</sup> + κ<sup>n</sup> Sn /l n , κ is the thermal conductivity of the semiconductor materials,I g is the operational electrical current of a multi-couple Peltier cell.

A key parameter used to measure the performance of any air-conditioning system is the COP, defined as the useful thermal power output per unit of heat power. Its mathematical expression can be given as follows [42]:

$$\text{U} = \text{S} \cdot \text{L}$$

$$\text{COP}\_{\text{(blerman)}} = \frac{\text{Us} \text{fefall Power (k}\text{W}\text{)}}{\text{Input Power (k}\text{W}\text{)}} \tag{5}$$

The air-conditioned systems can be used in heating and cooling modes. In this work, the heating cycle is only considered, so the COP in heating mode for conventional system is given by [43]

\_Yuc\_ кону сопусимлича, эм ше соп плівашан поме мо сичсимлов узсип з руслоу [ $\mu$ ]

$$\text{COP}\_{\text{(bat)}} = 1 + \frac{T\_s' - \Lambda \ T\_{sup}'}{T\_{sum}' - T\_s' \Lambda \ T\_{sup}' + T\_{sup}'} \tag{6}$$

where Ta ′ is the ambient temperature outside the evaporator in the heating mode (° K), Troom ′ is the room air temperature outside the condenser in the heating mode (° K), Tcond ′ is the temperature difference between refrigerant in condenser and ambient temperature (° K) and Tevap ′ is the temperature in the evaporator (° K).

In the case of thermoelectric system, the ideal COP in the heating mode is given by [43]

$$\text{COP}\_{\text{(heat)}} = \frac{T\_h}{T\_h - T\_c} \left( 1 - 2 \frac{1 + Z \, T\_{w=1}}{Z \, T\_m} \right) \tag{7}$$

the operational lifetime of thermoelectric device reported by Marlow Industries. Inc. [41] is in the range of 20,000–350,000 h at normal conditions, and Mitsubishi Company guarantees 15 years for inverter air-conditioning [44]. It is estimated that the physical lifetime of the structure is 30–40 years because the structural design combines durability, resistance and anti-corrosive materials. Also, it is assumed that the technological lifetime of the THU system is as long as the lifespan of the building (30–40 years), since it has a digital display that allows controlling the Peltier system and a sophisticated PLC that can be reprogrammed to the user necessities.

In addition to an economic assessment, the THU systems have social benefits that play an important role in taking care of the environment. In other words, the benefits associated with the use of THU systems are mainly related to reducing carbon dioxide emission. THU sys-

systems, because they do not have a working fluid. Therefore, THU systems are a good option for avoiding greenhouse gas emissions. Their electronic components can also be recycled. Moreover, a photovoltaic system could be added into this system to generate electricity and

The investment costs of the THU v1.2 prototype and conventional air-conditioning system are reported in **Table 3**. The results show that the overall cost of this protect was approximately 84,860 Euros. This cost is because the authors considered the architectural and engineering aspects of both prototypes. Also, it can be observed that the highest value was for the engineering costs at 69.27% of the total investment cost, so that it is suggested that the designer

The improvements of THU v1.1 prototype reduced the total investment cost by 30%. This percentage is directed directly related to the design, manufacture process and size of the prototype. On the other hand, **Table 3** shows that the supply/handing cost represented no more than 18.89% of the investment cost and that the auxiliary cost contributed only 14.54%, as it was expected. The above data indicate that the design plays an important role in engineering aspects. This means that the designer should select appropriate construction materials, the number of Peltier cells and the distribution of each system considering their cost. Also, the results indicate that the conventional v2.0 system is more economically viable than THU v1.2 because the THU system is the first product built in a prefabricated module. This prototype

would be more viable if a considerable number of THU systems were manufactured.

Concerning manufacturing process of heating system, it was noted that investment costs are directly influenced by the size and number of Peltier modules, that is, an increase of Peltier modules increases the number of finned heat sinks, so that the investment costs increase. Also, the use of heat pipe sinks increases the investment costs by 30%. Although the heat pipe sinks offer better performance in terms of heat dissipation, the manufacturing process of a finned heat sink is less complicated than that of a heat pipe sink, so that the finned heat sink

could reduce the annual operational costs, according to [14, 15].

has to pay attention for proposing competitive and viable prototypes.

in the operational and maintenance phase as inverter air-conditioning

Techno-Economic Analysis of a Peltier Heating Unit System Integrated into Ventilated Façade

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**3.3. Environmental benefits**

**4. Results and discussion**

tems do not emit CO2

where Th is the hot side temperature at ceramic plate location in a thermoelectric module (° K), Tc is the cold side temperature at ceramic plate location in a thermoelectric module (° K), Z is the figure of merit of thermocouple and Tm is the arithmetical average temperature of a thermocouple(° K) .
