**3. Techno-economic parameters**

#### **3.1. Economic indicators**

The economic evaluation is based on investment costs, operational costs and maintenance costs. The investment costs consider the cost of each piece of the prototype, including the electrical equipment, structure, heating system and instrumentation equipment and electrical installation. For the determination of the investment costs, these costs were divided into three categories: engineering costs, supply/handing cost and auxiliary costs. The engineering costs combine design, manufacturing processes, modelling of the pieces, architectural plans and installations. The supply/handing costs involve the material supply. In this case, the prices are quoted for Pamplona, Spain. Finally, the auxiliary costs depend on the finishing touches of the project.

Operational costs refer to the costs for the proper operation of each prototype. These costs mainly depend on the electrical consumption of the prototype subsystems (cooling–heating system, ventilation and control system). The THU v1.2 prototype under investigation was designed with a power nominal consumption of 1 kW, while that the conventional air-conditioning system is of 1.04 kW.

Maintenance costs consider all types of activities related to the repair and replacement of damaged pieces in the prototype subsystems. These costs have been estimated based on the price of the prototype and the maintenance of each subsystem. In the case of the conventional v2.0 system (Split 1x1MSZ-HJ35VA Mitsubishi), these costs are related to the use of special chemicals, checking the pressure, voltage drop, amperage drop, cleaning and blowing the dirty parts. According to [40], the maintenance cost of this system varies from \$737 to \$2156 Euros each year, depending on the capacity of cooling/heating. It represents between 10 and 20% of the total investment cost of the Split cost. In the case of THU v1.2, the authors have estimated that the maintenance cost could be approximately 6–10% of the heating system cost. This estimation was based on 1.5 years of test with the prototype [36].

#### **3.2. Lifetime of the prototypes**

The lifetime of the prototypes reflects the useful life of each system or the prototypes during a determined time. It includes the operational, physical and technological lifetime. In this study, 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.

#### **3.3. Environmental benefits**

difference between refrigerant in condenser and ambient temperature (° K) and Tevap

the cold side temperature at ceramic plate location in a thermoelectric module (°

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

*Th* − *Tc*

of merit of thermocouple and Tm is the arithmetical average temperature of a thermocouple(°

(1 − 2

is the hot side temperature at ceramic plate location in a thermoelectric module (°

The economic evaluation is based on investment costs, operational costs and maintenance costs. The investment costs consider the cost of each piece of the prototype, including the electrical equipment, structure, heating system and instrumentation equipment and electrical installation. For the determination of the investment costs, these costs were divided into three categories: engineering costs, supply/handing cost and auxiliary costs. The engineering costs combine design, manufacturing processes, modelling of the pieces, architectural plans and installations. The supply/handing costs involve the material supply. In this case, the prices are quoted for Pamplona, Spain. Finally, the auxiliary costs depend on the finishing touches of the project.

Operational costs refer to the costs for the proper operation of each prototype. These costs mainly depend on the electrical consumption of the prototype subsystems (cooling–heating system, ventilation and control system). The THU v1.2 prototype under investigation was designed with a power nominal consumption of 1 kW, while that the conventional air-conditioning system is

Maintenance costs consider all types of activities related to the repair and replacement of damaged pieces in the prototype subsystems. These costs have been estimated based on the price of the prototype and the maintenance of each subsystem. In the case of the conventional v2.0 system (Split 1x1MSZ-HJ35VA Mitsubishi), these costs are related to the use of special chemicals, checking the pressure, voltage drop, amperage drop, cleaning and blowing the dirty parts. According to [40], the maintenance cost of this system varies from \$737 to \$2156 Euros each year, depending on the capacity of cooling/heating. It represents between 10 and 20% of the total investment cost of the Split cost. In the case of THU v1.2, the authors have estimated that the maintenance cost could be approximately 6–10% of the heating system cost.

The lifetime of the prototypes reflects the useful life of each system or the prototypes during a determined time. It includes the operational, physical and technological lifetime. In this study,

This estimation was based on 1.5 years of test with the prototype [36].

<sup>1</sup> <sup>+</sup> *<sup>Z</sup> <sup>T</sup>* \_\_\_\_\_\_\_*<sup>m</sup>*−<sup>1</sup>

perature in the evaporator (° K).

where Th

130 HVAC System

of 1.04 kW.

**3.2. Lifetime of the prototypes**

*COP*(*heat*) <sup>=</sup> *<sup>T</sup>* \_\_\_\_\_*<sup>h</sup>*

**3. Techno-economic parameters**

**3.1. Economic indicators**

′ is the tem-

K), Tc is

K) .

K), Z is the figure

*<sup>Z</sup> Tm* ) (7)

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 systems do not emit CO2 in the operational and maintenance phase as inverter air-conditioning 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 could reduce the annual operational costs, according to [14, 15].
