*6.2.5. Solar furnace (SF)*

These devices are used in tests, high-temperature processes, and other applications and are constituted by one or more heliostats, which track the Sun, reflecting the sunrays horizontal and parallel to an optical axis of the parabolic concentrator, which in turn concentrates the incoming rays into the focus of the parabola. This reflector can be composed of a parabolic mirror or a group of spherical mirrors. The furnace power can be attenuated by a shutter, which controls the amount of solar radiation. The concentrated radiation reaches the test area, which is located at the concentrator focus [44]. One of the most important advantages is that it can reach temperatures above 2000°C, allowing the scientific community to do specific researches. However, this technology is the most expensive between STT and needs high technical knowledge to operate them.

your temperature range, it can be possible to select one of them. For example, if the project wants to transform solar energy into solar water heating with a range of 90°C, the possible

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The last aspect to take into account is the heat transfer fluid selection. This fluid is critical for storing and transferring thermal energy and can be used to directly drive a turbine to produce power or more commonly, be combined with a heat exchanger and secondary cycle to gener-

The HTFs can be divided into six main groups, according to the type of material [49]:

• *Air and other gases*. It is not common. However, the very low dynamic viscosity compared to the one of molten salts gives good flow that favors the heat transfer and may compensate

• *Water/steam*. They present corrosion problems and imply high operating pressures and

• *Thermal oils*. Mainly in PTC. There are three types: mineral oil, silicone oil, and synthetic oil

and can be thermally stable only up to 400 °C. They have high cost.

technologies to use will be LFR and PTC.

ate steam. Desired characteristics include [49]:

• High boiling point and thermal stability.

• High heat capacity for energy storage.

• Low vapor pressure (lower than 1 atm) at high temperature.

**Figure 6.** (a) Solar thermal energy technologies and (b) concentration ratio of STT [6].

• Low corrosion with metal alloys used to contain *HTF*.

• Low melting point.

• Low viscosity.

• Low cost

• High thermal conductivity.

its low thermal conductivity.

complex controls for plant operation.

### **6.3. How to select one of the solar thermal technologies**

There is no single criterion to make the selection of one of all STTs presented in this chapter; however, by looking applied examples of each technology, it is possible to facilitate the choice of the best technology for a project. Solar collectors have been used in a variety of applications. In **Table 5**, there are listed the most important solar thermal applications with the type of collector that can be used in each case. Other way to decide the best technology is to know first the temperature required for your process. As it is shown in **Figure 6(b)** depending on


**Table 5.** Solar energy applications and type of collectors used [9].

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**Figure 6.** (a) Solar thermal energy technologies and (b) concentration ratio of STT [6].

your temperature range, it can be possible to select one of them. For example, if the project wants to transform solar energy into solar water heating with a range of 90°C, the possible technologies to use will be LFR and PTC.

The last aspect to take into account is the heat transfer fluid selection. This fluid is critical for storing and transferring thermal energy and can be used to directly drive a turbine to produce power or more commonly, be combined with a heat exchanger and secondary cycle to generate steam. Desired characteristics include [49]:

• Low melting point.

transferring the thermal energy onto the receiver. The heat transportation system consists of pipelines, pumps, and valves, where the fluid flows in a closed circuit between receiver and storage tank. Some of the advantages of these are highly effective as much in the solar collection as in its transformation to electricity. Also, there is no necessity to flatten the field; therefore, this technology can be installed in a hill. One of the most important disadvantages is the higher cost of the solar tracking system compared with the same system installed in PTC because in ST, it is necessary to install in each heliostat one of these systems and in PTC, the

These devices are used in tests, high-temperature processes, and other applications and are constituted by one or more heliostats, which track the Sun, reflecting the sunrays horizontal and parallel to an optical axis of the parabolic concentrator, which in turn concentrates the incoming rays into the focus of the parabola. This reflector can be composed of a parabolic mirror or a group of spherical mirrors. The furnace power can be attenuated by a shutter, which controls the amount of solar radiation. The concentrated radiation reaches the test area, which is located at the concentrator focus [44]. One of the most important advantages is that it can reach temperatures above 2000°C, allowing the scientific community to do specific researches. However, this technology is the most expensive between STT and needs high

There is no single criterion to make the selection of one of all STTs presented in this chapter; however, by looking applied examples of each technology, it is possible to facilitate the choice of the best technology for a project. Solar collectors have been used in a variety of applications. In **Table 5**, there are listed the most important solar thermal applications with the type of collector that can be used in each case. Other way to decide the best technology is to know first the temperature required for your process. As it is shown in **Figure 6(b)** depending on

**Application Collector** Solar water heating (temp range ≈ 90°C) LFR PTC Space heating and cooling (temp range ≈ 90°C) LFR PTC PD Solar refrigeration (temp range ≈ 150–200°C) LFR PTC PD Industrial process heat (temp range ≈ 80–240°C) LFR PTC PD Solar desalination (temp range ≈ 100°C) LFR PTC PD Solar thermal power systems (temp range ≈ 800–2000°C) PD ST SF High performance experiment like melting tungsten (temp range ≈ 3000°C) PD SF

tracking system can be installed by row [48, 53].

technical knowledge to operate them.

**6.3. How to select one of the solar thermal technologies**

**Table 5.** Solar energy applications and type of collectors used [9].

*6.2.5. Solar furnace (SF)*

56 Sustainable Air Conditioning Systems


The HTFs can be divided into six main groups, according to the type of material [49]:


• *Organics*. The most common are biphenyl/diphenyl oxide, which is a mixture of biphenyl (C12H10) and diphenyl oxide (C12H10O).

**7.3. Life cycle assessment**

*7.3.1. Phase 1: objectives and scope definition*

CAC system, in terms of CO2

of material.

the construction site.

**Figure 7.** Life cycle Assessment phases.

different systems based on a common function.

According to the international standards ISO 14040 and 14044, LCA is defined as the assessment of the environmental impacts associated with a product, process, or service throughout their life cycle, tied in closely with the paradigm of "cradle to grave." This methodology consists of four phases, which can cross-interact at any point of the assessment, as shown in **Figure 7**.

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At this phase, it is important to fully understand the system under consideration and then be able to define the objectives and scope of the analysis. The functional unit and the system limitations are defined during this phase. The functional unit will allow to compare the two

• Objective: to compare the environmental performance between a ACASS system and a

• Scope: the stages of construction and operation are analyzed. The end-of-life stage is not considered in this study; however, it can be anticipated that this stage can lead to avoid impacts if a good final disposal scenario is proposed based on the recycling of the components, and this scenario would be a greater advantage for ACASS for ACS for the amount

• System limitations: the construction stage will cover the material inputs, the energy consumption during the assembly of main components, and the transport of materials up to

> **Phase 4: Interpretaon**

eq).

Therefore, the following aspects are defined at this phase for the case study:

**Phase 1: Objecves and scope definion**

**Phase 2: Life-cycle inventory analysis**

**environmental impact assessment Phase 3: Life-cycle**

equivalent (CO2

