*4.3. Final Energy and Cost Considerations*

This section has considered best available technologies (BAT), which are innovative and economically viable [48]. Hydronic technologies are compatible with radiant systems, such as WFG and radiant floors and walls. Air-to-air heat pumps are used to compare the final energy consumption and cost of different cooling systems. WFG can be a part of hydronic HVAC systems, and it is compatible with water-to-water heat pumps. Tables 6 and 7 illustrate the final energy consumption with different energy generators. It takes into account the effect of the operative temperature of the system [63]. The performance of water-to-water heat pumps (WWHP) depends on the inlet temperature of the WFG (θ*IN*), and the source inlet temperature (*Ts,i*) in the heat pump. A typical value of *Ts,i* ranges from 20 ◦C in ground source heat pumps (GSHP) to 35 ◦C in other WWHPs. The source and load sides are relevant when it comes to calculating the performance of the cooling device. Air-to-air heat pumps (AAHP) for heat recovery on ventilation are also analyzed. The parameters that influence air-to-air heat pumps' performance are the dry bulb exterior air temperature (*Te\_db*) and the dry bulb interior return air temperature (*Tri\_db*).




<sup>1</sup> Energy efficiency ratio (ERR) values are taken from Appendix A in [63].

<sup>1</sup> ERR values are taken from Appendix A in [63].

PEF stands for the primary energy factor from final energy (FE) to non-renewable final energy (NRFE). The Spanish code for thermal systems in buildings (RITE) recommends a value of 1.954. The factor of CO2 emissions for electricity was 0.331 [64]. The RITE aims to establish primary energy factors and CO2 emission factors, for each final energy consumed by buildings in Spain and for each geographic area with a different electricity generation source.

Table 6 shows that the best performance belongs to WWHP when the inlet temperature (θ*IN*) is close to 18 ◦C, and the source inlet temperature (*Ts,i*) in the heat pump is 20 ◦C. Figure 16 shows that it is possible to keep the cabin's indoor temperature within the comfort range by setting θ*IN* between 18 ◦C and 22 ◦C. Other systems, such as fan-coils, need lower operating temperatures. The lower the difference between *Ts,i* and θ*IN* the higher the EER coefficient. The NRFE consumption of GSHP is 0.065 kWh per m2 of WFG, and the average NRFE use of air-to-air heat pumps is 0.155 kWh per m<sup>2</sup> of WFG. When it comes to CO2 emissions, air-to-air heat pumps generate an average of 0.027 KgCO2, twice as much as the CO2 emitted by GSHP.
