Results Air temperature at the top of the roof in three different days (ambient temperature and solar

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10 irradiation are shown in Figure 6) for the investigated cases are reported in Figure 7。 Temperatures are displayed both for PV and conventional tiles with E-W and N-S orientations。 At midday, the air temperature can be higher than ambient ones from 4 °C to 20 °C in winter and in summer, respectively。 Air temperatures are almost independent of the roof orientation mainly because of the roof symmetry with respect to the cardinal points。 The adoption of conventional tiles allows higher air temperatures of about 1°C than PV one thanks to the lower emissivity and the absence of power production。 The high air temperature in summer can also be directly used for covering the thermal load with further thermodynamic advantages, but increasing the plant complexity (a direct air-water heat exchanger should be installed together with the heat pump evaporator)。 The air mass flowrate and heat recovered for conventional and PV tiles in N-S orientation are shown in Figure 8。 The air mass flowrate is higher for the conventional case, in particular in wintertime。 For all cases, a slope variation can be noted both in the morning and in the afternoon。 It occurs when the heat recovery begins also from the north side of the roof which happens when the solar altitude is higher than roof tilt or the diffuse radiation is significant。 For a mass flowrate of 0。4 kg/s, the air velocity at the top of the roof is about 0。3 m/s。 The heat recovered ranges from 2 kW in December to 7 kW in July。 The curves of the heat recovered have the same slope variation already discussed in the mass flowrate。 Average values of air temperatures and mass flowrate at the top of the roof are summarized in Table 6。 Due to the different properties of the tile, the natural convection begins at different hours from case to case (the average reported in the table is made on the same time range for all cases)。 In general, natural convection starts first with the conventional tile and in the E-W orientation due to the lower incidence angle (i。e。 higher incidence solar radiation)。 The heat recovered in the E-W case is slightly higher in wintertime with respect to N-S one。 The opposite occurs in summertime。 This result is consequence of the sun incidence angle variation along the year (the same happens in solar power plants [33])。 The heat recovered with the conventional tile is about 15% higher than the PV one throughout the whole year。 The calculated outlet temperature, air mass flowrate and heat recovered are used as inputs for the heat pump model to determine the amount of heat generated at the desired temperature together with the COP of the heat pump。 The resulting COP of the heat pump is reported in Figure 9。 Advantages of the solar driven air pump are mainly in winter and spring。 In winter, COP can be as high as 3。6 compared to 3。3 of the reference machine, while in spring COP increases by about 20% (4。2 vs。 3。6)。 In summer, there are negligible differences because the evaporation temperature limit occurs。 As for the thermal model, there is no significant difference between the two considered orientations。 Finally, COP absolute differences between PV and Conv tiles are limited to 0。1。 This difference happens when the air temperature variation at the evaporator is kept equal to 6 °C, hence heat pump performances depend on Tout。 Otherwise, the heat pump with conventional tile will have same COP than PV ones, but higher thermal power will be produced。 Overall energy balances together with EPI for the considered systems are summarized in Table 7。 The heat produced by the solar assisted heat pump both in PV and Conv configuration can supply about half of the heat load。 The heat load is fully covered from March till September, while it reduces down to 30% in December and January。 In summertime, there is a significant amount of wasted heat because of the limited heat load。 E-W orientation has the highest yearly production because it is favorite in winter, as previously discussed, and it is not penalized in summer because most of the heat is wasted anyway。 As far as the PV production is concerned, it is about twice the thermal production because the excess can be