## 4 Conclusions  
In this study, a procedure for the determination of the thermal emissivity by Heat Flux Meter Apparatus has been presented. The developed method was used to measure the infra-red emissivity of pains mixtures containing a different percentage of aluminium paint. The results show a variation of the emissivity from 0.41 to 0.88, depending on the aluminium paint concentration. It is worth noting that the paint mixture containing a 50% of aluminium paint with a reduced metallized effect present a reduction of emissivity in comparison to a matte paint from 0.88 to 0.60. The results are encouraging \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Config** & \(\overline{T_{air}}\) & \(\overline{T_{mr}}\) & \(\overline{\Delta T_{pr,X}}\) & \(\overline{T_{op}}\) & \(\overline{PMV}\) & \(\overline{PPD}\) \\  & [\({}^{\circ}\)C] & [\({}^{\circ}\)C] & [\({}^{\circ}\)C] & [\({}^{\circ}\)C] & & [\({}^{\circ}\)C] \\ \hline a100 & 22.88 & 21.84 & 1.63 & 22.36 & \(-0.40\) & 9.00 \\ a50 & 22.69 & 21.44 & 2.28 & 22.07 & \(-0.47\) & 9.68 \\ a0 & 22.62 & 20.98 & 2.90 & 21.80 & \(-0.56\) & 11.64 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Summary of the results obtained from the Indoor Climate Analyzer. \(\mathrm{T_{air}}\) is the average air temperature of the heated room. Figure 13: (a) Room average \(T_{mr}\) and \(T_{op}\) results as a function of the wall surface emissivity; (b) average radiant planar asymmetry \(\overline{\Delta T_{pr}}\) and average predicted mean vote \(\overline{PMV}\) as a function of the wall surface emissivity. and they highlight that paints with good aesthetic value (limited metalized effect), and reduced emissivity, can be specifically developed for the application as interior radiation control coating. Furthermore, the effect of the different Interior Radiation Control Coatings IRCC was investigated through an experimental campaign in a double climatic chamber apparatus. The experimental results demonstrate that the application of IRCC determines:  
* a significant reduction of the indoor surface heat transfer coefficient, respectively of \(\sim\)35% with 100% aluminium paint and 19% with 50% aluminium paint that can result in the slightly but non-negligible reduction of the wall heat losses (especially in non-insulated walls);
* a decrease of the measured wall _U_-value above 20% (from 3.49 to 2.74 W/m\({}^{2}\) K) with a 100% aluminium paint. However, it is worth mentioning that, for a slightly insulated wall (_U_-value = 0.5 W/m\({}^{2}\) K), the _U_-value reduction that can be achieved is below 4%, meaning that the effect of the low emissivity coating is negligible for more insulated building components; and,
* an increase of the indoor mean radiant temperature of \(\sim\)0.9 \({}^{\circ}\)C and \(\sim\)0.5 \({}^{\circ}\)C and of the operative temperature of \(\sim\)0.6 \({}^{\circ}\)C and \(\sim\)0.3 \({}^{\circ}\)C respectively with 100% and 50% of aluminium paint. The above-mentioned results highlight that the application of IRCC shows a slight improvement of the indoor comfort condition as well as a marginal reduction of the heat losses. However, the results are encouraging especially considering that:  
* IRCC represents a low-cost solution that can be easily applied on the interior side of the external walls;
* IRCC can be easily coupled with other insulating technologies (i.e., aerogel rendering and coatings [17]) making it a promising solution for all the interventions, in which space-saving represents a constraint; and,
* further improvements in the paint emissivity properties can be achieved working towards optimization of the final mixture. Moreover, possible higher exploitation of these materials can be envisioned in envelopes for special environments i.e., ice rinks, temporary buildings, automotive, and marine sector. All the authors contributed equally to the conception, the design, the experimental campaigns and the writing of this paper. All authors have read and agreed to the published version of the manuscript.