# Energy Saving Potential of PCMs in Buildings under Future Climate Conditions
## 4 Results  
### Effect of PCM on Indoor Environment  
To evaluate the performance of PCMs, researchers usually look at the indoor temperature profile during a short representative period in the summer, winter, or mid-season [(44; 14)]. The evaluation then compares the energy used with and without the PCM. Therefore, this study considers two days in August (the cooling period) and two days in January (the heating period) to evaluate the indoor environment. Figures 4 and 5 show the zone air temperature for 14-15 August and 14-15 January in Hong Kong. The figures show that integrating PCMs resulted in a reduced indoor air temperature peaks in August (Figure 4) and an indoor air temperature between 17 \({}^{\circ}\)C and 21.9 \({}^{\circ}\)C, which is near the comfort range of 18 \({}^{\circ}\)C-24 \({}^{\circ}\)C for Hong Kong, in January (Figure 5). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Characterization of Climate** & **Seoul-Korea** & **Tokyo-Japan** & **Hong Kong-China** \\ \hline Latitude & 37\({}^{\circ}\)29\({}^{\prime}\) N & 36\({}^{\circ}\)10\({}^{\prime}\) N & 22\({}^{\circ}\)19\({}^{\prime}\) N \\ Longitude & 126\({}^{\circ}\)38\({}^{\prime}\) E & 140\({}^{\circ}\)25\({}^{\prime}\) E & 114\({}^{\circ}\)10\({}^{\prime}\) E \\ Time zone (GMT) & +9.0 & +9.0 & +8.0 \\ Elevation (m) & 38 & 35 & 65 \\ Climate description & Humid tropical & Humid tropical & Subtropical \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Characterization of the climate in Seoul, Tokyo, and Hong Kong according to the Köppen-Geiger classification. This model used PCMs with melting points of 21.6 \({}^{\circ}\)C (DuPonEnergainPCM), 25 \({}^{\circ}\)C (MRUBITHRMPCM), and 29 \({}^{\circ}\)C (BioPCM). When the zone reached the melting temperature, the PCMs melted and stored energy as latent heat through the process of melting (changing phases), which prevented the ambient temperature of the zone from rising. At night, when the temperature decreased below 21.6 \({}^{\circ}\)C, 25 \({}^{\circ}\)C, or 29 \({}^{\circ}\)C, the PCMs resolidified, discharging the stored heat and increasing the zone ambient temperature. Thus, incorporating PCMs reduced the average temperature of the zone by 1.2-2 \({}^{\circ}\)C in August (Figure 4) and increased it by 0.3-0.5 \({}^{\circ}\)C in January (Figure 5) in Hong Kong. Figures 4 and 5 also show that integrating the PCMs decreased the time in which the zone temperature was outside the comfort zone. Figures 6 and 7 show the operative temperature with and without PCMs for 14-15 August and January in Tokyo. As shown in the figures, installing a PCM on the interior surface of the building envelope reduced the peak operative temperature about 1 \({}^{\circ}\)C in August in Tokyo. The PCMs also  
Figure 4: Effect of PCMs on indoor air temperature in summer, Hong Kong (14–15 August). Figure 5: Effect of PCMs on indoor air temperature in winter, Hong Kong (14–15 January). maintained the operative temperatures during both the heating and cooling seasons; for example, with a PCM, the operative temperature remained within range on both 14-15 January (17-21.2 \({}^{\circ}\)C) and 14-15 August (23.3-24.6 \({}^{\circ}\)C). In contrast, the operative temperature swung up and down from right to day without a PCM, 16.7-22.1 \({}^{\circ}\)C and 22.6-24.8 \({}^{\circ}\)C in January and August, respectively. Moreover, a significant mitigation of the swings in daily surface temperature can be observed when using a PCM, as shown in Figures 8-11: for example, in Figure 9, the peak surface temperature of the east wall in August decreased from 25.7 \({}^{\circ}\)C on the first day to 24.6 \({}^{\circ}\)C during the second day, and the surface temperature of the east wall in January increased from 18.1 \({}^{\circ}\)C on the first day to 23.5 \({}^{\circ}\)C during the second day, as shown in Figure 11. The differences are clear between the surface temperatures of the south and east walls with and without a PCM (Figures 8-11).