Fig. 5 shows the time series of electricity consumption by
educational facility. The electricity consumptions of elementary,
middle, and high schools are higher in summer and in winter. In
particular, it is highest in December annually. The time series of
electricity consumption tends to increase each year and have seasonality
of one cycle per year. At the 5% significance level, if the
absolute value of t-statistics to the auto-correlation coefficient is
larger than the critical value ‘1.25’, it can be determined that seasonality
exists in the time series [44,62]. As shown in Table 2, the
absolute value of t-statistics to the auto-correlation coefficient in all
three types of educational facilities is larger than the critical value
‘1.25’. Therefore, it can be determined that seasonality exists in the
time series of electricity consumption by educational facility with a
time lag of 12 months.