Monthly Domestic Household Income (HK$)20012006 Weather effect The weather effect contributed positively to the energy use change of the sector (increase by 2,369 TJ or 11.6% of the total energy change of the sector). This is consistent with the higher level of use of air-conditioning systems in the Residential sector. Figure 4.1 shows the increase in cooling degree days of Hong Kong from 1990 to 2007. With the use of air-conditioning systems highly dependent on weather conditions, the warmer weather of Hong Kong over the years contributed positively to the increase in the energy end-use of the sector. EMSD Symposium 2011 Symposium on Electrical and Mechanical Safety & Energy Efficiency - Engineering a Safe and Low-carbon Environment Figure 4.1 Cooling Degree Days, 1990–2007 Cooling Degree Days (CDD), 1990-2007Enclosure (Page 10 of 11) 1 7001 8001 900200021 0022002300199019 921 994199619982000200220042006YearNumber of CDD Source: [7] 5. SUMMARY AND CONCLUSION This section summarized an