Spatio-temporal variation characteristics of degree days (hours) in Tianjin area

 Taking Tianjin as an example, based on the meteorological data of national meteorological stations and automatic stations, studies the spatio-temporal variation characteristics of heating/cooling degree days. The results show that, affected by climate warming, from 1961 to 2017, the mean heating degree days in Tianjin area significantly decreased by 9.5 ℃·d/a, but the cooling degree days significantly increased by 1.1 ℃·d/a. From 1991 to 2017, the heating degree days decreased by 9.7% and the cooling degree days increased by 72.3% compared with 1961-1990. There are obvious spatial distribution differences of the degree days in Tianjin area, and the spatial difference increases with the climate warming, with 18.7% and 134.9% of the maximum difference of the heating degree days and cooling degree days in recent 30 years, respectively. There are also obvious spatial differences in the degree hours based on automatic station data, with 37.8% and 80.0% of the maximum difference of the heating degree hours and the cooling degree huors, respectively. The effect of climate warming on degree days (hours) should be fully considered and the degree days (hours) should be updated in time for building energy saving design. In addition, the energy saving design parameters (such as degree days) calculated from the data of a meteorological station are difficult to meet the energy saving design requirements of whole city. The spatial differences of the design parameters should be taken into account. The data of automatic meteorological stations of a whole city can be used as the basis for accurate energy saving design of buildings.