Field test for solving frequent start-up of the first stage in double-stage coupled heat pumps

Compares the start-up period and the heating characteristics of the first stage machines under two regress temperature difference. The field test results show that the first stage machines operating with large regress temperature difference will lower the start-up frequency to three times per hour and keep up higher energy efficiency. Analyses the effect of the enlarging regress temperature difference on the water temperature of terminal loop. Discusses the method for determining the maximal regress temperature difference.