Method for terminating defrosting of an evaporator by use of air temperature measurements
A method for terminating defrosting of an evaporator ( 104 ) is disclosed. The evaporator ( 104 ) is part of a vapour compression system ( 100 ). The vapour compression system ( 100 ) further comprises a compressor unit ( 101 ), a heat rejecting heat exchanger ( 102 ), and an expansion device ( 103 ). The compressor unit ( 101 ), the heat rejecting heat exchanger ( 102 ), the expansion device ( 103 ) and the evaporator ( 104 ) are arranged in a refrigerant path, and an air flow is flowing across the evaporator ( 104 ). When ice is accumulated on the evaporator ( 104 ), the vapour compression system ( 100 ) operates in a defrosting mode. At least one temperature sensor ( 305 ) monitors a temperature T air , of air leaving the evaporator ( 104 ). A rate of change of T air is monitored and defrosting is terminated when the rate of change of the temperature, T air , approaches zero.
1. A method for terminating defrosting of an evaporator, the evaporator being part of a vapour compression system, the vapour compression system further comprising a compressor unit, a heat rejecting heat exchanger, and an expansion device, the compressor unit, the heat rejecting heat exchanger, the expansion device and the evaporator being arranged in a refrigerant path, and an air flow flowing across the evaporator, the method comprising the steps of:
operating the vapour compression system in a defrosting mode,
monitoring, by at least one temperature sensor, at least one temperature, T air , of air leaving the evaporator,
monitoring a rate of change of the temperature, T air , and
terminating defrosting when the rate of change of the temperature, T air , approaches zero.
2. The method according to claim 1 , wherein the step of terminating defrosting is performed when the rate of change of the temperature, T air , has been smaller than a predetermined threshold value for a predetermined time.
3. The method according to claim 1 , wherein during the defrosting mode a hot gas from the compressor unit is supplied to refrigerant passages of the evaporator.
4. The method according to claim 3 , wherein the hot gas heats the evaporator from the top to the bottom.
5. The method according to claim 3 , wherein air in the evaporator and the air surrounding the evaporator are heated by means of convection.
6. The method according to claim 3 , wherein the hot gas heats the evaporator from the bottom to the top.
7. The method according to claim 1 , wherein the evaporator is in a flooded state.
8. The method according to claim 1 , wherein the method further comprises the steps of:
monitoring, by at least two additional temperature sensors, an evaporator inlet temperature, T e,in , at a hot gas inlet of the evaporator and an evaporator outlet temperature, T e,out , at a hot gas outlet of the evaporator,
monitoring a rate of change of a difference between T e,in and T e,out , and
terminating defrosting when the rate of change of the difference between T e,in and T e,out approaches zero.
9. The method according to claim 8 , wherein the step of terminating defrosting is performed when the rate of change of the difference between T e,in and T e,out has been smaller than a predetermined threshold value for the predetermined time.
10. The method according to claim 1 , wherein the step of monitoring at least one temperature, T air , comprises monitoring a first air temperature, T air,in , at an air inlet of the evaporator and a second air temperature, T air,out , at an air outlet of the evaporator.
11. The method according to claim 2 , wherein during the defrosting mode a hot gas from the compressor unit is supplied to refrigerant passages of the evaporator.
12. The method according to claim 4 , wherein air in the evaporator and the air surrounding the evaporator are heated by means of convection.
13. The method according to claim 4 , wherein the hot gas heats the evaporator from the bottom to the top.
14. The method according to claim 5 , wherein the hot gas heats the evaporator from the bottom to the top.
15. The method according to claim 2 , wherein the evaporator is in a flooded state.
16. The method according to claim 3 , wherein the evaporator is in a flooded state.
17. The method according to claim 4 , wherein the evaporator is in a flooded state.
18. The method according to claim 5 , wherein the evaporator is in a flooded state.
19. The method according to claim 6 , wherein the evaporator is in a flooded state.
20. The method according to claim 2 , wherein the method further comprises the steps of:
monitoring, by at least two additional temperature sensors, an evaporator inlet temperature, T e,in , at a hot gas inlet of the evaporator and an evaporator outlet temperature, T e,out , at a hot gas outlet of the evaporator,
monitoring a rate of change of a difference between T e,in and T e,out , and
terminating defrosting when the rate of change of the difference between T e,in and T e,out approaches zero.