Method of operating a transport refrigeration unit

• US 5,201,185 A
• Filed: 07/11/1991
• Issued: 04/13/1993
• Est. Priority Date: 07/11/1991
• Status: Expired due to Term

• Current Assignee: Thermo King Corporation (Trane Technologies plc)
• Original Assignee: Thermo King Corporation (Trane Technologies plc)
• Inventors: Berge, Jeffrey B., Hanson, Jay L., Seshadri, Jayaram, Nixon, James E., Jurewicz, Romuald M.
• Primary Examiner(s): RIVELL, JOHN A
• Application Number:
  US07/728,472
• Time in Patent Office: 642 Days
• Field of Search: 62/81, 62/126, 62/129, 62/155, 62/156, 62/234
• US Class Current: 62/81
• CPC Class Codes: B60H 1/3207 for minimizing the humidity of the air
• CPC Class Codes: B60H 1/3232 particularly adapted for load transporting vehicles B60H1/3226 takes precedence
• CPC Class Codes: F25B 13/00 Compression machines, plants or systems, with reversible cycle defrosting cycles F25B47/02
• CPC Class Codes: F25B 47/022 hot gas defrosting
• CPC Class Codes: F25D 21/006 with electronic control circuits
• CPC Class Codes: F25D 29/003 for movable devices

Abstract

The invention relates to methods of defrosting an evaporator coil of a transport refrigeration unit which includes microprocessor based electrical control. The electrical control maintains the temperature of a conditioned space at a predetermined set point temperature via hot gas heating and cooling cycles. The evaporator coil is defrosted to remove frost and ice by closing a damper to the served space and initiating a heating cycle. At the termination of defrost, a cooling cycle is initiated, but the damper is maintained in a closed position for a predetermined period of time to remove heat built up during the defrost process. The invention also detects damper malfunctions, including failure to close prior to defrost, and failure to open after defrost. The invention also evaluates manual and timed requests for a defrost operation, overriding the requests in response to predetermined conditions.

Claims

1. A method of defrosting an evaporator coil of a transport refrigeration unit having a refrigerant circuit which includes a compressor and an evaporator coil having a coil temperature sensor, and microprocessor based electrical control for controlling the temperature of a served space by drawing air from the served space, conditioning the air with the evaporator coil, and returning the conditioned air to the served space, comprising the steps of:

requesting a manual defrost operation,

determining whether the evaporator coil temperature sensor is functional, or faulty,

overriding the request for the manual defrost operation when the determining step finds the evaporator coil temperature sensor is faulty,

determining if the compressor of the transport refrigeration unit is running,

determining if the transport refrigeration unit is set to operate in a cycling mode when the compressor is not running,

and overriding the request for the manual defrost operation when the compressor is not running and the transport refrigeration unit is not set to operate in a cycling mode.

2. The method of claim 1 including the steps of:

checking the temperature of the evaporator coil when the determining step finds the evaporator coil temperature sensor functional,

and overriding the request for the manual defrost operation when the temperature of the evaporator coil exceeds a predetermined temperature.

3. The method of claim 1 including the steps of:

providing a timed defrost operation,

determining if a timed defrost operation has been requested,

and overriding the request for the manual defrost operation in response to a request for a timed defrost operation.

4. The method of claim 1 including the step of starting the compressor when the compressor is not running, and the transport refrigeration unit is set to operate in the cycling mode.

5. A method of defrosting an evaporator coil of a transport refrigeration unit having a refrigerant circuit which includes a compressor and an evaporator coil having a coil temperature sensor, and microprocessor based electrical control for controlling the temperature of a served spaced by drawing air from the served space, conditioning the air with the evaporator coil, and returning the conditioned air to the served space, comprising the steps of:

requesting a manual defrost operation,

determining whether the evaporator coil temperature sensor is functional, or faulty,

overriding the request for the manual defrost operation when the determining step finds the evaporator coil temperature sensor is faulty,

checking the temperature of the evaporator coil when the determining step finds the evaporator coil temperature sensor is functional,

providing defrost in response to a timed request,

determining if a timed request for defrost has been generated,

determining if the compressor is running,

determining if the transport refrigeration unit is set to operate in a cycling mode when the compressor is not running,

allowing the request manual defrost operation, in the absence of a timed request, when the temperature of the evaporator coil is below a predetermined temperature, and the compressor is running,

allowing the request manual defrost operation, in the absence of a timed request, when the temperature of the evaporator coil is below a predetermined temperature, the compressor is stopped, and the transport refrigeration unit is set to operate in a cycling mode,

and starting the compressor when it is stopped, in response to the step of allowing the request manual defrost operation.

6. A method of defrosting an evaporator coil of a transport refrigeration unit having a refrigerant circuit which includes a compressor and an evaporator coil having a coil temperature sensor, microprocessor based electrical control for controlling the temperature of a served space to a predetermined set point temperature by drawing air from the served space, conditioning the air with the evaporator coil, and discharging the conditioned air to the served space, and a discharge air temperature sensor, comprising the steps of:

providing a timed request for defrost,

determining whether the evaporator coil temperature sensor is functional, or faulty,

determining if the set point temperature is above a predetermined value, when the coil temperature sensor is found to be faulty,

allowing the timed request to initiate a defrost operation when the set point temperature is not above the predetermined value,

overriding the timed request when the set point temperature is above the predetermined value,

determining whether the discharge air temperature sensor is functional, or faulty,

terminating defrost in response to the discharge air temperature reaching a predetermined value, when the discharge air temperature sensor is found to be functional,

and terminating defrost in response to time when the discharge air temperature sensor is found to be faulty.

7. A method of defrosting an evaporator coil of a transport refrigeration unit having a refrigerant circuit which includes a compressor and an evaporator coil having a coil temperature sensor, and microprocessor based electrical control, including a defrost interval timer, for controlling the temperature of a served space to a predetermined set point temperature by drawing air from the served space, conditioning the air with the evaporator coil, and returning the conditioned air to the served space, comprising the steps of:

providing a timed request for defrost initiated by the defrost interval timer,

determining whether the evaporator coil temperature sensor is functional, or faulty,

checking the temperature of the evaporator coil when the determining step finds the evaporator coil temperature sensor is functional,

determining if the compressor is running,

allowing the timed request to initiate defrost when the checking step finds the temperature of the evaporator coil is below a predetermined value and the compressor is running,

comparing the temperature of the served space with the set point temperature to determine if the temperature of the served space is within a predetermined range of set point,

and setting the time interval between timed defrost requests in response to whether the temperature of the served space is inside or outside the predetermined range of the set point temperature.

8. The method of claim 7 including the step of overriding the timed request for defrost when the compressor is not running.

9. The method of claim 8 including the step of resetting the defrost interval timer in response to the step of overriding the timed request.