Reverse cycle defrost refrigeration system and method

1. A method of defrosting an indoor coil in a refrigeration system in which a refrigerant is circulatable in a first direction, to transfer heat out of a volume of air in a controlled space when the refrigeration system is operating in a refrigeration mode, and in which the refrigerant is circulatable in a second direction at least partially opposite to the first direction when the refrigeration system is operating in a defrost mode, the refrigeration system comprising an outdoor coil at least partially immersed in ambient air at a plurality of ambient temperatures to facilitate transferring thermal energy from the refrigerant in the outdoor coil to the ambient air, the method comprising:

(a) while the system is operating in the refrigeration mode, with a controller of the refrigeration system, determining a defrost commencement time at which the refrigeration system is to commence operating in the defrost mode;

(b) with the controller, initiating at least one defrost energy conservation process prior to the defrost commencement time, to decrease a rate at which thermal energy is transferred from the refrigerant in the outdoor coil to the ambient air;

(c) permitting said at least one defrost energy conservation process to continue until at least one defrost energy conservation termination criterion is satisfied;

(d) upon said at least one defrost energy conservation termination criterion being satisfied, terminating said at least one defrost energy conservation process; and

(e) upon termination of said at least one defrost energy conservation process, commencing operation of the refrigeration system in the defrost mode by energizing a reversing valve to direct the refrigerant to flow in the second direction into the indoor coil, to defrost the indoor coil.

2. The method according to claim 1 in which said at least one defrost energy conservation process comprises de-energizing a fan motor operatively connected to a fan positioned to direct the ambient air through the outdoor coil, wherein the rate of thermal energy transfer from the refrigerant in the outdoor coil to the ambient air is decreased.

3. The method according to claim 1 in which said at least one defrost energy conservation process comprises alternately (i) de-energizing a fan motor operatively connected to a fan positioned to direct the ambient air through the outdoor coil, and (ii) energizing said fan motor, to decrease the rate of thermal energy transfer from the refrigerant in the outdoor coil to the ambient air.

4. The method according to claim 1 in which said at least one defrost energy conservation process comprises modulating a speed of rotation of a fan positioned to direct the ambient air through the outdoor coil, to decrease the rate of thermal energy transfer from the refrigerant in the outdoor coil to the ambient air.

5. The method according to claim 1 in which:

the outdoor coil is positioned in a partially enclosed space in an outdoor coil housing and the ambient air is in fluid communication with the partially enclosed space via an opening in the outdoor coil housing, the opening having a size that is variable by a damper that is positionable to cover at least part of the opening; and

said at least one defrost energy conservation process comprises, with the damper, decreasing the size of the opening, to decrease the rate of thermal energy transfer from the refrigerant in the outdoor coil to the ambient air.

6. The method according to claim 1 additionally comprising pre-heating a drain pan positioned for collection of a melted condensate that has melted off the indoor coil, prior to the refrigeration system commencing operation in the defrost mode, in order to impede the melted condensate from refreezing in the drain pan.

7. The method according to claim 6 in which pre-heating the drain pan commences upon commencement of said at least one defrost energy conservation process.

8. The method according to claim 7 in which pre-heating the drain pan is terminated upon termination of said at least one defrost energy conservation process.

9. The method according to claim 7 in which the termination of said at least one defrost energy control process is delayed until the drain pan is heated sufficiently to impede refreezing of the melted condensate on the drain pan.

10. The method according to claim 1 in which said at least one defrost energy conservation termination criterion is a predetermined discharge pressure of the refrigerant.

11. The method according to claim 1 in which said at least one defrost energy conservation termination criterion is a predetermined time period.

12. A refrigeration system in which a refrigerant is circulatable in a first direction, to transfer heat out of a volume of air in a controlled space when the refrigeration system is operating in a refrigeration mode, and in which the refrigerant is circulatable in a second direction at least partially opposite to the first direction when the refrigeration system is operating in a defrost mode, the refrigeration system comprising an outdoor coil at least partially immersed in ambient air at a plurality of ambient temperatures to facilitate transferring thermal energy from the refrigerant in the outdoor coil to the ambient air, the refrigeration system comprising:

a controller configured for determining, while the system is operating in the refrigeration mode, a defrost commencement time at which the refrigeration system is to commence operating in the defrost mode;

the controller additionally being configured to initiate at least one defrost energy conservation process prior to the defrost commencement time, to decrease a rate at which thermal energy is transferred from the refrigerant in the outdoor coil to the ambient air;

the controller additionally being configured to permit said at least one defrost energy conservation process to continue until at least one defrost energy conservation termination criterion is satisfied;

the controller additionally being configured, upon said at least one defrost energy conservation termination criterion being satisfied, to terminate said at least one defrost energy conservation process; and

the controller additionally being configured, upon termination of said at least one defrost energy conservation process, to commence operation of the refrigeration system in the defrost mode by energizing a reversing valve to direct the refrigerant to flow in the second direction into the indoor coil, to defrost the indoor coil.