Defrost control system for a refrigeration heat pump apparatus

• US 4,538,420 A
• Filed: 12/27/1983
• Issued: 09/03/1985
• Est. Priority Date: 12/27/1983
• Status: Expired due to Fees

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Nelson, Lorne W.
• Primary Examiner(s): Tanner, Harry
• Application Number:
  US06/566,018
• Time in Patent Office: 616 Days
• Field of Search: 62/140, 62/155, 62/156, 62/151, 62/234, 62/128, 62/129, 62/154
• US Class Current: 62/140
• CPC Class Codes: F25D 21/002 Defroster control

Abstract

A control system for a refrigeration heat pump having an outdoor coil through which air is blown by a fan for extracting heat from outdoor air with means to defrost the coil periodically has a differential pressure responsive means responding to the differential air pressure across the outdoor coil. A time control means periodically operates the heat pump for a time controlled operation for predetermined time period (such as 90 minutes of elapsed operating time) and measures and stores the value of the differential pressure across the coil at the end of the time period in memory. A control means controls the heat pump between the periodically time controlled operations for normal operations for a total elapsed time operation in a pressure controlled operation until the pressure differential as previously stored occurs at which time a defrost cycle is initiated. Periodically a time controlled operation is initiated to update the pressure stored in the memory.

Claims

1. In a control system for refrigeration heat pump having an outdoor coil through which air is blown by a fan extracting heat from outdoor air and defrost means to periodically heat the outdoor coil to remove the frost comprising,

differential pressure responsive means adapted to respond to the differential air pressure across the outdoor coil,

time controlled means adapted for periodically operating the heat pump for a predetermined total time controlled operation sufficient to bring about the frosting of the outdoor coil under predetermined outdoor ambient conditions and thereafter operating said defrost means, whereby a value of differential pressure is measured at the end of said time total period,

memory means for maintaining said value of differential air pressure across the coil at the end of said predetermined total time period,

control means adapted to control the heat pump between said periodic total time controlled operations for normal operations for new time period extending until said pressure responsive means responds to said value of differential air pressure, and

connection means connecting said differential pressure responsive means to operate said defrost means when said value of differential air pressure is attained.

2. The invention of claim 1 wherein said time controlled means, said memory means and said control means is a microprocessor.

3. The invention of claim 1 comprising

means connected to said time controlled means for performing several of said total time controlled operations of said heat pump, and

means for selecting the highest differential pressure of said several operations for storage in said memory.

4. The invention of claim 1 wherein

said normal operations of said heat pump comprising a number of individual operations each of which increases the degree of frost build up on the outdoor coil to establish a higher differential pressure at the end of each of said individual operations, and comprising

second memory means connected to said control means for storing values of a plurality of differential pressures from earlier operations and as the differential pressures of a present operation deviates from the stored values, a fault is detected.

5. The invention of claim 4 comprising

alarm means connected to said control means, said alarm means being responsive to a predetermined deviation in the present values from said stored values to energize said alarm means.

6. The invention of claim 5 wherein said time control means, said control means, said memory, said second memory means is a microprocessor apparatus.

7. In a control system for refrigeration heat pump having an outdoor coil through which air is blown by a fan for extracting heat from outdoor air and defrost means to periodically heat the outdoor coil to remove the frost comprising,

condition responsive means adapted to respond to a condition indicative of frost formation on the outdoor coil,

space temperature responsive means adapted to control the refrigeration heat pump upon a need for heat in a space,

time controlled means adapted for periodically allowing the heat pump to operate upon a call for heat, by said space temperature responsive means, a predetermined total time period sufficient to bring about the frosting of the outdoor coil under predetermined outdoor ambient air conditions and thereafter initiate operation of said defrost means, whereby a value of said condition is measured at the end of said total time period,

memory means for maintaining said value of said condition at the end of said predetermined total time period, and

control means connected to said space temperature responsive means adapted to control the heat pump between said periodic time controlled operations for operations for a second total time period extending until said condition responsive means responds to said value of said condition and thereafter operate said defrost means to remove the frost from the outdoor coil.

8. The invention of claim 7 wherein said time controlled means, said memory means and said control means is a microprocessor control apparatus.

9. The invention of claim 7 comprising

means connected to said time controlled means for performing several of said predetermined total time period operations of said heat pump, and

means for selecting the most significant of said conditions of said several operations to be stored in said memory means.

12. The invention of claim 7 comprising

alarm means,

further memory means for maintaining various values of pressure at different operations of the heat pump,

deviation responsive means responsive to the differences between present operating air pressures and said various values of said memory, and

means connecting said alarm means to said deviation means to be responsive to said differences.

10. In a method of determining the need of defrost of a forced air heat exchanging outdoor coil of a refrigeration heat system having a condition responsive means responsive to a condition indicative of air flow restriction through the outdoor coil due to frost formation thereon and a time control unit comprising the following steps,

operating the heat pump for at least one predetermined total time operation before a defrost operation and then sensing the value of a condition of the coil,

operating the heat pump for a total time operation until the same value of condition of the coil exists, and

starting an outdoor coil defrost cycle by heating the outdoor coil when said same value of condition exists.

11. In a method of sensing the need of defrost of a forced air heat exchanged outdoor coil of a refrigeration heat system having a differential pressure responsive means responsive to the pressure across the outdoor coil and a time control unit comprising the following steps,

operating the heat pump for a timed operation before a defrost operation and then measuring the value of differential pressure existing across the outdoor coil,

operating the heat pump for successive operations until said measured value of differential pressure exists, and

starting an outdoor coil defrost cycle by heating the outdoor coil when said measured value of differential pressure exists.

13. In a defrost control system for refrigeration apparatus having an heat exchange coil through which air is blown by a fan for extracting heat from air and defrost means to periodically heat the coil to remove the frost comprising,

pressure responsive means adapted to respond to an air pressure indicative of a predetermined restriction of air flow through the coil,

time controlled operation means adapted for periodically operating the refrigeration apparatus for a predetermined total time period controlled operation sufficient to bring about the frosting of the coil under predetermined ambient conditions and thereafter operating said defrost means, whereby a value of said air pressure indicative of a predetermined restriction of air flow is measured at the end of said time period,

memory means for maintaining said value of air pressure at the end of said predetermined total time period, and

control means adapted to control the refrigeration apparatus and the defrost means between said periodic total time controlled operations for normal air pressure controlled operations for new time period extending until said air pressure reaches said value before the defrost means is operated to remove the frost from said coil.

14. In a control system for refrigeration heat pump having an outdoor coil through which air is blown by a fan for extracting heat from outdoor air and defrost means to periodically heat the outdoor coil to remove the frost comprising,

condition responsive means adapted to respond to a condition indicative of frost formation on the outdoor coil,

space temperature responsive means adapted to control the refrigeration heat pump upon a need for heat in a space,

time controlled means adapted for periodically allowing the heat pump to operate upon a call for heat by said space temperature responsive means a predetermined total time period sufficient to bring about the frosting of the outdoor coil under predetermined outdoor ambient air conditions, whereby a value of said condition is measured at the end of said total time period,

memory means for maintaining said value of said condition at the end of said predetermined total time period,

defrost control means for initiating a defrost cycle at the termination of said total time,

means for terminating said defrost cycle after a predetermined time of operation,

control means connected to said space temperature responsive means adapted to control the heat pump between said periodic time controlled operations for operations for a second total time period extending until said condition responsive means responds to said value of condition before the defrost means is operated to remove the frost from the outdoor coil, and

means responsive to said predetermined time of operation whereby if said time is greater than a selected time, said second total time period is reduced.

15. The invention of claim 14 wherein said second total time is reduced by changing said value of said condition to initiate a defrost operation in a time period shorter than said second total time.