Demand defrost control method and apparatus

• US 4,882,908 A
• Filed: 07/17/1987
• Issued: 11/28/1989
• Est. Priority Date: 07/17/1987
• Status: Expired due to Term

• Current Assignee: Ranco Incorporated of Delaware (Schneider Electric SE)
• Original Assignee: Ranco, Inc. (Schneider Electric SE)
• Inventors: White, Lee A.
• Primary Examiner(s): Ford, John
• Application Number:
  US07/074,907
• Time in Patent Office: 865 Days
• Field of Search: 165/12, 165/17, 165/29, 62/155, 62/156, 62/234
• US Class Current: 62/155
• CPC Class Codes: F25B 13/00 Compression machines, plants or systems, with reversible cycle defrosting cycles F25B47/02
• CPC Class Codes: F25B 2313/0315 Temperature sensors near the outdoor heat exchanger
• CPC Class Codes: F25B 2700/2106 of fresh outdoor air
• CPC Class Codes: F25D 21/006 with electronic control circuits

Abstract

A demand defrost controller for a heat pump. The controller compares the temperature of an outdoor heat exchange coil with an enable temperature. A timer is activated when the coil temperature is less than the enable temperature. When the timer senses the compressor has run for a predetermined time the controller checks outdoor and coil temperatures to determine if a defrost cycle of the heat pump should be conducted. A defrost cycle is achieved by reversing refrigerant flow in the heat pump system for a predetermined period or until the outdoor heat exchange coil has been heated to a termination temperature.

Claims

1. A method of defrosting an outdoor heat exchanger of a compressor-condenser-evaporator type heat pump unit in accordance with sensed conditions indicative of the need to perform a defrost cycle comprising:

(a) sensing the temperature of the outdoor heat exchanger;

(b) sensing the outdoor air temperature;

(c) monitoring compressor running time until a predetermined accumulated running time that varies as a function of outdoor air temperature has elapsed;

(d) enabling defrosting of the outdoor heat exchanger when said running time has elapsed;

(e) detecting the extent of the temperature differential between the sensed outdoor heat exchanger temperature and the sensed outdoor air temperature;

(f) determining a value indicative of the frosting condition of the heat exchanger which valve varies as a function of outdoor air temperature;

(g) comparing the value with the sensed temperature differential;

(h) enabling a defrosting cycle when the sensed temperature differential and the value bear a predetermined relationship to each other; and

,

(i) initiating a defrost cycle only when enabled by said compressor running time elapsing and enabled by said sensed temperature differential bearing a predetermined relationship to said value.

2. The method of claim 1 wherein accumulating compressor running time is only performed when the outdoor heat exchanger temperature is below an enable temperature.

3. A compressor-condenser-evaporator type heat pump system including a defrost controlling means for governing defrosting of the outdoor refrigerant heat exchanger by initiating a defrost cycle, said defrost controlling means comprising:

(a) an outdoor atmospheric air temperature monitoring sensor;

(b) an outdoor heat exchanger temperature monitoring sensor;

(c) a time defrost system for accumulating the aggregate running time of the compressor when the sensed heat exchanger temperature is below an enable temperature and enabling initiation of an outdoor heat exchanger defrost cycle after a predetermined compressor running time has been accumulated, said time defrost system constructed to enable defrosting at accumulated compressor run times which are relatively short at atmospheric temperatures approaching a relatively high predetermined temperature and lengthen as atmospheric temperatures are reduced from said relatively high predetermined temperature;

(d) a frosting condition responsive system for detecting the differential between the outdoor air temperature and the outdoor heat exchanger temperature and comparing said differential to a value which varies according to sensed outdoor air temperature, said frosting condition responsive system enabling initiation of a defrosting cycle when the differential and the value bear a predetermined relationship, said frost condition sensing system tending to enable initiation of defrosting cycles at relatively small sensed differential temperatures when atmospheric air temperatures are substantially below said predetermined temperature with the sensed temperature differential required to initiate defrost increasing as atmospheric air temperatures increase toward said predetermined level;

(e) controller means for initiating a defrost cycle in response to said time defrost system and said frost condition sensing system both enabling a defrost cycle; and

(f) said time defrost system and said frost condition responsive system coacting so that when outdoor air temperatures approach said predetermined temperature defrosting of said heat pump is initiated primarily in response to sensed temperature differential and when outdoor air temperatures are substantially below said predetermined temperature and heat pump is defrosted primarily in response to elapsed compressor run time.

4. A method of defrosting a heat pump comprising the steps of:

periodically sensing an ambient atmospheric air temperature and an outdoor heat exchanger coil temperature;

comparing the heat exchanger coil temperature with a preselected enable temperature;

enabling defrosting of the heat exchanger coil in relation to sensed temperature including, when the heat exchanger coil temperature is less than the enable temperature, accumulating compressor run time until a predetermined lockout period that varies as a function of ambient temperature has elapsed;

after the lockout period, comparing a difference between the ambient temperature and the heat exchanger coil temperature with a temperature difference value dependent on the ambient temperature; and

if the temperature difference between the ambient temperature and heat exchanger coil temperature is greater than or equal to the difference value, defrosting the heat exchanger coil.

5. The method of claim 4 wherein a defrost procedure is terminated after a predetermined time.

6. The method of claim 4 wherein the accumulated compressor run time is maintained when the coil temperature is above the enable temperature and the accumulated run time is updated when the coil temperature is above the enable temperature.

7. The method of claim 4 additionally comprising a step of monitoring an ambient temperature sensor failure and in the event of such a failure defrosting the heat exchanger coil at timed periods of compressor run time if the heat exchanger coil is below the enable temperature for said timed periods.

8. The method of claim 4 wherein the heat exchanger coil temperature used in the comparing steps is determined by averaging a number of successive sensed heat exchanger coil temperatures.

9. The method of claim 4 wherein the predetermined lockout period is increased at low temperature.

10. The method of claim 4 further including accumulating elapsed time during defrosting, sensing the coil temperature as the coil is being defrosted, terminating the defrosting step in response to a sensed coil temperature above a predetermined defrost termination temperature, and terminating defrosting upon the accumulation of a predetermined defrost time interval regardless of sensed coil temperature.

11. Heat pump control apparatus for use with a heat pump system having an indoor heat exchanger, outdoor heat exchanger, and a compressor operable to create a flow of refrigerant through said indoor and outdoor heat exchangers, said heat pump control apparatus comprising:

first temperature sensor means for monitoring ambient air temperature in proximity to said outdoor heat exchanger and second temperature sensor means for monitoring the temperature of said outdoor heat exchanger;

storage means for storing a preselected adjustable defrost enable temperature of said system and one or more parameters that define an outdoor heat exchanger function related to ambient temperature;

processor means for comparing the temperature of the outdoor heat exchanger with the adjustable enable temperature and setting a status indicator if the outdoor heat exchanger temperature is less than the enable temperature;

the processor means comprising means for establishing an outdoor heat exchanger frosting function value based on said parameters and sensed ambient temperature and comparing a difference between ambient temperature and outdoor heat exchanger temperature with the outdoor heat exchanger frosting function value; and

defrost means to defrost the outdoor heat exchanger;

said processor means having timing means to monitor the status indicator and activate the defrost means after the status indicator has been set for a predetermined compressor run period related to ambient temperature and the difference between ambient temperature and outdoor heat exchanger temperature bears a predetermined relationship to the outdoor heat exchanger frosting function value.

12. The control apparatus of claim 11 additionally comprising means to signal said processor means when the heat pump compressor is running to cause said processor means to begin comparing the outdoor heat exchanger temperature with the enable temperature.

13. The control apparatus of claim 11 wherein the processor means includes averaging means to average a number of successive outdoor heat exchanger temperature readings and provide an average outdoor heat exchanger temperature for comparing with the enable temperature.

14. A method of defrosting a heat pump outdoor heat exchanger comprising the steps of:

(a) defining a defrost lockout period relating a heat pump compressor run time with temperature, said lockout period increasing with decreasing ambient temperature;

(b) defining a heat exchanger frosting function relating a temperature difference between the outdoor heat exchanger and ambient temperature with sensed temperature;

said frosting function providing a value decreases with decreasing ambient temperature;

(c) monitoring compressor run time and temperature difference between the heat exchanger and ambient temperature; and

(d) defrosting the heat exchanger when the compressor run time exceeds the lockout period and the temperature difference bears a predetermined relationship to the frosting function value;

(e) said increasing lockout period and decreasing frosting function value causing the defrosting step to be principally controlled by the compressor run time at low temperature and by heat exchanger and ambient temperature difference at high temperature.

15. The method of claim 14 wherein monitoring compressor run time and temperature difference between the heat exchanger and ambient temperature is conducted only when the heat exchanger temperature drops below an enable temperature.

16. A method of initiating the defrosting cycle of a condenser-compressor-evaporator type heat pump unit in response to the existence of three necessary enabling conditions comprising:

(a) establishing a first defrost cycle enabling condition in response to outdoor heat exchanger temperature comprising;

(i) sensing the temperature of the outdoor heat exchanger;

(ii) monitoring the sensed heat exchanger temperature; and

(iii) enabling initiation of the defrost cycle when the monitored heat exchanger temperature is at or below a predetermined level;

(b) establishing a second defrost cycle enabling condition by determining that the compressor has run an aggregate time which exceeds a predetermined defrosting cycle lockout time period which varies with outdoor air temperature comprising the steps of;

(i) establishing a defrosting cycle lockout time period during which initiation of the defrosting cycle cannot be enabled;

(ii) monitoring operation of the compressor and determining the aggregate time the compressor operates during said lockout period;

(iii) increasing and decreasing the extent of said lockout period in response to sensed decreases and increases, respectively, of the ambient air temperature occurring during the lockout period; and

,

(iv) enabling initiation of the defrost cycle when the aggregated compressor run time exceeds the most recently established lockout time period;

(c) establishing a third defrost cycle enabling condition in response to the indication of frost or ice on said outdoor heat exchanger comprising;

(i) sensing the outdoor atmospheric air temperature and monitoring that temperature;

(ii) determining the difference between the sensed atmospheric air temperature and the sensed outdoor heat exchanger temperature; and

(iii) enabling initiation of a defrosting cycle when the sensed temperature difference bears a predetermined relationship to the sensed outdoor air temperature; and

,

(d) initiating said defrosting cycle when said first, second and third enabling conditions coexist.

17. The method of claim 16 wherein the second enabling step is initiated only while the outdoor heat exchanger is at or below the predetermined level.

18. A method for defrosting a heat pump comprising the steps of:

as the heat pump compressor is running periodically sensing an ambient temperature with an ambient temperature sensor and sensing an outdoor heat pump expansion coil temperature with an expansion coil temperature sensor;

comparing the expansion coil temperature with an enable temperature;

if the coil temperature is less than the enable temperature accumulating compressor run time until a predetermined compressor lockout period has elapsed;

testing to determine the operative status of the ambient temperature sensor and in the event of a failure in the ambient temperature sensor, defrosting the expansion coil once the lockout period has elapsed;

if the ambient temperature sensor is operative, subsequent to the lockout period, comparing a difference between the ambient temperature and the coil temperature with a temperature difference value dependent on the ambient temperature and if the difference between the ambient and coil temperature is greater than or equal to the difference value, defrosting the expansion coil.

19. The method of claim 18 wherein the compressor lockout period is determined on the basis of ambient temperature if the ambient temperature sensor is operative and the compressor lockout period is fixed if the ambient temperature sensor has failed.

20. Heat pump control apparatus for use with a heat pump system having an indoor heat exchanger, outdoor heat exchanger, compressor, and flow control means to direct a flow of refrigerant through said indoor and outdoor heat exchangers, said heat pump control apparatus comprising:

first temperature sensor means for monitoring ambient temperature in proximity to an outdoor heat exchanger coil and second temperature sensor means for monitoring outdoor heat exchanger coil temperature;

storage means for storing an adjustable enable temperature to adjust defrosting of said system;

processor means to compare the temperature of the heat exchange coil with the adjustable enable temperature and to set a status indicator if the heat exchanger coil temperature is less than the enable temperature; and

defrost control means to defrost the heat exchange coil;

said processor means having timing means to monitor the status indicator and activate the defrost control means after the status indicator has been set for a predetermined compressor run period related to ambient temperature and further having means for sensing a failure in said first temperature sensor means and means for adjusting the predetermined compressor run period to a constant independent of ambient temperature in the event of such a failure.

21. The heat pump control apparatus of claim 20 wherein the processor means includes means for sensing a failure in said second temperature sensor and suspending controlled defrosting in the event of such a failure in the second temperature sensor.

22. A heat pump defrosting control apparatus for use with a heat pump unit having an indoor heat exchanger, an outdoor heat exchanger and a compressor operable to circulate refrigerant through said heat exchangers, the apparatus comprising:

(a) a first temperature sensor for detecting the temperature of atmospheric air and producing an output signal which varies according to variations in sensed atmospheric air temperature;

(b) a second temperature sensor for detecting the temperature of the outdoor heat exchanger and producing an output signal which varies according to sensed heat exchanger temperature;

(c) first defrost cycle enabling means for producing a defrost enabling condition in response to sensed atmospheric air temperature below a predetermined value;

(d) second defrost cycle enabling means for producing a second defrost enabling condition in response to accumulated compressor running time comprising;

(i) timer means for accumulating the running time of said compressor;

(ii) adjustment means for increasing and decreasing the extent of a lockout period during which a defrost cycle can not occur in response to sensed decreases and increases, respectively, of the ambient air temperature occurring during the lockout period; and

(iii) means for enabling initiation of a defrost cycle in response to the aggregated compressor run time exceeding the most recently established lockout time period;

(e) third defrost cycle enabling means for producing a third defrost enabling condition in response to an indication of frost or ice on the outdoor heat exchanger comprising

(i) first processing means for determining the difference between the sensed atmospheric air temperature and the sensed outdoor heat exchanger temperature; and

(ii) second processing means for enabling initiation of a defrost cycle when the sensed temperature difference bears a predetermined relationship to the sensed outdoor air temperature, and

(f) defrost means for initiating a defrost cycle in response to the said coexistence of the first, second, and third enabling conditions.