US-12618605-B2 - Refrigeration system with demand fluid defrost

Abstract

A refrigeration system including an evaporator defining an evaporator envelope and positionable to condition an airflow, the evaporator including an airflow inlet, an airflow outlet, and one or more refrigerant coils. The refrigeration system also includes a pressure sensor that is positioned to detect an outlet air pressure at or adjacent the outlet, and positioned to detect one or both of an ambient air pressure and an inlet air pressure and to generate a signal indicative of the corresponding air pressure. A control system in operative communication with the pressure sensor to determine a pressure differential based on the signal indicative of the outlet air pressure and the signal indicative of the ambient air pressure or the inlet air pressure, the control system configured to selectively initiate a demand defrost of the evaporator based on the determined pressure differential.

Inventors

• Michael D. Lyons

Assignees

• HUSSMANN CORPORATION

Dates

Publication Date

20260505

Application Date

20230922

Claims (20)

1. 1 . A refrigeration system comprising: an evaporator defining an evaporator envelope and positionable to condition an airflow, the evaporator including an airflow inlet, an airflow outlet, and one or more refrigerant coils; a pressure sensor positioned to detect an outlet air pressure at or adjacent the airflow outlet and to generate a signal indicative of the outlet air pressure, the pressure sensor further positioned to detect an ambient air pressure and to generate a signal indicative of the detected air pressure; and a control system including a controller in operative communication with the pressure sensor to determine a pressure differential based on the signal indicative of the outlet air pressure and the signal indicative of the ambient air pressure, the control system configured to selectively initiate a demand defrost of the evaporator based on a decrease in the determined pressure differential below a pressure trigger value.
2. 2 . The refrigeration system of claim 1 , wherein the pressure sensor includes a single pressure sensor operatively coupled to the airflow outlet and to an exterior of the refrigeration system via a pressure tube.
3. 3 . The refrigeration system of claim 2 , wherein the pressure sensor includes respective ports operatively coupled to the airflow outlet and to the exterior of the refrigeration system.
4. 4 . The refrigeration system of claim 1 , wherein the control system is configured to stop the demand defrost based on another determined pressure differential after the demand defrost has been initiated.
5. 5 . The refrigeration system of claim 1 , wherein the pressure sensor is configured to detect the ambient air pressure exterior of the refrigeration system.
6. 6 . The refrigeration system of claim 1 , wherein the demand defrost is a fluid demand defrost.
7. 7 . The refrigeration system of claim 1 , wherein the evaporator is disposed in a merchandiser including a case defining a product storage or display area and a fan positioned in the case to generate the airflow through the evaporator and the case, and wherein the pressure sensor is positioned external to an envelope of the airflow to detect the ambient air pressure.
8. 8 . The refrigeration system of claim 7 , wherein the pressure sensor includes a single pressure sensor operatively coupled to the airflow outlet and to the case at a location exterior of the refrigeration system including the fan and the evaporator.
9. 9 . The refrigeration system of claim 8 , wherein the pressure sensor includes a first vacuum tube connected to the location exterior of the refrigeration system to sense the ambient air pressure and a second vacuum tube connected to the case at or downstream of the airflow outlet.
10. 10 . The refrigeration system of claim 7 , wherein the case includes an electrical raceway and the pressure sensor is positioned in or exterior of the electrical raceway.
11. 11 . The refrigeration system of claim 7 , wherein the pressure sensor is a first pressure sensor, the merchandiser further comprising a second pressure sensor positioned to detect a pressure of the airflow at or adjacent the airflow inlet.
12. 12 . The refrigeration system of claim 7 , wherein the control system is configured to stop the demand defrost based on another determined pressure differential after the demand defrost has been initiated.
13. 13 . A method of controlling a demand defrost in a refrigeration system including an evaporator and a fan configured to generate an airflow through the refrigeration system, the method comprising: sensing a first air pressure in the refrigeration system via a first sensor at a first location at or downstream of an outlet of the evaporator, the evaporator defining an evaporator envelope; generating a first signal indicative of the first air pressure; sensing a second air pressure exterior to the refrigeration system via a second sensor at a second location outside the evaporator envelope, the second location further outside an envelope of the airflow; generating a second signal indicative of the second air pressure; determining a pressure differential based on the first signal and the second signal via a control system operatively communicating with the first sensor and the second sensor; and selectively initiating the demand defrost of the evaporator via the control system in response to the determined pressure differential decreasing below a pressure trigger value.
14. 14 . The method of claim 13 , further comprising establishing the pressure trigger value during startup or initialization of the refrigeration system.
15. 15 . The method of claim 13 , further comprising determining an alarm condition based on the determined pressure differential.
16. 16 . The method of claim 13 , wherein the first sensor and the second sensor comprise one sensor, the method further comprising sensing the first air pressure via a first vacuum tube operatively coupled to the first location and sensing the second air pressure via a second vacuum tube operatively coupled to the second location.
17. 17 . The method of claim 13 , further comprising determining whether a time threshold has been exceeded prior to initiating the demand defrost.
18. 18 . The method of claim 17 , wherein the time threshold includes one or more of a refrigeration window, a time from previous defrost, and a length of time that the determined pressure differential is below the pressure trigger value.
19. 19 . The method of claim 13 , further comprising iteratively determining additional pressure differentials and determining an average pressure differential based on the iterative determinations.
20. 20 . The method of claim 19 , further comprising determining an alarm condition associated with the refrigeration system based on the average pressure differential.

Description

This application claims priority to U.S. Provisional Patent Application No. 63/376,656, filed on Sep. 22, 2022, and entitled “Refrigeration System With Fluid Defrost”, the content of which is hereby incorporated by reference in its entirety. BACKGROUND Background The present invention relates to refrigeration systems and, more particularly, to fluid defrost of heat exchangers in refrigeration systems. Refrigeration systems are well known and widely used in supermarkets, warehouses, and elsewhere to refrigerate product that is supported in a refrigerated space. Conventional refrigeration systems include a heat exchanger or evaporator, a compressor, and a condenser. The evaporator provides heat transfer between a refrigerant flowing within the evaporator and a fluid (e.g., water, air, etc.) passing over or through the evaporator. The evaporator transfers heat from the fluid to the refrigerant to cool the fluid. The refrigerant absorbs the heat from the fluid and evaporates in a refrigeration mode, during which the compressor mechanically compresses the evaporated refrigerant from the evaporator and feeds the superheated refrigerant to the condenser, which cools the refrigerant. From the condenser, the cooled refrigerant is typically fed through an expansion valve to reduce the temperature and pressure of the refrigerant, and then the refrigerant is directed through the evaporator. Some evaporators operate at evaporating refrigerant temperatures that are near or lower than the freezing point of water (i.e., 32 degrees Fahrenheit). Over time, water vapor from the fluid freezes on the evaporator (e.g., on the coils) and generates frost. Accumulation of frost decreases the efficiency of heat transfer between the evaporator and the fluid passing over the evaporator, which causes the temperature of the refrigerated space to increase above a desired level. Maintaining the correct temperature of the refrigerated space is important to maintain the quality of the stored product. To do this, evaporators must be regularly defrosted to reestablish efficiency and proper operation. Many existing refrigeration systems use electric heaters that are placed underneath the evaporator to defrost the evaporator using convection heat. Other existing systems re-route hot gaseous refrigerant from the compressor directly to the evaporator so that heat from the hot refrigerant melts the frost on the evaporator (i.e. reverse hot gas defrost). Some evaporators draw air through a coil of the evaporator, which creates turbulent airflow through the coil. The turbulent airflow is further intensified with higher volumes of air, common in commercial refrigeration units. Many existing refrigeration systems include a sensor to measure a pressure differential within the coil. However, a pressure differential within the coil is generally higher than the pressure differential in the remainder of the refrigeration system due to the turbulent airflow within coil. In addition, the sensors are typically located within the volume or envelope of the coil, which reduces the capacity of the evaporator to condition the airflow because fins of the evaporator need to be adjusted or trimmed. Trimming the fins has a negative impact on coil performance. SUMMARY Frost and ice that forms on an evaporator of a commercial refrigeration system, such as a refrigerated merchandiser, acts as an insulating barrier that reduces heat transfer and can lead to reduced airflow across the coil. The rate of frost accumulation can vary significantly depending on variables such as ambient conditions, shopping volume, and/or case maintenance. Demand defrost, embodying the invention as described herein, initiates defrost cycles only when there is sufficient frost accumulation (as detected by appropriate mechanisms), which reduces overall energy usage and improves average product temperatures. In one aspect, the present invention provides a refrigeration system having a refrigerant circuit including a condenser, an evaporator, a compressor, and a control system. The compressor is configured to circulate a cooling fluid through the refrigerant circuit. The refrigerant circuit has an inlet line fluidly connecting the condenser to the evaporator and a suction line fluidly connecting the evaporator to the compressor. The control system begins a defrost cycle for the refrigeration system based on a differential pressure of the evaporator. Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a cross-section of a refrigerated merchandiser including a product display area and an evaporator that is disposed in a refrigerant circuit of a refrigeration system embodying the present invention. FIG. 1B is a cross-section of a refrigerated merchandiser including a product display area and an evaporator that is disposed in a refrigerant circuit of a refrigeration system embodying anot