US20080060366A1

US20080060366A1 - System for monitoring the performance of a gas absorption cooling unit and related method

Info

Publication number: US20080060366A1
Application number: US11/519,433
Authority: US
Inventors: David Leistner; Wayne A. Schneider; Carl Onken; Santosh Nerur
Original assignee: Norcold Inc
Current assignee: Norcold Inc
Priority date: 2006-09-12
Filing date: 2006-09-12
Publication date: 2008-03-13

Abstract

The present teachings provide control systems and methods for monitoring the performance of an absorption refrigerator. The system includes a temperature sensor that senses the temperature of a generator of a cooling arrangement. The circuit may communicate with the sensor and turn off a heat source of the cooling unit if a sensed temperature condition of the generator exceeds a predetermined temperature condition.

Description

INTRODUCTION

Absorption refrigerators provide quiet operation and employ heat to vaporize the coolant—water mixture (typically ammonia—water) thereby driving the refrigeration loop. Popular heat sources include electrical heaters and fuel burners. The fuel burners typically employ propane which is readily available at camping supply stores, barbeque supply stores, and numerous gas stations. Though, any liquid or gaseous fuel would work well and be controllable through simple, automated control systems.
The heat source drives a generator for heating a coolant mixture to release ammonia vapor. The generator has an optional temperature range. Operation of the generator outside this optional temperature range may result in compromised performance.
It remains a need in the pertinent art to provide an improved system for monitoring the performance of a cooling unit of an absorption refrigerator by controlling heating of the generator under predetermined temperature conditions.

SUMMARY

According to one aspect, the present teachings provide a control system for a refrigerator having an absorption cooling arrangement with a generator. The control system may include a control circuit with a temperature sensor that senses the temperature of a generator. The circuit may communicate with a signal from the cooling unit that indicates when a predetermined temperature condition has been exceeded. The circuit may also communicate with the sensor and turn off the power to the refrigerator upon sensing of a predetermined temperature condition. Alternatively, the circuit may communicate with the sensor to turn off the heat source of the cooling unit.
According to another aspect, the present teachings provide an absorption refrigerator defining an interior volume and including an absorption system to cool the interior volume. The absorption system includes a generator. A heat source provides energy to drive the absorption cooling system. A temperature sensor may be adapted to sense a temperature of the generator. A circuit may be in communication with the sensor. The circuit may be adapted to turn off the heat source if a sensed temperature condition exceeds a predetermined temperature condition.
In another aspect, the present teachings may provide a method of controlling a cooling unit. The method may include sensing a temperature of a generator of the cooling system and determining a sensed temperature condition of the generator. The method may additionally include the step of comparing the sensed temperature condition to a predetermined temperature condition. The method may further comprise the step of turning off a heat source of the cooling system when the sensed temperature condition exceeds the predetermined temperature condition.
In still yet another aspect, the present teachings may provide a gas absorption cooling arrangement including a boiler tube and a plurality of electric heater tubes. At least one of the electric heater tubes may be secured to the boiler tube through a pair of welds. The pair of welds may extend substantially along the length of the respective electric heater tube.
Further areas of applicability of the present teachings will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the particular embodiments of the present teachings, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

DESCRIPTION OF THE DRAWINGS

The present teachings will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a rear perspective view of an exemplary gas absorption refrigerator including a control system in accordance with the present teachings.

FIG. 2 is a schematic view of the control system of an absorption refrigerator in accordance with the present teachings.

FIG. 3 is an enlarged detail view of a portion of the refrigerator of an absorption refrigerator including a control system in accordance with the present teachings, a sensor shown mounted in close proximity to a generator of the cooling arrangement.

FIG. 4 is an enlarged perspective view similar to FIG. 3 shown with the canister removed for purposes of illustration.

FIG. 5 is an enlarged perspective view of a sensor mounting bracket of FIGS. 2 and 3 shown removed from the remainder of the absorption refrigerator for purposes of illustration.

FIG. 6 is an enlarged perspective view of a canister mounting bracket according to the present teachings.

FIG. 7 is a top view of the canister mounting bracket of FIG. 5.

FIG. 8 is a schematic view of a control device of the control system of the present teachings, the control device illustrated as a switch in series with the main power (e.g., +12 VDC) that powers the refrigerator.

FIG. 9 is a schematic view of an alternative control device of the control system of the present invention, the control device illustrated as a valve in line with a gas source and the burner flame.

FIG. 10 is a flow-chart illustrating a method in accordance with the present invention for evaluating the operational performance of an absorption refrigerator.

FIG. 11 is a front view of a portion of an absorption cooling system in accordance with the present teachings, the cooling system shown to include three electric heater tubes secured to a boiler tube.

FIG. 12 is a cross-sectional view taken along the line 12-12 of FIG. 11.

DESCRIPTION OF VARIOUS ASPECTS

The following description of the present teachings is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
The methods and systems described herein can be applied to a wide variety of cooling units. For the purpose of illustration, though, a typical absorption refrigeration system is used that has a cold storage compartment. Those skilled in the art will understand that the illustrative refrigeration system does not limit the invention in any way, but is used only to explain the invention.
With general reference to the drawings, an exemplary absorption refrigerator 10 including a control system in accordance with the present teachings is illustrated. The refrigerator 10 includes a cooling system 11 including an absorption cooling arrangement 12 mounted on a back wall 14 of a cabinet 16. The cabinet 16 encloses an insulated compartment (not specifically shown). The cooling arrangement 12 may include conventional gas absorption cooling components. In this regard, the cooling arrangement 12 may include an absorber, an evaporator, a condenser and a generator. The generator includes a boiler tube. Insofar as the present invention is concerned, it will be understood that these basic components of the gas absorption refrigerator 10 are conventional in both construction and operation.
The cooling arrangement 12 may be controlled electrically or with a gas source. In this regard, the cooling arrangement 12 may additionally include a DC electrical heater, an AC electrical heater and a gas burner. The cooling arrangement 12 may further include a burner and control box 18. The generator and heaters may be contained within a generator enclosure or canister 20 that upwardly extends proximate the burner box 18.
As is well known in the art of absorption cooling, the coolant mixture (typically ammonia and water) is heated in the generator or boiler tube 22 to preferentially releasing ammonia vapor. From the generator, the ammonia vapor flows to the condenser. In the condenser, the ammonia vapor cools and condenses. By gravity, the cool liquid ammonia flows from the condenser and into the evaporator. In the evaporator, the liquid ammonia absorbs heat from the interior of the refrigerator 10 thereby cooling the interior of the refrigerator 10. The vaporized ammonia then flows from the evaporator to the absorber where the partially depleted water—ammonia mixture absorbs the ammonia vapor to complete the refrigeration cycle.
Heat is required to vaporize the ammonia in the ammonia—water mixture. The heat source may be an electrical heater, a burner flame, or any other conventional heat source. More particularly, the electric heater may be either an A/C (e.g., 240 V.A.C.) or a D.C. (e.g., 12-48 V.D.C) heater. In the alternative, both types of electrical heaters and a burner flame may be provided with controls to allow the user to switch between the three sources of heat. When the refrigerator 10 is operating with the electrical heat source a relatively large quantity of electrical power must be supplied from a source external to the refrigerator 10 (e.g. from the recreational vehicle electrical system or from a hook up provided at the camp site). In certain applications, the refrigerator 10 may automatically choose the best available energy source upon which to operate.
It is desirable to operate the generator of the cooling arrangement 12 within an optimum temperature range. Accordingly, the present inventors recognized a need to monitor a temperature condition of the generator and control the cooling arrangement 12 when the generator temperature condition is outside an optimum temperature range, thereby improving the cooling performance efficiency of the cooling arrangement 12 inside the refrigerator 10.
Turning now to the schematic illustration of FIG. 2, the control system 11 defines a control circuit that communicates with a temperature sensor 24 and a control device 26. The control circuit 25 may include a control panel 28 having a processor 30, a PROM, EEPROM, an ASIC chip, a hardwired circuit or the like. The temperature sensor 24 may be a thermocouple, a thermistor, an RTD (resistance thermal detector), or any other temperature sensing device that is well known in the art.
The circuit 25 may operate to control the control device 24 to turn off the source of heat to generator or boiler tube 22 when a second temperature exceeds a predetermined temperature condition. The predetermined temperature condition may simply be a predetermined temperature. It will be noted that the predetermined temperature may be significantly above the optimum operating range of the generator temperature. The circuit 25 may alternatively or additionally operate to maintain the generator temperature substantially within the optimum operating range. In this regard, the circuit 25 may operate to reduce the source of heat to the generator upon detection of a generator temperature above the optimum operating range. The source of heat may be reduced by temporary interruption of the power source (e.g., the power to the unit 10 or the gas source) until such time that the generator temperature is sufficiently within the optimal operating range. Conversely, the circuit 25 may operate to increase the source of heat to the generator upon detection of a generator temperature below the optimum operating range.
In FIGS. 3 and 4, an exemplary location of the thermal sensor 24 is shown. In FIG. 4, the canister 20 is shown removed and the thermal sensor 24 is shown proximate the generator 22 of the absorption cooling arrangement 12. The thermal sensor 24 may be carried by a mounting bracket 36.
The mounting bracket 36 may include a first portion or lower portion 38 that may be secured to the burner box 18. The lower portion 38 may be secured with discrete fasteners 40, through welding, or in any other suitable manner. The mounting bracket 36 may additionally include an upper portion 44 to which the sensor 24 may be mounted. The mounting bracket 36 may be constructed from metal. Importantly, the sensor 24 is positioned within the canister 20 proximate the generator or boiler tube 22.
Turning to FIGS. 6 and 7, another sensor mounting structure in the form of a canister bracket 50 is illustrated. The canister bracket 50 will be understood to effectively define a lower portion of the canister 20. In this regard, the canister bracket 50 has a diameter roughly equivalent to the diameter of the canister 20. An upper portion of the canister bracket 50 may be secured to the canister 20 with fasteners 40 or welds. A lower portion of the canister bracket 50 may be secured to the burner box 18 with fasteners 40 or welds. The lower portion of the canister bracket 50 is provided with an apertured mounting tab 54 for this purpose.
The canister bracket 50 may include a sensor mounting portion 56. The sensor mounting portion 56 may be inwardly displaced from a cylindrical wall 58 of the canister bracket 50. The sensor mounting portion 56 may include a general planar segment 60 to which the sensor 24 may be conventionally attached. Importantly, the sensor 24 is positioned within the canister 20 for sensing of the generator temperature.
As shown in FIGS. 6 and 7, the canister bracket 50 may be formed of a single piece to define the sensor mounting portion 56. Alternatively, the sensor mounting portion 56 may be a discrete element that engages the remainder of the canister bracket 50. Such an alternative may provide for easier manufacturing,. In either case, the canister bracket 50 may be formed of metal.
Turning to FIG. 8, a schematic diagram illustrates one control device 26. The control device is illustrated as a switch 26 in series with the absorption cooling arrangement 12 and a main source of power 64 (e.g., +12 VDC) for powering the refrigerator 10. The switch 26 is controlled to open and thereby power down the refrigerator 10 in response to detection of a generator temperature condition outside a predetermined temperature condition.
Turning to FIG. 9, schematically illustrated is an alternative control device 66. The control device includes a control valve 66 positioned in line between a source of gas 66 and a burner flame 70. The control valve 66 may be controlled to close in response to detection of a generator temperature condition above the predetermined temperature condition, for example.
During operation, the circuit 25 receives signals representative of the temperature of the generator 22 from the temperature sensor 24. If a sensed generator temperature condition is calculated to be above the predetermined temperature condition, the circuit 25 may operate the control device 26 or 66. In this regard, the sensed generator temperature condition may simply be the sensed generator temperature and the predetermined temperature condition may simply mean a predetermined temperature. Alternatively, the sensed temperature condition may be a function of elapsed time within one or more temperature bands above a predetermined temperature. In this scenario, the predetermined temperature condition may be a predetermined time within on or more temperature bands above the predetermined temperature. In this regard, impact to the generator performance may be significantly more critical at increasingly higher temperatures above the predetermined temperature. In such an arrangement, a computer may continuously calculate the sensed temperature condition.
The refrigerator 10 may incorporate a three-way heat supply including both an A.C and a D.C. heater along with a fuel system for the fire heat source. Accordingly, a relay may be provided to open the current paths to the A.C. and D.C. heaters and to close the valve 66, thereby ensuring that the three heat sources are each turned off when it is desired to stop driving the generator. Note also, that if it should become necessary to turn off the heat source(s), the circuit 25 may illuminate a monitor (not shown) to alert the user to the possibility that the refrigerator 10 may need attention and/or maintenance. Thus, those skilled in the art will recognize that reference to opening and closing the valve 66 includes turning the electric heaters off and on (e.g., through opening and closing of the switch 26) as applicable. Conversely, reference to turning the electric heaters off and on includes opening and closing the valve 66.
In the event that the sensed temperature condition of the generator remains above the predetermined temperature condition, the circuit 25 may suspend further heating of the generator 22. When the condition clears, the circuit 25 may resume commanding the control device 26. In certain applications, the control system 11 may operate such that the control device 26 renders further heating of the generator impossible until the control system 11 is reset. For such applications, a reset switch may be provided to reset the circuit 25. The reset switch may be a push button switch. Alternatively, the reset switch may be a toggle switch or any other well known device capable of generating a binary (i.e., on/off) signal for the circuit. Upon being reset, the circuit 25 clears the control system 11 and begins monitoring the temperature sensor 24 anew. The circuit 25 may include a memory for storing an indication of whether the sensed temperature condition of the generator exceeded the predetermined temperature condition. The memory may be a flip flop, a relay, RAM or any conventional device capable of storing a binary state. Resetting of the circuit 25 may require authorized maintenance of the refrigerator 10.
In alternative embodiments, if the circuit closes the valve 66 or opens the switch 26 because the sensed temperature condition of the generator 22 is above the predetermined temperature condition, the circuit 25 may wait for pre-selected time. At the end of the time, the circuit 25 may then re-open the valve 66 (or the switch 26) and allow the heat source to resume driving the cooling system 12. If the predetermined temperature condition is again exceeded, the circuit 25 may then close the valve 66 (or open the switch 26) again. Moreover, because two attempts to produce the desired performance appear to have not succeeded, the circuit 25 preclude further heating of the generator.
Turning now to FIG. 10, an exemplary method in accordance with the present invention is illustrated. The method 100 includes sensing the temperature of the cooling system 12 proximate the generator. In a first step 102, the sensed temperature is compared to a predetermined temperature. If the sensed temperature is less than the pre-determined temperature then step 102 repeats until such time that the temperature increases above the pre-determined temperature. When the temperature rises above the pre-determined temperature, then step 104 operates the control device 26 or 66 to discontinue heating of the cooling arrangement. If a reset occurs, the method includes returning to step 102.
Accordingly, it will be understood that a control arrangement or the present teachings may be incorporated into a passive in-line device for a refrigerator 10. In this regard, the present teachings may be utilized without a need to modify normal refrigerator controls by simply interrupting a source of heating power upon sensing of a predetermined temperature condition. Alternatively, the present teachings may be incorporated into a microprocessor configured to receive a signal indicative of a predetermined sensed temperature condition. The microprocessor may accordingly control the refrigerator otherwise in the manner discussed herein.
Turning to FIGS. 11 and 12, a portion of a gas absorption cooling system 120 is illustrated. The cooling system 120 includes a boiler tube 122. A plurality of electric heater tubes 124 are secured to boiler tube 122. The heater tubes 124 may be each secured to the boiler tube 122 through a pair of welds 126. Through the incorporation of multiple heater tubes 124 each with a pair of welds 126, an arrangement is provided which reduces heat flux across the electric heater tube welds, reduces temperatures on the boiler and lowers thermal stress on the boiler.
The description of the invention is merely exemplary in nature and, thus, variations that do now depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

Claims

1. A control system for a refrigerator having an absorption cooling arrangement with a generator, the control system having:

a temperature sensor adapted to sense a temperature proximate the generator;

a control device selectively operative to turn off a heat source of the control system; and

a circuit in communication with the sensor and the control device, the circuit adapted to determine a sensed temperature condition and control the control device to turn off the heat source if the sensed temperature condition exceeds a predetermined temperature condition.

2. The system according to claim 1, wherein the control device is operative in a first mode for allowing operation of the heat source and a second mode for preventing operation of the heat source.

3. The system according to claim 2, wherein the circuit controls the control device to operate in the first mode when the sensed temperature condition is above the predetermined temperature condition and in the second mode when the sensed temperature condition is below the predetermined temperature condition.

4. The system according to claim 3, further comprising a memory device to store an indication of whether the circuit has operated the control device in the second mode.

5. The system according to claim 1, wherein the control device is a valve in line with a gas source.

6. The system according to claim 1, wherein the control device is a switch in series with a power source for the refrigerator.

7. The system according to claim 1, wherein the sensed temperature condition is a sensed temperature and the predetermined temperature condition is a predetermined temperature.

8. The system according to claim 1, wherein the sensed temperature condition is a function of time of a sensed temperature within one or more temperature bands above a predetermined temperature.

9. The system according to claim 1, in combination with the refrigerator.

10. An absorption refrigerator comprising:

an interior volume;

an absorption system to cool the interior volume, the absorption cooling system including a generator;

a heat source to provide the energy to drive the absorption cooling system by heating the generator;

a temperature sensor adapted to sense a temperature of the generator; and

11. The absorption refrigerator of claim 10, wherein the circuit includes a control device for turning off the heat source.

12. The absorption refrigerator of claim 11, wherein the absorption refrigerator further comprises a power source and wherein the control device comprises a switch in series with the power source.

13. The absorption refrigerator of claim 10, wherein the absorption refrigerator includes a burner flame powered by a source of fuel and the control device comprises a valve positioned between the source of fuel and the burner flame.

14. The absorption refrigerator of claim 10, wherein the sensed temperature condition is a sensed temperature and the predetermined temperature condition is a predetermined temperature.

15. The absorption refrigerator of claim 10, wherein the sensed temperature condition is a function of time of a sensed temperature within one or more temperature bands above a predetermined temperature.

16. The absorption refrigerator of claim 10, wherein the temperature sensor is positioned proximate the generator.

17. The absorption refrigerator of claim 10, further comprising a canister, the generator and the temperature sensor disposed within the canister.

18. The method of claim 10, wherein the generator includes a boiler tube and a plurality of electric heater tubes, each heater tube mounted to the boiler tube with a pair of welds extending substantially along the length of the respective heater tube.

19. A method of controlling a cooling system of an absorption refrigerator, the method comprising:

sensing a temperature of a generator of the cooling system;

determining a sensed temperature condition;

comparing the sensed temperature condition to a predetermined temperature condition; and

turning off a heat source of the cooling system when the sensed temperature condition is above the predetermined temperature condition.

20. The method of claim 18, wherein the turning off a heat source of the cooling system when the sensed temperature condition is above the predetermined temperature condition includes one of:

the step of opening a switch positioned between a power source of the refrigerator and the heat source; and

closing a valve positioned between a gas source and a burner flame of the cooling system.