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(11) | EP 1 519 129 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Refrigerator having an auxiliary battery pack |
| (57) An absorption refrigerator which allows the user to determine if the refrigerator
is running on gas even when no external power is available. The refrigerator includes
an absorption refrigeration coolant loop containing a coolant, a fuel supply to supply
fuel to an igniter to burn the fuel and to warm the coolant; a flame detector (102),
a battery (106), and a light emitting diode (108) responsive to the flame detector
(102) to indicate whether the flame is present. Moreover, the flame detector (102)
may be a thermocouple communicating with the light emitting diode (108) through a
switch or relay (104). Additionally, the battery (106) may be rechargeable and communicating
with a charging system of the refrigerator so that the battery (106) may be recharged. |
FIELD OF THE INVENTION
[0001] The present invention relates to a flame monitor for an absorption refrigerator, and more particularly to a battery powered flame monitor.
BACKGROUND OF THE INVENTION
[0002] Vehicles, including but not limited to recreational vehicles ("RVs", in the United States and "Caravans" in Europe), tractor trailers, airplanes, boats, trains and the like, often incorporate refrigerators for the comfort and convenience of the occupants. For example, recreational vehicle campers often find it convenient, or even necessary, to refrigerate food, drinks, and medicine during their journal and while at their campsites. While many prepared camp sites in parks and commercial campgrounds provide for electrical outlets, many do not. Moreover, many highly desirable camping locations exist outside of these prepared sites. Thus a popular solution has been to equip the recreational vehicle with an absorption refrigerator.
[0003] Absorption refrigerators employ heat to vaporize the coolant - water mixture (typically ammonia - water) thereby driving the refrigeration loop in a manner well known to those skilled in the art. Popular heat sources include electrical heaters and fuel burners. Further, 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.
[0004] Regardless of the heat source employed, if the heat source fails then refrigeration is lost. Moreover, if a fuel burner is employed, safety dictates that the fuel supply be shut off in the event of such a failure. Accordingly it is important to the campers to know that the heat source remains on.
[0005] Those refrigerators employing a fuel burner typically include an electronic flame monitor or fire eye which may control an automatic shut off valve. Unfortunately the required electronics depend on a source of electrical power external to the refrigerator. Thus, either the recreational vehicle must supply power or a battery must be included in the refrigerator. If the recreational vehicle supplies the power and the battery significantly discharges, then the engine of the vehicle must be run for a period sufficient to recharge the recreational vehicle battery. In the worst case situation, (e.g. where the power supply external to the refrigerator the battery may be completely discharged as a result.
[0006] If a battery is added to the refrigerator, it is important to note that space aboard recreational vehicles comes at a premium. Typically, the recreational vehicles come equipped with a small kitchen in which the refrigerator is installed. Nearby, a sink, a stove, several cabinets, and an occupant work area are usually provided within the confines of the recreational vehicle. Thus, the refrigerator design must maintain acceptable refrigerator dimensions (e.g. the envelope in which the refrigerator must fit). Since adding a battery large enough to power the entire set of refrigerator electronics would either cause an envelope violation or reduce the usable (cold) volume of the refrigerator, adding such a battery to the refrigerator is not acceptable.
[0007] Yet other solutions have employed an access hole with a lens embedded in the insulation to view the flame. Thus, heat flows directly into the cold interior of the refrigerator from the flame. Accordingly, the efficiency of the refrigerator suffers markedly. Moreover, the low level of illumination escaping from the lens may not be bright enough to be easily visible to the user.
[0008] Nonetheless, the flame must be monitored as noted previously. Accordingly, it remains a need in the pertinent art to provide a flame monitor for a vehicle refrigerator that overcomes the disadvantages associated with the prior art.
SUMMARY OF THE INVENTION
[0009] The present invention is directed to an absorption refrigerator suitable for use by campers. More particularly, the present invention is directed to an economical, reliable, and low power flame monitor. In one particular application, the flame monitor of the present invention consumes less than milli-watts thereby enabling operation from an auxiliary battery pack.
[0010] The present invention provides an improved absorption refrigerator which includes a coolant loop, a fuel supply, and a light emitting diode (LED) flame monitor. The coolant loop provides the refrigeration function. The fuel supply supplies a fuel such as propane to warm the coolant as the coolant passes through the evaporator of the coolant loop. Near the flame which warms the coolant a flame detector detects the presence or absence of the flame. Depending on the type of flame detector employed, the flame detector may instead be placed in the flame. The flame detector causes the monitor to indicate whether the flame is present. Moreover, because the flame detector and monitor require little energy, the flame monitor may be powered by an auxiliary battery pack rather than requiring external power.
[0011] Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
Figure 1 is a cross-sectional side view of an absorption refrigerator including a light emitting diode flame monitor in accordance with a preferred embodiment of the present invention;
Figure 2 is an enlarged detail view of a portion of the refrigerator of Figure 1;
Figure 3 is a top view of the control panel of Figure 1; and
Figure 4 is a schematic view of the flame monitor circuit of a preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
[0014] The preferred embodiment of the present invention provides economical, reliable, and low power indication of the presence (or absence) of a flame in an absorption refrigerator installed in a vehicle. In one particular application, the absorption refrigerator is intended for use in a recreational vehicle. Those skilled in the art, however, will appreciate that the teachings of the present invention have broader application to other vehicles and refrigerator uses. Additionally, the preferred embodiment limits the power consumed by the flame monitor circuit so that continuous external power is not required to provide the flame indication.
[0015] With general reference to the drawings and with particular reference to Figure 1, an absorption refrigerator 10 in accordance with a preferred embodiment of the present invention may be seen. The refrigerator 10 conventionally includes an interior volume 12 in which the user desires to store perishables and other items needing cooling. An outer shell 16 provides protection for the various components of the refrigerator 10. The shell 16 also prevents warm air intrusion into the interior 12 and prevents cold air seepage from the interior 12. An insulating layer 18 (typically fiberglass) limits heat conduction into the interior 12 from the exterior 14. An inner shell 17 provides similar functions as that of the outer shell 16.
[0016] A door 20 allows the user access to the interior 12. The door 20 also includes a portion of the insulation 18. Somewhere on the refrigerator 10 viewable by the user, a control panel 22 is provided so that the user can turn the refrigerator on and off, adjust the temperature of one or more interior sections, and monitor the performance of the refrigerator 10. Controls for these functions are provided such as the on/off switch 23, a temperature indicator 25, and a temperature set point selector 27 as shown in Figure 3. More particularly, the control panel 22 includes a flame monitor 29 to allow the user to determine whether the flame driving the refrigeration system is present or absent, as will be discussed more below.
[0017] Continuing with reference to Figure 1, the refrigerator 10 also includes an absorption refrigeration system 24. Insofar as the present invention is concerned, the absorption refrigeration system 24 is conventional in construction and operation. Briefly, the absorption system 24 includes a generator 26, a condenser 28, a receiver 30, and an evaporator 32 arranged in a loop. In the generator 26, the coolant mixture (typically ammonia and water - anhydrous ammonia) absorbs heat thereby preferentially releasing ammonia vapor. From the generator 26, the ammonia vapor flows to the condenser 28.
[0018] In the condenser 28, the ammonia vapor cools and condenses. Outside air driven by a fan may be employed to provide the heat transfer necessary to condense the vapor in the condenser 28. By gravity, the cool liquid ammonia flows from the condenser 28 and into the receiver 30.
[0019] From the receiver 30, the liquid ammonia bleeds through an orifice (not shown) into the evaporator 32. In the evaporator 32 the liquid ammonia absorbs heat from the interior 12 thereby cooling the interior 12. The flow of ammonia to the evaporator 32 may be controlled by a control valve rather than the orifice described above, thus providing closed loop control of the temperature in the interior 12 without departing from the spirit and scope of the present invention. The vaporized ammonia then flows from the evaporator 32 to the generator 26 wherein the partially depleted water - ammonia mixture absorbs the ammonia vapor to complete the refrigeration cycle.
[0020] Not shown, for clarity, is the insulation around evaporator 32 required to maximize the efficiency of the evaporator 32. Nor are the air registers and duct work to route air from the interior 12, through the evaporator 32, and back to the interior 12 shown in the figures. Though a fan is shown schematically as part of evaporator 32. Instead, evaporator 32 is shown protruding into the interior 12 to signify that the air in the interior 12 and the cooling surfaces of evaporator 32 are in thermal communication. Other arrangements of the evaporator 32 may be provided without departing from the spirit and scope of the present invention.
[0021] Referring particularly now to Figure 1 and 2, heat is required to preferentially vaporize the ammonia in the ammonia - water mixture. The heat source may be an electrical heater or a fire. In the alternative, both an electrical heater and a fire may be provided with controls to allow the user to switch between sources of heat. In a preferred embodiment, the refrigerator may automatically choose the best available energy source upon which to operate. For instance, the Thetford Corp. of Ann Arbor, Michigan offers the Smart Energy Selection (SES) system in its superior line of absorption refrigerators. Though, when the refrigerator 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)
[0022] In contrast, when the refrigerator 10 is operating with the flame heat source the coolant loop requires no external energy to operate. Though, the flame monitor 29 and associated circuitry generally requires electrical power. With prior art flame monitors, the refrigerator 10 still consumes an appreciable amount of energy even when the flame heat source has been selected. In contrast, the present invention provides a flame monitor which requires a significantly reduced amount of energy, thereby enabling operation powered only by an auxiliary battery pack.
[0023] Where a flame 42 is employed, (say to reduce the need for electricity at remote camp sites) a fuel system is included in the refrigerator 10. The fuel system includes a fuel pipe, or source 34, a fuel shutoff valve 38 (shown with control wires), and a connection 37 for an external fuel bottle 36. Since propane is a commonly available fuel, propane is frequently used for the fuel. Though other fuels, solid, liquid, or gaseous, could be employed without departing from the spirit or scope of the present invention.
[0024] An igniter 40 is also provided to ignite the fuel from a burner 39 and create the flame 42 as required. See Figure 2. Here the igniter 40 is shown as a spark igniter with electrical wires.
[0025] However, a number of causes may extinguish the flame 42. For example, either the fuel may run out or the flow of fresh air to the flame 42 could be interrupted. Additionally, if exposed to the weather or drafts, wind could blow out the flame 42 or precipitation could quench the flame 42. No matter what the reason for the flame 42 failing, the user needs to know that a problem has occurred so that corrective action can be taken before the interior 12 warms too much.
[0026] The generator 26 may incorporate the burner 34 as an integral component along with a fan and duct work to move fresh air into, and exhaust gases out of, the generator 26. For clarity, the burner 39 is shown external to the generator 26 and the duct work and fans are omitted from the figures. Even where the burner 39 is not integral with the generator 26 it will typically be at the rear of the refrigerator 10 enclosed within the refrigerator 10. Accordingly, the flame 42 will not be visible to the user.
[0027] Thus, a flame monitor or detector is required. Turning now to Figure 4, a schematic of the flame detection circuit 100 is shown. According to the present invention the flame detection circuit 100 includes a flame detector 102, a switch, logic circuit, or relay 104, a battery 106, the flame monitor 108, and provisions 110 for connection to a battery re-charger and D.C. power supply. Of course, the refrigerator 10 may include the battery re-charger and even a rectifier to convert external A.C. (preferentially either 230 or 120 volts) power to D.C. power (preferentially 12 volts). The circuit 100 may be located within the control panel 22. In the alternative, the circuit 100 may be located to minimize the length of wiring between the flame detector 102 and the circuit 100 so long as the temperature of the components remains within well known acceptable limits.
[0028] The flame detector 102 is placed in (or near) the flame so as to detect the presence or absence of the flame. In particular, the flame detector 102 may be a thermocouple placed in the flame. When the flame is present the thermocouple 102 produces approximately 30 milli-volts. Other types of known flame detectors may also be employed such as thermistors, temperature switches, resistance thermal detectors (RTDs) and the like.
[0029] As noted previously, when the flame heats the thermocouple 102, a voltage develops across the dissimilar metal junction. A transistor or amplifier 112 may sense the voltage across the thermocouple 102 and drive the relay 104. Adjustment means (not shown) may be provided so that the temperature set point at which the relay 104 changes positions may be adjusted. When the set point is reached, the relay 104 changes position and completes the circuit between the battery 106 and the monitor 108. The battery 106 may be either a non rechargeable battery or, as is preferred, a rechargeable 12 volt battery such as a nickel-cadmium battery.
[0030] Additionally, the monitor 108 may be any type of indicator. Generally, a light producing indicator is preferred so that when external electricity is unavailable the monitor 108 (located preferentially on the control panel 22) may be seen in the dark. In particular a light emitting diode is preferred because of the associated low current draw of light emitting diodes. Thus, a light emitting diode monitor 108 enables the battery 108 to power the circuit 100 for long periods of time without re-charging.
[0031] It should be noted that a pair of diodes 114 may block current flow from the battery 106 to the remainder of the control circuitry of the refrigerator (not shown) and the vehicle and external power systems. Also, because the remainder of the refrigerator control circuitry may include a battery pack, the battery pack 106 may be deemed an auxiliary battery pack 106. Moreover, as described above, the auxiliary battery pack 106 may be limited to powering only the circuit 100. Though, relay 104 may provide a pair of contacts such that the relay 104 may control a fuel supply shut off valve (not shown).
[0032] As illustrated the present invention provides a superior flame monitor for an absorption refrigerator. In particular, because of the low power draw of the flame monitor circuit, the present invention provides a flame monitor which will continue functioning despite the absence of external power for long periods of time. Moreover, the present invention provides a flame monitor that the user may see even in the event the power to the vehicle lighting is also absent.
1. An absorption refrigerator comprising:
an absorption refrigeration coolant loop to contain a coolant;
a fuel supply to supply a fuel;
an igniter to ignite the fuel to create a flame at a location, the flame to warm the coolant; and
a flame detector to detect the flame;
a light emitting diode responsive to the flame detector to indicate whether the flame is present; and
a battery in communication with the LED to power the LED.
2. The refrigerator of Claim 1, wherein the flame detector further comprises a thermocouple.
3. The refrigerator of Claim 1, further comprising a switch responsive to the flame detector
and communicating with the battery and LED, whereby the switch to switch the battery
power to the LED if a flame is present.
4. The refrigerator of Claim 3, wherein the switch further comprises a relay.
5. The refrigerator of claim 1, further comprising an electrical power system, the power
system to power the LED.
6. The refrigerator of claim 5, further comprising a charging system to recharge the
battery, the battery to be rechargeable.