I. Field of the Invention
The present invention relates generally to continuous cycle absorption refrigeration units of the type commonly used in recreational vehicles and campers. More particularly, the present invention relates to such coolers fitted with apparatus for monitoring temperatures in selected, critical operating areas, and for controlling the refrigeration apparatus in response. Known prior art includes cooling apparatus of the type classified in United States Patent Class 62, Subclasses 476 and 479, and includes controlling apparatus for such units of the type classified in U. S. Patent Class 62, subclasses 132 and 141.
II. Description of the Prior Art
Many campers and recreational vehicles (i.e., RV's) use a refrigerator with an absorption type cooling or refrigeration unit. Such popular continuous cycle RV absorption cooling units use a mixture of ammonia/water and hydrogen as a refrigerant mixture, and sodium chromate as a rust inhibitor. Characteristically they operate at a single pressure. A heat source such as an electric resistance heating element or a propane burner heats a boiler tube to start the refrigeration process, and the operator thus has a choice of energy sources. The ability to operate the absorption cooling unit with a propane burner is desirable in recreational vehicles because it facilitates operation of the refrigerator unit in remote areas where no electricity is readily available. Absorption refrigeration units are further desirable for recreational vehicles because they are compact and lightweight, they have few moving parts, and operation is very quiet.
Absorption cooling units are unique in refrigeration because they have no moving parts and they are virtually noiseless. So-called “Single Pressure Continuous-Cycle Absorption Cooling Units”, such as unit 9 illustrated in
For an absorption cooling unit to operate properly, certain conditions must be met. First, the apparatus must be deployed and operated in a level condition. Because there are no moving parts, an absorption cooling unit relies on gravity to move refrigerant throughout the system for the process to be continuous. Non-level operating conditions can adversely affect fluid transfer in critical circuit pathways.
Second, absorption cooling units require the correct heat input from the chosen heat source. Absorption refrigerators employ heat to vaporize the water/ammonia mixture, thereby driving the refrigeration process in a manner well known to those skilled in the art.
Third, such units must be well ventilated in order for the condenser to cool the vaporized ammonia and transform it into liquid ammonia refrigerant for use in the evaporator section, thus keeping the absorption refrigeration process “continuous.”
In a typical recreational vehicle, the absorption refrigerator unit is typically mounted in an opening in a wall. There is usually a space or cavity between the back of the absorption cooling unit and the exterior wall of the recreational vehicle (hereafter referred to as the cooling unit compartment). This compartment has a vent to let fresh air in the bottom and an exhaust vent at the top to expel heat produced by the cooling unit. The desired ventilation arrangement contemplates a lower vent, through which fresh air is drawn, and an exhaust vent located at the top of the cooling unit compartment that protrudes through the roof of the RV to let hot air exit. This conventional arrangement is desirable because hot air will naturally rise up and out the vent located in the roof, and hot air will not become stagnate in the cooling unit compartment.
Recently it has become a common practice for RV manufacturers to place the absorption refrigerator in a user-deployable “slide-out” room. When an RV is traveling, the so-called slide-outs are retracted and nested within the main body of the RV, providing a low traveling profile and decreased wind resistance. Once a camping destination is reached, for example, the slide-outs are deployed by unfastening them, and pulling them out of the retracted state to increase the effective volume of the camper unit by adding small rooms or dormers to the internal camper volume. The deployed room slides in and out of the side wall or other portion of the camper. When such a cooling unit is deployed within a slide-out, the ventilation arrangement is less desirable because it is not possible to deploy an exhaust vent on the roof of the retractable slide-out. This is because the room slides in and out of the camper or recreational vehicle and its pathway cannot be obstructed. In this type of installation, both vent openings are on the exterior side wall of the vehicle.
The placing of both vents on the side wall of the vehicle is usually less desirable because the upper exhaust vent is often lower than the condenser portion of the cooling unit. When the exhaust vent is even with or lower than the condenser assembly, several anomalies can occur, decreasing the cooling unit efficiency. An absorption cooling unit becomes less efficient when hot air collects or stagnates around the condenser section of the cooling unit. This stagnation limits the cooling unit's ability to convert vaporous ammonia to liquid. As a result, the cooling unit has to run for longer periods of time to maintain cold temperatures in the refrigerated space, which decreases the efficiency of the absorption cooling unit. In addition to being less efficient, the overall system temperatures of the cooling unit increases and can thermally stress critical cooling unit tubing, thus decreasing the useful life of the cooling unit.
Furthermore, it has become necessary for RV manufacturers and absorption refrigerator manufacturers to place exhaust fans on the cooling unit or in the cooling unit compartment to help move heated air out the upper sidewall vent. It is common for these exhaust fans to be operated by thermal switches that activate a fan when a predetermined temperature is reached in the cooling unit compartment. Once the temperature in the condenser area has decreased to a predetermined efficient temperature, the thermal switch opens the circuit, shutting off power to the exhaust fan. It has come to the attention of this inventor that no safety devise exists to determine if the exhaust fans are operational and take appropriate action if necessary.
In practice, however, it has been found by the present inventor that various problems might interfere with normal ventilation, thus increasing the temperature around the condenser to a point where the refrigeration process is no longer continuous, while concurrently leaving the heat source driving the refrigeration system on.
In some cooling units a vent tube bypasses the evaporator section. Those skilled in the art often refer to this tube as a “bypass tube”. During a normally continuous refrigeration cycle, this tube has no real purpose in the refrigeration cycle. However, as the temperature in the rectifier section and the condenser sections rise, and the cooling unit compartment overheats, less ammonia vapor is converted to liquid. Then less ammonia liquid enters the liquid ammonia tube that carries the liquid ammonia to the inlet of the evaporator. At this time the heat source in the boiler continues to drive more ammonia vapor up the rectifier and into and through the condenser, and because it cannot travel down the liquid ammonia tube, it starts to pass down the bypass tube, returning to the absorber vessel. The present inventor considers the cooling unit to now be operating improvidently, a “semi-continuous” state. Operation is not continuous because no refrigerant is entering the evaporator, and the cooling unit is no longer cooling the refrigerated space. Technically, said process is not “discontinuous” because the hot ammonia vapor is bypassing the evaporator and returning to the absorber tank through the by-pass or equalizer tube, where it is mixing with the strong ammonia water solution in the absorber tank and thus able to continue a supply of strong solution to the boiler and percolator pump.
One such anomaly that causes the ammonia cooling unit to become semi-continuous and pass hot ammonia vapor through the equalizer tube and back to the absorber tank is impaired ventilation. This can result from ventilation fan failure, or it can be caused by thermal switch failure, and in some less desirable sidewall venting arrangements no ventilation fans are present at all. It is also possible for the condenser fins to be obstructed by accumulated debris that would prevent proper airflow through condenser fins. Another cause of a semi-continuous refrigeration cycle is operating the absorption unit in extreme ambient conditions with less than desirable ventilation arrangement.
Furthermore it is well known to those skilled in the art that it is preferred to operate an absorption cooling unit in a level orientation. Because the absorption cooling relies on gravity to circulate the flow of refrigerant, and because the absorption cooling unit requires a heat source to drive the refrigeration process, non-level operation can destroy the cooling unit if the heat source is left uninterrupted. An amount of water containing a weak amount of ammonia flows through the boiler, removing heat from the heated tube. This flow of weak solution is continuous and regulates the temperature of the boiler tubing. After leaving the boiler this weak solution trickles down the absorber coil and returns to the absorber vessel. Operating an absorption cooling unit off level can cause this flow of weak solution to pool, decreasing the flow back to the boiler. A decreased flow of solution causes the boiler temperature to rise because less heat is being removed. If the heat source is not interrupted, excessive temperature can thermally stress the boiler tubing. One form of destruction is fatigue cracks along the welds in the boiler tubing that can release flammable refrigerant. Because an ignition source is near by, several fires have been associated with fatigue cracks in the boiler tubing. In another form of destruction, the inhibitor in the refrigerant solution can crystallize when subjected to excess heat. The crystallization of the inhibitor can restrict the flow of refrigerant in the pump tube. Furthermore if the inhibitor is removed from the weak solution, destruction of the interior walls of the boiler tubing can occur in the form of pitting which can weaken the tubing. This also can lead to ruptures of the tubing.
There are previous inventions that control the boiler temperature by placing a sensor on the boiler tubing to measure the temperature of the weak solution inside. This method is disclosed in U.S. Pat. No. 8,056,360. Since the sensor is deployed within the boiler housing, it is very time consuming and difficult to service the sensor apparatus. Substantial disassembly of the the boiler housing is required to access the sensor during boiler pipe service. Also, if the sensor is placed in close proximity to the flue pipe (also enclosed in the boiler housing), the high temperature of the flue pipe while the cooling unit is operating on propane can cause the sensor to fail or to trigger prematurely. This patent also illustrates positioning of its main temperature sensor 22 below the unit's weak solution line 28.
An improvement proposed herein is to locate a sensor on the rectifier portion of the cooling unit to measure a change in the vapor temperatures inside the rectifier. A sensor located above the weak solution level and outside the boiler housing, where the sensor can be accessed easily, will not be influenced by flue pipe temperature during propane operation, which is an improvement over current methods. When ammonia vapor leaves the boiler pump it carries with it some amount of steam that is condensed in the rectifier and by gravity returns to the boiler as a liquid. During off-level operation the amount vapor entering the rectifier increases, thus causing the vapor temperature in the rectifier to increase.
Previous art does not recognize a critical temperature relationship at the critical boundary between the pump tube and the boiler tube where heat is introduced to the pump tube to begin the pump action. In many absorption cooling units it is common for the boiler tube to make direct metal-to-metal contact with the pump tube near the bottom of the pump tube. The purpose of this contact point is made to deliver heat directly to the pump tube without overheating the weak solution surrounding the pump tube. It is at this critical contact point with the pump tube where an increase in vapor is produced by the pump tube when the cooling unit is operated unlevel.
In U.S. Pat. No. 7,050,888 a sensor on evaporator fins determines if the refrigeration process is continuous. It is felt that sensing evaporator fins to determine whether a refrigeration process is continuous is often inefficient, because the heat source is allowed to continue heating for a significant amount of time even after the refrigeration process stops. There is a time lag before the temperature at the fins has reached a predetermined high limit, partly because the sensor is in an insulated and sealed refrigerated location. Furthermore, if the sensor attached to the evaporator fins is covered by frost, it can give false readings of a continuous refrigeration process. In the latter case the heating unit wastefully continues to provide heat to the boiler. Since it is desirable to conserve energy, instant invention recognizes a need to turn off the heat source when the refrigeration cycle is no longer continuous. It is desired to provide an apparatus and process that determines non-continuous operation as fast as possible. This approach conserves power, reduces thermal stress on cooling unit tubing.
Other prior art includes U.S. Pat. Nos. 8,056,360, 7,050,888, 5,355,693, and 6,318,098, and prior publications US2012/0255317, US2012/0102981, and US2008/0178631.
This invention provides an improved absorption refrigeration unit, an improved protective controller for absorption cooling unit, and a method for thermally sensing and controlling absorption refrigeration units. The refrigeration unit comprises a boiler/generator outputting to a rectifier section, a condenser, an evaporator section, an absorber, and an absorber vessel. The system is charged with water, ammonia and hydrogen. The invention is adapted for use in recreational vehicles to prevent absorption coolers from overheating due to off level operation, or from restricted or reduced air flow over the condenser. The invention increases cooling unit efficiency by quickly determining if the observed cooling cycle is continuous.
The preferred automatic control device is in communication with thermal sensors in three critical zones in communication with each other and in contact with the structural tubing in critical areas.
In Zone 1, the rectifier temperature is monitored. The thermal sensor in Zone 1 measures vapor temperature to determine if the unit is operating in a level condition. If the vapor temperature in zone 1 elevates to a predetermined unsafe temperature, the control unit interrupts power to the boiler. When the temperature has been reduced to a predetermined safe temperature, it can automatically close the circuit and restore power to the boiler.
In Zone 2 the condenser temperature is sensed. If the thermal switch in Zone 2 detects an unsafe rise in vapor temperature at the condenser exit it can energize suitable fans to increase condenser airflow. If the condenser temperature returns to a predetermined safe level, fan power is automatically interrupted.
However, if fan activation fails to correct the rise in condenser temperature, and hot vapor subsequently enters the evaporator bypass tube, an additional thermal sensor in zone 3 signals the controller which interrupts power to the heating unit. This occurs if the temperature of the bypass tube reaches a predetermined temperature that would indicate the refrigeration cycle is no longer continuous.
Thus a basic object of my invention is to extend the useful life of a typical absorption cooling unit by reducing thermal stress on the system.
Another basic object of my invention is to provide an improved absorption cooling unit that is highly reliable.
A further object is to provide a method and apparatus for absorption cooling units for determining if the refrigeration process is continuous as fast as possible, and for using that data to control the cooling unit.
A related basic object is to provide a method and apparatus of the character described that increases the efficiency and reliability of absorption cooling units.
Another basic object is to provide a method and apparatus for determining if absorption refrigeration processes are continuous, and for controlling the process in response to sensed data.
Stated another way, it is an object to provide an apparatus and process that determines non-continuous operation as fast as possible, thereby conserving energy, and reducing thermal stress on cooling unit apparatus and tubing.
A related object is to reduce thermal stresses on absorption cooling systems by interrupting heat sources when the sensed cooling process is not continuous.
Another related object is to guard against component breakdown and cooling unit damage by monitoring the cooling fan operation.
Another basic object is to protect absorption coolers from off- level operation by monitoring the vapor temperature in the rectifier circuit.
Yet another related object is to monitor critical temperatures within an absorption cooling unit to determine if ventilation is adequate.
It is also an object to make service easier. It is a feature of this invention that sensors normally placed within complex boiler housings can be relocated to provide easier access.
A further object is to improve the airflow over condenser fins in an absorption refrigeration unit if sensed ventilation is deemed inadequate.
These and other objects and advantages of the present invention, along with features of novelty appurtenant thereto, will appear or become apparent in the course of the following descriptive sections.
In the following drawings, which form a part of the specification and which are to be construed in conjunction therewith, and in which like reference numerals have been employed throughout wherever possible to indicate like parts in the various views:
The boiler section 10 is supplied with heat to start the refrigeration process. Tubing connecting the absorber vessel 14 and the boiler section 10 comprises a pair of concentric inner and outer tubes forming a “tube within a tube” construction. As will be recognized by those with skill in the art, the inner tube 16b carries a supply of a strong ammonia/water solution to the boiler 10 where, in the boiler, the inner tube is referred to as the pump tube 16, and works similarly to a percolator tube in a coffee machine. Heat applied to the boiler section starts percolation. The annular space between pump tube 16 and outer tube 18 forms a pathway for a weak solution 26 of water with very little ammonia absorbed in it.
A conventional refrigeration process begins as heat is applied to the boiler tubing via a flue pipe 17, which causes the ammonia in the pump tube to vaporize and travel up and out the top of the pump tube into the rectifier section 15 and towards the condenser section 11. As the ammonia vapor moves up the pump tube, water that falls out the top of the pump tube and into the annular space 26 and makes up the weak solution circuit which, when full, empties into the top of the absorber coil via rising line 19; this is because gravity causes this liquid to seek a similar level within the pump tube annulus and the absorber section junction. The weak solution is water with little ammonia and it flows within the pump tubing annular space 26 then 19 to the absorber. But, as the ammonia vapor leaves the pump tube, it carries with it some water vapor that must be condensed and returned to the boilers weak solution circuit.
Obstructions 20 in the rectifier 15 are contacted by ammonia and water vapor passing through, and because the rectifier is at a lower temperature than the boiler section 10, the water vapor condenses on these obstructions and returns to the boiler by gravity. The ammonia vapor, characterized be a lower condensing temperature.,passes through the water separator line from rectifier 15 into the condenser section 11. In the condenser ammonia vapor is cooled by a series of heat exchange fins, and forms a liquid.
The tubing that makes up the condenser 11 is lined with fins that, as air passes over, extracts heat from the ammonia vapor. In the condenser, ammonia vapor temperature is lowered enough that the ammonia gas changes state (i.e., condenses) and leaves the condenser as liquid ammonia, which falls and travels downwardly by gravity to the top of the evaporator 12 via the liquid ammonia tube 21. Herein ammonia liquid and hydrogen gas meet and extract heat from the refrigerated space. In the evaporator 12, liquid ammonia trickles downwardly by gravity and settles in small grooves. Ammonia vapor that is not condensed by the time it leaves then condenser section is returned to the tank via a bypass tube 23. The evaporator is also being fed with large amounts of hydrogen gas. The hydrogen passing over the pools of ammonia allow the ammonia to evaporate at a low pressure and temperature. As the ammonia evaporates, it pulls heat from the refrigerated space as it evaporates and changes to the gas phase, cooling the refrigerated space. The vaporous ammonia mixes with the hydrogen and travels down and out of the evaporator 12 through a return tube and returns to the absorber vessel 14 through a return tube 23.
Importantly, a demarcation line 25 has been drawn in
The ammonia/hydrogen vapor coming from the evaporator passes over the strong ammonia/water solution housed in the absorber vessel 14. Because ammonia has a strong affinity for water, enough ammonia is absorbed from the hydrogen/ammonia mixture that is light enough to start making its assent up the absorber coils 13. As the now slightly weaker hydrogen/ammonia solution travels up the absorber coils 13, it passes over a flow of weak solution that is trickling down the absorber. This weak solution absorbs more and more of the ammonia from the hydrogen/ammonia mixture, and, as it nears the top of the absorber, only pure hydrogen remains, which enters the evaporator section 12 again and travels to the top. The weak solution that entered the top of the absorber coil and trickled down becomes a strong solution again by the time it returns to the absorber tank 14. The strong solution of ammonia/water is stored in the absorber vessel and continuously feeds the boiler section 10. Bypass tubing has been designated by the reference numerals 22 (
The tilt monitor associated with U.S. Pat. Pub. 2012/255,317 involves a controller to measure the position angle of the absorption refrigerator. A tilt sensor 28 (
In
In
Referring to
The thermal sensor in zone 1 measures vapor temperature to determine if the unit is operating in a level condition. The preferred “Zone 1” temperature sensor location for the present invention is designated by the reference numeral 40 in
In
In
The heater or burner 32 (
In the current drawings of this invention temperature reading were taken in zones along the vapor section of the cooling unit beginning at the top of the boiler above the weak solution section of the cooling unit. In zone 1, temperature sensors were placed along the rectifier section, sensors in zone 2 were on the exit tube of the condenser, and zone 3 sensors are on the bypass tube near the exit tube of the condenser. Also the lower absorber coil and the boiler tube. Also the air temperature was recorded in the cooling unit cabinet near the top of the condenser and a sensor was placed on the evaporator fins. Also the ambient temperature was recorded.
In
In step 56 zone 1 monitoring commences. Step 57 initiates sampling of the zone 1 sensor. If the zone 1 temperature is normal (i.e., not excessive) the “Zone 1 over temp” step 59 returns at line 58. If zone 1 temperature is excessive, step 60 can turn off the heat source. A hold off period begins with step 61, which is followed by resampling of zone 1 temperature at step 62. If the zone 1 temperature is excessive, the holding step 61 repeats from signaling on line 64. If the temperature is not excessive, step 65 signals on line 66 to restart the boiler.
Step 55 also starts zone 2 monitoring in step 68 followed by temperature sensing in zone 2 step 69. In step 70 if excessive zone 2 temperature is sensed in step 70 then step 71 powers the auxiliary fans 47 (
Step 55 initiates zone 3 activity as well, by starting step 80, which is followed monitoring of the zone 3 temperature sensor in step 81. If below the safe level step 82 returns on lane 83. If not, step 85 can start a monitor count down, and step 86 determines if zone 3 temperature has returned to a safe level. Step 86 can turn the heat source off by repeating or initialing step 60 mentioned earlier. Otherwise return is indicated on line 88. Step 82 concurrently initiates step 89 for repeating or starting step 71 to activate auxiliary cooling fans through step 71.
Referencing
The boiler weak solution temperature is represented by line 160. The vapor temperature of the rectifier is represented by line 161. Line 162 shows the vapor temperature of the upper rectifier near the entrance to the condenser. Line 163 shows the vapor temperature of the vapor bypass tube. Line 164 shows the temperature of the evaporator fins inside the refrigerated space similar to that of sensor 30 (
The test begins with the rooftop vent open and the upper sidewall vent closed to simulate a desirable ventilation arrangement. At the beginning of the test the absorption cooling unit was allowed to reach a steady state temperature in all zones. Line 166 on the graph shows the point at which the rooftop vent was closed and the upper sidewall vent was opened to simulate a less than desirable ventilation arrangement such as that in a camper slide out room. Also at line 166 the exhaust fan was activated. Note that the boiler temperature line 160 has no noticeable immediate reaction to the change in the venting arrangement. Also no immediate change is noticeable in the evaporator fin sensor line 164 was recorded at this time. However there is a significant change in the vapor temperature of the zone 3 sensor indicated by line 163 on the graph. This indicated that less ammonia is being converted to liquid in the condenser which is forcing hot vapor to enter the bypass tube 22 (
Referencing line 167 on the graph (
At line 168 on the graph the absorption cooling unit was tilted at six degrees off level. Box 169 in the graph area shows the relationship between the boiler weak solution temperature 160 and the rectifier vapor temperature 161 of zone 1. The graph data shows that being tilted off level at six degree, the boiler temperature can reach critical temperatures within twenty minutes, and if left uninterrupted can cause degradation of the inhibitor as well as thermal stress on the tubing that can lead to ruptures of the pressurized tubing. Several forms of prior art teach to locate a sensor in contact with the boiler tubing weak solution circuit located inside a boiler housing. It is the novel idea of the current invention that a better method to determine if an absorption cooling unit is operating in a level condition is to deploy a temperature sensor in contact with the rectifier tube to measure the its vapor temperature. It is taught in this current invention that the vapor temperature 161 (box 169) in the rectifier 15 is directly affected by off level operation because the boiler tube is in direct contact with an internal pump/percolator and the pump tube drives ammonia vapor up to the rectifier. Because a temperature sensor located on the rectifier tube 40 (
From the foregoing, it will be seen that this invention is one well adapted to obtain all the ends and objects herein set forth, together with other advantages which are inherent to the structure.
It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations.
As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.
This utility conversion application is based upon, and claims priority from, a previously filed, pending U.S. application entitled “Method and Apparatus for Monitoring and Controlling Absorption Cooling Units”, Ser. No. 62/131,439, Filed Mar. 11, 2015 by inventor Wick G. Weckwerth.
Number | Date | Country | |
---|---|---|---|
62131439 | Mar 2015 | US |