GB2462109A

GB2462109A - Condenser cleaning method and apparatus

Info

Publication number: GB2462109A
Application number: GB0813591A
Authority: GB
Inventors: David Downham
Original assignee: Fortune Products Ltd
Current assignee: Fortune Products Ltd
Priority date: 2008-07-24
Filing date: 2008-07-24
Publication date: 2010-01-27
Also published as: GB0813591D0

Abstract

There is described an apparatus and method for cleaning the condensers 16 in the refrigeration circuits of retail chiller cabinets 1, wherein an enclosure 20 is placed over the condenser and the air passages 54 of the condenser 16 are sequentially sprayed with detergent, water, and air to remove blockages from the air passages. The enclosure 20 may include a movable spray bar 28 having nozzles 29 for spraying air and/or water into the air passages. Sensors 51, 52 may be provided to determine the degree of blockage of the air passages either before or after cleaning, either by optical means or by blowing through the passages and detecting pressure or airflow at the exit. Liquids may drain from the enclosure through a drain opening into a collection tray placed beneath the enclosure, from where the liquid may be pumped to a collection container or to a drain.

Description

Condenser cleaning apparatus and method.

The present invention provides a method and apparatus for cleaning heat exchangers, particularly for cleaning the condenser heat exchanger of a refrigeration unit, and most particularly for cleaning the condenser of a refrigeration unit of a chilled produce retail display cabinet.

A commercial chiller cabinet comprises a chilled storage area with an open front section and a refrigeration unit which produces a circulation of cold air to cool products stored in the chilled storage area. The refrigeration unit may be an integral part of the apparatus, or it may be removable to simplify repair or replacement of faulty refrigeration units or parts. The refrigeration unit is generally located at the bottom of the apparatus, at or near ground level, and comprises a compressor, a condenser and an evaporator. Shop chiller cabinets are effectively used to chill impulse-buy products, such as carbonated drinks and juices.

Within the refrigeration apparatus air is drawn in through the front of the apparatus by a fan, at or near ground level, and passed through the condenser to remove heat from the refrigerant fluid. The air is warmed as it passes through the condenser, and the warmed air is expelled through the rear of the apparatus. For efficient operation of the refrigeration circuit, air must be able to flow through the condenser heat exchanger at or above a predetermined speed or flow rate. In a second air flow, air is drawn by a second fan from the chilled storage area and passed through the evaporator, this air being cooled in the process. The cool air is then delivered to the chilled storage area of the apparatus to chill products therein, before returning to the refrigeration unit to be passed again through the evaporator.

The refrigeration unit is usually thermostatically controlled, the operation of the compressor and fans being controlled by control circuitry operating on the basis of a temperature sensor placed in the chilled storage area. The refrigeration unit will typically also include means to detect overheating of the compressor or condenser, and the control circuitry is arranged to stop operation of the compressor if overheating is detected.

The condenser heat exchanger comprises a matrix of passages through which air can flow. A persistent problem with condenser heat exchangers is that the air in the first air flow contains a significant amount of fibres, dust and grease, and these materials accumulate within the air passages of the heat exchanger (condenser) and progressively block them, impeding the free flow of air through the condenser.

This will eventually lead to a reduction in the heat exchange capability of the condenser, and may cause overheating and malfunction in the refrigeration unit.

Regular cleaning of the condenser matrix is currently performed to combat this problem. The cleaning operation is time-consuming, in that it requires the front panel of the apparatus to be removed, to afford access to the condenser. The removal of dust and other particles is effected by brushing or scraping across the faces of the heat exchanger. Experience has shown that current cleaning methods succeed in removing accumulated fibres and dust from the exterior surfaces of the heat exchanger, but in many cases the accumulation of detritus within the air passages is not satisfactorily removed because the brushing or scraping does not effectively penetrate into the air passages of the condenser.

It is desirable therefore to replace the present cleaning regime with a more effective method and apparatus for removing deposits of dust and other particles from the air passages of the heat exchanger matrix.

While it is known to clean heat exchangers of, for example, air-conditioning units by using high-pressure water jets, such a technique is applicable only where the heat exchangers are mounted outdoors. The present invention seeks to provide a method and apparatus for the cleaning of condenser heat exchangers which can be applied to refrigeration equipment mounted indoors, and particularly to the refrigeration units found in retail chiller cabinets.

According to a first aspect of the present invention, there is provided a heat exchanger cleaning apparatus comprising: an enclosure adapted to be placed over a heat exchanger, the enclosure having a drain opening at a lower part thereof, a nozzle adapted to spray liquid into the passageways of the heat exchanger, a nozzle adapted to blow gas into the passageways of the heat exchanger, respective means for supplying liquid and gas to the nozzles, means for removing liquid from the enclosure via the drain opening, and control means to control the supply of liquid and gas.

In one embodiment, the enclosure comprises side walls and a top wall adapted to surround and cover a heat exchanger, the bottom of the enclosure of being open to form a drain for the egress of fluids. A collection tray may be placed beneath the heat exchanger, to collect liquid draining out of the enclosure. Liquid collected in the tray may be removed by a suction pump, to a collection vessel or to a disposal drain.

In one embodiment, an array of nozzles is provided within the enclosure. The same nozzle or nozzles may be used for spraying liquid and gas, or separate nozzles may be provided. The nozzle array may extend over the entire extent of the heat exchanger, so that all air passages are treated simultaneously.

Alternatively, a linear array of nozzles may extend across the heat exchanger in a first direction, the array being movable in a second direction perpendicular to the first direction so that the nozzles of the array can spray or blow into all of the passages of the heat exchanger sequentially. In a further alternative, a nozzle may be mounted for movement in two perpendicular directions within the enclosure, and "scanned" over the heat exchanger to treat the air passages sequentially.

In a preferred embodiment, a carriage is provided within the enclosure, movable along a guide extending along a wall of the enclosure, and a linear array of spaced nozzles is provided on a spray bar mounted to the carriage, the arrangement being such that as the carriage is moved from end to end within the enclosure, nozzles of the array are sequentially brought into alignment with the air passages of the heat exchanger so that all of the air passages are treated. The carriage may be moved manually, or a drive arrangement may be provided to move the carriage and nozzles.

In another embodiment, sensor means are provided to detect the degree of blockage of the heat exchanger passages, and control means are provided to operate the sequence of spraying and blowing steps in dependence on the results of one or more sensing steps. The sensor means maybe an optical sensor, or may detect an air flow or air pressure to determine a degree of blockage of the passageways.

The sensor means may be mounted to the enclosure, or alternatively it may be mounted on a carriage movable along a guide in the enclosure, to enable sensing to be performed at different locations. The same carriage may carry the sensor means and a nozzle array, or separate carriages may be provided, running on the same or different guides.

A second aspect of the present invention provides a method for cleaning a heat exchanger having air passages therethrough, comprising the steps of: placing an enclosure over the heat exchanger, the enclosure having a drain opening at a lower part thereof; spraying liquid jets into the air passages of the heat exchanger from one or more nozzles arranged within the enclosure to remove blockages from the air passages; blowing gas jets into the air passages of the heat exchanger from one or more nozzles arranged within the enclosure to dry the heat exchanger; and removing the enclosure from the heat exchanger.

In one embodiment, the step of spraying liquid jets comprises a first liquid spraying step of spraying detergent on to the heat exchanger, a delay step after the application of the detergent, and a second spraying step of spraying water on to the heat exchanger to remove blockages from the passages. The first spraying step of spraying detergent may be carried out at a low pressure simply to soak the blockages with detergent, and the second spraying step may be carried out at a higher pressure to dislodge blockages using the kinetic energy of the jet.

In a further embodiment, the method comprises a step of sensing the degree of blockage of the passages either before or after a spraying step, and performing or repeating cleaning steps on the basis of the sensed degree of blockage. In one embodiment, the first step of the procedure is to sense the degree of blockage of the passages, and to determine whether a cleaning process is needed or not in dependence on the result of the sensing step.

Embodiments of the invention will now be described in detail with reference to the accompanying drawings, in which: Figure 1 is a cutaway perspective view of a chiller cabinet; Figure to is a schematic view of a cleaning apparatus according to the present invention; Figure 3 is a schematic view showing a sensor carriage for use with the apparatus of the present invention; and Figure 4 shows a further embodiment of the cleaning apparatus, in place on a condenser heat exchanger.

Referring out to figure 1, there is seen a chiller cabinet 1 having a base part 2 which houses the refrigeration equipment, and a display area 3 for the chilled display of produce.

The display area 3 comprises a pair of end walls 4 and 5, and a rear wall 6. The rear wall 6 houses a duct 7 in which is positioned a fan 8, which blows air upwardly within the real wall 6 to deliver the air into the display area through outlet openings 9 at the upper end of the rear wall 6. At the lower front of the display area, a line of air inlet openings 10 communicate with a horizontal duct 11 defined between the lowest shelf 12 of the display area 3 and an air guide plate 13. The horizontal duct 11 communicates with the duct 7 through an evaporator heat exchanger 14, so that they are passing from the horizontal duct 11 to the duct 7 is cooled by the heat exchanger 14.

The base part 2 of the chiller cabinet 1 houses a refrigeration circuit comprising a compressor' 15 and a condenser 16 mounted within an air duct extending from a front grille 17 to a rear grille 18. Air is drawn through the duct from the front grille 17 to the rear grille 18 by a fan 19. In a typical arrangement, the refrigeration equipment is mounted to the base part 2 as a "cassette", so that by removing the front panel of the base part, the refrigeration equipment can be slid forward to expose the working parts for maintenance procedures. Access to the condenser 16 for cleaning is afforded by sliding the refrigeration apparatus cassette forward until the condenser 16 is positioned forward of the front edge of the shelf 12.

The condenser 16 is a heat exchanger having an intake face and an outlet face joined by a number of air passages extending through the condenser. In operation, the fan 19 draws air into the intake face, through the air passages and out of the outlet face of the condenser 16.

Figure 2 shows a first embodiment of the cleaning apparatus of the present invention. The apparatus comprises an enclosure 20 having a top wall 21, a pair of end walls 22, and a pair of side walls 23. In the embodiment shown, the underside 24 of the container is open.

Mounted within the enclosure 20 is a guide 25 extending parallel with the side walls 23, and positioned adjacent the top wall 21. A carriage 26 is mounted for movement along the guide 25. In the embodiment shown, a motor 27 and drive transmission 28 is connected to the carriage 26 to propel the carriage along the guide 25. The drive transmission 27a illustrated is a chain or belt passing over pulleys or sprockets mounted within the enclosure, but other drive transmissions are possible such as a linear motor, a leadscrew and ball nut, or a mechanical linkage such as a lazy tongs.

The carriage 26 supports a spray bar 28 which extends downwardly from the carriage adjacent a side wall 23, and an array of nozzles 29 are mounted to the spray bar and are directed towards the other side wall 23.

Fluids are supplied to the spray bar 28 by means of a flexible pipe 30 extending through a wall of the enclosure 20. As an alternative to the flexible pipe 30, the supply duct from the selector valve 38 may be attached to the carriage 26, and may leave the enclosure 20 via a slot (not shown) extending parallel to the guide 25. The slot may be provided with sealing means such as rubber lips to close the slot on either side of the supply duct.

A detergent reservoir 31 and a water reservoir 32 are connected via respective supply lines 33 and 34 to a first selector valve 35. From the selector valve 35 a liquid supply line 36 carries liquid to a pump 37 whose outlet is connected to an inlet of a second selector valve 38.

A supply 39 for a drying gas, which may be compressed air or an inert gas such as nitrogen, is connected to a second inlet of the second selector valve 38. In the illustrated embodiment, the drying gas is contained within a reservoir. If compressed air is to be used as the drying gas, then the supply 39 may include an air compressor.

A control circuit 40 having input switches 41 and indicators 42 is connected to the motor 27, the first and second selector valves 35 and 38, and the pump 37 via control lines 43. The control circuit 40 includes a processor, and a memory in which are stored a number of cleaning operation sequences, with instructions for controlling the pump, valves and motor to perform the cleaning operations required.

Cleaning of the condenser of a chiller cabinet is effected by first exposing the condenser 16 and removing any ancillary equipment such as fans which may be necessary so that the enclosure 20 may be placed over the condenser 16, with the spray bar 28 and nozzles 29 directed at either the intake or the outlet face of the condenser 16. While it may be preferable to "back-flush" the condenser by directing the nozzles 29 at the outlet face of the condenser, structural constraints may mean that the enclosure 20 has to be placed over the condenser 16 with the nozzles 29 directed at the intake face of the condenser 16.

Once the enclosure 20 is in position over the condenser 16, a collection tray (not shown) is placed under the condenser 16, to catch any liquid falling through the open bottom 24 of the enclosure 20.

Liquids falling into the collection tray may be removed by a suction pump (not shown) either for collection in a collection vessel, or for disposal in a drain.

After ensuring that adequate supplies of detergent, water and drying gas are present in the reservoirs 31, 32 and 39, the operator selects the cleaning programme to be performed and initiates the programme using the input controls of the control circuit 40.

In the typical cleaning process of the apparatus of figure 2, the carriage 26 is first moved to one end 16 of the condenser. The first selector valve 35 is then operated to select an input from the detergent reservoir 31, and second selector valve 38 is operated to select input from the pump 37. The pump is then started, so that detergent is delivered from the reservoir 31 to the nozzles 29 of the spray bar 28.

Motor 27 is also started, so that the carriage 26 and spray bar 28 are moved in a first traverse from one end of the condenser 16 to the other. This ensures that all of the air passages of the condenser 16 are treated with the detergent. At the end of the first traverse of the spray bar 28, the pump 37 is stopped so that no further detergent is delivered.

The control circuit then optionally initiates a time delay period, during which the detergent is left to penetrate the air passages of the condenser 16.

First selector valve 35 is then operated to connect the pump inlet to the water reservoir 32, and optionally the pump 37 may then be run for a predetermined period to purge the spray bar and nozzles of detergent. With the pump 37 running, the motor 27 is again operated to traverse the spray bar back along the length of the condenser 16, so that each of the air passages is treated with a water jet to remove the detergent and any dirt or other blockages from the air passages. The pump may be operated at a higher output during this traverse, so that the water jet is at a higher pressure than Lhe spray of detergent. In the embodiment shown, with a single spray bar 28, a pump 37 capable of delivering 3.5 gallons per minute (16 L per minute) has been found to be adequate to supply the spray bar with washing water. The pump may be operated at a lower rate when supplying detergent, to reduce wastage.

At the end of the second traverse, the pump 37 is stopped, the motor 27 is stopped, and optionally a further time delay is initiated to enable water to drain from the air passages of the condenser 16.

The control circuit 40 then operates the second selector valve 38 to connect the drying gas reservoir 39 to the spray bar 28, and operates the motor 27 to perform a third traverse of the spray bar during which drying gas is blown through the air passages of the condenser 16 to remove remaining water. At the end of the third traverse, the motor 27 is stopped, and the second selector valve 38 is operated to cut off the supply of drying gas to the spray bar 28.

The enclosure 20 is then removed from the condenser 16, and any necessary reassembly work is performed on the refrigeration equipment cassette, which is then replaced in the base 2 of the chiller 1.

While the embodiment described in figure 2 is controlled by a control circuit 40, it will be appreciated that a simpler embodiment is possible in which the carriage 26 and spray bar 28 moved manually, and the selector valves 35 and 38 and the pump 37 are also operated manually. Instructions for manual operation may be provided, optionally as a printed display on the enclosure top.

In a further embodiment of the invention, a sensor may be provided for detecting the degree of blockage of the air passages of the condenser 16. In Figure 3, there is shown schematically a sensor unit comprising a sender 51 and a detector 52 mounted to a carriage 53. The carriage 53 is mounted to a guide within the enclosure 20, possibly to the same guide 25 as supports the carriage 26 and spray bar 28. Movement of the carriage 53 along the guide brings the sender 51 and detector 52 sequentially into alignment with air passages 54 of the condenser 16.

The sender 51 may be a light source, and the detector 52 may be a photocell to detect light from the sender 51 which has passed through an air passage 54.

Blockage of the air passage 54 will attenuate the amount of light passing through the air passage, and will reduce the output of the detector. When the output of the detector falls below a predetermined threshold level, the air passage 54 is considered to be obstructed and in need of cleaning.

Alternatively, the sender 51 may be a nozzle through which an air jet is blown to cause air to flow through the air passage 54. In this case, the detector 52 may be a pressure sensor, or an airflow detector such as a hot-wire anemometer. If the passage 54 is unobstructed, the airflow through the passage will be greater than that through a blocked passage, and this difference in airflow will be detected either as a difference in pressure at the detector 51, or as a difference in air speed. If the airflow or pressure is below a predetermined threshold level, the air passage 54 is considered to be obstructed and in need of cleaning.

As the carriage 53 is traversed along the length of the condenser 16, the sender 51 and detector 52 will be sequentially aligned with a number of air passages 54. The detector outputs for each of the passages 54 may then be recorded and compared with a threshold level, and if a predetermined proportion of the passages return outputs above the required threshold level then the condenser 16 can be considered as having been adequately cleaned.

In a further embodiment, the carriage of 53 may be provided with a position sensor so that outputs from the air passages 54 may be correlated with the position of the carriage 53. This data can be used to determine zones of the condenser 16 where the air passages 54 are clear, and zones where the air passages 54 are obstructed. On the basis of this determination, cleaning operations may be conducted only in the zones where the passages are obstructed, thus avoiding unnecessary expenditure of cleaning materials and reducing the overall time taken for the cleaning operation. Alternatively, the entire condenser may be cleaned, but with the traversing speed of the carriage reduced at zones where the passages are obstructed, in order to concentrate the cleaning effort at those zones.

Movement of the carriage 53, and recording of the output from sensor 52, may be made under the control of the circuit 40, which may also produce an output indicating the areas of the condenser where most blockage was detected.

In a further embodiment, not illustrated, one of the nozzles 29 attached to the spray bar 28 may serve as a sender 51 delivering a gas jet into an air passage 54 of the condenser 16, and a detector 52 may be mounted to the carriage 26 and positioned on the other side of the condenser 16 in alignment with the nozzle 29 to detect airflow through the air passage 54. In operation, the carriage 26 may be traversed along the length of the condenser 16 while air is blown from the nozzles 29, and the detector 52 measures the airflow through the air passages 54 sequentially. Such a sensing traverse may be performed before a cleaning operation is started, or may be performed at an intermediate point during a cleaning operation to determine whether the air passages 54 have yet been sufficiently cleared.

Figure 4 shows at an alternative embodiment of the cleaning apparatus, in position on a condenser 16.

The apparatus is substantially the same as is shown in Figure 2, and like parts are given like reference numerals. The description of those parts will not be repeated. In this embodiment, however, a sensor is provided to determine the degree of blockage of the air passages 54. The sensor comprises a sender 51 and a detector 52, mounted to opposite side walls 23 of the enclosure 20, and connected to the control circuit by conductors 55. The sender 51 and detector 52 are preferably mounted on the enclosure at a position corresponding to an air passage 54 in the condenser which is particularly prone to blockage, such as an air passage which is in line with the fan 19 of the refrigeration equipment cassette. In this embodiment, light or an air jet emitted by the sender 51 passes through the air passage 54 and impinges on the detector 52, which then provides an output representative of the degree of blockage of the air passage 54. The control circuitry 40 then operates the spray bar 28 and nozzles 29 to perform cleaning operations on the basis of the detected degree of blockage, for example adjusting the traversing speed of the carriage and spray bar 28 so that if the passages are relatively clear, the carriage is rapidly traversed whereas if the passages are blocked, it carriage is slowly traversed to give any longer jetting time of her for each passage. The sensor may again be interrogated after cleaning operations have been completed, and if the blockage has not been adequately removed the cleaning operation may be repeated. The control circuitry may include a means to limit to the number of times the cleaning operation is repeated.

In the embodiments described, the spray bar 28 and nozzles 29 are positioned only on one side of the condenser, so that fluids are sprayed through the air passages 54 in only one direction during the cleaning process. It is however foreseen that nozzles 29 may be provided at both sides of the enclosure, so that air and/or liquid may be jetted into the air passages 54 from both directions. Preferably, the nozzles are staggered along the length of the condenser so that liquid is not simultaneously jetted into both ends of the same air passage 54.

Alternatively, in an arrangement where nozzles are provided on both sides of the enclosure, the nozzles may be mounted to the same carriage and operated so that on a first traverse the nozzles facing the intake face of the condenser are operated to spray liquid through the condenser in the normal airflow direction, and on a second traverse the nozzles facing the outlet face of the condenser are operated to "back-flush" the air passages. In an advantageous method, detergent may be sprayed onto the outlet face of the condenser in a first traverse, and after an optional delay water may be sprayed onto the outlet face in a second traverse, followed by spraying water on to the inlet face of the condenser in a third traverse, and finally air may be blown on to the inlet face of the condenser in a final, drying, traverse.

The condenser 16 of a chiller cabinet 1 may have ducting extending out of the condenser from its end faces to convey refrigerant to and from the condenser.

In order to accommodate these ducts, but to maintain a waterproof enclosure around the condenser, the enclosure 20 may be formed with slots extending upwardly from its open side at locations where ducting enters or leaves the condenser 16. The slots may be provided with sealing arrangements such as overlapping rubber lips, which permit the ducts to move up the slots about re-seal the slots at regions below the ducts when the enclosure is in position. The number and location of the slots will be provided so as to accommodate a range of different condenser arrangements.

In an advantageous system for cleaning condensers in chiller cabinets, each condenser may be marked with an identifying code such as a bar code, and the enclosure may be provided with a bar code reader linked to the control circuitry. The control circuitry may then be arranged to note the time and date at which the enclosure was placed over a particular condenser for cleaning, and may also note the result of a detection of the degree of blockage of the condenser prior to each cleaning operation. On the basis of these recorded observations, a prediction of the rate of blockage of the condenser may be made, and a maintenance schedule for each chiller cabinet may be generated so that the cabinets are cleaned when the projected amount of blockage reaches a predetermined threshold. Unnecessarily frequent cleaning of the condenser's can therefore be avoided, saving operator time and making the cleaning operation more efficient.

Claims

Claims: 1. A cleaning apparatus for cleaning heat exchangers having air passageways therethrough, the apparatus comprising: an enclosure adapted to be placed over a heat exchanger and having a drain opening at a lower part thereof; a nozzle adapted to spray liquid into the air passageways of the heat exchanger; a nozzle adapted to blow gas into the passageways of the heat exchanger; respective means for supplying liquid and gas to the nozzles; and means for removing liquid from the enclosure via the drain opening.
2. An apparatus according to claim 1, wherein the enclosure comprises side walls and a top wall adapted to surround and cover a heat exchanger, the bottom of the enclosure of being open to form a drain for the egress of fluids.
3. An apparatus according to claim 1 or claim 2, further including a collection tray adapted to be placed beneath the heat exchanger, to collect liquid draining out of the enclosure.
4. An apparatus according to claim 3, further including a suction pump for removing liquid collected in the tray to a collection vessel or to a disposal drain.
5. An apparatus according to any preceding claim, wherein an array of nozzles is provided within the enclosure.
6. An apparatus according to claim 5, wherein the nozzle array extends over the entire extent of a wall of the enclosure, so that all air passages of a heat exchanger may be treated simultaneously.
7. An apparatus according to claim 5, wherein a linear array of nozzles extends within the enclosure in a first direction, the array being movable in a second direction perpendicular to the first direction.
8. An apparatus according to claim 5, wherein a nozzle is mounted for movement in two perpendicular directions within the enclosure.
9. An apparatus according to claim 7 or claim 8, wherein a carriage is provided within the enclosure, movable along a guide extending in a first direction within the enclosure, and a linear array of spaced nozzles is provided on a spray bar mounted to the carriage and extending in a direction perpendicular to the guide.
10. An apparatus according to claim 9, wherein the carriage and nozzles are movable manually,
11. An apparatus according to claim 9, wherein a drive arrangement is provided to move the carriage and nozzles.
12. An apparatus according to any preceding claim, wherein the same nozzle or nozzles is or are used for spraying liquid and gas.
13. An apparatus according to any of claims 9 to 12, further including control means to control the movement of the carriage and the supply of liquid and gas to the nozzle or nozzles.
14. An apparatus according to any preceding claim, further including sensor means to detect the degree of blockage of the heat exchanger passages.
15. An apparatus according to claim 14, wherein the sensor means is an optical sensor.
16. An apparatus according to claim 14, wherein the sensor means is arranged to detect an air flow or air pressure.
17. An apparatus according to any of claims 14 to 16, wherein the sensor means is mounted to the enclosure.
18. An apparatus according to any of claims 14 to 16, wherein the sensor means is mounted on a carriage movable along a guide in the enclosure.
19. An apparatus according to claim 18, wherein the same carriage carries the sensor means and a nozzle array.
20. An apparatus according to claim 18, wherein the sensor means and the nozzle array are mounted to separate carriages.
21. An apparatus according to any of claims 14 to 20, as dependent on claim 13, wherein the control means is arranged to control the movement of the nozzle or nozzles and the supply of liquid and gas to the nozzle or nozzles in dependence on an output from the sensor means.
22. A method for cleaning a heat exchanger having air passages therethrough, comprising the steps of: placing an enclosure over the heat exchanger, the enclosure having a drain opening at a lower part thereof; spraying liquid jets into the air passages of the heat exchanger from one or more nozzles arranged within the enclosure to remove blockages from the air passages; blowing gas jets into the air passages of the heat exchanger from one or more nozzles arranged within the enclosure to dry the heat exchanger; and removing the enclosure from the heat exchanger.
23. A method according to claim 22, wherein the step of spraying liquid jets comprises: a first liquid spraying step of spraying a detergent on to the heat exchanger; a delay step after the application of the detergent; and a second spraying step of spraying water on to the heat exchanger to remove blockages from the passages.
24. A method according to claim 23, wherein first spraying step of spraying detergent is carried out at a low pressure, and the second spraying step is carried out at a higher pressure.
25. A method according to any of claims 22 to 24, and further comprising the steps of: sensing the degree of blockage of the air passages either before or after a spraying step; and performing or repeating spraying steps on the basis of the sensed degree of blockage.
26. A method according to any of claims 22 to 26, wherein the first step in the method is to sense the degree of blockage of the air passages, and to determine whether cleaning is needed or not in dependence on the result of the sensing step.
27. An apparatus for cleaning a heat exchanger, substantially as herein described with reference to Figure 2, Figure 3 or Figure 4 of the accompanying drawings -
28. A method of cleaning a heat exchanger, substantially as herein described.