GB1591142A - Air conditioning installations - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO AIR CONDITIONING INSTALLATIONS (71) We, WEETABIX LIMITED, a British Company of Weetabix Mills, Burton Latimer, Kettering, Northants, NN15 5JR, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an air conditioning installation in combination with a processing plant producing hot waste gases.

According to the present invention we provide an air conditioning installation for an area in a building in combination with a processing plant able to produce hot waste gases at a temperature above the ambient temperature in said area, the installation comprising an air handling unit through which air at ambient temperature can be drawn for conditioning and ducting to the area, and a heat exchanger through which the hot waste gases can pass separate from and in counterflow flow to further air which is drawn from the exterior of the building and which is thereby heated for selective admixture with said air admitted into the air handling unit to raise the temperature of the latter, waste gas collection ducting extending between the processing plant and an inlet of the heat exchanger and damper controlled diverting duct means upstream of said inlet for egressing the hot waste gases to a location other than the heat exchanger when a predetermined situation prevails.

The application of this invention to a processing plant provides substantial energy conservation with consequent considerable economic advantages.

The processing plant is preferably a food processing plant and in particular comprises a food baking oven which may be fired by any convenient means. For example, the oven may be fired by gas, oil and/or electricity.

An example of the present invention will now be described as applied to a food processing plant and with reference to the accompanying drawings in which: Figure 1 is a plan view of the food processing area of the food processing plant; Figure 2 is a plan view of a heat recovery and air conditioning installation for use with the food processing plant; Figure 3 is an elevation on the line III III in Figure 2; Figure 4 is a cross-sectional elevation, to an enlarged scale, on the line IV - IV in Figure 2; Figure 5 is a cross-sectional elevation, to an enlarged scale, on the line V - V in Figure 2; Figure 6 is a fragmentary perspective view, to an enlarged scale, of the portion indicated by arrow VI in Figure 2; Figure 7 is a view to an enlarged scale of part of Figure 3, portions of which have been broken away, and showing greater detail there in; and Figure 8 is a plan view of part of Figure 7.

The food processing plant comprises a food processing area 20 with an adjacent heat recovery and air conditioning installation for the plant housed within a nearby separate building. The plant is arranged so that food to be processed is admitted to the area 20, pro cessed therein, and thence passes on one of a plurality of conveyors through one of a plural ity of ovens disposed along the length of the area 20. In Figure 1, only two ovens 21 and 22 are shown. After cooling, the baked processed food is packaged and transported by conveyor to an adjacent warehouse (not shown).

The oven 21 is a direct fired oven, such as is sold under the Registered Trade Mark TURBO RADIANT of Baker Perkins Holdings Limited, with five gas-fired burner points 23. To prevent contamination of the food within the oven 21 by fumes from the oil burners within the burner points 23 heated air is passed around the outside of a jacket (not shown) within the oven 21.

Lying parallel with the oven 21 and disposed above it are two subsidiary waste gas collector ducts 24 and 25 which merge with a main col lector duct 26 disposed perpendicular thereto.

Each of the subsidiary collector ducts 24 and 25 is made up of pipe sections with expansion joints 27 between adjacent pipe sections. At each of the burner points 23, exhaust ducts 28 and 29 merge with the subsidiary collector ducts 24 and 25 respectively. The ducts 28 collect the flue products and hot air from the oil burners and from around the jacket within the oven 21, whereas the exhaust ducts 29 col lect hot air and moisture from within the jacket in the oven 21. The waste hot gases from the oven and the oven burners are collected in the separate subsidiary ducts 24 and 25, again to prevent any possible contamination of the baking food by the flue products.To prevent backflow of the waste gases along the subsidiary collector ducts 24 and 25 upstream of each of the exhaust ducts 28 and 29 where these merge with respective collector ducts 24 and 25 is a suction fan 30 and a butterfly damper (not shown).

The oven 22 is a semi-direct fired oven, such as is sold under the Registered Trade Mark CONVECTORADIANT of Baker Perkins Holdings Limited, and has three gas-fired burner points 31. As the oven burners are gas burners, there are no flue products which can contaminate the food within oven 22 so that within the oven the hot air from the burners comes into direct contact with the food.

Above the oven 22 and parallel therewith is a single subsidiary collector duct 32 which again merges with the main collector duct 26.

At each of the burner points 31, an exhaust duct 33 merges with the collector duct 32 and carries flue gases, hot air and moisture from within the oven 22 to the collector duct 32. As with subsidiary collector ducts 24 and 25, a suction fan and butterfly damper are positioned downstream of each point of entry of the exhaust ducts 33 into the collector duct 32, which is again made up of pipe sections with an expansion joint between adjacent sections.

Arranged adjacent the outlets from the ovens 21 and 22 are coolers (not shown) through which the baked food is passed for cooling before packaging. Also, in the case of the oven 21, a microwave oven (not shown) is interposed between the cooler oven outlet.

Waste heat from the coolers and the microwave oven is also ducted to the subsidiary collector ducts 24 and 32 by exhaust ducts 34.

Before entering the main collector duct 26, each of the subsidiary collector ducts 24, 25 and 32 has an outlet to a vertical chimney 35.

Each of the chimneys 35 for the ducts 24, 25 and 32 terminates in a discharge cowl 36 and within the cowl 36 is a butterfly damper (not shown) which is normally closed. Downstream of each of the chimneys 35 in each of the subsidiary collector ducts 24, 25 and 32 are further butterfly dampers (not shown) driven by motors 37 which are normally open and cooperate with the dampers in each of the discharge cowls 36 as will be described later. These dampers within the subsidiary collector ducts and the cowls are operated by the motors 37 and controls are provided for the manager of the food processing area to open or close these as desired.

The main collector duct 26 is highly insulated to prevent heat loss and passes over the roof of the food processing area into the building 39 housing the heat recovery and air conditioning installation, as aforesaid. Downsteam of each of the points of entry of the subsidiary collector ducts 24, 25 and 32 into the main collector duct 26 is a fan (not shown) which sucks the waste hot gases from the subsidiary collector ducts into the main collector duct 26 and maintains a constant negative pressure on the ovens to prevent pressure build-up therein.

A pressure sensor 40 is located in the main collector duct and is linked to the butterfly dampers in the ducts 24, 25 and 32 respectively and the dampers in the cowls 36. If the sensor 40 detects an increase in pressure in the main collector duct above a predetermined value, which pressure increase may, for example, be caused by a blockage in the main collector duct, then the appropriate damper is closed by the motors 37 and the corresponding damper in the cowl 36 is opened by an override mechanism so that one or more of the subsidiary collector ducts 24, 25 or 32 is vented to atmosphere and the duct inlet into the main collector duct 26 closed. Thus, the baking process in all ovens can carry on uninterrupted if for any reason the heat recovery installation is closed down or is working at reduced capacity.It is envisaged that the venting may be other than to atmosphere, for example to a secondary heat exchanger.

After receiving the hot waste gases from each of the subsidiary collector ducts, the main collector duct 26 passes into the building 39.

However, before passing into the building 39, the main collector duct 26 is fitted with an inlet 41 for fresh air. The inlet 41 can be opened or closed by a valve controlled by a motor 42 and the inlet of fresh air into the duct 26 is thermostatically controlled to maintain a substantially constant input temperature of gas into the heat recovery installation and thereby maintain an optimum efficiency of a heat exchange carried out during the heat recovery process in the installation as will be described.

The heat recovery and air conditioning installation comprises a heat exchanger 43 whereby heat is transferred from the hot waste gases produced in the food processing plant to fresh air, and at least one air handling unit 44 which also utilizes fresh air and the heated fresh air from the heat exchanger to air condition all parts of the food processing plant.

The heat exchanger 43 comprises a unit containing, in a central portion 45 thereof, aluminium sheets spaced approximately one inch apart. The sheets separate the hot exhaust gases from the fresh air which circulate in counterflow over the sheets. The heat exchanger 43 has diametrically opposed inlets 46 and 47 for the hot waste gases and the fresh air respectively. In a similar fashion, there are diametrically opposed outlets 48 and 49 for the waste exhaust gases and the now heated fresh air respectively. Across the inlet 46 is a filter 50 to prevent any food particles carried in the ex haust gases from entering the heat exchanger 43. The temperature of gases through the heat echanger 43 is automatically controlled through a control stat 51 and a limit stat 52 so that optimum efficiency of the heat exchanger 43 is maintained.The automatic controls are also linked to the pressure sensor 40 in the main collector duct 26 so that a constant pressure can be maintained at the baking ovens 20 and 21. Also at the inlets 46 and 47 and at the outlet 48 there are manually controllable dampers 53.

The efficiency of the heat exchanger 43 is improved by the removal of latent heat from the moisture of the gases passing through the heat exchanger and for this purpose a condensate trap 54 is provided beneath the central portion 45.

For maintenance purposes, the heat exchanger 43 is provided with an access door (not shown) and the top of the exchanger 43 can be removed for internal cleaning. A by-pass duct 55 is also provided whereby the hot exhaust gases can be ducted away from the heat exchanger 43 and discharged directly to atmosphere via a vertical chimney 56, the dampers 53 in this case being closed.

After passing through the heat exchanger 50, the waste exhaust gases, now in a cooled condition, are also discharged into the atmosphere via the vertical chimney 56. The chimney 56 has a cowl 57 and is connected by a transistion duct 58 to a collection chamber 59 which is connected by ducting to the outlet 48. At the inlet to the collection chamber 59 is an extraction fan (not shown) driven by a motor 60 to suck the waste gases from the heat excahnger 43 and prevent pressure buildup therein by helping to maintain a constant pressure on the whole system. Also, at the inlet to the collection chamber 59 there is an automatically-controlled iris damper 61, which damper 61 controls the rate of waste gas outflow from the chimney 56.

The fresh air is introduced into the heat exchanger 43 by means of an inlet 62 in the side of the building 39. The inlet 62 is covered by a bird guard to prevent blockage occuring, and the fresh air is drawn into the inlet 47 by a fan 63 driven by a motor 64.

After passing through the heat exchanger 43, the now heated fresh air is ducted along a duct 65 to the air handling unti 44. Other ducts, such as duct 66 can be led off to further air handling units (not shown) as required. The duct 65 splits into two branches 67 and 68, branch 67 leading into the air handling unit and branch 68 being a bleed to atmosphere to control pressure within the duct system as will be described below.

The air handling unit 44 is designed to supply fresh air for air conditioning to any part of the food processing plant or elsewhere as desired. The temperature of the air so supplied is predetermined and is thermostatically controlled, a thermostat in the air conditioned area being linked to the air handling unit 44. When the air handling unit is in operation, fresh air is continuously drawn into a plenum chamber 69 of the unit 44 through an inlet louvre 70 which is covered by a bird guard. The inlet louvre 70 is located in a wall of the building 39 in an area 71 of the building 39 which is open to the atmosphere.

Once inside the air handling unit, the fresh air is filtered and can be heated, cooled or left at ambient temperature before being ducted to the area to be air conditioned according to the thermostat setting.

The fresh air within the air handling unit 44 is heated by admixture with the heated fresh air from the heat exchanger 43 and can be additionally heated, if a higher temperature than can be achieved by this admixture is required, by a gas-fired heating unit 72 which is controlled from the thermostat but also has a manual override control panel 73.

The heated fresh air from the duct 67 is admitted to the air handling unit 44 through a plurality of hollow air distribution fingers 74 forming a unit 75 as shown in Figure 6. The air distribution finger unit 75 is located at the entrance of the plenum chamber 69 in the air handling unit 44 and the cooler fresh air enters the plenum chamber 69 by flowing around and between the fingers 74. To reduce the pressure drop of the cooler air as it flows around the fingers 74, the front or upstream side of each finger 74 is fitted with a cover 76 of semicircular cross-section.

Each of the distribution fingers 74 comprises an elongated box construction with an air inlet aperture 77 at the upper end thereof. The air outlet from each finger 74 comprises two vertical slits 78 at either side of the front of the elongate box. Within each finger 74 is an inclined partition 79 which causes the finger to taper towards its lower end. This tapering shape together with the shape of the outlet slits 78 causes the heated fresh air to be distibuted evenly into the cool air stream in the plenum chamber 69 without stratification by ensuring an equal air velocity along the vertical length of the finger 74.

When the heated air is not required to be admixed with the cooler fresh air in the air handling unit 44, each of the air distribution fingers 74 is closed by at its inlet aperture 77 by a damper (not shown). These dampers are linked together so that the whole of the unit 75 can be closed. The operation of the dampers is controlled by a motor 80 which is itself controlled according to the signal from the thermostat in the area to be air conditioned. The dampers can shut off tightly the inflow of air to the fingers 74 and are able to withstand a build-up of pressure when closed and high temperatures.

The control of the air pressure within the duct 65 and generally throughout the duct system through which the heated fresh air from the heat exchanger flows, especially when the damper is preventing egress of air from the distribution unit 75, is achieved by selectively operating a motorised damper 81 in a duct 82 to permit the heated air to discharge to the atmosphere. As previously stated, the duct 68 branches off from the main duct 65 from the heat exchanger and a bleed of the heated fresh air passes along this duct 68 past a pressure sensor 83. The pressure sensor 83 selectively controls a motor 84 which drives the damper 81 permitting air to egress to the atmosphere via the duct 82 when a pressure build-up occurs. The controls are pre-set so that a substantially constant pressure is maintained throughout the heated fresh air duct system.

The control setting is such that the pressure drop along the path comprising the open damper 81, the outlet slits 78 of the fingers 74, and the connecting branch duct 68 from the main duct 65 is overcome.

Thus, it can be seen that the heat recovered from the hot waste gases can be utilized selectively to heat fresh air for air conditioning the food processing plant or discharged to atmosphere. Further heating of the air can be accomplished by use of the heating unit 72 as required. After heating, the air passes through a filter unit 85 adjacent the heating unit 72 in the air handling unit before being ducted to the required area.

When cooled fresh air is required, then the hot-waste gases are discharged to atmosphere through the chimneys 35, no heat exchange takes place and the distribution fingers are closed. The air flowing through the air handling unit 44 is cooled by passing over coils containing chilled water. These coils are contained within a region 86 of the air handling unit, downstream of the filter unit 85.

Chilled water is supplied to the coils in the region 86 from one or more packaged air cooled dillers 87, two of which are depicted in the drawings. The chillers 87 are located in the area 71 of the building 39 which is open to the atmosphere, adjacent the inlet louvre 70 to the air handling unit 44. The chillers 87 operate in a known manner similar to a refigerator to produce the chilled water which travels around a closed path between each chiller 87 and the coils within the air handling unit 44.

When more than one chiller 87 is installed, they are operated in sequence according to the load and are controlled by a thermostat 88. The thermostat 88 prevents the chillers 87 from operating below a predetermined temperature, which will vary according to the climate, when atmospheric air can be used for cooling by admixture in a greater proportion with the already heated air supplied by the distribution fingers 74.

Each chiller 87 has inlet and outlet pipes, 89 and 90 respectively. The outlet pipe 90 is connected to a pipe 91 through a valve 92 which pie 91 then rises vertically upwards and enters a horizontal header pipe 93 for pumps 94. Two pumps 94 and 94A are provided, one 94A being a stand-by for use in the event of the other breaking down or as an additional backup. A further pump 94B can also be supplied for future use if the number of chillers 87 is to be increased. The pumps 94 and 94A are supplied with water from the header pipe 93 down vertical pipes 95. A further valve 96 is also provided in each of the pipes 95 so that the pumps can be isolated from the header pipe 93.The pumps 94 are connected at their outlet to further pipes 97, in each of which there is a valve 98 so that the pumps 94 can be completely isolated, and the pipes 97 all enter a common pipe 99 which conducts the chilled water to the coils in the air handling unit 44.

At the location of the air handling unit 44, the pipe 99 is fitted with a valve 100 and a strainer 101 before leading into a vertical header pipe 102 which is fitted with four connecting points for pipes from the coils within the air handling unit. Between the strainer 101 and the header pipe 102, the pipe 99 is also connected to one port of a three-way valve 103 which regulates the flow of chilled water as will be described. The vertical header pipe 102 is fitted with an air cock 104 at its upper end, so that any air within the pipe work can be bled off, and a drain valve 105 at its lower end.

After passing around the coils, the water leaves the air handling unit 44 and enters a second vertical header pipe 106, which is again fitted with an air cock 107 and a drain valve 108. From the header pipe 106, one pipe 109 leads into a second port of the three-way valve 103 and a second pipe 110 leads via a valve 111 directly into a return pipe 112 for the water back to the chillers 87. The third port of the three-way valve 103 is also connected to the return pipe 112. The return pipe 112 terminates in a horizontal header pipe 113 at the location of the chillers 87 and from this header pipe 113 vertical pipes 114 lead off which are connected via valves 115 to each of the inlet pipes 89 of the chillers 87.

Thus, it can be seen that by opening and closing of the appropriate ports of the way valve 103 and the vlaves 100 and 111 the flow of chilled water around the coils can be controlled. This control is automatic and the three-way valve 103 regulates the flow of chilled water at the dictate of the thermostat in the air conditioned area. Also provided is a frost thermostat 116 which starts the pumps 94 during cold weather to circulate water through the pipe work and coils to prevent freezing of the pipe work.

The air handling unit 44 can thus supply air conditioning over a wide temperature range according to demand by selective operation of hot air from the distribution finger unit 75, the gas-fired heating unit 72, and the chillers 87. As previously stated, fresh air is sucked into the air handling unit 44 from the exterior and this is accomplished by a motor-driven, non overloading fan 117 with backward curved blades located at the outlet of the air-handling unit 44. The fan 117 blows the air conditioning air from the air handling unit 44 into a duct 118 for transport to the appropriate area in the food processing plant. A damper 119 is provided adjacent the fan 117 so that the volume of air passing through the duct 118 can be set manually.

In the present example, duct 118 leads to the food processing area 20 where it runs along and to one side of the ceiling. Approximately half-way along the length of the area 20, the duct 118 branches into two further ducts 120 and 121. Duct 121 leads into a further T-shaped duct system which is used for distributing air throughout the area 20 whereas duct 121 leads off to another area of the plant.

Motorised butterfly dampers 122 and 123 are positioned in the duct 118 before division into ducts 120 and 121, and at the inlet to duct 121 respectively.

The T-shaped duct system comprises a stem 124 which runs longitudinally through the area 20. Grilles 125 with adjustable louvre blades and volume control dampers are positioned in the stem duct 124 at spaced intervals. The cross bar 126 of the T-shaped duct system runs transversely across the area 20 and spaced grilled outlets 127 are provided there along, which outlets can be swivelled in a vertical plane.

In use, the hot waste gases from the ovens 21 and 22 are ducted to the heat recovery and air conditioning system wherein a heat exchange takes place with transfer of the heat from the waste gases to fresh air. The air handling unit 44 draws in fresh air from the atmosphere and according to a pre-set thermostatic control in the area to be air conditioned selectively operates heating or cooling systems to bring the fresh air to the desired temperature. Use is made of the heated fresh air from the heat exchange to admix with air in the air handling unit 44 as necessary and further heating by use of the heating unit 72 is only carried out when the desired temperature cannot otherwise be attained. The conditioned air is then ducted to the appropriate area of the plant or elsewhere for spatial heating or cooling.The use of more than one air handling unit 44 would enable heated and cooled conditioned air to be ducted respectively areas simultaneously as required. Thus the whole heat recovery and air conditioning system forms a pre-set automatically controlled unit for the supply of conditioned air to any region as desired.

While references have been made to air at ambient temperature it should be understood that such references hereinbefore and in the claims are to be construed as including air recirculated from the location being air conditioned.

While the installation has been described solely for air conditioning purposes, it is envisages that the hot waste gases may also be employed in part for, inter alia, water heating purposes.

WHAT WE CLAIM IS: 1. An air conditioning installation for an area in a building in combination with a processing plant able to produce hot waste gases at a temperature above the ambient temperature in said area, the installation comprising an air handling unit through which air at ambient temperature can be drawn for conditioning and ducting to the area, and a heat exhanger through which the hot waste gases can pass separate from and in counterflow flow to further air which is drawn from the exterior of the building and which is thereby heated for selective asmixture with said air admitted into-the air handling unit to raise the temperature of the latter, waste gas collection ducting extending between the processing plant and an inlet of the heat exchanger and damper controlled diverting duct means upstream of said inlet for egressing the hot waste gases to a location other than the heat exchanger.

2. A combination as claimed in Claim 1 in which the processing plant is a food processing plant including a food baking oven.

3. A combination as claimed in Claim 1 or 2, in which the diverting duct means comprises a chimney, flow through which is controlled by a motorised damper operable by a pressure sensor located in the gas collection ducting.

4. A combination as claimed in Claim 3, comprising within the gas collection ducting, a motorised damper operable by the pressure sensor to be open when the chimney damper is closed and vice versa.

5. A combination as claimed in Claim 3 or 4, in which the motorised dampers in the chimney and gas collection ducting can also be operated independently of the pressure sensor.

6. A combination as claimed in any of Claims 1 to 5, in which the gas collection ducting upstream of the heat exhanger incorporates a thermostatically controlled damper associated with an air inlet via which air at a temperature lower than the hot waste gases can enter for admixture with the latter to ensure that the efficiency of the heat exchanger is not impaired.

7. A combination as claimed in any one of Claims 1 to 6 in which the heat exchanger has connected to an exit for the cooled waste gases a transfer duct through which the latter are delivered via a motorised damper to a chimney, a fan being provided for assisting gas flow from the heat exchanger through the chimney.

8. A combination as claimed in any one of Claims 1 to 7, comprising transfer ducting for said heated air between the heat exchanger and the air handling unit, there being a bleed to atmosphere to control pressure within the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (20)

**WARNING** start of CLMS field may overlap end of DESC **. 87. As previously stated, fresh air is sucked into the air handling unit 44 from the exterior and this is accomplished by a motor-driven, non overloading fan 117 with backward curved blades located at the outlet of the air-handling unit 44. The fan 117 blows the air conditioning air from the air handling unit 44 into a duct 118 for transport to the appropriate area in the food processing plant. A damper 119 is provided adjacent the fan 117 so that the volume of air passing through the duct 118 can be set manually. In the present example, duct 118 leads to the food processing area 20 where it runs along and to one side of the ceiling. Approximately half-way along the length of the area 20, the duct 118 branches into two further ducts 120 and 121. Duct 121 leads into a further T-shaped duct system which is used for distributing air throughout the area 20 whereas duct 121 leads off to another area of the plant. Motorised butterfly dampers 122 and 123 are positioned in the duct 118 before division into ducts 120 and 121, and at the inlet to duct 121 respectively. The T-shaped duct system comprises a stem 124 which runs longitudinally through the area 20. Grilles 125 with adjustable louvre blades and volume control dampers are positioned in the stem duct 124 at spaced intervals. The cross bar 126 of the T-shaped duct system runs transversely across the area 20 and spaced grilled outlets 127 are provided there along, which outlets can be swivelled in a vertical plane. In use, the hot waste gases from the ovens 21 and 22 are ducted to the heat recovery and air conditioning system wherein a heat exchange takes place with transfer of the heat from the waste gases to fresh air. The air handling unit 44 draws in fresh air from the atmosphere and according to a pre-set thermostatic control in the area to be air conditioned selectively operates heating or cooling systems to bring the fresh air to the desired temperature. Use is made of the heated fresh air from the heat exchange to admix with air in the air handling unit 44 as necessary and further heating by use of the heating unit 72 is only carried out when the desired temperature cannot otherwise be attained. The conditioned air is then ducted to the appropriate area of the plant or elsewhere for spatial heating or cooling.The use of more than one air handling unit 44 would enable heated and cooled conditioned air to be ducted respectively areas simultaneously as required. Thus the whole heat recovery and air conditioning system forms a pre-set automatically controlled unit for the supply of conditioned air to any region as desired. While references have been made to air at ambient temperature it should be understood that such references hereinbefore and in the claims are to be construed as including air recirculated from the location being air conditioned. While the installation has been described solely for air conditioning purposes, it is envisages that the hot waste gases may also be employed in part for, inter alia, water heating purposes. WHAT WE CLAIM IS:

1. An air conditioning installation for an area in a building in combination with a processing plant able to produce hot waste gases at a temperature above the ambient temperature in said area, the installation comprising an air handling unit through which air at ambient temperature can be drawn for conditioning and ducting to the area, and a heat exhanger through which the hot waste gases can pass separate from and in counterflow flow to further air which is drawn from the exterior of the building and which is thereby heated for selective asmixture with said air admitted into-the air handling unit to raise the temperature of the latter, waste gas collection ducting extending between the processing plant and an inlet of the heat exchanger and damper controlled diverting duct means upstream of said inlet for egressing the hot waste gases to a location other than the heat exchanger.

2. A combination as claimed in Claim 1 in which the processing plant is a food processing plant including a food baking oven.

3. A combination as claimed in Claim 1 or 2, in which the diverting duct means comprises a chimney, flow through which is controlled by a motorised damper operable by a pressure sensor located in the gas collection ducting.

4. A combination as claimed in Claim 3, comprising within the gas collection ducting, a motorised damper operable by the pressure sensor to be open when the chimney damper is closed and vice versa.

5. A combination as claimed in Claim 3 or 4, in which the motorised dampers in the chimney and gas collection ducting can also be operated independently of the pressure sensor.

6. A combination as claimed in any of Claims 1 to 5, in which the gas collection ducting upstream of the heat exhanger incorporates a thermostatically controlled damper associated with an air inlet via which air at a temperature lower than the hot waste gases can enter for admixture with the latter to ensure that the efficiency of the heat exchanger is not impaired.

7. A combination as claimed in any one of Claims 1 to 6 in which the heat exchanger has connected to an exit for the cooled waste gases a transfer duct through which the latter are delivered via a motorised damper to a chimney, a fan being provided for assisting gas flow from the heat exchanger through the chimney.

8. A combination as claimed in any one of Claims 1 to 7, comprising transfer ducting for said heated air between the heat exchanger and the air handling unit, there being a bleed to atmosphere to control pressure within the

transfer ducting and heat exchanger.

9. A combination as claimed in Claim 8, in which the air handling unit comprises a plenum chamber through which said ambient temperature air is drawn past a plurality of spaced air distribution fingers into which said heated air is delivered by said transfer ducting for controllable egression to admix with said ambient temperature air.

10. A combination as claimed in Claim 9, in which each air distribution finger is of elongate box construction with a cover of semi-circular cross-section around which said ambient temperature air flows into the plenum chamber.

11. A combination as claimed in Claim 10 iin which each air distribution finger is open at one end for ingress of said heated air and in its surface opposed to the cover has two spaced vertical slits for egress of said heated air.

12. A combination as claimed in Claim 11 in which each air distribution finger has an inclined partition causing the finger to taper towards its closed end.

13. A combination as claimed in Claim 11 or 12 in which each air distribution finger has a damper for closing its open end, the dampers being linked together for simultaneous operation by a motor.

14. A combination as claimed in any one of Claims 1 to 13, in which the air handling unit incorporates a heating unit to provide supplementary heat if required.

15. A combination as claimed in any one of Claims 1 to 14 in which the air handling unit is provided with a motor driven non-overloading fan with backward curved blades for delivering the conditioned air from the air handling unit to said area of the building.

16. A combination as claimed in any of Claims 1 to 15 in which the air handling unit contains coils through which water pumped from a chiller can be circulated whereby said ambient temperature air can be cooled.

17. A combination as claimed in Claim 16 in which a pump is provided for circulating the chilled water through the coils, there being a stand-by pump for emergency or back-up purposes.

18. A combination as claimed in Claim 16 or 17 in which a three-way valve is provided for controlling chilled water flow through the coils.

19. A combination as claimed in Claim 17 or Claim 18 when dependent on Claim 17, comprising a frost thermostat for starting the pumps during cold weather to circulate water through the coils to prevent freezing and a second thermostat to prevent operation of the chiller when the ambient temperature is below a predetermined temperature.

20. An air conditioning installation in combination with a processing plant producing hot waste gases, substantially as hereinbefore described with reference to the accompanying drawings.