《肉制品冷冻技术》（英文版） Part 15 Specifying, designing and optimising refrigeration systems

15 Specifying, designing and optimising refrigeration systems In specifying refrigeration equipment the function of the equipment must be absolutely clear. Refrigeration equipment is always used to control tem- perature. Either the meat passing through the process is to be maintained it its initial temperature, for example as in a refrigerated store or a packing operation, or the temperature of the meat is to be reduced, for example in a blast freezer. These two functions require very different equipment. If a room is to serve several functions then each function must be clearly iden- ified. The optimum conditions needed for that function must be evaluated and a clear compromise between the conflicting uses made. The result will inevitably be a room that does not perform any function completely effectively. There are three stages in obtaining a refrigeration plant. The first stage is determining the process specification, the second stage is drawing up the engineering specification, i.e. turning processing conditions into terms which a refrigeration engineer can understand, independent of the food process, and the third and final stage is the procurement of the plant 15.1 Process specification Poor design in existing chillers/freezers is due to a mismatch between what the room was originally designed to do and how it is actually used. The first task in designing such a plant is therefore the preparation of a clear speci- fication by the user of how the room will be used In preparing this speci fication the user should consult all parties concerned. These may be officials enforcing legislation, customers, other departments within the company and

15 Specifying, designing and optimising refrigeration systems In specifying refrigeration equipment the function of the equipment must be absolutely clear. Refrigeration equipment is always used to control tem￾perature. Either the meat passing through the process is to be maintained at its initial temperature, for example as in a refrigerated store or a packing operation, or the temperature of the meat is to be reduced, for example in a blast freezer. These two functions require very different equipment. If a room is to serve several functions then each function must be clearly iden￾tified. The optimum conditions needed for that function must be evaluated and a clear compromise between the conflicting uses made. The result will inevitably be a room that does not perform any function completely effectively. There are three stages in obtaining a refrigeration plant. The first stage is determining the process specification, the second stage is drawing up the engineering specification, i.e. turning processing conditions into terms which a refrigeration engineer can understand, independent of the food process, and the third and final stage is the procurement of the plant. 15.1 Process specification Poor design in existing chillers/freezers is due to a mismatch between what the room was originally designed to do and how it is actually used. The first task in designing such a plant is therefore the preparation of a clear speci- fication by the user of how the room will be used. In preparing this speci- fication the user should consult all parties concerned.These may be officials enforcing legislation, customers, other departments within the company and

04 Meat refrigeration engineering consultants or contractors, although the ultimate decisions taken in forming this specification are the user's alone. 15.1.1 Throughput The throughput must be specified in terms of the species to be handled and whether they are split, whole, quartered, primal joints, and so on. If more than one species or type of cut is to be processed then separate specifica tions must be made for each product. The range and average weight and fatness of each product should also be specified. For example, large car casses can take twice as long to chill as small carcasses under the same con- ditions, so it is important to be realistic in deciding on the weight range. To say that all types and weights of animals slaughtered are to go through one chiller or freezer will inevitably mean that compromises must be made he design stages which will lead to an inadequate syste A throughput profile is needed. Few meat plants slaughter the same number and weight of animals on each day of the week and therefore the average throughput is not adequate in the specification. The maximum capacity must be catered for and the chiller/freezer should also be designed to chill/freeze carcasses adequately and economically at all other 15.1.2 Temperature requirements The range of temperature requirements for each product must also be learly stated. In deciding what this is or these are, several requirements, often conflicting, must be considered. First of all, what legislative require ments are there, for instance the eEC requirement at 7"C? What customer requirements are there? These may be your existing customers or they may be future customers who you are hoping to attract What standard do you ourself have? Some companies sell a quality product under their own brand name, which should include a cooling specification. Finally it must be decided to what extent the above standards may be allowed to slip. The reason for this will become apparent later. Almost everyone in the meat industry allows their standards to slip to some extent; those that get caught and are called to task for this lose orders or have their production disrupted. These firms have turned their back on this problem and not dealt with it consciously and clearly. There are others who know well to what extent they can push the inspectors, or their customers and ensure that they stay within ccepted limits. 15.1.3 Weight loss If it is intended to save weight from the meat both during chilling/freezing and storage, it is useful to quantify at an early stage how much extra money can be spent to save a given amount of weight

engineering consultants or contractors, although the ultimate decisions taken in forming this specification are the user’s alone. 15.1.1 Throughput The throughput must be specified in terms of the species to be handled and whether they are split, whole, quartered, primal joints, and so on. If more than one species or type of cut is to be processed then separate specifica￾tions must be made for each product. The range and average weight and fatness of each product should also be specified. For example, large car￾casses can take twice as long to chill as small carcasses under the same con￾ditions, so it is important to be realistic in deciding on the weight range. To say that all types and weights of animals slaughtered are to go through one chiller or freezer will inevitably mean that compromises must be made in the design stages which will lead to an inadequate system. A throughput profile is needed. Few meat plants slaughter the same number and weight of animals on each day of the week and therefore the average throughput is not adequate in the specification. The maximum capacity must be catered for and the chiller/freezer should also be designed to chill/freeze carcasses adequately and economically at all other throughputs. 15.1.2 Temperature requirements The range of temperature requirements for each product must also be clearly stated. In deciding what this is or these are, several requirements, often conflicting, must be considered. First of all, what legislative require￾ments are there, for instance the EEC requirement at 7 °C? What customer requirements are there? These may be your existing customers or they may be future customers who you are hoping to attract. What standard do you yourself have? Some companies sell a quality product under their own brand name, which should include a cooling specification. Finally it must be decided to what extent the above standards may be allowed to slip. The reason for this will become apparent later. Almost everyone in the meat industry allows their standards to slip to some extent; those that get caught and are called to task for this lose orders or have their production disrupted. These firms have turned their back on this problem and not dealt with it consciously and clearly.There are others who know well to what extent they can push the inspectors, or their customers and ensure that they stay within accepted limits. 15.1.3 Weight loss If it is intended to save weight from the meat both during chilling/freezing and storage, it is useful to quantify at an early stage how much extra money can be spent to save a given amount of weight. 304 Meat refrigeration

Specifying, designing and optimising refrigeration systems 305 15.1.4 Future use All the information collected so far and the decisions taken will be from existing production. Another question that needs to be asked is, will there be any changes in the use of the chiller/freezer in the future? In practice the answer to this question must always be 'yes. Looking back into the past no meat processor has remained static and within the foreseeable life of a chiller/freezer, anything between 10 and 50 years judging by present quantified in as much detail as possible? s be envisaged and can these be It is still not possible at this stage in the design to finalise the factory layout and operation. However, some estimate of how the factory will be operated, how it will be laid out, the size of chiller/freezer needed, and so on must be made at this point. This must be kept flexible until engineering specification has been formulated (see later). It is common practice for the factory layout and operation to be decided in advance writing the chilling/freezing specification. Lack of flexibility in changing these is often responsible for poor chiller performance once the factory is completed 5.1.5 Plant layout Chilling or freezing is one operation in a sequence of operations. It influ- ences the whole system and interacts with it. An idea must be obtained of how the room is to be loaded, unloaded and cleaned, and these operations must always be intimately involved with those of the slaughter line, the sales team, the cutting and boning room, and the loading bay. Questions that need to be addressed include where will meat be sorted for orders?" and where will meat not sold be stored until a future date There is often a conflict of interests within a chiller/freezer. In practice the chiller/freezer is often used as a marshalling yard for sorting orders and as a place for storing car casses that have not been sold. If it is intended that either of these opera- tions are to take place in the chiller/freezer the design must be made much more flexible in order to cover the conditions needed in a marshalling area or a refrigerated store Meat must be loaded into and out of the freezer or chiller and the process may be continuous, batch or semicontinuous. In the case of batch and semi- continuous processes, holding areas will be required at the beginning and nd of the process in order to even out flows of material from adjacent processes. The time available for the process will be in part dictated by the space available; a slow process will take more space than a fast process, for a given throughput. It may also be dictated by commercial constraints, such as the delivery of 'l-day-old meat to distribution outlets. The above specifications will dictate the processing conditions. Most processes use air as a processing medium and its temperature, velocity and relative humidity are all usually critical to the process. The processes may

15.1.4 Future use All the information collected so far, and the decisions taken, will be from existing production. Another question that needs to be asked is, will there be any changes in the use of the chiller/freezer in the future? In practice the answer to this question must always be ‘yes’. Looking back into the past, no meat processor has remained static and within the foreseeable life of a chiller/freezer, anything between 10 and 50 years (judging by present chiller/freezer population), can any changes be envisaged and can these be quantified in as much detail as possible? It is still not possible at this stage in the design to finalise the factory layout and operation. However, some estimate of how the factory will be operated, how it will be laid out, the size of chiller/freezer needed, and so on must be made at this point. This must be kept flexible until the engineering specification has been formulated (see later). It is common practice for the factory layout and operation to be decided in advance of writing the chilling/freezing specification. Lack of flexibility in changing these is often responsible for poor chiller performance once the factory is completed. 15.1.5 Plant layout Chilling or freezing is one operation in a sequence of operations. It influ￾ences the whole system and interacts with it. An idea must be obtained of how the room is to be loaded, unloaded and cleaned, and these operations must always be intimately involved with those of the slaughter line, the sales team, the cutting and boning room, and the loading bay. Questions that need to be addressed include ‘where will meat be sorted for orders?’ and ‘where will meat not sold be stored until a future date?’ There is often a conflict of interests within a chiller/freezer. In practice the chiller/freezer is often used as a marshalling yard for sorting orders and as a place for storing car￾casses that have not been sold. If it is intended that either of these opera￾tions are to take place in the chiller/freezer the design must be made much more flexible in order to cover the conditions needed in a marshalling area or a refrigerated store. Meat must be loaded into and out of the freezer or chiller and the process may be continuous, batch or semicontinuous. In the case of batch and semi￾continuous processes, holding areas will be required at the beginning and end of the process in order to even out flows of material from adjacent processes. The time available for the process will be in part dictated by the space available; a slow process will take more space than a fast process, for a given throughput. It may also be dictated by commercial constraints, such as the delivery of ‘1-day-old’ meat to distribution outlets. The above specifications will dictate the processing conditions. Most processes use air as a processing medium and its temperature, velocity and relative humidity are all usually critical to the process. The processes may Specifying, designing and optimising refrigeration systems 305

306 Meat refrigeration be in a single stage, in which case steady values will be specified, or they may be time dependent, as in a multi-stage process. In choosing the proce conditions there will be an interaction with the earlier specified constraints. Some compromise may be needed, adjusting the time available for the process in order to obtain an optimal solution. Once the process conditions re fixed and the throughput and materials specified, the product load will also be fixed although this may not always be known. Where design data exist, they should be utilised to specify the product load Other refrigeration loads also need to be specified. Many of these, such as infiltration through openings, the use of lights, machinery and people working in the refrigerated space, are all under the control of the user and must be specified so that the heat load given off by them can be incorpo- rated in the final design. Ideally, all the loads should then be summed ime basis to produce a load profile. If the refrigeration ess is to be incorporated with all other processes within a plant, in orde to achieve an economic solution, the load profile is important The ambient design conditions must be specified. These refer to the temperatures adjacent to the refrigerated equipment and the temperatures of the ambient surroundings to which heat will ultimately be rejected. In stand-alone refrigerated processes this will often be the wet and dry bulb emperatures of the outside air. If the process is to be integrated with heat reclamation then the temperature of the heat sinks must be specified Finally, the defrost regime should also be specified. There are times in any process where it is critical that a defrost does not take place and that the oil is cleared of frost before commencing this part of the process. The above requirements should all be specified by the end-user. It ommon practice throughout European industry to leave much of this specification to refrigeration contractors or engineering specialists. Often they are in a position to give good advice on this. However, since all the above are outside their control, the final decision should always be taken by the end-user, using their knowledge of how well they can control their overall process. 15.2 ngineering specification The aim of drawing up an engineering specification is to turn the process- ing conditions into a specification that any refrigeration engineer can then construct and deliver without knowledge of the meat process involved. If he first part of the process specification has been completed, the engi neering specification will be largely in place. It consists of the environmen- tal conditions within the refrigerated enclosure, air temperature, air velocity ind humidity(the way the air will move within the refrigerated enclosure), the size of the equipment, the refrigeration load profile, the ambient design conditions and the defrost requirements. The final phase of the engineering

be in a single stage, in which case steady values will be specified, or they may be time dependent, as in a multi-stage process. In choosing the process conditions there will be an interaction with the earlier specified constraints. Some compromise may be needed, adjusting the time available for the process in order to obtain an optimal solution. Once the process conditions are fixed and the throughput and materials specified, the product load will also be fixed although this may not always be known. Where design data exist, they should be utilised to specify the product load. Other refrigeration loads also need to be specified. Many of these, such as infiltration through openings, the use of lights, machinery and people working in the refrigerated space, are all under the control of the user and must be specified so that the heat load given off by them can be incorpo￾rated in the final design. Ideally, all the loads should then be summed together on a time basis to produce a load profile. If the refrigeration process is to be incorporated with all other processes within a plant, in order to achieve an economic solution, the load profile is important. The ambient design conditions must be specified. These refer to the temperatures adjacent to the refrigerated equipment and the temperatures of the ambient surroundings to which heat will ultimately be rejected. In stand-alone refrigerated processes this will often be the wet and dry bulb temperatures of the outside air. If the process is to be integrated with heat reclamation then the temperature of the heat sinks must be specified. Finally, the defrost regime should also be specified. There are times in any process where it is critical that a defrost does not take place and that the coil is cleared of frost before commencing this part of the process. The above requirements should all be specified by the end-user. It is common practice throughout European industry to leave much of this specification to refrigeration contractors or engineering specialists. Often they are in a position to give good advice on this. However, since all the above are outside their control, the final decision should always be taken by the end-user, using their knowledge of how well they can control their overall process. 15.2 Engineering specification The aim of drawing up an engineering specification is to turn the process￾ing conditions into a specification that any refrigeration engineer can then construct and deliver without knowledge of the meat process involved. If the first part of the process specification has been completed, the engi￾neering specification will be largely in place. It consists of the environmen￾tal conditions within the refrigerated enclosure, air temperature, air velocity and humidity (the way the air will move within the refrigerated enclosure), the size of the equipment, the refrigeration load profile, the ambient design conditions and the defrost requirements. The final phase of the engineering 306 Meat refrigeration

Specifying, designing and optimising refrigeration systems 307 lould be drawing up a schedule for testing the engineering specification prior to handing over the equipment. This test will be in engi eering and not product terms. During this process the user must play an active part because a number f the decisions taken in this stage will affect other aspects of the opera tion. The specification produced should be the document that forms the basis for quotations, and finally the contract between the user and the contractor must be stated in terms that are objectively measurable once the chiller is completed. Arguments often ensue between contractors and their clients from an unclear, ambiguous or unenforceable specifica tion. Such lack of clarity is often expensive to all parties and should be 15.2.1 Environmental conditions The first step in this process is iterative and is shown symbolically in Fig 15.1. First, a full range of time, temperature and air velocity options must be assembled for each cooling specification covering the complete range each product. The list should also include future cooling specifications. Each must then be evaluated against the factory operation. For example, using a particular temperature and air speed around one product may give a chill ing time to meet the temperature requirements already laid down of 18h. If the factory operation calls for maximum chilling time of only 12h then clearly the temperature/time combinations currently under review will not -el /time options Fit plant operation? Is there another Is this best optic Alter standards or factory operation YES RH times for product range Fig 15.1 Flow diagram for a selection of the environmental conditions

specification should be drawing up a schedule for testing the engineering specification prior to handing over the equipment. This test will be in engi￾neering and not product terms. During this process the user must play an active part because a number of the decisions taken in this stage will affect other aspects of the opera￾tion. The specification produced should be the document that forms the basis for quotations, and finally the contract between the user and the contractor must be stated in terms that are objectively measurable once the chiller is completed. Arguments often ensue between contractors and their clients from an unclear, ambiguous or unenforceable specifica￾tion. Such lack of clarity is often expensive to all parties and should be avoided. 15.2.1 Environmental conditions The first step in this process is iterative and is shown symbolically in Fig. 15.1. First, a full range of time, temperature and air velocity options must be assembled for each cooling specification covering the complete range of each product.The list should also include future cooling specifications. Each must then be evaluated against the factory operation. For example, using a particular temperature and air speed around one product may give a chill￾ing time to meet the temperature requirements already laid down of 18h. If the factory operation calls for maximum chilling time of only 12 h then clearly the temperature/time combinations currently under review will not Specifying, designing and optimising refrigeration systems 307 Temp./vel./time options for a product range Fit plant operation? NO NO NO YES YES Is there another option? Alter standards or factory operation YES Is this best option? Final temp., time, RH & times for product range Fig. 15.1 Flow diagram for a selection of the environmental conditions