Project Report 6 REFRIGERATION ENERGY USE IN THE FOOD CHAIN PROJECT REFERENCE (TBA) CONTRACT REFERENCE (TBA)

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1 Project Report 6 REFRIGERATION ENERGY USE IN THE FOOD CHAIN PROJECT REFERENCE (TBA) CONTRACT REFERENCE (TBA) by Professor Ian W. Eames Professor John Missenden Professor Graeme Maidment, Mr Tarek El-Shafey Department of Engineering Systems London South Bank University Summary This report summarises the research so far carried out by the LSBU team into the 'Food Chain Refrigeration Energy Use '. The report describes the results of a literature investigation so far into modelling refrigeration systems 06 December 2007

2 Contents 1 Introduction 2 Transient model 3 Coupling of the food and refrigeration model 4 Progress to date 5 Conclusion

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4 1. Introduction A project objective for LSBU is to develop integrated transient refrigeration food process system models to test (and optimise) various refrigeration systems used in the industrial production chain for food. This report describes the results of LSBU's progess upto 06 December Transient Model The transient model (VCR) was further developed by validating the simulation results with different manufacturers catalogue data. The results proved that some modelling equations needed improving by choice of initial conditions, so more development of the equations was done. Also, several simulation tests were done with the VCR program, showing up bugs in some modelling routines, these were corrected to avoid errors during simulation. The evaporator sizing using the VCR model was investigated and it was decided that the user will be able to find a compromise for the optimum evaporator size relative to peak, average and minimum loads. This process is still in progress. The final flow chart for the VCR model is shown in figures 1 and 2. Figure 1: First part of VCR model flow chart

5 Figure 2: Second part of VCR model flow chart Lists of output that can be generated by the VCR model were prepared and discussed and the final draft is presented for agreement. The list would consider: Energy consumption for refrigeration system components individually Food temperatures (not just initial) Weight loss Air temperature (dynamic i.e. resulting from loads and refrigeration plant performance) Relative humidity of air Air velocity over food Evaporator size and fans required to produce the above air velocity Door opening and product loading strategies Cold store construction Ancillary equipment and 'people' loads Evaporator icing and defrost strategies Control systems Ambient conditions

6 The VCR outputs are modified to be generated in the form of Excel / text files as an appropriate solution for storing the results, and the dynamic charts to plot the data. The data required for the validation of the model, using the pork-pie case study is in progress. The definition of an ideal cycle was investigated, and decided that it would be considered the minimum practical amount of cooling, not the Carnot calculation. The initial conditions values were enhanced by using design balance point calculator as shown in figure 3. Figure 3: Design balance point calculation An investigation of the literature was performed on the correlations and air distribution factors for air velocities across the space with respect to the cold store geometry and the results were forwarded to FRPERC. The air-flow velocity over the product, will consider the use of these factors, based upon minimum and maximum flow distribution efficiencies. The typical flow distribution efficiency will be integrated into the Food DLL model. It was decided that at a later stage, the following items would be required: more detailed U values for walls/ floors, more detailed values for door opening effectiveness, and defrost effect. The problem of the different time step between the two models was resolved by specifying the VCR model time step that is divisible by the food model time step. 3. Model integration A lot of activity has taken place in this area, especially to ensure that the two models communicate. It was agreed at previous meetings that the communication parameters between two models, would be as shown in figure 4. The food model to be used is foodtemp, which is written in a different programming language version to the

7 system model. To enable communication between the two, the foodtemp was compiled as a DLL (dynamic link library), to be called by the VCR exe program. Figure 4: demarcation for Foodht and VCR models FRPERC have provided LSBU with a DLL component to pass the food heat transfer value to the VCR model. The component was tested for different operating systems and computers, and proved to be efficient in exchanging the data for about 80% of the computers, after several debugging sessions. The DLL was further developed to operate on any operating version, but some problems are still experienced in locating the DLL component on some machines. This matter is a small issue that can be overcome, but requires further investigation. Table 1 shows the parameters passed between the VCR model and the DLL. Communicated Items By DLL By VCR model 1 Product heat load Air temp off evaporator 2 Moisture released by product Air moisture off evaporator 3 Weight loss for product per kilogramme of product 4 Total heat release or enthalpy change per kilogramme of product Number of products (set at design stage) cold-space air temperature 5 Product surface temperature cold-space moisture content 6 Product mean temperature Table 1: Communicated items between VCR and DLL As a result of previous meetings, it was agreed between LSBU and FRPERC, to decouple the primary and secondary air flow rates. The evaporator primary fan would

8 be analyzed to satisfy the flow and pressure drop across the evaporator only. The secondary fan would be required to satisfy the flow and pressure drop across the cold store, as shown in figure 5. Primary fan Secondary fan 4. Progress to date Figure 5: Schematic diagram for integrated fans Figure 6: Previous Gantt chart Figure 7: New Gantt chart

9 5. Conclusion The VCR transient model was completed with the defrost option. The programming routines are being tested and some bugs were resolved, and debugging is still in process. Several transient simulations were done and the model is proving to be generating reasonable results. A case study is being prepared by FRPERC to validate the transient VCR model with actual case. More refrigerants and mechanical components will be required to be modelled in VCR model.