Specifying, designing and optimising refrigeration systems 309 Table 15.1 Refrigeration loads for a beef chiller Refrigeration load(kw Peak Average Store Product load Infiltration 0.5(<17 Fabric nil Lightin nil Evaporator fans 25(10%) Defrost (<12) 18h running Totals 66.8 278 85(<25) refers to the maximum load at the end of loading, averag load during chilling when the product is at its average value, tore to the loads present when the chiller is used to store lously cooled sides. open for short periods and that fully established airflow will never occur However, most chiller doors stand open for ca &h in every 24 h and they are certainly open while the chiller is being loaded. This infiltration load occurs at the same time as the peak product load, i.e. immediately at the end of the loading period, and it is therefore important that the infiltration load is added to the product load to find the maximum loading on the chiller. Experimental data obtained by FRPERC have shown that the ASHRAE calculations are approximately correct and are therefore rec ommended. They are often of an order of magnitude higher than figures used by designers of chill rooms. The infiltration load during chilling, when the average product load occurs, is much smaller because the door is nor mally closed or only opened for short intervals. It is therefore more accept able to use quite small infiltration loads during this time to allow for air exchange through faulty door seals or for short door openings only When the room is being used as a store, particularly if it has been unloaded, there may be periods when the infiltration load rises to maximum levels again and this has been shown in Table 15.1 The fabric load is shown next in Table 15.1 and is insignificant compared to the previous two loadings. The same applies to the heat load imposed by people in the chiller and by lighting. Unfortunately both these loads are normally concurrent with the peak product and infiltration loads and must therefore be added to these to calculate the total peak load The evaporator fans also produce quite high loads. At this point in the design an approximate figure for evaporator fan power must be used but when the final design is completed and more accurate data are available, this must be substituted and the calculations reworked. In the currentopen for short periods and that fully established airflow will never occur. However, most chiller doors stand open for ca. 8 h in every 24h and they are certainly open while the chiller is being loaded. This infiltration load occurs at the same time as the peak product load, i.e. immediately at the end of the loading period, and it is therefore important that the infiltration load is added to the product load to find the maximum loading on the chiller. Experimental data obtained by FRPERC have shown that the ASHRAE calculations are approximately correct and are therefore rec￾ommended. They are often of an order of magnitude higher than figures used by designers of chill rooms. The infiltration load during chilling, when the average product load occurs, is much smaller because the door is nor￾mally closed or only opened for short intervals. It is therefore more accept￾able to use quite small infiltration loads during this time to allow for air exchange through faulty door seals or for short door openings only. When the room is being used as a store, particularly if it has been unloaded, there may be periods when the infiltration load rises to maximum levels again and this has been shown in Table 15.1. The fabric load is shown next in Table 15.1 and is insignificant compared to the previous two loadings. The same applies to the heat load imposed by people in the chiller and by lighting. Unfortunately both these loads are normally concurrent with the peak product and infiltration loads and must therefore be added to these to calculate the total peak load. The evaporator fans also produce quite high loads. At this point in the design an approximate figure for evaporator fan power must be used but when the final design is completed and more accurate data are available, this must be substituted and the calculations reworked. In the current Specifying, designing and optimising refrigeration systems 309 Table 15.1 Refrigeration loads for a beef chiller Refrigeration load (kW) Peak Average Store Product load 40 16.8 nil Infiltration 17 0.5 0.5 (<17) Fabric 2 2 2 People 0.25 nil nil Lighting 1.5 nil nil Evaporator fans 6 6 6 Contingency – 2.5 (10%) – Defrost – (<12) (<12) 18 h running – – Totals 66.8 27.8 8.5 (<25) ‘Peak’ refers to the maximum load at the end of loading, ‘average’ to the load during chilling when the product is at its average value, and ‘store’ to the loads present when the chiller is used to store previously cooled sides