Figure 3 compares the energy performance of a new 2,100,000 ft³ mixed warehouse Is the Erathe of Ammonia Liquid Overfeed with energy performances ofEnding? many North American warehouses employing the plant concepts as marked (red dots). The warehouse represented by the stars is serviced by a dual stage NH3 DX plant that also provides refrigeration capacity to blast Figure Energy Performance Comparison for 2,100,000 ft³ DX warehouse with Conventional Plant. freeze3.300 metric tonnes of meat in cartons per week.
Figure 3. Energy Performance Comparison for 2,100,000 ft³ DX warehouse with Conventional Plant. plant condenser is marginally more At the 2017 GCCA Expo in Chicago, star represents storage only without Again, pattern Elimination of theADX liquefiedblast refrigerant from the oversized thanathesimilar condenser of the is visible. the presentation “Low Charge freezing. This is a calculated corsuction line network appears to deliver significant energy performance benefits. liquid overfeed plant. The energy perAmmonia” by Watters and Nelson rection based on the amount of product formance records in both cases cover highlighted similar energy performance frozen. minimum one year – for the older plant for centralized, DX NH3 for Does this mean end of an era for The blue star represents actualimprovements electricity consumption records the first four the months several years. refrigerating plant versus liquid overthe liquid recirculation concept? To of 2021. These are the warmerfeed. months in Australia. The green star represents storage The “best practice” in this context The improvement range presented answer this question, it is important to only without blast freezing. This is a calculated correction on the theenergy amount of is a polynomial regression analysis of was 18% to 38%, but there were con- based quantify performance penalty productSEC-values frozen. for a range of the recorded ceptual differences in the practical plant associated with mixing relatively high centralized, low charge NH3 refrigeratcomparisons made to enable postulation density liquefied refrigerant into the ing plant servicing mixed refrigerated thisfor range. suction network of a large, Does this mean the end of an ofera the liquid recirculation concept? To answer thisexpansive warehouses across Australia. The best Figure 3 compares the energy perforcentralized ammonia refrigerating plant. question, it is important to quantify the energy performance penalty associated with practice graph enables the comparison mance of a new 2,100,000 ft³ mixed Based on the practical observation mixing high density liquefied refrigerant the suction network of a 2, large, of SEC values relatively for dissimilar refrigerated warehouse with the energyinto performancillustrated in Figure it is postulated expansive centralized ammonia refrigerating plant. warehouses here that the energy performance penvolumes. es of many North American The recorded energy performance employing the plant concepts as marked alty caused by liquid overfeed can be as penalty associated with the presence (red dots). The warehouse represented high as 30%. of high density, liquefied refrigerant in by the stars is serviced by a dual stage The facilities that the comparison the suction network is in this practiNH3 DX plant that also provides in Figure 2 is based on are singlecal example around (1-0.97/1.4)*100 refrigeration capacity to blast freeze 300 story buildings with ceiling suspended ≈ 31%. Put another way, the liquid metric tonnes of meat in cartons per induced draught coolers and valve overfeed plant consumes 1.4/0.97=1.44 week. stations and NH3 pipelines in the ceiltimes more energy per unit refrigerated Again, a similar pattern is visible. ing space. At each evaporator outlet is, volume. Elimination of the liquefied refrigerant therefore, a wet riser. Although this may This difference is not explained in from the suction line network appears not be ideal for liquid overfeed, it reprefull by the minor conceptual differences to deliver significant energy perforsents a very, very common design. between the two refrigerating plants. mance benefits. There is little doubt that had these Rather, it is likely that the bulk of the The blue star represents actual wet risers been avoidable, the energy energy performance difference is caused electricity consumption records for the performance penalty recorded could by the differences in refrigerant feed first four months of 2021. These are the have been less or perhaps even nonmethods. warmer months in Australia. The green existent. However, as most practitioners 28
| CONDENSER | August 2021 | A Publication of the International Institute of Ammonia Refrigeration
www.iiar.org
