ASHRAE Journal - February 2009 - (Page 30) air, appropriate techniques to reduce that 0.012 infiltration rate should be pursued. This Saturation Line may require repairing seals, maintaining 0.010 door control, reducing openings (e.g., for conveyors), and ensuring an appropriate 0.8 pressure balance between spaces at dif0.008 fering conditions. Further information on these strategies can be found in several 0.6 0.006 40°F papers.3,8,9 Process Line If the source of moisture is from prodOriginal Dock Condition With Lower 0.4 Dock Set ucts that are being processed, consider 30°F 0.004 Unfavorable Temperature alternative means that can reduce moisProcess Line 20°F Revised Dock ture loss. Strategies for reducing product 0.2 Temperature 0.002 moisture loss can include: packaging ADP –10°F 10°F 0°F prior to cooling/freezing; pre-cooling product; and crust-freeze product using 0.000 a cryogenic fluid prior to finish-freezing –20 –10 0 10 20 30 40 50 60 Dry-Bulb Temperature (°F) with a mechanical freezing system (flash freezing will create a crust on the product Figure 4: Psychrometric chart showing process lines for a lower dock set temperature to surface to minimize desiccation). Tech- improve favorability of the freezer coil frosting condition. niques to reduce moisture loss have the added benefit of increasing product yield. Yield savings almost ing systems, the extent of unfavorable frost conditions can be certainly will far outweigh energy cost benefits from reduced minimized but not eliminated. moisture loads on evaporators. For many low-temperature freezFor spaces such as holding freezers, one common approach Humidity Ratio www.info.hotims.com/23932-8 30 ASHRAE Journal February 2009 http://www.digi-cool.com http://www.digi-cool.com http://www.info.hotims.com/23932-8
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