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| Water Vapor Transmission | The rate of water vapor flow expressed in grains/h-ft.2. A pound contains 7,000 grains, or a gram is equal to 15.43 grains. |
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| Permeance | The water vapor transmission of a material under unit vapor pressure difference between two specific surfaces. The unit of permeance is the perm which is equal to grains/h-ft.2-in. Hg. One square foot of a material with a rating of 0.1 perm will transmit approximately 2 fluid ounces of water in one year. |
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| Permeability | The water vapor transmission of a homogeneous material under unit vapor pressure between two specific surfaces, per unit thickness. The unit is perm-inch which is equal to grains-in./h-ft.2-in. Hg. Permeability is the permeance of unit thickness of a material. |
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| Refrigeration, ton of | The removal of heat at a rate of 12,000 Btu per hr. This figure is obtained from the commercial unit of refrigerating capacity which is the heat required to melt 2,000 lb. of pure ice to water at 32°F in 24 hours. The latent heat of ice is 144 Btu per lb. Therefore, a ton of refrigeration is 144 x 2,000: 288,000 Btu per 24 hr. or 12,000 Btu per hr. |
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| Cooler | In cold-storage practice, an insulated room maintained at 30°F or above. |
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| Freezer | In cold-storage practice, an insulated room where the temperature is kept below 30°F. |
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| Sharp Freezer | In cold-storage practice, a freezer room generally operating at -10°F or lower. |
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