Refrigerations Design Rules of the thumbs:

1. A ton of refrigeration is the removal of 12,000 Btu/hr of heat.
2. At various temperature levels: 0―50˚F, chilled brine and glycol solutions; ― 50-40˚F, ammonia, freons, butane; ―150―50˚F, ethane or propane.
3. Compression refrigeration with 100˚F condenser requires these HP/ton at various temperature levels: 1.24 at 20˚F; 1.75 at 0˚F, 3.1 at ―40˚F; 5.2 at ―80˚F.
4. Below -80°F, cascades of two or three refrigerants are used.
5. In a single stage compression, economy is improved with interstage flashing and recycling, so-called reconomiser operation.
6. Absorption refrigeration (ammonia to -30°F, lithium bromide to +45°F) is economical when waste steam is available at 12 psig or so.