The selection of hot and chilled water coils will have a substantial impact on the fan energy use.
Traditional AHU design specifies coil sizes assuming a face velocity of between 400 and 500 feet per minute. A new design technique called low face velocity, high coolant velocity or LFV/HCV has been researched at the University of Adelaide, Australia. This technique uses a "thin" coil design that is roughly half the number of tubes in depth as in conventional designs but double the coil face area. The net result is a face velocity in the range of 150 to 200 feet per minute (FPM) with much higher heat transfer efficiency and lower pressure drop than in conventional designs. Because the coil's pressure loss is proportional to the velocity at a square rate, face velocity reduction can result in pressure drops of one-fourth or less compared to the equivalent, traditionally designed coil. [Micro-Electronics Facility Efficiency Workshop, 1995]
A preheat coil is commonly used to control condensation inside the HVAC system for laboratories that use 100 percent outside air or when the outside air temperature falls below freezing. If a heating coil is used downstream, the preheat coil should become inactive to save energy when outdoor temperatures reach 45 degrees F. Preheat coils are also used to warm the outside air stream, assuring better air stream mixing and providing free humidification. [Suhail, 1989]
