TABLE OF CONTENTS Cold-air distribution systems commonly use ice storage systems or nonstorage plants as the source of cooling. These systems distribute chilled water or a secondary coolant to remote air-handling units. However, cold-air distribution is also applied with packaged or built-up direct refrigeration air-handling equipment, in which the cooling coil is the evaporator for the refrigeration system.
A chiller or ice storage cooling plant must be selected to provide the coolant temperatures required to generate the desired supply air temperature. The required coolant temperature is determined by the performance characteristics of the cooling coils. A useful rule of thumb for preliminary analysis is that the supply air can be cooled to within 6 F (3 C) of the fluid temperature entering the coil. For example, for a 45 F (7 C) coil discharge air temperature, a fluid temperature of about 39 F (4 C) will be required.
Chilled-water storage systems storing water at 40 F (4 C) can produce supply air temperatures of 46 F to 50 F (8 C to 10 C). By using additives to lower the maximum density point and freezing point of water, stratified chilled-water storage systems may be able to store fluid at temperatures as low as 30 F (-1 C), allowing them to generate the same low air temperatures as ice systems.
Cold-air distribution systems with fluid supply temperatures of less than 40 F (4 C) may require increased insulation on pipes. Typically, the standard insulation thickness is increased by 0.5 in. (13 mm). Section 4.6.2 discusses determination of the appropriate insulation thickness to prevent condensation on ducts. The...
