TABLE OF CONTENTS A secondary coolant is the fluid chilled by the primary refrigeration system that then performs the refrigeration by absorbing heat through its rise in temperature. A secondary coolant could conceivably undergo a change in phase, condensing at the primary refrigeration system and boiling at the point of refrigeration load. In the pre-CFC era, R-11 was sometimes used for-that purpose, and CO 2 continues to serve in this manner. The scope in this chapter will be restricted, however, to fluids that remain in the liquid phase and thus change temperature to accomplish heat transfer.
The terms secondary coolants, brines, and antifreezes are sometimes used interchangeably. This chapter will use secondary coolant as the general description of a fluid with freezing temperatures below those of water. Brines are one class of secondary coolants formed by the aqueous (with water) solution of a salt.
Secondary coolants have been used for years, and the number of applications seems to be growing rather than declining. Despite the cost penalties for pumping the secondary coolant and the lower evaporating temperature required to overcome the additional temperature differences due to the interposition of an extra fluid, some recent trends maintain the importance of secondary coolants. In the case of ammonia, the refrigerant charge can be contained in a compact chiller, and a leak in the distribution system will not cause damage to stored refrigerated products. The use of secondary coolants in ammonia systems supports the trend to low-refrigerant-charge systems. In the...
