25 May 2005
Figure 5-3. Chillers
Closed Brine Systems. Closed brine systems are chilled water systems
in which calcium chloride, sodium chloride, or a mixture of sodium chloride and calcium
chloride has been added to the water to lower its freezing point sufficiently to maintain it
as a liquid (ice-free) at temperatures of -1 to 10 C (30 to 50 F). Brine systems have
been largely replaced by glycol systems.
Closed Glycol Systems. Closed glycol systems are chilled water systems
that contain a mixture of water and glycol (ethylene or propylene) that will not freeze at
the system operating temperature of -7 to 2 C (20 to 35 F).
Combined Hot and Chilled Water Systems. Some closed systems serve
the dual purpose of producing circulating hot water during the cold season and chilled
water during the hot season.
Diesel Engine Jacket Cooling Systems. Diesel engine cooling systems
are considered closed systems, even when surge tanks are open to the atmosphere.
The heat transfer from the circulating water is usually accomplished using a heat
exchanger, not by evaporation. These systems have low water losses. Several of the
metals used in these systems require good corrosion control. The three basic types of
diesel engine cooling systems are described below.
Air-Cooled Diesel Cooling Systems. Air-cooled diesel cooling systems
are used on most small engines as well as some large engines. The jacket water is
circulated through an air-cooled radiator. Antifreeze must be used in these systems
when radiators are exposed to low-temperature atmospheric air or when the water
temperature exceeds the boiling point (100 C [212 F]).