A chiller is a device that removes heat from a liquid, usually water, through a vapor compression or absorption refrigeration cycle. Chillers are used to cool air and water in a variety of areas, such as large industrial sites, commercial facilities, and even institutional buildings. These machines can also utilize their heat rejection to warm water supplies where necessary, such as in Canada’s cold climate. This article will provide some basic information on how chillers work, and the process by which vapor compression cools water.
Vapor compression chillers compose the four major aspects of the vapor compression refrigeration cycle, meaning that they have a compressor , an evaporator, a condenser, and a metering device. A chiller can cool a very large building or complex, and can make use of cooling towers to increase their effectiveness. There are four types of compressors used in vapor compression in water chillers – reciprocating compression, scroll compression, screw-driven compression, and centrifugal compression are mechanical compression types. Let’s take a look at how these various types of compressors work.
Centrifugal compressors , sometimes called radial compressors , work by achieving pressure by adding velocity to a continuous flow of fluid (in the case of chillers this is generally water) through a rotor. This slows the flow of fluid through a diffuser, thus increasing the static pressure. They have several advantages, such as fewer rubbing parts (thus cutting down on maintenance), energy efficiency, and a high efficiency. Reciprocating compressors are compressors that use pistons driven by a crankshaft to create pressure. Intake enters a suction manifold, and then flows into a compression cylinder to be compressed by pistons moving in a reciprocating motion, and is then discharged.
Another popular type of vapor compression in chillers is the scroll compressor , often called a spiral compressor , a scroll pump, or a scroll vacuum pump. The concept of a scroll compressor can be a little difficult to explain, but imagine two spirals, one set inside the other, spiraling in the same direction but twisted so that the tail of one spiral is opposite the other. If both spirals are going clockwise, then the inner spiral will also move clockwise, thus pushing fluid towards the center of the spiral. Rotary screw compressors work in much the same fashion as screw pumps, using a screwing motion to push fluid towards a single point, without giving it the chance to go back out the other way.
