Types of Scroll Refrigeration System

Types of Scroll Refrigeration System Points : Types of Scroll Refrigeration System, Air cooled, scroll DX cooler, Air cooled, scroll heat pumps, Scroll chillers, AIR COLLED, SCROLL DX COLLER As in the reciprocating system, the currently used scroll refrigeration systems for air conditioning are mainly for small to medium-size system (packaged units & heat pumps) with a cooling capacity often btw slightly less than 1 ton & 25 tons (3.5 & 90 kw) used in light commercial, industrial & residential buildings, these include the following:
• Air cooled, scroll DX cooler
• Air cooled, scroll heat pumps
• Scroll chillers AIR COLLED, SCROLL DX COLLER It consist of two scroll compressors, an air cooled condenser two DX coils, & two thermostatic expansion valve. A scroll refrigeration system has almost the same refrigerant piping & safety controls as the reciprocating system except there is no crankcase heater.

Scroll Compressor A scroll compressor consists of two identical spiral scroll mated face to face; each scroll is bound on one side to a flat plate the upper scroll is stationary & contains the discharge port the lower one moves in an orbit around the shaft center of the motor at an amplitude equal to the orbit radius the two scrolls are fitted together to form vapor pockets b/w their respective base plate & lines of contacts of their vane walls, during suction, vapor ; refrigerant enters the space b/w the two scrolls through he lateral openings. The openings are then sealed off to form trapped vapor pocket, thus completing the intake process.

During the successive revolutions of the motor shaft, the volume of the trapped vapor pockets is reduced, and the compression process is complete when the gaseous refrigerant is compressed to its maximum pressures & just before the compressed gaseous pocket is deepened to the discharge port, during discharge, the trapped gas pockets opens to the discharge ports all compressed hot gas is discharge, through the discharge port to the discharge line. The volume of the gas pockets is reduced to zero. The sequence of intake, compression & discharge occurs simultaneously in the two trapped gas pockets. Scroll Chillers Scroll chillers are often available with a cooling capacity of 10 to 60 tons (35 to 210 kw), they are gradually replacing reciprocating chillers. Scroll chillers can again be divided into air cooled scroll chillers & water cooled scroll chillers.

Air Cooled Scroll Chillers An air-cooled scroll chiller consists of mainly an air cooled condenser, two or more scroll compressors, a single or dual refrigerant circuit, a thermostatic expansion valve, a distributor, a direct expansion liquid cooled &controls. A direct-expansion liquid cooler can be easily connected to dual refrigerant circuits, & multiple — compressors.

An air cooled scroll chiller always has a microprocessor based control of the chilled water temperature leaving liquid cooler. There are usually two capacity control steps for small air cooled scroll chillers & four capacity steps for large scroll chillers. Water Cooled Scroll Chillers A water cooled scroll chiller is similar in construction & control to an air cooled scroll chiller except that a shell & tube water cooled condenser is used instead, of an air cooled condenser. A water cooled scroll chiller is usually located in machinery room, of the air conditioning building. Capacity Control There are two types of capacity variable speed & variable- displacement compressors. In a variable- speed scroll compressor a variable speed drive is used to reduce the speed at part load operation so that the cooling capacity is reduce to meet the reduce system load. The operating frequency often varies, from 15 to 150 Hz. in a variable —displacement scroll compressor; there are poring boles in the fixed scroll. By connecting or disconnecting the compression chamber to the Suction side through the closing & opening of the porting holes, the cooling capacity of the scroll compressor is varied, if all porting holes are closed, the compressor is operating at full capacity.