What is an Industrial Chiller?
Industrial chillers are refrigeration systems that removes heat from a process fluid or dehumidifies air in commercial and industrial facilities. The chiller will use either a vapour compression or absorption cycle to cool the water. Chilled water circulation has various applications from space cooling to process oriented applications.
Types of Industrial Chillers
- (1) Air-Cooled
- (2) Water-Cooled
A chiller is rated between one to 1000 tons of cooling energy. There are two different types of chillers:
Components of an Industrial Chiller
- (1) Evaporator
- (2) Compressor
- (3) Condenser
- (4) Expansion valve
The mechanical compression cycle has four basic components through which the refrigerant passes:
The evaporator in the chiller will operate at a lower pressure and lower temperature than the condenser.
How an Industrial Chiller Works:
First, the condenser brings the high pressure vapour to a saturated condition (de-superheated). Enough heat must be transferred from the refrigerant to lower its temperature to the saturation temperature. At this point, condensation begins. As heat continues to be transferred from the refrigerant vapour to the air (or water, if it is a water cooled chiller), the quality of the refrigerant (% of the refrigerant in the vapour state) will continue to decrease, until the refrigerant has been completely condensed. In an ideal system, this occurs at the outlet of the condenser. In the real world, some subcooling would be expected at the condenser outlet. Subcooled liquid provides insurance against liquid flashing as the refrigerant experiences pressure losses in the tubing and components.
The refrigerant is in the liquid state now, and at a high pressure and temperature. It must undergo one more change before it becomes a useful heat transfer medium; a reduction in temperature. This is accomplished by reducing the pressure. You can count on the refrigerant’s pressure – temperature relationship to be an infallible law. If the pressure of a saturated liquid is reduced, the law governing its existence requires it to assume the saturation temperature at the new pressure.So, in order to reduce the temperature, the pressure has to be reduced, and some sort of restriction is required for this to occur. It would be preferable if the restriction could regulate itself as the system load demands change. This is exactly what the thermostatic expansion valve does; it is an adjustable restriction which causes a reduction in liquid refrigerant pressure, yet will modulate in an effort to maintain constant superheat at the evaporator outlet. The thermostatic expansion valve is a superheat control, and will not maintain a constant vapour pressure. It only provides the restriction necessary to reduce the pressure to some level, which will be determined by compressor size, thermostatic expansion valve, size load, load demand and system conditions. If a constant evaporator temperature is required, it can be achieved very simply by maintaining the pressure corresponding to the saturation temperature required. This is accomplished by adding an evaporator pressure regulating valve to the system.
Our ideal cycle has experienced a pressure drop in the thermostatic expansion valve. Subcooling or superheat cannot exist where there is a mixture of liquid and vapour. Therefore any place in the system where the refrigerant exists in two states, it will be at the saturation temperature for its pressure.
Some of the liquid refrigerant is required to boil as a means of removing the heat necessary to achieve this lower temperature. Yet another heat transfer process, which yields a lower liquid temperature. The liquid that is sacrificed in the boiling process explains the increase in refrigerant quality. The greater the difference between the liquid temperature and evaporator temperature, the more liquid will have to be boiled in order to achieve the new saturation temperature. This results in an even higher refrigerant quality.
The final portion of the refrigerant’s journey is as a mixture of saturated liquid and vapor, traveling through the evaporator tubing. Warm air is blown across the evaporator, where its heat content is transferred to the boiling refrigerant. This is a latent heat gain to the refrigerant, causing no temperature increase, while experiencing a change of state. In the ideal cycle, the last molecule of saturated liquid boils off at the evaporator outlet, which is connected to the compressor inlet. Hence, the vapor at the inlet of the compressor is saturated. The cycle continues this way until the refrigerated space temperature is satisfied, and the equipment cycles off. (Information from Sporlan, Inc.
Evaporators in Industrial Chillers
Shell & Tube Evaporators: Typically configured with the refrigerant flowing through the tube side and the process fluid through the shell side of the unit. Tube construction can be copper, cupronickel, or stainless steel. Shell construction can be cast iron, brass, cupronickel, or stainless steel. This style of evaporator has lower pressure drops than Brazed Plate technology and is available up to 500 tons in standard construction
Brazed Plate Evaporators: Cooling Technology, Inc was one of the first in the United States to utilize this innovative design in heat transfer. The major advantages of this technology are the supreme efficiency that is achieved, lower costs, and 316L stainless steel or copper construction. This style is available from fractional tonnages to 140 tons
Compressor Types in Industrial Chillers
Reciprocating Compressor: A reciprocating compressor is a compressor that uses pistons driven by a crankshaft. It is used for delivering a small amount of refrigerant at a very high pressure. Reciprocating compressors may carry a dual voltage and range from three to sixty horsepower. Reciprocating compressors are usually semi – hermetic compressors, which simply means that they are serviceable.Centrifugal Compressor: Centrifugal compressors have few moving parts which make them a favorite in the industry. They are also very energy efficient and give a higher refrigerant flow than a similarly sized reciprocating compressor. Centrifugal compressors are more suited to higher volume but low pressure applications, such as those that use ventilation fans, cooling units, and air movers. The centrifugal compressor operates by using the centrifugal force applied to an air mass to achieve compression. Typical capacities range from sixty to several hundred tons. These are hermetically sealed, magnetic bearing compressors and are 230 volts OR 460 volts.
Screw Compressor: The screw compressor is almost exactly as it sounds. There are two screws (male & female) in a screw compressor that are fitted together in stationary housing. As the rotors rotate, the gas is compressed by direct volume reduction between the two rotors. These compressors are also semi – hermetically sealed compressors, carry a dual voltage, and range from 40 – 1000 horsepower. There are also single screw compressors which rely on a single rotating screw passing through two star wheels to provide the compression.
Location of Industrial Chillers
Large industrial chillers are commonly located in mechanical equipment rooms within the building close to the process in which they are cooling. Some industrial chillers may be located directly beside the process, depending on the size of the chiller and compressor. Some may even be placed completely outdoors.
Applications: What Can A Chiller Be Used For?
As one can imagine chillers are extremely important in the industrial world where there are literally millions of machines that generate a lot of heat. If these machines are to last any time at all, they need to be cooled. This is where chillers come in. A chiller can be used to cool any machine or process that operates at 60° F or lower. A cooling tower can be used to cool any machine or process that operates at 85° F or higher. Some of the more common applications are listed below:Read More....