In this article we will be exploring the various chiller system types. They can be categorised according to: how the condenser is cooled, weather they use vapour compression or absorption and the required chilled water temperature…
News Article No.17
Air Cooled Chiller System Types
This type of chiller uses the ambient air to cool the refrigerant in the condenser. Fans suck the air through the condenser fins and so exchanging heat energy from the refrigerant and into the air. They are particularly popular in the UK due to the low ambient temperatures. They are also used in the Middle East, but the higher ambient means that they run less efficiently. Read more about air cooled chillers
Water Cooled Chiller System Types
This type of chiller uses a shell and tube condenser to remove the heat energy from the refrigerant. The refrigerant condenses from a gas and into a liquid on one side of the tubes. On the other side of the tubes, condenser cooling water is being pumped through and so absorbing latent heat from the refrigerant. The water flows up to a cooling tower where it cascades down through trays and into the sump. In the opposite direction, air is blown up through the cooling tower and so creating the required heat exchange. The cooled condenser water is then pumped back to the chiller. This kind of system is more often used with large capacity chillers. Read more about water cooled chillers
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Vapour compression is the most popular kind of chiller. An electric motor drives a compressor. The refrigerant is then discharged into the condenser where the heat energy is rejected from the refrigerant as it cools down into a liquid. It goes through an expansion valve where it drops in pressure and temperature. Then, the refrigerant goes into the evaporator where it boils off absorbing latent heat from the water being chilled. The refrigerant is then sucked back into the compressor. This is called The Basic Refrigeration Cycle read about it in detail.
HFC chiller refrigerants, such as, R407c were developed to replace refrigerants which contained chlorine. This is because chlorine was found to have caused a hole in the ozone layer. The downside to HFC refrigerants is that they have a high Global Warming Potential. That is to say that when they find their way into the atmosphere due to refrigerant leaks, their heat trapping qualities add to the greenhouse effect.
The photo is of two ammonia chillers with air cooled condensers on top. A steel braided refrigerant charging hose can be seen coming into the foreground of the photo. This refrigerant has a zero global warming potential and so is environmentally friendly. The downside to this refrigerant is that it is highly toxic and corrosive. Therefore, special procedures, equipment and training is required to handle it. Read more about ammonia chillers
Propane didn’t really catch on in the UK due to the higher initial cost of the chiller. It is, however, popular on the continent in countries such as Italy. The downside to this refrigerant is that it is highly flammable. Intrinsically safe equipment is required to handle the refrigerant and so aiding with a spark free environment. Read more about propane chillers
This kind of chiller uses a heat source rather than electricity to drive the cooling process. It employs a chemical reaction between two substances, such as, lithium bromide and water. Read about absorption chillers in detail. This type of chiller is a lot less efficient than vapour compression systems. The coefficient of performance is usually around 0.5, were as with a HFC chiller it is usually upwards of 4. Therefore, they are most often used where there is a surplus of waste heat being produced by a process, such as, in a power station.
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High Temperature Chiller System Types
Laser cutters use a chiller which operates with a high temperature set point of around 25°C. The laser head and the oscillator need to be cooled to a very close deadband of usually around 0.2°C. If there is a problem with the laser chiller, the controls shut the laser cuter down to prevent expensive failures from occurring.
Medium Temperature Chiller System Types
Most chillers operate at this temperature which is used for a variety of applications including…
The Cooling of Buildings
The chilled water set point is usually around 6°C. Large capacity chillers are used which supply chilled water to the building. A plant room is located near to the chillers where a pump discharges into the chillers. The water system pressure is maintained using a pressurisation unit. A different pump is used to supply fan coils around the building. The fans blow air across the chilled coils and so cooling the spaces in the building. This heat exchange warms the chilled water which returns back to the chillers.
The Plastics Industry
Two popular ways of forming plastic are by using: plastic extrusion moulding machines and plastic injection moulding machines. Plastic granules or powder is melted down and forced through a die or into a mould. Chilled water is then used to control the cooling of the newly formed plastic to below its freezing point. Small chillers are used next to each of the plastic forming machines. Alternatively, large, centralised chillers are used to provide chilled water to the whole factory.
Low Temperature Chiller System Types
Breweries are a good example of the use of low temperature chillers. The setpoint is often around -5°C with glycol being added into the water to prevent it from freezing. The water/ glycol solution is pumped around the jackets of stainless steel vats which are used to brew the beer. The fermentation process created by the yeast is temperature critical and so is controlled by the chilled water.
Air Cooled Chiller Maintenance
Industrial Refrigeration Ammonia
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