How does a water-cooled scroll chiller work
Chiller: function, scheme, manufacturer & costs
The cold water set (also chiller, cold set, liquid chiller or liquid cooler) lowers the temperature of water in order to cool rooms, large halls or technical processes with process cooling. It is mainly used in trade and industry and is available in different performance classes. The way it works is based on the same principle as that of a refrigerator or a heat pump. In the following sections we explain how a water chiller works in detail, how the devices are constructed and what needs to be considered during planning, installation and maintenance. In addition, we show the most important areas of application for the chillers.
The topics at a glance
What is a water chiller and what does it do?
The water chiller is a technical device that cools down liquids. Typical is the connection to a water circuit in which 6 to 7 degrees Celsius cold water circulates driven by a pump. It absorbs heat from rooms or processes and flows back to the chiller at higher temperatures. This dissipates the heat carried along in order to cool the water down again.
The temperature determines the refrigerant
Depending on the desired temperatures, the liquid in the cooling circuit can also be mixed with an antifreeze. Glycol and ammonia are used, among other things. These media lower the freezing point and ensure that the coolant can flow through the system at temperatures below 0 degrees Celsius without icing up. Ammonia refrigeration systems are used particularly in the industrial sector, as they can provide high outputs very efficiently. A special low-temperature water chiller is used for particularly low temperatures. These reach up to -45 degrees Celsius.
Definition: water chiller and refrigeration unit
Various terms and definitions for the water chiller can be found in technology today. For example, DIN EN 378 describes the refrigeration unit as a fully assembled refrigeration system. This is located in a sturdy frame or housing so that it can be transported in one part or in several individual parts. The refrigerant-carrying parts are pre-assembled at the factory, which means that installation on site can be carried out relatively easily, quickly and safely.
Chiller, liquid chiller, liquid chiller and other terms
While the term “water chiller” is familiar to many experts, there are numerous other names for the same device. Terms such as “chiller” or “liquid cooler” are widespread. But also "water chiller", "liquid chiller" or "cold water generator" refer to the same device.
The exact designation requires further information
Since there are many different types and sizes of water chillers today, further information is required for a precise designation. For example, the attributes “air-cooled” or “water-cooled” describe the way in which the cooling device releases the absorbed heat to the environment. Information about the type of compressor is also of interest.
Turbo cold water set particularly powerful
If it is a turbo chiller, it is equipped with a particularly powerful turbo compressor, which means that the possible cooling capacity is very high. The latter can typically be easily identified and at least roughly classified using terms such as Mini, XL or XXL. Because it is already clear at first glance that mini chillers have very low capacities, while XXL chillers are suitable for large systems and cooling loads.
Basis: Carnot process for the chiller function
Nicolas Léonard Sadi Carnot laid the foundation for the water chiller function as early as 1824. Because he designed the so-called Carnot process, which describes the ideal principle of technology. The cycle process is made up of four processes, which can be shown, for example, in a pV diagram (pressure - volume).
- Step 1: A working medium absorbs heat from the environment and expands isothermally (the volume increases at the same temperature).
- Step 2: A compressor compresses the working medium adiabatically (without heat exchange with its surroundings), which increases its temperature.
- Step 3: The working medium gives off heat to its surroundings, whereby its temperature remains constant.
- Step 4: A working medium expands almost suddenly. It expands adiabatically (without heat exchange with the environment), whereby the temperature of the medium drops to the initial state.
By the way: The Carnot process also takes place in a heat pump. However, the benefits are different here: While the chiller is supposed to dissipate thermal energy from the inside to the outside, the heat pump makes heat from the outside usable for heating.
Chiller: structure and function of the cooling units
Regardless of its performance, a water chiller basically consists of four components. These enable the practical implementation of the theoretical circle or Carnot process. Just like with a heat pump, the following components are required:
- the evaporator
- the compressor
- the condenser
- the expansion valve
Function simply explained
The function of a water chiller can be explained quite simply. At the evaporator (a heat exchanger), heated water from the connected cooling circuit meets the refrigerant. The substances do not mix - but transfer heat from the higher to the lower temperature level. As this happens, the coolant cools down. The refrigerant absorbs the thermal energy and evaporates at the same time. In the gaseous state of aggregation, it then flows to a compressor, which increases the temperature of the medium with the pressure.
Heat transfer to ambient air
When the hot refrigerant vapor emerges from the compressor, it flows to the condenser. This is a second heat exchanger that transfers the energy of the refrigerant vapor to another system (for example the ambient air). The refrigerant gives off heat and then flows to an expansion or relief valve. Here it expands suddenly, with the temperature returning to its original state. The medium changes into the liquid state of aggregation and the process starts all over again. The following diagram shows the principle of the function again graphically.
Chiller: refrigerants enable the special functionality
Refrigerants are used to ensure that the water cooler works. These are substances with special properties. Among other things, they have a low vapor volume, a low condensing pressure and a high chemical stability. Which medium is suitable depends, among other things, on the performance of the water chiller and the temperature conditions at the place of use.
Basically, a wide variety of refrigerants are available today. These can be identified with simple identification, which in the case of organic refrigerants is made up of the letter "R" and three digits. The numbers stand for:
- Digit: number of carbon atoms minus 1
- Digit: number of hydrogen atoms plus 1
- Digit: number of fluorine atoms
Inorganic refrigerants, on the other hand, can be recognized by a “7” as the first digit. The other numbers stand for the molar mass of the substances. In order to be able to differentiate media with the same molar mass, letters can be appended (a, b, c, etc.).
The following table provides an overview of the chiller refrigerants and their properties (selection).
It is important to know that many fluorinated refrigerants need to be replaced to protect the environment. The deadline ends in 2030 and applies to the previously common substances R134a, R404A, R507, R407C and R410A.
Evaporator and condenser on the chiller: heat exchanger
Evaporator and condenser are the names of the two heat exchangers in the chiller. They have the task of absorbing heat from the cooling circuit (water or brine) and later transferring it to another system. The two processes take place with material separation. That means: refrigerant from the inside of the chiller never comes into contact with other media. It is not used up and usually does not have to be topped up.
Compressors increase the temperature of the refrigerant with the pressure
Compressors have a particularly important task for the chiller function: They absorb the vaporous refrigerant and increase the pressure through compression. As this happens, the temperature of the medium also rises. This step is necessary because heat naturally only flows from the higher to the lower temperature level. In order to be able to transfer the thermal energy from the water cooler to another system, the refrigerant temperature must always be above the ambient temperature. The type of compressor has a decisive influence on the chiller performance, as the following table shows.
If the water chiller has to achieve a very large pressure difference between liquefaction and evaporation (for example a low-temperature water chiller), special systems are required. One example of this is booster operation, in which two compressors work one after the other. In addition, the two-stage arrangement of the refrigerant circuit is also possible. Two compressors are used, each of which works in its own circuit.
Expansion valve returns refrigerant to its original state
The expansion valve is particularly important for the functional principle of the chillers. Because it ensures that the pressure of the refrigerant drops after the condenser and the medium assumes the liquid state of aggregation. In addition, the component also ensures a continuous and needs-based supply of refrigerant to the evaporator. There are basically two types of construction used: thermostatic and electrical expansion valves. Thermostatic expansion valves (TEV) work without auxiliary energy. When it comes to the optimal control of efficient refrigeration systems, on the other hand, electrical expansion valves (EEV) are used.
Lubricating oils in the refrigerant circuit of the chillers
Oil ensures that all moving parts in the refrigerant circuit are adequately lubricated. They must have a favorable viscosity and are important for a long service life of the refrigeration systems. Which lubricating oils can be used in a system depends on the information provided by the compressor manufacturer.
Pipelines for the circulation of refrigerant in the circuit
All components of the water cooler are connected to one another via pipes. The chiller piping is usually made of copper in accordance with DIN EN 12735. It is important to know that the pipes from nominal size DN 32 are subject to the Pressure Equipment Directive and must therefore meet special requirements.
Pay attention to pressure losses
When it comes to planning, experts have to pay attention to a low pressure loss. It is crucial to design the piping as small as possible and as large as necessary. Only with this approach can an optimal compromise between low operating costs (low pressure loss) and low system costs (small pipelines and lower refrigerant charge) be achieved.
Avoid connecting pieces
During installation, care must also be taken to reduce the detachable connections in the system to a minimum in order to reduce the risk of leakage. The same goal is pursued by a pressure test that must be carried out after the system has been completed and filled.
Types of water chillers: air-cooled, water-cooled, split systems
Depending on the way in which a chiller gives off heat to the environment, different types can be distinguished from one another. The water chiller is available air-cooled, water-cooled or as a so-called split device.
Air-cooled water chiller: heat dissipation via fans
Air-cooled water chillers are equipped with fans. The latter direct ambient air over the condenser, which causes the refrigerant to give off heat. If a water chiller is air-cooled, it is not suitable for indoor installation. The devices are compact, reliable and can usually be set up outside or connected to an air duct network.
Water-cooled water chiller: Flexible heat dissipation to the environment
If the water chiller is water-cooled, the condenser is also connected to a cooling water circuit. This allows water to circulate between the cooling device and a source of cold water. For the latter, various dry coolers are used, which can also be set up away from the air conditioning unit. There are compact wall-mounted water chillers that can stand and work directly in the technical room.
Split water chiller: components divided between outdoor and indoor units
The third type are split devices. In these, the water chiller consists of an indoor unit and an outdoor unit. The indoor unit contains, for example, the evaporator, the compressor and the expansion valve. The outdoor unit, on the other hand, contains the condenser and is the only component installed outdoors (for example on the roof).
The heat is absorbed in the object
The refrigeration technology in the house absorbs the heat from the cooling water. It then raises the temperature level so that the outdoor unit can give off heat to the environment. Both components are connected with refrigerant lines and should be viewed as a whole. Split units can also be found in other areas of refrigeration technology. For example with home air conditioners. Here, the indoor unit (direct evaporator) is usually designed as a ceiling unit or ceiling cassette or wall unit and connected to the outdoor unit via refrigerant lines.
Low temperature water chiller
Cryogenic water chillers, also known as ultra low temp chillers, can, as the name suggests, reach lower temperatures than normal water chillers. Low-temperature water chillers reach temperatures as low as minus 45 degrees Celsius. There are different levels - 5 degrees Celsius, minus 25 degrees Celsius and then the even more complex water chillers that can reach minus 40 - minus 45 degrees. These devices are then equipped with special refrigerants such as the refrigerant R449.
Areas of application of the low-temperature water chiller
These low temperatures are often required for test procedures and test procedures in the automotive, chemical and pharmaceutical industries. For example, to cool vaccines. But these devices are also used to freeze food in large food stores.
Direct evaporator and free cooling: alternative modes of operation
The water chiller uses a cooling water circuit in order to be able to dissipate thermal energy from a room or process. If the air conditioner works with a direct evaporator, this can transfer heat directly to the refrigerant. This works without glycol or water as a heat transfer medium, requires no additional piping and enables more energy-efficient operation. However, devices with direct evaporators (e.g. split air conditioning systems) are not suitable for every area of application. For example, the distance between the individual components is limited. The cooling water network gives water coolers greater freedom in system planning. In addition, various heat exchangers are used in the room (ceiling cassette, wall unit, cooling ceiling).
Free cooling as an alternative
With free cooling, the water chiller works without a condenser and compressor. Because the heat to be dissipated can be transferred directly to the environment without any technical steps. This is possible, for example, when the outside temperatures are very low in winter.
Cooling circuit: structure and functionality simply explained
The cooling circuit works in the same way as a heating circuit. A pump sends cold water through pipes to various heat exchangers. The latter absorb thermal energy from rooms or processes so that the cooling water can transport it to the water chiller. While process heat exchangers can be integrated into the technical devices, the cooling water can also flow through a cooling ceiling or through the heat exchanger of a ventilation system.
Store cold in the buffer
As with heating systems, it is also possible to store cold water in a cold storage tank. In this way, chillers in particular can be operated evenly for a long time without an inverter. The cold water is then available to rooms or processes from the buffer tank as required.
It is important to know that the cooling unit must always have a constant flow of cooling water. An overflow valve upstream of the chiller can ensure this.
Increase the efficiency of the water chiller
The chiller efficiency (EER or Energy-Efficiency-Ratio) can be determined from the ratio of the cooling capacity to the electrical compressor capacity. A high amount stands for low power consumption with high cooling capacity at the same time. Basically, the efficiency decreases with increasing difference between the cooling and ambient temperature. Because then the compressor has to do more to achieve the desired effects.
EER considers full load
The disadvantage is that the EER assessment takes the full load case into account. However, since chillers do not perform at full capacity for a long time in the year, the ESEER rating (European Seasonal Energy Efficiency Ratio) is more informative when it comes to efficiency. Because this key figure takes into account the chiller efficiency in different operating levels.
Calculate the design correctly
In order to optimize the efficiency of the water cooler, it is first of all a question of a precisely fitting design. The water chiller can only work efficiently and economically if all components are coordinated with one another, with the refrigerant used and with the location of use. Measures such as the installation of inverter motors or heat exchangers always have a supportive effect.
Inverter motors can be regulated and are particularly efficient
Inverter motors are used in many areas of our life, such as washing machines or heat pumps. They use a frequency converter to precisely regulate the motor power. In the chiller, the inverter ensures that the compressor always works as required. This saves energy and ensures that the system operates more quietly.
Chiller heat recovery
In order to save energy and increase the efficiency of the cooling devices, the water chiller can be used with heat recovery. Manufacturers install a heat exchanger between the compressor and condenser. In this way, the heat carried along by the refrigerant can be used, for example, to heat water or to support the heating system. The following graphic shows a principle diagram of the technology.
Chiller services at a glance
The 100kW water chiller is most popular, followed closely by the small 5kW system. The bestseller in third place is the chiller with 200kW power. Here you will find the typical product overview of the chillers:
Chiller: planning, installation and maintenance
When it comes to the design of a chiller, the individual prerequisites and requirements must first be determined. Important parameters and properties are:
- Temperature and humidity conditions (including evaporation temperature and chiller flow temperature)
- Thermal loads such as the electrical connected load
- Humidity loads from people and material flows
- Simultaneous cooling and moisture loads
- Regulation accuracy
- permissible frequency of exceeding the temperature
If the above information is available, specialist planners can calculate the water chiller. An essential part of the design is the cooling load calculation according to VDI 2078. This enables a simulation of the seasonal cooling loads and is therefore the basis for calculating the performance.
Design components with cooling load calculation
Once the latter has been established, the components of the refrigeration technology can be designed and optimally coordinated with one another. Here, experts also define the chiller flow temperature and the spread of the cold water network, among other things. An individual and needs-based chiller planning is particularly important in order to be able to guarantee efficient and economical operation.
Integration into the building architecture
If the characteristic values of the cooling technology are known, it is a matter of integrating the system into the existing or planned building architecture. This is followed by the invitation to tender and the awarding of the construction work before the specialist planners get into the detailed and assembly planning. Once this is done, the skilled tradesman will install the water chiller. They ensure the professional connection to the cold water network and put the entire system into operation. A chiller is checked and the entire system is handed over to the end customer. The latter receives a detailed briefing on how to operate the technology and react quickly to malfunctions.
The following overview shows the flow of chiller planning step by step:
- Create and review requirements profile
- Determine cooling requirement (according to VDI 2078)
- System design and building integration
- Calculate the components of the water chiller
- Attachment to tender and award of contract
- Plan assembly and implement projects
- Commission and adjust the system
- Instruct the user and hand over the technology
- Operation and regular chiller maintenance
Setting up the water chiller: These points must be observed
Chillers can basically be set up indoors and outdoors. Experts should install the devices on vibration and noise-insulating surfaces and use flexible pipes when connecting the water chiller. Both help to reduce sound transmission and significantly increase the comfort of the system. Cladding on the walls, ceilings and floors of the installation rooms in the building also have a supportive effect. Depending on the installation location and the type of refrigerant, there are also different requirements for the installation of the refrigeration technology.
The following points must be observed when installing outdoors:
- In the event of leaks, refrigerant must not enter the ventilation or door opening.
- The requirements for water protection (Water Management Act WHG) must be taken into account (shutdown in the event of leakage, fill level monitoring, oil and glycol collecting pan, gas sensors, double pipes)
The following points, among other things, must be observed in specially set up engine rooms:
- The machine room must be protected from unauthorized access.
- Refrigerant must not be able to penetrate into openings or other rooms.
- In emergencies, it must be possible to leave the engine room quickly (at least one emergency exit).
- Walls, floors and ceilings must be tight and fire-resistant.
- It must be possible to switch off the water chiller from outside
- There must be mechanical ventilation.
- Sufficient space must be available for installation and maintenance of the chiller.
Installation in common rooms is only permitted if:
- the amount of refrigerant is limited to a permissible value.
- How high this is depends on the refrigerant, the type of room (general installation area, monitored installation area, areas only accessible to authorized persons) and its size.
In addition, there are special requirements for water chillers with ammonia, as the natural refrigerant is highly toxic:
- Outdoor installation is preferable for air-cooled condensers.
- Without a machine room, no more than 50 kg of ammonia may be in the system.
- Installation of incineration systems and compressed air systems in the same room is not permitted.
- Only authorized persons are allowed to access the water chiller.
- If there is a leak, the machine room air must be conducted outside without risk (alternative: recirculation system with absorber).
Commissioning and documentation of the systems
The professional commissioning of the chiller is only permitted if the operator has the most important documents. This includes the declaration of conformity as well as an operating manual from the system manufacturer and a specialist contractor's declaration, which contains all the important test certificates.
If these documents are available, the operator creates operating instructions. This contains warnings and information:
- the refrigerant used,
- to the pressure and temperature levels
- on what to do in emergencies,
- for protective equipment
- to first aid services
Before the system can go into operation, a technical expert must fill the water chiller and determine that the entire system is tight. The following documents must also be put together in a folder for the system documentation:
- As-built drawings (floor plans, hydraulic scheme, etc.)
- Functional descriptions of the refrigeration system
- Operating instructions from the manufacturer
- Data sheets for the most important system components
- Electrical circuit diagrams and schemes for regulating control schemes
- Test reports for measurements that were carried out during the adjustment
- Target values (overview, list)
- Chiller maintenance plans
- Inspection plans
- Repair instructions and spare parts lists
Chiller maintenance and inspection
Maintenance and inspection must be carried out at regular intervals so that the refrigeration system runs safely and reliably over the entire period of use. Dates and responsible persons can be seen in the system documentation.
Leak test very important
One of the most important tasks is a leak test, which is usually required annually. In addition, the water chiller must be visually inspected at regular intervals (weekly or fortnightly). Trained staff pays attention to obvious damage and compliance with the target values of the refrigeration system. If these are no longer correct, you have to go to troubleshooting in the refrigeration system.
Areas of application in trade and industry
The chiller is available in a wide variety of power ranges. There are smaller systems with a cooling capacity of just a few kilowatts and large systems with a cooling capacity of several hundred kilowatts. While a smaller chiller is suitable for single-family houses with cooling ceilings, laboratories, office or commercial buildings, XXL chillers are used in industry and for cooling large buildings using industrial air conditioning systems.
There are many manufacturers of water chillers. Here you will find an overview of the manufacturers we know:
Advantages and disadvantages of the chillers
The special design of the refrigeration devices now has a number of advantages. The refrigerant charge is comparatively low. Gas and water plumbers can also install systems, as the refrigeration technology was largely pre-assembled by the manufacturer. Another advantage: If systems with direct evaporation can no longer be implemented due to long pipelines, water chillers provide a remedy. Because with cold water networks connected in between, great distances are also possible. The disadvantage, however, is the large amount of space required, which is not always the case, especially when retrofitting a chiller in old buildings.
Frequently asked questions about the water chiller
What is a water chiller?
A water chiller is a device that cools down a liquid. The heat that is extracted from the liquid is mostly given off to the surrounding air. The cold liquid is brought to where it is needed via a cooling circuit and released into the room or the process. The heated liquid flows back and is cooled down again.
How does a water chiller work?
The way a water chiller works is based on the same principle as that of a refrigerator or a heat pump. We explain here how a water chiller works in detail, how the devices are constructed and what needs to be considered during planning, installation and maintenance.
What does a water chiller cost?
That depends on the size and the manufacturer. Chillers are already available for a few thousand euros. There are no upper limits, depending on the complexity of the system. However, when it comes to refrigeration technology in particular, it is important to get good advice. Otherwise, maintenance costs, repair costs and ongoing energy costs can quickly cost you tens of thousands of euros too much.
Refrigeration costs: prices and price lists
Chillers can be planned individually and are available in various performance classes and designs. For this reason it is not possible to provide general price lists. Anyone interested in the technology will receive precisely calculated offers from the manufacturers and suppliers of the chillers alone. There are two fundamentally different contract models, on the one hand you can buy a water chiller or you can rent the water chiller for a certain period of time. In this case, one speaks of rental refrigeration.
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