September 26 2025

Overview of Chiller Options

Introduction

Modern chillers can be equipped with a wide range of optional extras that extend their operating range and improve energy efficiency. Choosing the right options at the selection stage can ensure stable operation of the chiller system under different conditions, reduce operating costs and increase equipment reliability.

Chiller options can be roughly divided into several groups:

compressor starting systems;
means of ensuring operability at low outdoor temperatures;
functional extensions (freecooling, heat pump operation, heat recovery);
design options (built-in or remote hydromodule, economiser);
additional elements (frost protection, inverter fans, monitoring systems, noise protection solutions).

Each of the listed options has a direct impact on the performance of the unit.

If you need help in selecting a chiller for your facility – contact EVROPROM engineers – we will find the optimal solution taking into account your wishes and operational peculiarities.

Compressor starting systems

The compressor starting system determines the level of starting current, dynamic loads on mechanical components and the degree of impact on the electrical network. The following options are used in industrial refrigeration units:

Star/delta starting scheme

When the motor windings are connected in a star pattern, the voltage on each phase is reduced by a factor of √3, which reduces the starting current to 30-40 per cent of the rated current. After motor acceleration, the motor is switched to a delta circuit for full torque. The star/delta arrangement is typical for small and medium capacity compressors where short-term inrush currents are permissible.

Advantages: simplicity of implementation, low cost, high reliability of the circuit.

Disadvantages: sharp current and torque surge during switching, which leads to dynamic loads on the compressor and drive elements.

Soft starter (soft starter)

The soft starter limits the initial current by gradually increasing the voltage across the motor windings. The inrush current is 150-250 % of the rated current, which is significantly lower than direct start. Soft start is recommended for medium and high capacity compressors when it is necessary to reduce peak current loads on the mains supply.

Advantages: reduced mains loads and mechanical shocks to the compressor, increased motor life.

Disadvantages: lack of speed control in operating mode, limitation of functionality to the start-up process only.

Frequency converter (VFD)

The frequency converter ensures compressor start-up with minimum starting current (usually not more than 110-120 % of the nominal current) and allows to regulate the motor speed in the operating mode. This enables the chiller’s performance to be adapted to varying thermal loads and contributes to a higher seasonal energy efficiency ratio (SEER). VFDs are most effective in systems with variable loads and high energy efficiency requirements.

Advantages: minimisation of inrush currents, ability to regulate performance, improved energy efficiency at partial loads.

Disadvantages: higher cost, the need to install filters to compensate for higher harmonics, additional requirements for cooling of power electronics.

Fig. 1 – Variation of starting current at different motor starting systems

Winter starting of the chiller

The operation of chillers at low outside temperatures presents a number of technical challenges, the main one being maintaining the required condensing pressure level. At air temperatures below 10 °C, there is a risk of excessive condensing pressure drop, resulting in unstable operation of the thermostatic expansion valve (TRV), disruption of the liquid refrigerant supply to the evaporator and possible activation of low-pressure protections.

Special technical solutions are used to ensure stable start-up and further operation in winter.

Hot gas bypass (vapour bypass line)

The most common method is to provide a hot steam bypass line from the compressor discharge line to the liquid receiver or condensate line. The addition of superheated vapour to the liquid line allows to maintain the minimum required condensing pressure and liquid temperature upstream of the TRV.

Parameters:

minimum condensing pressure for stable operation of the majority of TRVs – 7…9 bar (depending on the type of refrigerant);
optimum temperature of liquid refrigerant at the inlet to the TRV should exceed the boiling point by 4…6 °C to prevent “charging” of the evaporator with vapour-liquid mixture.

The use of the bypass line ensures stable operation of the chiller at outdoor temperatures down to -15…-20 °C.

Fig.2 – Hot gas bypass line to the line receiver

Fig.3 – Schematic diagram of the hot gas bypass line

Condenser fan speed control

In addition to hot gas bypass, systems for controlling the air flow through the condenser are widely used:

step regulation by switching fans off/on;
step control by means of frequency converters;

When the outside air temperature drops, fan speeds are reduced, which helps to maintain the required condensing pressure. The combined use of fan control and vapour bypass provides the greatest stability.

Compressor crankcase heating

At low outside temperatures, there is an increased risk of refrigerant migration into the compressor crankcase when the compressor is not in operation. Crankcase heaters are used to prevent dilution of the oil with liquid refrigerant. The heating should ensure that the oil temperature is 10-15 K above the suction line temperature.

Range of permissible operating conditions

The technical documentation of the leading manufacturers specifies the minimum outdoor temperatures at which the chiller with the appropriate options can be started up and operated sustainably:

basic version without options – start-up is possible at 10… 12 °C;
with fan speed control – at 0… 5 °C;
with hot steam bypass line and crankcase heating – down to -15…-20 °C;
in special “low ambient kits” (e.g. Johnson Controls or Carrier) – to -25…-30 °C.

Thus, winter start-up of compressors is a complex task, which is solved by a combination of the following measures: maintaining condensing pressure, preventing refrigerant migration and ensuring reliable compressor start-up.

Freecooling option

Freecooling (free cooling) is a mode of operation of the refrigeration system, in which the coolant is partially or completely cooled by the outside air without participation of the refrigeration cycle. This mode is realised by including in the system an additional heat exchanger (dry cooler), operating in parallel or in series with the chiller evaporator.

Operating principle

When the outside air temperature drops below the return temperature of the coolant, part of the heat load can be removed directly through the dry cooler. During transitional periods of the year (autumn, spring) or in winter, it is possible to achieve full cooling capacity without switching on the compressors.

Free-cooling can be realised in two variants:

Parallel scheme – the drycooler operates simultaneously with the chiller. The cooled coolant in the drycooler is mixed with the flow to the evaporator. The compressor is operated at reduced load.

Sequential scheme – the coolant first passes through the drycooler and then, if necessary, is additionally cooled in the evaporator.

Energy effect

The efficiency of free-cooling depends directly on the climatic conditions as well as the operating mode of the chiller. As an example, when operating in the standard mode of 7/ 12 °C:

if the outside temperature is below 8… 10 °C, partial free-cooling is possible;
at temperatures below 1… 2 °C, full free-cooling can be achieved.

Seasonal energy savings in temperate climates can reach 20-35 %. In northern regions with a long cold season, the savings can exceed 50 %.

Design features

Realisation of the free-cooling mode requires:

an additional heat exchanger (dry cooler) with fan cooling;
a system of three-way valves for switching the coolant flow;
hydraulic pipework with the possibility of flow control;
an automation system to control the switching of modes.

Some manufacturers (e.g. Climaveneta, Trane) produce units in monoblock design with integrated free-cooling.

Thus, the availability of the free-cooling option allows to significantly reduce energy consumption in the cold season, but requires analysis of climatic conditions and technological schedule of the object.

Hydromodule: integrated and remote

The hydronic module is an integral part of the refrigeration system and ensures the circulation of the coolant through the chiller evaporator and the consumer system. As a rule, the hydronic module includes circulation pumps, expansion tank, valves and, if necessary, a buffer tank.

Two versions are available from manufacturers:

built-in hydromodule– placed inside the refrigerating machine housing;
remote hydromodule – supplied in a separate unit and mounted on site.

Built-in hydraulic module

The built-in hydronic module is completed at the factory. All components are housed in the chiller casing or in a separate compartment integrated into the frame.

Advantages:

factory assembly and testing – minimising the risks of installation errors;
shorter commissioning times;
compact design and space saving in the machine room;
buffer tank adapted to the evaporator’s characteristics.

Disadvantages:

limited flexibility – pump capacity and tank volume are factory fixed;
difficulty of modernisation – replacement or addition of pumps is complicated by the design;
increased size and weight of the unit, which makes transport difficult.

Built-in hydromodules are more often used in air conditioning systems of buildings (offices, hotels, shopping malls), where compactness and minimisation of installation works are important.

Fig. 4– Trane 430 kW chiller (presented in our catalogue)

Remote hydraulic module

The hydraulic unit is manufactured as a separate pumping station. It can be installed in the machine room, on the technical floor or in a separate room.

Advantages:

possibility to select pumps with the required characteristics (head, capacity, energy efficiency);
ease of maintenance – easy access to pumps, filters, expansion tank;
possibility of system scaling (adding parallel pumps, redundancy);
reduced size and weight of the unit, simplified transport.

Disadvantages:

more complicated installation and adjustment at the site;
higher requirements for hydraulic linkage and equipment placement;
increased machine room area.

Remote hydraulic modules are mainly used in industrial facilities and in systems with long pipelines, where individual selection of pumping equipment is required.

The choice between integrated and remote hydromodules is determined not only by the equipment layout but also by the hydraulic characteristics of the system as a whole. The integrated hydromodule offers compactness and ease of installation, while the remote hydromodule allows flexible adaptation to the individual requirements of the site.

Take a look at our catalogue of chillers – units in various configurations, carefully checked for defects, set to the required temperature settings and shipped to you in perfect condition.

Using an economiser to increase the coefficient of energy performance (COP)

An economiser is an additional heat exchange circuit with intermediate throttling designed to sub-cool the liquid refrigerant. The best effect is achieved in screw compressors with interstage injection: part of the refrigerant after the condenser is throttled, vaporised in the economiser and the resulting vapour is fed into the compressor to cool the compressed mixture. The liquid fraction thus enters the evaporator with a lower enthalpy, which increases the cooling capacity and COP.

For low-temperature applications (boiling below -5 to -10 °C), the economiser can compensate for the drop in efficiency. Experience with Johnson Controls and Bitzer units shows an 8-12 % increase in capacity and a 5-10 % increase in COP.

Fig. 5 – Schematic diagram of a refrigeration system with economiser

Economiser operation requires precise regulation by a separate electronic control valve. Excessive injection leads to a drop in compressor efficiency, insufficient injection leads to uselessness of the scheme.

An additional positive effect is the reduction of discharge temperature and motor load, which increases equipment life. However, the increased cost and complexity of automation is only justified at low boiling temperatures or high energy efficiency requirements.

Heat recovery

Heat recovery in chillers is realised by installing an additional heat exchanger in the discharge line or in the condensing circuit. The aim is to utilise part of the condensing heat for DHW preparation or process media heating. There are two main variants: partial recovery (10-30 % of the condenser capacity is taken away) and full recovery, in which almost the entire heat load is utilised and the discharge to the environment is minimised.

The use of recuperation improves the overall energy efficiency of the plant. It is important to consider the temperature level of the heat transfer medium: water heating up to 40-50 °C is achievable in almost all systems, and above 60 °C only in chillers with screw or centrifugal compressors designed for high discharge temperatures.

Attention must be paid to the balance of modes: when there is no heat demand, the extraction must be switched off, otherwise the condensing pressure may rise and the COP may drop. The optimum solution is the use of electronically controlled plate heat exchangers. Practical experience of Trane and Daikin units shows that with year-round heat utilisation, the payback period of the option is 1.5-3 years.

Additional options

Frost protection

Enables circulation of the thermal fluid at critical temperatures or heating of the pipework. Minimum coolant temperature is maintained by automation; prevents ice formation in evaporator and pipework. Critical when using water instead of glycol.

Inverter condenser fans

Adjust speed to maintain condensing pressure and reduce energy consumption. Smooth adjustment reduces motor peak loads and noise, improves stability at partial loads.

Monitoring systems

Integration via BACnet or Modbus provides monitoring of temperature, pressure, flow and energy consumption. Allows failure prediction and optimised maintenance, reducing the risk of accidents.

Fan noise reduction

Utilises large diameter low speed fans, profiled blades and silencers. Reduces acoustic load without critical impact on energy efficiency, important for installation in urban environments or enclosed spaces.

Conclusion

Knowledge of the available features and options on the market is critical to the engineer designing, selecting and operating equipment. Each option affects the reliability, energy efficiency, operational stability, and life of the equipment. Understanding the operation of soft start, frequency start, winter start with hot steam bypass, free-cooling, economiser, heat recovery, integrated or remote hydro, inverter fans and monitoring systems allows you to properly assess the feasibility of their application in a particular facility.

An engineer with a full understanding of the options available is able to: correctly match the chiller to the design loads, minimise operational risks, ensure optimum energy efficiency and extend the life of the equipment. Ignoring these options often leads to unstable operation, increased wear and tear and higher operating costs.

Thus, a technical understanding of all available options is an indispensable tool for the professional refrigeration engineer when designing and operating modern refrigeration systems.

If you still have questions on equipment selection – contact Europrom specialists. We will help you to choose a suitable solution and offer reliable chillers presented in our catalogue.

What you get with EVROPROM

Optimal chiller selection for your tasks – we take into account operating modes, seasonal load fluctuations, reliability and energy efficiency requirements. We help you choose the optimal compressor type depending on the specifics of the facility.

Technical expertise and calculations – we provide energy efficiency comparisons (COP, EER), forecast operating costs, and calculate payback period for equipment replacement.

Up-to-dateand proven equipment – a wide range of chillers of world brands with different types of compressors and heat exchangers, adapted for industrial, commercial and infrastructure facilities.

Reduced operating costs – by using energy efficient solutions (turbo compressors, frequency control, optimised hydraulics) we reduce annual energy consumption and service costs.

Support at all stages – from the survey of existing systems and design to delivery, installation, commissioning and subsequent maintenance.

Author of the article:

Andrey Kohan, refrigeration equipment engineer

26.09.2025