What is an evaporator and what does it do?
The four main components of the refrigeration cycle are the compressor, condenser, expansion valve and evaporator. The refrigerant leaving the expansion valve at low pressure and temperature evaporates in the evaporator, absorbing heat from the water (chiller) or air (air conditioner, cold room). The evaporator is one of the surfaces that determines the cooling capacity of the system. Fouling, freezing or disrupted flow directly affects capacity and compressor health.
Evaporator types
| Type | How it works | Typical use | Service note |
|---|---|---|---|
| Brazed plate | Thin stainless steel plates joined by brazing; the refrigerant and water pass through alternating channels | Air-cooled chillers with scroll compressors, heat pumps, small and medium capacity | Compact and efficient; cannot be disassembled. Sensitive to fouling and freezing, a strainer is essential upstream of the water |
| Shell-and-tube, direct expansion (DX) | The refrigerant usually evaporates inside the tubes and the water flows on the shell side between baffle plates (it may be the reverse depending on the manufacturer) | Medium and large capacity screw and scroll chillers | Oil return is good; the tube side can be cleaned, while the shell side is mostly cleaned chemically |
| Flooded shell-and-tube | The refrigerant floods the tubes in the shell, and the water passes through the inside of the tubes | Large screw and centrifugal chillers | High efficiency; the water side can be cleaned mechanically with a brush. The refrigerant charge is larger, and oil management is a separate circuit |
| Falling film | The refrigerant is distributed over the tubes as a thin film, and the water is inside the tubes | Large screw and centrifugal chillers | Lower refrigerant charge and high efficiency; the distribution system is sensitive and requires manufacturer information |
| Double-pipe (coaxial) | One pipe inside another; the two fluids flow in opposite directions | Small water-cooled packaged units and heat pumps | Compact at small capacities; scale and freezing can cause hidden damage in the inner pipe |
| Finned coil (DX) | Copper tubes and aluminum fins; the air is cooled as it passes over the fins | Split and VRF indoor units, ducted air conditioners, rooftop units | Filter and fin fouling reduces capacity; the drain pan must be clean |
| Air cooler (unit cooler) | Finned coil, fan and defrost system in one housing | Cold rooms, freezers, process cooling | Defrost type and fin spacing are chosen according to room temperature |
Defrost methods for cold room air coolers
- Electric heater defrost: the most common method
- Hot gas defrost: used in large systems, and is fast
- Air (natural) defrost: for applications where the room temperature is above zero
- Defrost sensor, duration and termination settings: a wrong setting leads to ice buildup or unnecessary heating
Direct expansion or flooded?
| Feature | Direct expansion (DX) | Flooded |
|---|---|---|
| Refrigerant charge | Lower | Higher |
| Efficiency | Good | Generally higher; the temperature difference between the refrigerant and the water is small |
| Oil return | Generally easy | Requires an oil recovery circuit |
| Capacity range | Small and medium | Medium and large |
| Cleaning | Water side mostly chemical | Mechanical brushing inside the tubes is possible |
What to look for when choosing an evaporator
| Criterion | Why it matters |
|---|---|
| Capacity and water temperatures (7/12 °C, low temperature with glycol) | Selection is based on actual operating conditions, not nominal capacity |
| Refrigerant (R134a, R410A, R32, R513A, R1234ze, etc.) | Pressure class, material and oil compatibility depend on the refrigerant |
| Water quality and filtration | Scale, sludge and chlorides cause clogging and corrosion in plates and tubes |
| Water-side pressure drop | Affects pump selection and flow balance |
| Freeze protection | Glycol ratio, flow switch and low-temperature protection are part of the design |
| Material (stainless steel plate, copper or steel tubes, steel shell) | Corrosion resistance and service life are determined by this |
| Cleanability | Types that can be cleaned mechanically are advantageous with dirty water |
| Insulation, layout and service access | Sweating and ease of maintenance |
| Pressure class and certificates (CE/PED) | Pressure vessel safety |
For flow, glycol and heat exchangers, you can use the chiller flow calculator, glycol freezing point and heat exchanger LMTD calculators for preliminary calculations.
Why is evaporator freezing dangerous?
When water freezes, its volume increase cracks the plates or tubes; a crack lets water and refrigerant mix. The most common causes are low water flow, a dirty strainer, a bypassed flow switch, a setpoint that is too low, an insufficient glycol ratio and low load.
- The flow switch or differential pressure switch must be in the circuit
- The glycol ratio must be measured and checked according to the season
- Low-temperature and low-pressure protections must be tested
- The strainer must be cleaned regularly
- There must be an operating interlock between the pump and the chiller
For glycol and winter preparation, see our chiller winter preparation article.
What is done in evaporator maintenance?
- Water-side strainer cleaning
- Water quality and glycol check
- Recording approach temperature, superheat and water ΔT
- Water-side pressure drop and flow check
- Insulation and sweating check
- Coil fin and drain pan cleaning
- Defrost parts and sensor check (cold room)
- Pressure test when a cross-leak is suspected
For fault symptoms, repair options and replacement, see our evaporator repair and replacement page; for periodic maintenance, see chiller maintenance.
Note: This page is for general technical information. For a unit-specific decision, the manufacturer's manual and on-site measurement apply. YOİ Mühendislik is an independent technical service for these brands; it does not claim to be an authorized service except for LG.
Facilities we serve
Our headquarters is in Etimesgut, Ankara. We provide this service daily in Ankara, and on a project and contract basis in all 81 provinces of Türkiye, including İstanbul, İzmir, Bursa, Antalya, Konya, Kayseri, Eskişehir, Kocaeli, Adana, Gaziantep, Samsun and Trabzon. See the areas we serve.
Frequently asked questions
Which is better, a plate or a shell-and-tube evaporator?
Neither is absolutely superior. The plate type is compact and efficient but cannot be disassembled and is sensitive to dirty water. The shell-and-tube type is more tolerant, and on the flooded type in particular the inside of the tubes can be cleaned mechanically. The choice is made based on capacity, water quality and ease of service.
What is the difference between an evaporator and a condenser?
In the evaporator the refrigerant absorbs heat by evaporating; in the condenser it rejects heat by condensing. Both are heat exchangers; their operating pressures and temperatures differ.
What happens if evaporator capacity drops?
The chilled water outlet temperature rises and the compressor runs for a long time; low-pressure or freeze alarms may appear.
How long does an evaporator last?
It depends on water quality, filtration, freezing incidents and the maintenance routine; giving a fixed period would not be accurate.
Which refrigerants are used?
Refrigerants such as R134a, R410A, R32, R513A and R1234ze, according to the refrigerant on the unit nameplate. A change of refrigerant also affects evaporator selection.
Do you provide evaporator service for every brand?
As an independent technical service, we carry out diagnosis, repair, and equivalent evaporator selection and replacement for all brands. Lead time and parts availability are stated in writing in the quote.