Evaporative Condensers
An evaporative condenser combines refrigerant condensation and evaporative heat rejection in one piece of equipment.
Hot, high-pressure refrigerant vapor enters condenser tubing located inside the evaporative condenser. Water is pumped from the sump and sprayed over the outside of the condenser tubes.
As some of the spray water evaporates, heat is removed from the refrigerant inside the tubes. The refrigerant condenses and leaves the unit as high-pressure liquid.
What You Will Learn
By the end of this lesson you should be able to:
Describe how it rejects refrigerant heat through evaporation of water.
Recognize that the condenser tubing carrying refrigerant is located inside the evaporative condenser.
Describe how water is pumped from the sump and sprayed over the condenser tubing.
Recognize that evaporation of spray water removes heat from the refrigerant.
Describe how fans can increase airflow and assist the evaporative heat-rejection process.
Recognize that an evaporative condenser contains the refrigerant condenser tubing inside the unit.
How an Evaporative Condenser Works
An evaporative condenser places the refrigerant condenser coil directly inside the evaporative heat-rejection equipment.
Water stored in the sump is pumped upward and sprayed over the outside of the condenser tubing.
The refrigerant remains inside the tubes while the spray water flows over their outside surfaces.
Technician Point
The condenser coil is inside the evaporative condenser.
This is the major physical distinction between an evaporative condenser and a conventional cooling-tower system.
Follow the Refrigerant
Hot Vapor Enters
Hot, high-pressure refrigerant vapor arrives through the compressor discharge line and enters the condenser tubing.
Heat Leaves the Refrigerant
Heat passes through the condenser tube wall to the water and air surrounding the tubing.
Refrigerant Condenses
As heat is removed, the refrigerant changes from high-pressure vapor to high-pressure liquid.
Liquid Refrigerant Leaves
High-pressure liquid refrigerant exits the condenser and continues through the refrigeration system.
About the Refrigerant Inlet
The hot, high-pressure vapor entering the evaporative condenser comes from the compressor discharge line.
The compressor may be physically remote from the evaporative condenser.
Follow the Spray Water
The water used for evaporative cooling circulates through its own loop inside the condenser.
Water Collects in the Sump
The lower portion of the evaporative condenser stores the recirculating spray water.
The Pump Moves the Water
A pump draws water from the sump and sends it to the spray distribution system.
Water Is Sprayed Over the Tubes
The spray water flows over the outside surfaces of the refrigerant condenser tubing.
Water Returns to the Sump
Water that does not evaporate falls back into the sump and can be circulated again.
Evaporation Removes Heat
When spray water contacts the warm condenser tubing, some of the water evaporates.
Evaporation requires heat. That heat is drawn from the condenser tubing and the refrigerant inside it.
Contains heat that must be rejected.
Transfers heat from the refrigerant to the outside surface.
Receives heat from the condenser tubing.
Evaporation carries heat away from the condenser.
Heat-Transfer Path
Refrigerant → Tube Wall → Spray Water → Outdoor Air
Fans Assist the Cooling Process
Fans may be used to increase airflow through the evaporative condenser.
Moving air assists evaporation and carries heat and water vapor away from the condenser tubing.
Water Provides Evaporative Cooling
Spray water contacts the condenser tubing and absorbs heat.
Air Carries Heat and Moisture Away
Airflow assists evaporation and removes the resulting heat and water vapor from the unit.
Fan Control and Head Pressure
The condenser fan can be controlled in response to refrigerant head pressure.
When additional heat rejection is required, fan operation increases airflow through the evaporative condenser and assists the cooling process.
Head Pressure Changes
The refrigeration system responds to changing operating conditions.
Fan Operation Responds
The condenser fan is controlled according to head-pressure requirements.
Airflow Changes
Changing airflow changes the evaporative condenser’s heat-rejection capability.
Evaporative Condenser vs. Cooling Tower
These two types of equipment can look similar, but they do not perform the refrigeration-system heat exchange in the same location.
Cooling Tower System
The refrigerant condenser is a separate component.
Refrigerant transfers heat to condenser water in the water-cooled condenser. The heated water then travels to the cooling tower.
Evaporative Condenser
The refrigerant condenser tubing is inside the evaporative condenser.
Spray water and airflow remove heat directly from the condenser tubing containing refrigerant.
Remember the Difference
Cooling Tower: cools condenser water.
Evaporative Condenser: directly cools refrigerant condenser tubing with water and air.
Compare the Heat Paths
Heat Path
Refrigerant → Condenser Water → Cooling Tower → Outdoor Air
Refrigerant → Condenser Tube → Spray Water / Air → Outdoor Air
Evaporative Condensers Also Require Water Management
Some spray water continually evaporates during normal operation.
As water evaporates, dissolved minerals remain behind in the recirculating water and can become more concentrated.
Makeup water, blowdown, and water treatment are therefore important parts of maintaining an evaporative condenser.
Water Treatment Comes Next
The next water-treatment lesson will examine mineral concentration, scale, corrosion, pH, conductivity, makeup water, blowdown, and computerized treatment controls in greater detail.
Put the Concepts Together
An evaporative condenser contains refrigerant condenser tubing inside the evaporative unit.
Hot, high-pressure vapor enters the condenser tubing through the compressor discharge line.
Water is pumped from the sump and sprayed over the condenser tubing.
Some spray water evaporates and removes heat from the refrigerant.
Water that does not evaporate returns to the sump and can be recirculated.
Fans may be used to increase airflow and assist evaporation.
Fan operation may be controlled in response to head pressure.
An evaporative condenser is different from a cooling tower because the refrigerant condenser tubing is located inside the evaporative unit.
Can You Explain Evaporative Condenser Operation?
You should be able to answer these questions before continuing.
1. Where is the refrigerant condenser tubing located in an evaporative condenser?
2. What refrigerant condition enters the condenser tubing?
3. Where does the spray water come from?
4. What component moves water from the sump to the spray system?
5. Where is the water sprayed?
6. How does evaporation remove heat from the refrigerant?
7. What happens to spray water that does not evaporate?
8. What purpose do fans serve?
9. What operating condition may be used to control the condenser fans?
10. What is the major difference between an evaporative condenser and a cooling tower?
What You Should Have Learned
Evaporative condensers combine refrigerant condensation and evaporative heat rejection in one unit.
Refrigerant flows inside condenser tubing located within the evaporative condenser.
Water is pumped from the sump and sprayed over the outside of the condenser tubing.
Evaporation of spray water removes heat from the refrigerant.
Water that does not evaporate returns to the sump for recirculation.
Fans can assist evaporation by increasing airflow through the condenser.
Fan operation can respond to refrigeration-system head pressure.
A cooling tower cools condenser water, while an evaporative condenser directly cools refrigerant condenser tubing.
One Unit Combines the Two Processes
An evaporative condenser combines the refrigerant condenser coil with evaporative heat rejection.
Hot Vapor In · Water Sprays the Coil · Water Evaporates · Heat Leaves · Liquid Refrigerant Out
The key distinction is simple: the refrigerant condenser tubing is inside the evaporative condenser itself.