The condenser is where the chiller gets rid of heat. If it is undersized, the head pressure rises, the compressor works harder, and energy costs climb. If it is oversized, you pay more upfront and may still foul because water velocity is too low.
A shell and tube condenser is the standard choice for water-cooled chillers. It is robust, cleanable, and well understood. But selecting the right one takes more than picking a model number from a catalog.
Here is how to do it correctly.
Quick answer
For most water-cooled chillers, use a shell and tube condenser with refrigerant condensing on the shell side and cooling water flowing through the tubes. Select it using:
Heat rejection, not just cooling capacity
Condensing temperature and leaving water temperature (approach)
Water flow and allowable pressure drop
Fouling factor based on real water quality
Tube material matched to water and refrigerant
Code requirements: ASME, PED, AHRI, UL
Cleaning access and maintenance plan
If the water is dirty, the refrigerant is ammonia, or the pressure is high, the details change. Get those details right before you buy.
1. Gather the right design data
You cannot size a condenser from chiller tonnage alone. Collect these points:
Refrigerant type and charge
Cooling capacity in tons, kW, or Btu/h
Compressor power input at design condition
Heat rejection in kW or Btu/h
Condensing temperature
Entering and leaving cooling water temperature
Cooling water flow rate
Allowable water-side pressure drop
Design pressure and temperature
Water quality: hardness, chlorides, suspended solids, biological growth
Fouling factor
Code and certification requirements
Space, weight, and connection limits
A typical water-cooled chiller might have 85°F entering water, 95°F leaving water, and 105°F condensing temperature. That 10°F range and 10°F approach drive the size and cost.
2. Calculate heat rejection correctly
The condenser must reject the cooling load plus the compressor work.
Q_cond = Q_evap + W_compressor
Where:
Q_cond = condenser heat rejection
Q_evap = evaporator cooling capacity
W_compressor = compressor power input
For a rough estimate, heat rejection is often 1.15 to 1.30 times the cooling capacity. High-efficiency chillers are closer to 1.15. Older or low-efficiency units are closer to 1.30.
Use the chiller manufacturer’s data for the final number. Do not guess.
Water flow formula:
Q = 500 × gpm × ΔT (imperial, Btu/h)
Q = 4.18 × m³/h × ΔT (metric, kW)
If you know heat rejection and the water temperature range, you can calculate flow. If you know flow and range, you can calculate heat rejection.
3. Understand approach temperature
Approach temperature is the difference between the saturated condensing temperature and the leaving cooling water temperature.
Approach = Condensing temperature − Leaving water temperature
A smaller approach means more surface area, a larger condenser, and higher cost. It also means lower condensing pressure and better chiller efficiency.
Typical approaches:
High efficiency: 1–2°F (0.5–1°C)
Standard: 2–5°F (1–3°C)
Compact or low-cost: 5–10°F (3–6°C)
Do not specify a 1°F approach unless the energy savings justify the extra cost. In many projects, a 2–3°F approach is the right balance.
4. Set the water flow and pressure drop
Water velocity inside the tubes matters.
Too low: fouling, poor heat transfer, and sediment buildup.
Too high: erosion, noise, and high pump energy.
Typical water velocities for copper tubes are 3–8 ft/s (0.9–2.4 m/s). The exact range depends on tube material and water quality.
Allowable pressure drop is usually 5–15 psi (35–100 kPa) for the condenser water side. But check the whole system. The cooling tower, piping, valves, and strainers all add pressure drop. A condenser with low pressure drop may be larger and more expensive. A condenser with high pressure drop may save upfront cost but cost more to pump for years.
Compare total cost, not just purchase price.
5. Choose the right fouling factor
Fouling is the number one reason condensers underperform.
Common fouling factors:
| Water quality | Fouling factor (imperial) | Fouling factor (metric) |
|---|---|---|
| Clean, treated, closed loop | 0.0001–0.00025 h·ft²·°F/Btu | 0.000018–0.000044 m²K/W |
| Treated cooling tower water | 0.00025–0.0005 h·ft²·°F/Btu | 0.000044–0.000088 m²K/W |
| Poor quality, high solids | 0.0005–0.001 h·ft²·°F/Btu | 0.000088–0.000176 m²K/W |
Check AHRI 550/590 or your local standard for the exact value. A higher fouling factor means a larger condenser. That increases cost but protects performance as the tubes foul.
Do not use a clean-water fouling factor on a cooling tower system. It will foul, and the chiller will lose capacity.
6. Select tube material and construction
Copper tubes: Standard for clean water and most refrigerants. Good heat transfer. Not compatible with ammonia.
Cupronickel 90/10 or 70/30: Better for brackish water, seawater, and higher chloride levels. Higher cost, lower heat transfer than copper.
Stainless steel: Used for ammonia, some aggressive fluids, and high-purity applications. Lower heat transfer, higher cost.
Titanium: Best for seawater and highly corrosive water. High cost. Often used in marine and coastal plants.
Tube enhancements: Finned or enhanced tubes improve heat transfer. They can reduce size and cost. But they can also trap fouling. Match the enhancement to water quality.
Shell material: Carbon steel is standard. Stainless steel or specialty alloys may be needed for corrosive refrigerants or environments.
Heads and connections: Removable heads allow tube cleaning. This is important for almost every water-cooled condenser. Vent and drain connections, relief valves, and refrigerant connections must match the system.
7. Match the refrigerant
The refrigerant affects material compatibility, pressure, and oil return.
HFCs and HFOs: Common in chillers. Copper tubes and carbon steel shells are typical.
Ammonia (R717): Cannot use copper. Use steel or stainless steel tubes. High pressure and toxicity require special codes and ventilation.
CO2 (R744): Very high pressure. Condenser design pressure is much higher. Tube wall thickness and shell thickness increase.
Flammable refrigerants: A2L and A3 refrigerants require leak detection, ventilation, and code compliance.
Always confirm compatibility with the refrigerant manufacturer and the condenser builder.
8. Decide on passes and arrangement
Two-pass: Most common for chillers. Water enters one end, crosses the tube bundle, and returns. Good balance of heat transfer and pressure drop.
Four-pass: Higher water velocity and better heat transfer, but higher pressure drop. Used when water flow is low or a tighter approach is needed.
Single-pass: Lower pressure drop, but lower velocity. Used for large flows or when pressure drop is critical.
Flooded vs DX: In a flooded condenser, refrigerant condenses on the shell side and liquid drains to the bottom. In a DX condenser, refrigerant flows inside the tubes and water is in the shell. Flooded is common for large chillers. DX is common for smaller packaged units. Match the design to the chiller type.
9. Check codes and certifications
For most industrial and commercial chillers, the condenser must meet:
ASME Section VIII for pressure vessels in the US
PED for Europe
AHRI 550/590 for performance rating
UL or ETL for electrical and safety components
Local pressure vessel rules in your country
Do not assume a supplier’s standard unit meets your local code. Ask for the certificate and nameplate details.
10. Plan for maintenance
A condenser that cannot be cleaned will lose performance.
Removable water heads: Required for mechanical cleaning.
Tube cleaning access: Brush, rod, or hydroblast.
Chemical cleaning: Needed for scale. Check material compatibility.
Water treatment: Controls scale, corrosion, and biological growth.
Eddy current testing: Checks tube wall thickness over time.
Leak detection: Refrigerant leaks and water leaks must be found early.
Spare parts: Gaskets, tube plugs, and head gaskets should be available.
A condenser with a 20-year design life can fail in 5 years if water treatment is poor and tubes cannot be cleaned.
Common selection mistakes
Sizing on cooling tons only, ignoring compressor heat.
Using a clean-water fouling factor on cooling tower water.
Specifying copper tubes for ammonia.
Allowing too little pressure drop, then fouling because velocity is low.
Allowing too much pressure drop, then paying high pump energy.
Choosing a non-cleanable condenser for dirty water.
Ignoring refrigerant compatibility and code requirements.
Buying on purchase price instead of total cost.
Forgetting freeze protection in cold climates.
Not checking tube velocity and water quality together.
FAQ
How do I size a shell and tube condenser for a chiller?
Calculate heat rejection as cooling capacity plus compressor power. Then use the condensing temperature, water flow, temperature range, approach, and fouling factor to select surface area and tube count.
What is a good condenser approach temperature?
2–3°F (1–1.5°C) is a practical target for many chillers. A 1°F approach is possible but costs more and may not pay back.
What fouling factor should I use?
Use 0.00025 h·ft²·°F/Btu for good treated cooling tower water. Use 0.0005 or higher for poor water quality. Check AHRI 550/590 and your water treatment report.
Can I use copper tubes with ammonia?
No. Ammonia attacks copper and copper alloys. Use steel or stainless steel tubes.
How many passes should a condenser have?
Two passes are standard for most chillers. Four passes increase heat transfer but also increase pressure drop. Choose based on flow, pressure drop, and approach.
How often should I clean the condenser?
Inspect annually. Clean when approach temperature rises, pressure drop increases, or visual inspection shows fouling. Cooling tower systems may need cleaning more often.
What pressure drop is acceptable?
Typically 5–15 psi (35–100 kPa) on the water side. The right value depends on pump energy and the rest of the system.