Shocking Stats: How Much Water Do Chillers Really Remove?

When I plan to remove water from a chiller system, I do not estimate the volume by looking at the chiller alone. The water may also be sitting in supply and return pipes, air-handling coils, pumps, heat exchangers, buffer tanks, and expansion tanks.

That is why a system that appears compact can hold hundreds or thousands of gallons.

A gallon of water weighs about 8.34 pounds. A 1,000-gallon system contains roughly 8,340 pounds of water, equal to about 3.8 metric tonnes. The volume affects labor, drain time, lifting needs, transport, disposal, and the amount of water needed for refill.

A simple way to estimate the volume

For a rectangular tank or vessel, use this formula:

Length × width × water depth × 7.48 = gallons

The measurements must be in feet.

A tank that measures 8 feet long, 5 feet wide, and holds water to a depth of 4 feet contains:

8 × 5 × 4 × 7.48 = 1,196.8 gallons

That water weighs about 9,982 pounds.

Pipes need a different calculation:

0.0408 × pipe inside diameter² × pipe length = gallons

The diameter is measured in inches, and the pipe length is measured in feet.

A 6-inch pipe running for 200 feet holds about:

0.0408 × 6² × 200 = 293.8 gallons

A 4-inch pipe running for 500 feet holds about 326 gallons.

These figures cover the pipe only. Coils, vessels, and equipment add more water to the system.

Where the hidden water is located

I check each part of the circuit before choosing a removal method:

• Chiller evaporator
• Supply and return piping
• Air-handling unit coils
• Fan coil units
• Buffer tanks
• Pumps and strainers
• Heat exchangers
• Expansion tanks
• Low points in the pipe network
• Sections isolated by control valves

Low points often hold water after the main drain appears empty. A system may also contain trapped water behind closed valves or inside coils that do not drain well by gravity.

A drain valve near the chiller does not always remove the full system volume.

Water and glycol are not the same

Some chilled-water systems use a glycol mixture to reduce freezing risk. Propylene glycol and ethylene glycol require different handling practices.

I confirm the fluid type before draining. A glycol mixture may need to be collected, tested, reused, or sent to an approved waste handler. I do not treat it like ordinary water.

The concentration also affects system performance. After refill, I check the mixture with a suitable refractometer or test method. A weak mixture may not provide enough freeze protection. A stronger mixture can reduce heat transfer and raise pumping demand.

A practical removal process

I start with the system documents, valve layout, and equipment condition. If the drawings are outdated, I trace the piping before opening a drain.

Then I follow a controlled sequence:

1. Shut down the chiller and related pumps.
2. Follow the site lockout and tagout process.
3. Allow hot components to cool.
4. Confirm the system pressure has reached a safe level.
5. Isolate equipment that should not be drained.
6. Connect hoses or a transfer pump to suitable collection tanks.
7. Open vents at high points to reduce vacuum formation.
8. Drain from low points in a controlled way.
9. Check coils, strainers, tanks, and dead legs for remaining water.
10. Record the approximate volume removed.
11. Inspect the system before refilling.

A pump can speed up the work, but it does not remove the need to open high-point vents. Without proper venting, flow may stop while water remains in parts of the system.

I also protect floors, electrical equipment, insulation, and nearby materials. A small drain connection can release water faster than expected when the system is under pressure.

Disposal needs planning

Clean water from a closed loop may still contain corrosion particles, treatment chemicals, oils, or biological growth. Glycol-based fluid may need separate handling.

I avoid sending unknown system fluid into a storm drain, landscaped area, or public sewer without checking site requirements. The correct option may be a sanitary drain approved for the discharge, a temporary storage tank, or a waste service.

A simple fluid sample can help identify whether the water contains glycol, high solids, oil, or treatment chemicals. The sample is useful when the fluid must be reused or transferred to a waste handler.

Refilling can reveal another number

Removing 800 gallons is only part of the calculation. The replacement water must also be treated and introduced without trapping large air pockets.

After refill, I check:

• System pressure
• Air vents
• Pump seals
• Flanges and drain valves
• Coil connections
• Strainers
• Expansion tank pressure
• Water chemistry
• Flow readings
• Supply and return temperature

The first refill may not represent the final volume. Air removal, filter cleaning, and low-point drainage can change the amount needed.

For example, if a system removes 800 gallons but needs 60 gallons added during air purging and leak correction, the recorded refill volume may reach 860 gallons. That difference can help identify a leak, a measurement error, or water left in isolated sections.

My view

The most useful number is not a rough guess based on chiller tonnage. It is a measured estimate built from pipe length, pipe diameter, equipment volume, and tank capacity.

When I calculate the water before opening a drain, I can choose the right hoses, tanks, pump, labor, and disposal method. The process becomes safer, cleaner, and easier to document.

A chiller water removal plan should answer four questions:

• How much fluid is in the system?
• What type of fluid is it?
• Where will the fluid go?
• How will the system be refilled and checked?

Those answers prevent a small maintenance task from becoming an unexpected water-handling problem.

A chiller can lower air temperature without removing much water. Many users see a cooling capacity such as 5 tons or 60,000 BTU/h and expect a matching amount of moisture removal. That comparison does not work.

Cooling capacity covers both sensible heat and latent heat. Sensible heat lowers the air temperature. Latent heat changes water vapor into liquid water on the coil. Only the latent part creates condensate.

When I estimate water removal, I look at the coil temperature, room dew point, airflow, operating hours, and outdoor air volume. A chiller with a cold coil may collect several gallons of water each day. The same unit may collect very little in a dry room.

The basic water-removal calculation

A practical way to estimate condensate is:

Water removed per day = condensate collected per hour × operating hours

A second method uses latent cooling capacity:

Water removal per hour ≈ latent capacity ÷ 1,060 BTU

One pound of water needs about 1,060 BTU of heat removal when it changes from vapor to liquid. One gallon of water weighs about 8.34 pounds.

For example, if a system sends 2,000 BTU/h of its cooling capacity to moisture removal:

• 2,000 ÷ 1,060 = about 1.9 pounds of water per hour
• 1.9 pounds equals about 0.23 gallons per hour
• At 10 hours of operation, the result is about 2.3 gallons per day

This is an estimate, not a guaranteed output. The latent share changes as room conditions change.

Why a 5-ton chiller does not remove 5 tons of water

A 5-ton cooling system has a nominal capacity of about 60,000 BTU/h. The word “ton” refers to cooling capacity, not water removal.

If the room is warm and dry, most of that capacity may serve sensible cooling. The coil lowers the air temperature, yet the air may contain too little moisture to create much condensate.

If warm, humid air enters the room, the coil may remove more moisture. The system still has to cool that air, so the total capacity is divided between temperature control and dehumidification.

This is why two identical chillers can produce different amounts of drain water in different buildings.

The coil temperature sets the moisture limit

Air begins to release moisture when it touches a surface below its dew point. The chilled-water coil must be cold enough for condensation to form.

A room at 75°F with a 65°F dew point may produce limited condensate on a coil operating near 60°F. A room at 75°F with an 72°F dew point can create more condensation on the same coil.

Chilled-water supply temperature also matters. A supply temperature near 42°F may support stronger dehumidification than a supply temperature near 55°F, though the actual result depends on coil design and airflow.

A colder coil is not always the best answer. Very low coil temperatures can create frost, raise energy use, or cause poor airflow if the system is not designed for those conditions.

Airflow changes the result

Airflow controls how much air reaches the coil and how long that air stays in contact with the cold surface.

High airflow can deliver more total air to the coil, yet it may reduce contact time. Low airflow can improve moisture removal in some systems, but it may create low-temperature problems, weak room mixing, or reduced cooling performance.

The coil’s bypass factor, surface area, fin spacing, entering-air condition, and leaving-air condition all affect the result. A simple tonnage calculation cannot include these details.

A practical example

Imagine a small office with:

• 75°F indoor temperature
• 65% relative humidity
• 10 hours of daily chiller operation
• A coil leaving air near 55°F
• Moderate outdoor air entering through the ventilation system

A unit in this space may collect around 2 to 6 gallons of condensate per day, depending on airflow and weather. That range is more useful than assigning one fixed number from the chiller’s tonnage.

During a dry winter period, the drain pan may stay nearly dry. On a humid summer day, the same equipment may produce several times more water.

A light commercial office in Florida, for example, can have a steady condensate flow because outdoor air contains a large moisture load. A similar office in a dry inland climate may need little dehumidification even when the cooling load looks similar.

How I check the actual water removal

I use a simple field check:

1. Confirm that the drain line is clear and properly trapped.

2. Place a container at the condensate outlet or install a temporary flow meter.

3. Measure the water collected over 30 to 60 minutes.

4. Record indoor temperature, relative humidity, outdoor conditions, chilled-water temperature, and operating status.

5. Repeat the measurement during a humid period and a dry period.

If the system produces 0.4 gallons in one hour and runs for 10 hours, the daily estimate is about 4 gallons. A longer test gives a more useful result because compressor cycling and changing weather can affect short measurements.

What low condensate can mean

Low water production does not always indicate a fault. The room may already be dry, the system may be satisfying the temperature setpoint, or the unit may be using a warm coil temperature.

Low condensate can also point to:

• A blocked or dirty filter
• Low refrigerant in a direct-expansion system
• Incorrect chilled-water flow
• Excessive airflow
• A dirty coil
• A damaged drain pan
• Air leakage around the coil
• A faulty humidity sensor

A wet floor, overflowing pan, or sudden change in drain flow needs a separate inspection. The water may be coming from a blocked drain rather than normal dehumidification.

The useful answer is not a single gallon figure. I need to know the air entering the coil, the coil temperature, the airflow, and the number of operating hours. Once those values are measured, condensate output becomes easier to estimate and verify.

When I assess a chilled-water system, I do not look only at room temperature. A space can reach 72°F and still feel damp, smell musty, or show condensation on cold surfaces. The missing factor is often latent capacity—the part of the cooling process that removes moisture from air.

Chiller dehumidification data helps me answer practical questions:

• How much moisture can the coil remove?
• What leaving-air dew point should I expect?
• How much chilled-water flow is required?
• Why does a system cool well but control humidity poorly?
• Which numbers should I check before selecting equipment?

The key numbers behind dehumidification

1. Entering-air dew point

Dew point shows the temperature at which air begins to release moisture.

If the entering air has a dew point of 60°F, a cooling coil must have a surface temperature below 60°F to create condensation. A coil that stays above this point may lower dry-bulb temperature without removing much water.

Typical indoor targets vary by application:

• Office areas: about 50–55°F dew point
• Storage areas: often 45–55°F dew point
• Museums and archives: controlled to a narrower range
• Food processing spaces: set by product and sanitation needs
• Swimming pool rooms: often managed around 50–55% relative humidity

The target must match the space. A lower dew point usually needs colder coil conditions, more coil surface, lower airflow, or a separate desiccant system.

2. Coil apparatus dew point

The apparatus dew point, often called ADP, is a calculated coil reference temperature. It helps estimate the moisture-removal performance of a cooling coil.

A lower ADP usually indicates stronger dehumidification. It does not mean every point on the coil has that exact temperature. Water temperature, airflow, coil rows, fin spacing, bypass factor, and coil cleanliness all affect the result.

For many comfort-cooling systems, chilled-water temperatures around 42–45°F may support moisture removal when the entering air is warm and humid. The actual result depends on the coil design and air conditions.

3. Sensible heat ratio

Sensible heat ratio, or SHR, compares sensible cooling with total cooling:

SHR = Sensible cooling ÷ Total cooling

A system with a total capacity of 100,000 Btu/h and an SHR of 0.75 provides:

• 75,000 Btu/h of sensible cooling
• 25,000 Btu/h of latent cooling

That 25,000 Btu/h is the portion connected with moisture removal.

A lower SHR means more of the cooling capacity is being used for latent load. High outdoor-air rates, crowded spaces, kitchens, pools, and humid climates often create a lower SHR requirement.

4. Moisture removal rate

Moisture removal is often shown as pounds of water per hour or pints per hour.

The basic conversion is:

1 pound of water = about 0.12 gallons

A coil removing 20 lb of water per hour produces about 2.4 gallons of condensate per hour.

The same result can be expressed in pints:

20 lb/h × 0.96 ≈ 19.2 pints per hour

The exact condensate volume may vary with water temperature and measurement conditions, but this estimate helps size drain pans, traps, condensate pumps, and drain piping.

A simple airside calculation

I use the difference in humidity ratio to estimate moisture removal:

Moisture removal, lb/h = 4,500 × airflow, CFM × humidity-ratio difference

The humidity ratio is measured in pounds of water per pound of dry air.

Suppose a system moves 10,000 CFM. The entering air has a humidity ratio of 0.012, and the leaving air has a ratio of 0.009.

The calculation is:

4,500 × 10,000 × (0.012 − 0.009)

The result is about 135,000 lb/h, which is clearly too high because the constant must be used with the humidity ratio expressed in a compatible unit basis. A more practical HVAC form uses:

Moisture removal, lb/h ≈ 4.5 × CFM × humidity-ratio difference

The corrected calculation becomes:

4.5 × 10,000 × 0.003 = 135 lb/h

That equals about 16.2 gallons of water per hour.

This example shows why unit checks matter. A small error in the constant can create a large design mistake.

Chilled-water flow and coil capacity

Water-side capacity is often estimated with:

Btu/h = 500 × GPM × water temperature difference

If a coil receives 100 GPM and the chilled water rises by 10°F:

500 × 100 × 10 = 500,000 Btu/h

This value represents total heat removed from the water. It does not reveal how much capacity is sensible and how much is latent.

A coil may remove 500,000 Btu/h while providing poor humidity control if:

• The entering air is already dry
• The coil surface is not cold enough
• Air bypasses the active coil surface
• Airflow is too high
• The system cycles off before moisture removal occurs
• Reheat raises supply-air temperature after dehumidification

Water flow alone cannot prove that a system has enough latent capacity.

Why temperature control can hide a humidity problem

I often see this pattern in offices and retail spaces: the thermostat reaches its setpoint, so the chiller reduces output. The room temperature looks normal, yet relative humidity rises.

Short cooling cycles create this problem. The coil needs time to reach a condition where condensation forms. If the compressor or chilled-water valve closes soon after the room temperature falls, the system may deliver sensible cooling without removing enough water.

A space may also become humid when:

• Outdoor-air dampers remain open during mild weather
• Exhaust fans pull untreated outdoor air indoors
• Door traffic adds humid air
• The return-air sensor sits in a dry location
• The supply-air dew point is too high
• The cooling coil is dirty
• Condensate remains in the drain pan and re-evaporates

I treat humidity as an airside control issue, not only a chiller issue.

A practical example

Consider a small office with these conditions:

• Airflow: 8,000 CFM
• Entering air: 80°F dry bulb, 65°F dew point
• Leaving air: 55°F dry bulb, about 50°F dew point
• Chilled-water entering temperature: 44°F
• Chilled-water leaving temperature: 54°F
• Water flow: 60 GPM

The water-side capacity is:

500 × 60 × 10 = 300,000 Btu/h

The coil has a reasonable chance of removing moisture because:

• The coil surface is colder than the entering-air dew point
• The leaving-air dew point is lower than the entering-air dew point
• The water temperature rise shows heat transfer is taking place
• The leaving air is cool enough to support a lower room dew point

The design still needs a check against outdoor-air load, people load, envelope leakage, and the room’s moisture sources. A coil result cannot be judged by water temperature alone.

How I review a chiller dehumidification report

I check the data in this order:

Step 1: Confirm the entering-air condition

Look for dry-bulb temperature, wet-bulb temperature, relative humidity, dew point, and humidity ratio. A capacity rating without entering-air moisture data gives an incomplete picture.

Step 2: Check the leaving-air dew point

Leaving dry-bulb temperature may look good while leaving-air dew point remains too high. Dew point is the better measure when humidity control is the goal.

Step 3: Separate sensible and latent capacity

Review total capacity, sensible capacity, latent capacity, and SHR. Do not assume that total Btu/h equals moisture-removal capacity.

Step 4: Review airflow

High airflow can raise the leaving-air temperature and increase the bypass effect. Low airflow can improve moisture removal but may create low-temperature, noise, or distribution concerns.

Step 5: Confirm chilled-water conditions

Record entering-water temperature, leaving-water temperature, flow rate, valve position, and coil pressure drop. These values show whether the coil is receiving the conditions used in the selection data.

Step 6: Estimate condensate

Compare predicted condensate with the drain system. A drain pan designed for a small load may overflow when outdoor-air humidity rises.

Step 7: Check controls

Look for a humidity sensor location, dew-point setpoint, low-limit protection, valve response, outdoor-air control, and reheat sequence. Good coil data cannot compensate for poor control logic.

Common errors in interpreting statistics

A cooling coil rated at 500 tons does not remove a fixed amount of water under every condition. Latent output changes with air temperature, air moisture, water temperature, airflow, and coil condition.

Relative humidity also needs careful handling. At the same dew point, relative humidity changes when air temperature changes. A room can show a lower relative humidity after heating even though no moisture has been removed.

Energy use deserves attention as well. Lower chilled-water temperatures may support stronger dehumidification, but they can increase chiller lift and reduce efficiency. Some buildings use a dedicated outdoor-air unit, energy recovery, reheat, or desiccant equipment when the latent load is high.

The best design matches the moisture source to the control method. A comfort office may need a chilled-water coil with a suitable dew point. A pool room or low-humidity production area may need equipment designed for a much larger latent load.

When I review chiller dehumidification statistics, I focus on the full chain: entering-air moisture, coil surface condition, leaving-air dew point, sensible and latent capacity, chilled-water flow, condensate rate, and control response. One number rarely explains the whole system. A clear set of connected measurements gives a more reliable view of how the equipment will perform in the space.

Removing water from a chiller sounds simple: open a drain valve, wait for the water to leave, and close the system. In practice, that approach can leave water trapped in low points, damage heat exchangers, or allow air and moisture to enter parts of the system that should remain protected.

I have seen many maintenance problems begin with one assumption: if no more water comes from the drain, the chiller must be empty. That is not always true. Water can remain inside evaporators, condenser circuits, pumps, pipes, strainers, and flexible connections.

The correct method depends on the chiller design, the type of fluid, the reason for removal, and the expected outdoor temperature.

What “chiller water removal” really means

A water-cooled chiller and an air-cooled chiller may require different work.

A water-cooled unit usually has water in the chilled-water circuit and condenser-water circuit. Both circuits may need attention during shutdown or maintenance.

An air-cooled chiller may only have water or a water-glycol mixture in the evaporator side. The condenser does not use a separate cooling-water loop, but the evaporator and connected piping can still hold a large amount of fluid.

The fluid may also contain glycol, corrosion inhibitors, or treatment chemicals. It should not be discharged without checking the site procedure and local requirements. The fluid may need to be collected, tested, reused, or handled by a qualified service provider.

Refrigerant is a separate matter. Draining chiller water does not remove refrigerant from the refrigeration circuit. Opening refrigerant lines requires different equipment, training, and procedures.

Why a basic drain-down may fail

A chiller system often contains several points where fluid can remain:

• Low sections of piping
• Evaporator water boxes
• Condenser water boxes
• Pump casings
• Strainers and filters
• Automatic control valves
• Flexible hoses
• Heat recovery circuits
• Small bypass lines
• Pressure sensor lines

Some components do not drain by gravity because air cannot enter the system freely. A closed valve can also isolate a section and trap water behind it.

If the system may be exposed to freezing conditions, trapped water can expand and damage tubes, headers, valves, or fittings. A small amount of remaining water can create a large repair problem after a cold night.

A safer removal process

1. Confirm the reason for draining

I begin by asking why the water needs to be removed.

The procedure may be different for:

• Seasonal shutdown
• Heat exchanger cleaning
• Pump replacement
• Leak repair
• Chiller relocation
• Long-term storage
• Freeze protection
• Water treatment work

A short maintenance drain-down may not require full fluid removal. A long shutdown in a cold location may require draining, blowing out, or adding an approved antifreeze solution.

2. Review the equipment documents

The manufacturer’s service instructions should identify drain points, vent locations, isolation valves, and component limits.

A piping diagram is useful because it shows parts that may not be visible from the machine exterior. I also check whether the chiller has a factory-installed drain connection or a recommended method for removing residual water.

If the documentation is missing, a qualified technician should identify the circuit before any valve is opened.

3. Stop and isolate the chiller

The unit should be shut down through its normal control sequence. Pumps should stop, temperatures should reach a safe range, and pressure should be checked.

Electrical power may need to be isolated under the site’s lockout procedure. This matters because pumps, fans, and automatic valves can start during service if controls remain active.

The water circuit should be isolated from connected building piping. Isolation reduces the amount of fluid that must be removed and prevents water from flowing back into the chiller.

4. Relieve pressure carefully

Even a small water circuit can hold pressure. I confirm the pressure reading before loosening covers, strainers, hoses, or drain fittings.

A drain hose should lead to a suitable container or approved discharge point. Water can be hot, chemically treated, or under pressure. Personal protective equipment should match the site risk assessment.

Opening a vent or high point can help air enter while water leaves the low point. The vent should be opened in a controlled way, not removed suddenly.

5. Drain from the low points

The main drain is only part of the process. I check every low point shown on the piping diagram.

Water boxes may have separate drain plugs or valves. Pumps and strainers may need their own drain points. Some valves must be positioned to allow fluid to leave isolated sections.

The removed fluid should be collected when it contains glycol or treatment chemicals. A clean container also makes it easier to measure the amount removed and compare it with the expected system volume.

6. Remove remaining water

Gravity may not remove all fluid. Approved methods can include:

• Low-pressure dry air
• Nitrogen, where specified by the service procedure
• Vacuum equipment designed for the application
• Manual drainage from disconnected low points

High pressure should not be used as a shortcut. Excessive pressure may damage tubes, seals, gaskets, or control components.

When air or nitrogen is used, the pressure limit from the equipment documentation must be followed. The gas should be introduced slowly while the outlet remains controlled.

7. Check hidden sections

After the main drainage, I inspect strainers, pump casings, evaporator sections, condenser sections, bypass lines, and small connected circuits.

A useful field check is to open each approved drain point and observe whether fluid continues to appear after the system has been left undisturbed. The check should be repeated after changing valve positions according to the service instructions.

A moisture reading or visual inspection may help, but neither method proves that every internal surface is dry. Some systems are designed to remain filled with treated fluid rather than be completely dry.

8. Protect the system after removal

Leaving a chiller open to the atmosphere can allow dust and moisture to enter. Drain points should be closed or capped as required. Open pipe connections may need clean covers.

A maintenance record should include:

• Date of drainage
• Reason for the work
• Fluid type
• Approximate quantity removed
• Drain points used
• Areas that could not be fully emptied
• Freeze protection method
• Inspection date

This record helps the next technician understand the system condition.

A practical example

A small office building had a packaged chiller shut down for winter. The main drain released most of the water, so the operator closed the valve and left the unit isolated.

After a period of cold weather, a service technician found damage near a low section of the evaporator circuit. Water had remained in a section that was isolated by a closed valve. The main drain had worked correctly, but the full circuit had not been vented and checked.

The repair could have been avoided by reviewing the piping diagram, opening the approved high-point vent, and checking each isolated low point before storage.

When draining may not be the best option

Complete water removal is not always the preferred choice. In some systems, maintaining a treated water-glycol mixture provides better protection than leaving internal surfaces exposed to humid air.

The right choice depends on:

• Expected temperature
• Storage length
• Equipment design
• Fluid concentration
• Manufacturer guidance
• Condition of seals and internal surfaces
• Local handling requirements

A chiller should not be drained simply because it will be unused for a short period. A controlled shutdown with proper circulation and freeze protection may reduce maintenance work.

The main lesson is simple: water removal is a system task, not a single-valve task. I treat the chiller, pumps, valves, heat exchangers, and connected piping as one circuit. That approach reduces trapped water, protects the equipment, and gives the next maintenance team a clear record of what was done.

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ASHRAE, 2021, 2021 ASHRAE Handbook—Fundamentals

ASHRAE, 2020, 2020 ASHRAE Handbook—HVAC Systems and Equipment

ASHRAE, 2022, 2022 ASHRAE Handbook—Refrigeration

CIBSE, 2015, CIBSE Guide C: Reference Data

U.S. Environmental Protection Agency, 2016, Managing Used Antifreeze

U.S. Department of Energy, 2018, Chilled Water Systems Best Practices Guide