Evaporative Coolers

An evaporative cooler, also commonly known as a swamp cooler or desert cooler, is a cooling device that uses the natural process of water evaporation to lower air temperature. Unlike traditional air conditioners that rely on refrigerants and a closed-loop refrigeration cycle, evaporative coolers achieve their cooling effect by turning liquid water into water vapour.

When hot, dry air passes over water-soaked pads inside the cooler, the water evaporates and absorbs heat from the air. This process cools down the air before it is blown out into the room, providing a refreshing and cool breeze. Evaporative coolers work best in dry climates where the air is not already saturated with moisture.

Evaporative coolers and traditional air conditioning (AC) systems utilise distinct methods to cool air. An evaporative cooler chills air through the natural process of water evaporation, where water absorbs heat from the air. In contrast, traditional AC systems employ a refrigerant cycle involving compression and expansion to remove heat from the air.

A key difference lies in their use of refrigerants. Evaporative coolers operate solely with water, making them an environmentally friendly option. Traditional AC units, however, rely on chemical refrigerants, such as R-410A, which can have environmental implications if leaked.

Regarding energy consumption and operating costs, evaporative coolers are remarkably energy-efficient, primarily using power for a fan and a small water pump, resulting in significantly lower electricity bills. Conversely, traditional AC systems have high energy consumption due to their powerful compressors, leading to higher electricity expenses.

Climate suitability is another major differentiator. Evaporative coolers perform best in hot, dry climates with low humidity, as their effectiveness relies on the air's ability to absorb moisture. Traditional AC, on the other hand, is effective in all climates, including hot and humid conditions, as it actively removes moisture from the air, thereby dehumidifying the space. While evaporative coolers add moisture to the air (which can be beneficial in arid regions), AC systems remove it.

In terms of air quality, evaporative coolers continuously draw in fresh outdoor air, with some models offering basic filtration of airborne particles. Traditional AC systems recirculate indoor air, and their air quality performance depends on the effectiveness of their filters, which require regular changes.

Installation complexity also varies. Evaporative coolers are generally simpler to set up, with many portable units being plug-and-play. Central traditional AC units, however, often require complex professional installation. Environmentally, evaporative coolers are considered eco-friendly due to their lack of harmful refrigerants. Traditional AC systems, conversely, can contribute to greenhouse gas emissions if their refrigerants leak.

Finally, the optimal indoor environment for each system differs. Evaporative coolers necessitate open windows or doors for proper ventilation, allowing the humidified air to escape. Traditional AC systems require a sealed environment to achieve optimal cooling and maintain specific thermostat settings. While evaporative coolers can cool air by a significant amount (e.g. 8-22°C in dry conditions), AC systems offer precise temperature control to a specific thermostat setting.

Evaporative coolers are most effective in hot and dry climates with low humidity. The effectiveness for a specific room depends on the cooler's Cubic Feet per Minute (CFM) rating, which indicates how much air the cooler can move. To determine the appropriate size:

Here's a general guide for room sizes and cooler categories:

The installation process varies significantly depending on whether you have a portable unit or a more fixed/ducted system.

Portable units are generally very easy to set up.

Place the cooler near an open window or door to ensure a constant supply of fresh air and to allow the more humid air to escape. This is crucial for effectiveness and to prevent the room from becoming overly humid or feeling "muggy."

Ensure the location is stable and can support the unit's weight when filled with water.

Place it on a level surface to ensure proper water distribution.

Avoid placing it directly next to heat sources.

Open the water reservoir and fill it with clean, cool water.

Many models allow you to add ice packs or ice cubes to the water tank for enhanced cooling.

Some larger portable units may have a hose connection for continuous water supply, eliminating the need for manual refills.

Plug the cooler into a standard electrical outlet.

Turn on the unit and adjust the fan speed and mode (e.g., cool, fan-only, oscillate) according to your comfort.

Direct the vents towards the area you want to cool.

These installations are significantly more involved and typically require professional help.

Choose a structurally sound location, often on the roof or an external wall, that can support the unit's weight (especially when filled with water) and allows for unobstructed airflow.

Plan for ductwork to distribute cooled air throughout the building and for adequate exhaust vents.

Securely mount the cooler unit using appropriate brackets or a stable base. For rooftop installations, ensure the roof's structural integrity.

Connect the cooler to a continuous mains water supply (1-7 bar pressure is typical). An inline shut-off valve is recommended.

Install a float valve in the reservoir to automatically maintain the correct water level.

Connect a drain pipe to the cooler's drainage port to safely dispose of excess water and prevent mineral buildup. Ensure it connects to a suitable effluent point in accordance with local regulations.

Connect the cooler to an appropriate electrical supply (e.g., 230V 50Hz single phase for many residential/commercial units) and ensure proper grounding. This should be done by a qualified electrician.

Install insulated ductwork to distribute the cooled air to the desired areas. Ensure ducts are sealed properly to prevent air leakage.

Crucially, ensure adequate exhaust ventilation (e.g., roof vents, open windows/doors) to allow the warm, humid air to escape. Without proper exhaust, the system will not work effectively and can lead to excessive indoor humidity.

Testing and Commissioning:

Fill the water tank and check for leaks.

Power on the unit and test all functions (fan speeds, controls).

Ensure proper airflow and cooling performance.

Important Safety Note: Always consult the manufacturer's installation manual for your specific evaporative cooler model and adhere to all local electrical and water supply codes and regulations. If you're unsure, it's best to hire a qualified professional for installation.

Evaporative coolers are very energy efficient. Running costs are significantly lower than traditional air conditioning. For a typical unit, running costs can range from a few pence per hour for smaller portable units (e.g. 3-5p/hour for 140-220W) to around 12p to 27p per hour for larger industrial units (e.g. 500-1100W), based on typical UK electricity rates (e.g. 27p/kWh as of April-June 2025). This is considerably less than a typical portable air conditioner which can cost 21p-27p per hour for a smaller unit, and much more for larger fixed AC systems.