Freecooling Chiller Units: Operating Principle and Energy Efficiency
For facilities that need cooling throughout the year, outdoor air can be a useful cooling source when conditions allow. Freecooling chillers use this opportunity to reduce the need for compressor operation. The benefit depends not just on cold weather, but also on process water temperatures, the load profile and system design.
What is a freecooling chiller?
Free cooling transfers heat from the process fluid to the surroundings through an air-to-fluid heat exchanger under suitable outdoor conditions. In the hydronic arrangement discussed here, outdoor air is not mixed directly with process water or introduced into the production area.
The free cooling coil can be integrated into the chiller or provided through a separate dry cooler with suitable hydraulic connections. A conventional air-cooled chiller does not have free cooling simply because it operates outdoors; the function requires suitable heat exchangers, valves and controls.
Mechanical, mixed and full free cooling modes
In mechanical cooling mode, outdoor conditions are unsuitable for useful free cooling and the compressor-based refrigeration circuit meets the load. In mixed mode, outdoor air precools the returning fluid while compressors provide the remaining cooling.
In full free cooling mode, the heat exchanger can meet the current load at the required leaving temperature, allowing the compressors to stop. Fans, pumps and controls still consume electricity. Free cooling therefore does not mean zero electrical consumption.
At what temperature does free cooling start?
There is no single outdoor changeover temperature that applies to every project. Partial cooling requires a usable temperature difference between outdoor air and returning fluid. Full free cooling also requires sufficient heat exchanger capacity to meet the load and deliver the required supply temperature.
Heat exchanger approach temperature, flow, glycol concentration and any additional approach across an intermediate exchanger belong in the selection calculation. Where the process permits it, a higher supply temperature can increase free cooling opportunities; product or equipment temperature limits must not be exceeded to save energy.
Which applications should be assessed?
Data centers, plastics processing lines and industrial processes requiring year-round heat removal are candidates for assessment. Suitability depends more on actual temperature and load requirements than on the industry name. A facility operating only in summer may have a different economic outcome.
A country name alone is not enough to select a system for the Balkans, North Africa or any other region. Hourly climate data for the installation city, day and night conditions and the production schedule should be considered together. Processes needing very cold water may have fewer usable hours than circuits operating at higher temperatures.
Glycol, hydraulic separation and frost protection
Outdoor coils and pipework need protection against freezing. Glycol type and concentration depend on the lowest expected temperature, equipment manufacturer requirements and fluid compatibility. Changes in heat transfer properties and viscosity relative to water must be included in capacity and pump calculations.
If glycol is not wanted in the process circuit, an intermediate heat exchanger can separate it from the outdoor loop. This introduces additional pumping, pressure losses and temperature approach, which affect selection. Frost protection planning must also cover shutdowns and power failures.
Controls, maintenance and stable operation
Controls should monitor outdoor, return and supply temperatures and coordinate valves, fans, pumps and compressors. Flow limits must be maintained during mode changes. Control deadbands and minimum operating times should be set to project requirements to prevent excessive cycling.
Clean coil surfaces, accurate sensors, functioning valves and suitable water quality support performance. Layout should account for airflow short-circuiting, hot air recirculation and maintenance access. Having free cooling does not automatically provide redundancy or guarantee uninterrupted year-round operation.
How are savings and payback calculated?
The assessment should compare annual total electricity use for a reference system and a free cooling solution delivering the same cooling duty. It should include hourly outdoor conditions and load, compressor part-load performance, fan and pump consumption and hydraulic losses.
A universal saving percentage or fixed payback period is not appropriate. Additional capital cost, maintenance costs, electricity tariffs and actual operating hours affect the result. After commissioning, energy and temperature records should be used to check the calculation.
What information is needed for a quotation?
- Installation country and city; highest and lowest design outdoor temperatures
- Required supply and return water temperatures, flow and available pressure
- Hourly or seasonal cooling load and annual operating schedule
- Fluid type, glycol requirements and water quality
- Existing chiller, dry cooler and pipework details; layout and noise limits
- Electrical supply, control interfaces and redundancy requirements
- Energy prices, existing consumption measurements and investment criteria
These inputs can be reviewed with CEMS Chiller to assess a suitable project solution. An integrated or separate-loop arrangement should be defined against actual operating conditions and the technical quotation scope.
This article provides general information. Product selection and operating limits must be based on the relevant model’s technical documentation and project-specific calculations.
