Free cooling and economizers for data centers in Canada

Canada is one of the best places in the world to cool a data center without compressors. Long, cold winters and cool shoulder seasons mean outdoor air or outdoor-cooled water can remove server heat for much of the year. Economizers, the equipment and controls that make this possible, are the single biggest lever on cooling energy in most Canadian facilities.

The cold also brings challenges that warmer regions do not face: freezing coils, very dry winter air, snow and ice at intakes, and wildfire smoke in summer. This guide covers the main economizer types, how they suit different Canadian climates, and the details that make them work.

What counts as free cooling

Free cooling means rejecting heat without running refrigeration compressors, or while running them at reduced lift. The fans and pumps still use energy, so it is not literally free, but the savings over mechanical cooling are large. Economizers can operate in three modes:

• Full economizer: outdoor conditions handle the entire load.
• Partial or integrated economizer: outdoor conditions handle part of the load and chillers or DX trim the rest.
• Mechanical cooling: outdoor conditions are too warm or humid to help.

The warmer the supply temperature the data center accepts, the more hours fall into the first two modes. Raising server inlet setpoints toward the upper end of the ASHRAE TC 9.9 recommended range of 18 to 27 °C (64 to 81 °F) is therefore the first step in any economizer strategy.

Economizer types

Direct airside economizers

Outdoor air is filtered and supplied directly to the data hall, with hot exhaust air relieved outdoors or mixed back to temper the supply. This is the most efficient option in cool climates, but it exposes IT equipment to outdoor contaminants and humidity swings.

In Canada, direct airside systems need:

• Mixing with return air to keep supply temperature above the minimum and avoid thermal shock during very cold weather
• Humidity management, since cold outdoor air heated to supply temperature becomes very dry
• High-efficiency filtration, typically MERV 13 or better, with plans for wildfire smoke events
• Intake design that avoids snow ingestion, drifting and re-entrainment of exhaust or generator fumes

Indirect airside economizers

An air-to-air heat exchanger (plate, heat wheel or heat pipe) separates outdoor air from data hall air. Outdoor air cools the recirculating data hall air without mixing with it. Many units add evaporative cooling on the outdoor air side in summer. Indirect systems avoid contamination and humidity issues while still giving long economizer hours. They are large, so plan roof or yard space early.

Waterside economizers

In chilled water plants, a plate heat exchanger between the condenser water (or a glycol loop) and the chilled water loop lets cooling towers or dry coolers produce chilled water directly when outdoor conditions allow. The heat exchanger is usually piped in series with the chillers, so it can precool return water and let chillers trim the rest. See waterside economizers and free cooling in Canada for detail.

Dry coolers and pumped refrigerant economizers

Closed-circuit dry coolers with glycol reject heat to outdoor air without water consumption. They pair well with warm-water systems such as direct-to-chip liquid cooling. Some DX CRAC systems include pumped refrigerant economizers that bypass the compressor in cold weather and circulate refrigerant with a small pump.

Comparing options

Canadian climate considerations

Climates vary widely across the country, so economizer selection should be based on hourly weather data for the site. Use Canadian weather files for energy modeling and NBC climatic data for design extremes. See selecting outdoor design conditions for Canadian cities.

• Prairie cities such as Calgary and Edmonton: cold, dry winters and generally dry summers favour airside and dry cooler economizers. Calgary's altitude reduces air density, which affects fan and coil selections. Humidification may be needed with direct airside systems.
• Coastal British Columbia: mild temperatures year round with high humidity in winter. Long partial economizer hours, but fewer very cold hours.
• Ontario and Quebec: cold winters and warm, humid summers. Excellent winter free cooling, with mechanical cooling or evaporative assist needed on humid summer days.
• Northern sites: extreme cold makes freeze protection and mixing control critical.

Freeze protection and cold weather details

1. Use glycol in any outdoor loop that can be exposed to freezing, sized to the site's extreme low temperature. See glycol systems.
2. Isolate water-filled heat exchangers from glycol loops with plate heat exchangers.
3. Provide basin heaters, bypass valves and controls for cooling towers operated in winter, or drain them and use dry coolers.
4. On airside systems, design mixing boxes for good mixing to avoid stratification and frozen coils.
5. Protect intakes from snow with hoods, louvers rated for water and snow rejection, and adequate height above grade and roof.

Controls

Economizer savings depend on controls more than equipment. Good sequences:

• Switch between modes based on measured outdoor wet bulb or enthalpy, not fixed calendar dates
• Use integrated operation so chillers trim rather than shut off abruptly
• Reset chilled water and supply air temperatures upward when IT inlets allow
• Avoid unstable cycling between modes near changeover points
• Alarm and trend economizer status, so a stuck damper or valve is caught quickly

Trend reviews often show economizers that have been disabled for months after a fault. Regular checking is part of retro-commissioning.

Code and standard context

ASHRAE Standard 90.4 addresses data center mechanical efficiency, and economizers are a major contributor to compliance. NECB requirements for economizers apply to many building systems, and provincial adoption differs. Confirm with the authority having jurisdiction which energy code applies to your project.

Frequently asked questions

Is direct outside air safe for servers?

It can be, with good filtration, humidity control and monitoring. Facilities near industrial or wildfire-prone areas often prefer indirect systems to avoid contamination risk.

How many hours of free cooling can I expect?

It depends on site climate, supply temperature and system type. Energy modeling with hourly weather data gives a defensible answer for your site.

Key takeaways

• Economizers are the biggest cooling energy saver in Canadian data centers.
• Raising supply temperatures within the ASHRAE envelope increases free cooling hours.
• Choose between direct airside, indirect airside, waterside and dry coolers based on climate, contamination risk and water use.
• Freeze protection, intake design and humidity control are essential in Canada.
• Good controls and regular trend review keep economizers working.