Data center site selection and climate

Site selection for a data centre usually starts with power, fibre and land cost. Climate and the local environment come next, and they shape the cooling design more than any other factor. Two identical buildings in Vancouver and Toronto will have different cooling plants, different energy use and different risks.

Canada has a reputation as a good place to cool data centres, and for much of the year that is true. But the details matter: summer wet-bulb peaks, wildfire smoke, very dry winter air and altitude all affect design. This guide explains how an HVAC engineer evaluates a site.

Climate data that matters

Dry-bulb and wet-bulb hours

The number of hours each year below certain dry-bulb and wet-bulb temperatures determines how much cooling can come from outdoor air or cooling towers without running compressors. Air-side economizers depend mainly on dry-bulb temperature and dew point. Waterside economizers and evaporative systems depend on wet-bulb temperature.

Hourly weather files (for example, the Canadian Weather Year for Energy Calculation files used in energy modelling) let engineers count these hours for a site and the chosen supply temperatures. The higher the supply air or water temperature the IT equipment allows, the more hours qualify. The guide to free cooling and economizers for data centers in Canada shows how this works.

Design extremes

Peak capacity must be sized for extreme conditions, not averages. Data centre designers often go beyond the 1 percent or 0.4 percent design values used for comfort cooling, using extreme annual or even record conditions so that cooling does not fail on the hottest day. The NBC climatic data and ASHRAE Handbook design data are the starting points.

Climate is also shifting. Many owners now test designs against projected future conditions over the facility's life, particularly for wet-bulb peaks that drive cooling tower and evaporative performance.

Regional character

These are general characteristics only. Microclimate, elevation and proximity to water can change them.

Altitude

Air density falls with elevation. At Calgary's elevation of roughly 1,050 m (about 3,450 ft), air is around 12 percent less dense than at sea level. Each cubic metre carries less heat, so fans must move more volume for the same cooling, air-cooled condensers and dry coolers lose capacity, and IT equipment fan behaviour changes. ASHRAE thermal guidelines also derate maximum allowable inlet temperature at high elevation. The guide on altitude and HVAC design explains the corrections.

Outdoor air quality

Air-side economizers bring large quantities of outdoor air near sensitive equipment. A site evaluation should consider:

• Wildfire smoke. Smoke events have become a regular summer occurrence in Western Canada and beyond. Designs need a smoke mode that closes outdoor air and switches to mechanical cooling, usually triggered by particle sensors.
• Gaseous contaminants. Sulphur and nitrogen compounds from industry, traffic or agriculture can corrode circuit boards. ANSI/ISA-71.04 classifies environments by corrosion rate, and ASHRAE recommends maintaining a G1 (mild) environment for IT equipment. Copper and silver coupon testing at a candidate site is inexpensive.
• Salt air near coasts, which affects outdoor coils and dry coolers.
• Dust, pollen and agricultural activity, which load filters and coils.
• Nearby exhaust sources, such as generators, industrial stacks and kitchen exhaust.

Water availability

Evaporative cooling and cooling towers consume water. In many parts of Canada water is plentiful, but municipalities may still limit withdrawals, charge for sewer discharge of blowdown, or restrict use during drought. Water treatment, Legionella control and winter freeze protection add operating cost.

Owners increasingly evaluate designs on both energy and water. Dry coolers and air-cooled chillers use little or no water but more energy in summer. Hybrid systems that use water only on the hottest days are a common compromise. See water usage effectiveness and water-free cooling.

Cold climate challenges

Cold is an advantage, but it introduces its own design problems:

• Very dry winter air. Outdoor air at minus 25 C contains very little moisture. Heated to IT inlet temperature it can fall well below the dew point recommended by ASHRAE. Recirculation, mixing and possibly humidification are required with air economizers.
• Freeze protection. Coils exposed to outdoor air, cooling towers and condenser water piping need glycol, drain-down or heat tracing strategies.
• Snow and ice. Intakes, louvres and roof equipment must stay clear of drifting snow and ice fall.
• Low ambient controls for refrigeration equipment that must run year-round.

Natural hazards

Cooling infrastructure is often the most exposed part of a data centre because so much of it sits on the roof or in the yard.

• Seismic. Much of coastal BC and parts of Quebec and Ontario have significant seismic hazard under the NBC. Equipment anchorage, piping restraints and post-disaster importance categories affect cost.
• Flooding. Avoid placing chillers, pumps and electrical rooms in flood-prone areas or below grade.
• Wind and hail. Prairie hail can damage condenser and dry cooler coils; hail guards are worth considering.
• Wildfire. Beyond smoke, consider defensible space for yard equipment.

Power, carbon and heat reuse

Grid carbon intensity varies widely by province. Hydro-dominated grids in Quebec, BC and Manitoba offer very low operational carbon, while Alberta's grid has historically been more carbon intensive, which can shift the value of efficiency measures. Cooling energy is a large share of non-IT power, so the climate's effect on power usage effectiveness (PUE) is directly tied to operating cost and emissions.

A site near district energy systems, greenhouses or large heat users creates opportunities for data center heat reuse, which works particularly well in cold climates with long heating seasons.

A site evaluation checklist

1. Obtain hourly weather data and count economizer hours for the intended supply temperatures.
2. Establish extreme design conditions, including future climate projections.
3. Correct for altitude where relevant.
4. Assess outdoor air quality, including wildfire smoke history and corrosive gas risk.
5. Confirm water supply, discharge limits and costs.
6. Identify seismic, flood, wind and hail exposure.
7. Review grid carbon intensity and any heat reuse partners.
8. Use energy modelling to compare cooling options at each candidate site.

Key takeaways

• Climate determines how many hours a data centre can run on free cooling, so count hours with real weather data.
• Size peak cooling for extreme and future conditions, not comfort cooling design values.
• Altitude, very dry winters, wildfire smoke and corrosive gases all affect Canadian designs.
• Water availability and grid carbon intensity are now as important as energy in comparing sites.
• Natural hazards often hit cooling equipment first, so plan its location and protection early.