Seasonal testing and deferred commissioning

Buildings are rarely turned over in the season that tests every system. A project completed in January cannot demonstrate chiller capacity, cooling tower control or summer humidity performance. One completed in July cannot show how heating plant, freeze protection and winter humidification behave at -25 C. Canada's wide seasonal swings make this a bigger issue here than in many places.

Seasonal testing addresses the gap. Tests that cannot be performed under realistic conditions at turnover are scheduled for the appropriate season, usually within the first year of occupancy. Deferred testing is a broader term covering any commissioning activity postponed beyond turnover, whether because of season, incomplete construction, low occupancy or equipment delivery delays.

Why simulation is not always enough

During functional performance testing, many seasonal conditions can be simulated by overriding sensor values at the building automation system. Overriding the outdoor air temperature to -20 C in summer, for example, will show whether the economizer closes to minimum and the preheat valve opens. That verifies control logic.

What overrides cannot show is how the physical system performs under real loads:

• Whether the heating plant can meet the load on the coldest days.
• Whether preheat coils and freeze protection prevent coil damage when outdoor air is actually far below freezing.
• Whether the chiller plant stages properly and maintains supply temperature on a hot, humid afternoon.
• Whether cooling towers control properly at high wet bulb temperatures, and whether winter operation and basin heating work when needed.
• Whether dehumidification and humidification hold space conditions within the specified range.
• Whether control loops remain stable across the full range of load.

Real conditions also reveal problems that simulation never exposes, such as stratification in mixing plenums, coil freeze-ups at specific damper positions or sensors affected by solar radiation.

What to test in each season

The shoulder seasons deserve as much attention as the extremes. In much of Canada, buildings operate for long periods in mild weather when economizers, heat recovery and changeover logic matter most. See economizers: types, controls and common failures for why these functions often fail without anyone noticing.

Planning seasonal testing

In the commissioning plan

The commissioning plan should identify, from the outset, which tests may need to be deferred and the conditions required for each. Defining required conditions avoids arguments later. For example, a cooling plant test might require outdoor conditions within a few degrees of summer design, or a building cooling load above a stated percentage of design capacity. Design conditions for Canadian locations are found in the climatic data of the National Building Code. See selecting outdoor design conditions for Canadian cities.

In the contract documents

Seasonal testing only happens reliably if contractors are obligated to return for it. The specifications should require:

• Contractor participation in seasonal testing, including controls and mechanical trades and, where needed, equipment manufacturers.
• Correction of deficiencies found during seasonal testing under the contract or warranty.
• A defined window for seasonal tests, typically within the first 12 months after substantial completion.
• Holdbacks or other contractual mechanisms where the owner considers them appropriate.

In the schedule

Assign target dates based on climate. In Edmonton or Calgary, peak winter tests are typically planned for January or February. In Vancouver, extreme cold is rare, so winter testing focuses on heat pump performance and changeover in cool, wet conditions. In Toronto, summer testing in July or August is likely to see high humidity. Monitor forecasts and be ready to mobilize on short notice when suitable conditions arrive.

Running seasonal tests

1. Confirm conditions. Verify that outdoor and load conditions meet the criteria defined in the plan.
2. Review trend data first. Weeks of trends before the visit often show whether systems are performing and where to focus.
3. Execute the test procedures prepared during the construction phase, updated for any changes made since turnover.
4. Record results and enter deficiencies in the issues log.
5. Coordinate corrections with contractors while warranty obligations apply.
6. Retest as needed and update the commissioning report.

Trend data is particularly valuable for seasonal verification. A few weeks of good data during a cold snap or heat wave can verify many functions with little site time. See trend logging and using BAS data.

Other reasons for deferral

Seasonal tests are not the only deferred activities. Others include:

• Low occupancy. Ventilation, demand-controlled ventilation and some cooling tests are more meaningful once the building is occupied.
• Phased occupancy. Floors or tenant spaces completed after initial turnover.
• Late equipment. Items delivered or installed after substantial completion.
• Incomplete controls. Graphics, trending or integration finished after turnover.

Each deferred item should appear in the issues log with a responsible party and a target date.

Making sure deferred tests happen

Deferred testing has a habit of being forgotten once the building is occupied and the project team has moved on. Practical safeguards:

• Track all deferred items in one list, reviewed monthly.
• Schedule tests on calendar dates rather than "when conditions allow" alone.
• Link seasonal testing to the end-of-warranty review, often held about 10 months after substantial completion.
• Involve operations staff, who will be present when the right weather arrives.
• Keep the commissioning provider engaged through the first year.

Frequently asked questions

Can seasonal testing be skipped if overrides were tested?

Override testing verifies logic but not real performance. Skipping seasonal testing means capacity, stability and freeze protection under real conditions are never verified, which is a significant risk in Canadian climates.

Who pays for seasonal testing?

The commissioning provider's scope should include it, and the contractors' scope should include participation and correction of deficiencies. Defining both in the original contracts avoids extra cost disputes.

Key takeaways

• Overrides verify control logic, but only real seasonal conditions prove capacity, stability and freeze protection.
• Canadian climates make seasonal testing especially important for heating, cooling and shoulder-season functions.
• Define required test conditions, contractor obligations and timing in the commissioning plan and specifications.
• Use trend data during extreme weather to verify many functions efficiently.
• Track deferred tests actively and tie them to the warranty review. Our building commissioning scope includes first-year seasonal testing.