By: Nicole Imeson
Efficient building operation depends on HVAC sequences tailored to seasonal demands. Teams prioritize functional performance testing near project completion, focusing on systems actively in use—like heating during winter or cooling in summer. Off-season testing challenges arise without adequate system load, complicating commissioning tasks for systems such as chilled water plants in winter. Seasonal testing revisits systems under full operating load to validate functional performance, optimize system efficiency, reduce energy costs, and enhance thermal comfort.
“Seasonal testing allows the CxP to ensure the equipment and systems are meeting the design conditions. This is the next step in ensuring the owner’s project requirements and design intent are being met,” explained Craig Hatch, President of CFMS Alberta Ltd.
Seasonal Testing in Action
Seasonal functional performance testing enhances the overall commissioning process for New Construction (NCCx), Existing Building (EBCx), or Ongoing Commissioning (OCx) by testing each major system at peak demand during seasonal temperature shifts. During design, the CxP collaborates with the consulting team to optimize control sequences, reducing energy use while maintaining thermal comfort and ensuring the design meets the owner’s project requirements. For example, adjusting a heating plant on an outdoor air reset schedule decreases water temperature as outdoor temperatures rise and increases it as they fall, aligning heat output with building heat loss.
With the growing use of condensing boilers, outdoor air reset schedules play a critical role in cutting energy consumption, as boiler efficiency depends on the return water temperature. Balancing this requires delivering enough hot water to offset space heat loss at terminal units while minimizing water temperature to boost efficiency. Ventilation systems may also fluctuate the supply air temperature based on seasonal changes, supplying warmer air in winter to reduce localized reheating and cooler air in summer to offset additional solar gains in the building.
Shoulder Season
In spring and fall, when the outdoor air temperature aligns with the supply air temperature setpoint, buildings can take advantage of free cooling by increasing the outdoor air intake volume to cool the building. In winter, minimizing the outdoor air to its minimum position reduces the energy required to heat the outside air while maintaining ventilation rates. Similarly, when the outdoor air temperature exceeds the supply air temperature setpoint in summer, the outdoor air is reduced to the minimum position to limit the cooling energy required. Seasonal testing also optimizes the switchover between heating, free cooling, and mechanical cooling.
Heat pumps offer energy-efficient heating by transferring heat rather than generating it. However, heat pumps lose performance in cold temperatures and require supplemental heating. Fine-tuning the switchover point between the heat pump and supplemental heat is critical for minimizing utility costs and maintaining thermal comfort. The switchover point is related to the heat pump's Coefficient of Performance (COP) at colder outdoor air temperatures and the energy costs to operate the heat pump and supplemental heat source (electric or natural gas).
Conflicting Setpoints
“Testing systems under full-load conditions provide an opportunity to enhance or optimize the sequences of operation to improve energy efficiency,” explained Hatch.
Seasonal changes also impact different areas of a building. The north side of a building, which receives the least sun, often requires a smaller cooling load than south-facing spaces with higher solar loads. In locations with high solar gains in winter, there may also be times throughout the year, especially in the shoulder season (spring or fall), when the south zones call for cooling while the north zones call for heating. A central heat pump system can benefit by rejecting heat from the south zone and injecting it into the north zone.
Similarly, seasonal testing ensures spaces avoid simultaneous heating and cooling in a single zone, preventing unnecessary energy waste. Simultaneous heating and cooling are less likely in spaces controlled by a single thermostat. However, in older buildings, modified over time, multiple thermostats may control a single space, increasing the risk of conflicting setpoints that trigger heating and cooling simultaneously. When end users control both thermostats, this issue becomes difficult to resolve entirely. However, revising the system to use a single thermostat or adding controls programming to prevent conflicting temperature requirements can help mitigate the problem.
Hydronic heating and cooling systems must balance effectively delivering hot and cold water across zones. Proper balancing reduces pumping power and ensures the bypass (where applicable) opens only when most system valves are closed.
Automatic or Manual Switchover
In newer buildings, building automation systems (BAS) adjust supply air temperature, activate different equipment, or modify water temperatures based on outdoor air conditions. However, in older buildings, building operators may make seasonal changes, which can be a labor-intensive process, especially in regions with significant temperature fluctuations. For example, in Calgary, Alberta, Canada, it’s possible to see a 30-40°F temperature fluctuation over 24 hours. Operator time to implement seasonal changes should be included in controls upgrade or equipment replacement payback period calculations.
Seasonal testing enhances HVAC performance, ensuring consistent indoor temperatures and improved air quality. Occupants enjoy greater comfort year-round, while buildings benefit from energy-efficient operations, extended equipment lifespans, and lower utility and maintenance costs.
As energy costs continue to rise and sustainability targets become more ambitious, seasonal testing plays an increasingly vital role in the commissioning process. It increases energy efficiency, enhances thermal comfort, and creates long-term value for building owners. Seasonal testing offers significant benefits to buildings by optimizing heating and cooling systems through strategic adjustments.
By utilizing resources from the Building Commissioning Association (BCxA), building managers and operators can implement best practices in seasonal testing, maximizing efficiency while reducing environmental impact. With the right approach to seasonal testing, buildings can maintain peak performance regardless of seasonal changes, supporting both financial goals and environmental stewardship in today’s competitive landscape.