hvac shoulder season

HVAC Shoulder Seasons: Peak Relative Savings from HVAC Optimization

In the heating, cooling, and air conditioning (HVAC) world, there are three primary seasons. Peak heating season occurs during the winter months, when outdoor temperatures drop below comfortable levels. Peak cooling season is during the summer months, when there’s a high demand for air conditioning to keep spaces cool. Finally, the shoulder seasons consist of the transitional periods between peak heating and cooling seasons — typically the spring and fall.

When outdoor temperatures remain in the 55-75 degree Fahrenheit range, it can be considered a shoulder month. These months are unique because outside air temperatures are often close enough to a building’s internal temperature, meaning demand for heating or cooling are at their lowest points of the year. Sometimes no heating or cooling is required.

Due to minimal equipment usage, shoulder seasons offer a strategic window for conducting maintenance work, reviewing system performance from the most recent peak season, and upgrading equipment. They are also optimal months for realizing maximum relative savings.

Shoulder season scenarios

Shoulder season temperature fluctuations can overburden water-based cooling systems, leading to excess energy consumption. For example, a boiler could run from the early morning hours when it is 35 degrees, but building heat combined with rapidly increasing outdoor temperatures cause the indoor temperature to get too high, too fast. By the afternoon time, when it’s 70 degrees outside, the cooling towers and chillers are working overtime to normalize indoor temperatures. 

In a two-pipe HVAC system, hydronic piping is shared for both heating from the boiler and cooling from the chiller plant. This presents a complex challenge to energy, sustainability, and facilities managers, whose buildings can only run either heating or cooling. Determining when to make the switch from one to the other can have a significant effect on energy costs.

In a four-pipe HVAC system, heating and air conditioning are controlled through separate piping. During shoulder season, dramatic increases and decreases in outdoor air temperatures can lead some four-pipe systems to run heating and cooling simultaneously, or in rapid succession. Such activity will actually increase energy consumption since both systems are pulling electricity, or one is having to power-up unexpectedly. As a result, energy costs rise. 

How Beacon delivers savings

Real-world data from a 400,000+ square foot medical office building. The highest relative savings were realized during shoulder season, when the wet bulb temperature falls between 55-75 degrees Fahrenheit.

Regardless of system configuration, with the help of the right partner, commercial buildings operators can realize material savings during shoulder season. Beacon, Tagup’s machine learning software for optimization, improves building efficiency by continuously adjusting cooling system operations. 

Beacon ingests live data for any relevant variable impacting building energy consumption. Weather data, for example, is particularly important during shoulder season. It is generally hard to predict weather behavior, or even monthly average temperatures. Day-to-day conditions can easily change from zero demand on the HVAC system to a high load for either heating or cooling.

It’s for these reasons that, for example, a fixed setpoint strategy is a poor approach when shoulder seasons come around. Building operators can no longer count on efficient HVAC performance based on consistent temperatures. When setpoints are not adjusted to account for the wide range of weather conditions throughout the shoulder season, inefficiencies prevail and energy and money are wasted. 

Another reason why fixed setpoint doesn’t make sense during shoulder season is because of the chiller plant. Chillers are designed and operated to comfortably handle peak loads during the summer months. When the spring and fall are here, buildings will rarely come close to touching that maximum load. This means energy is wasted if control parameters aren’t readjusted to compensate for seasonal changes. 

Beacon maximizes efficiencies and reduces HVAC energy costs by dynamically and autonomously altering setpoints based on real-time, real-world conditions. This is evermore important and effective during shoulder seasons.

Schedule an estimate to see what Beacon can save your site(s).

Robert Lauer Ph.D.
Robert Lauer Ph.D.
Lead Data Scientist
August 21, 2023