In one of our previous posts, we have covered what weather-dependent load is and how it can provide valuable insights into building energy consumption. This week, we’re focusing on specific examples that showcase common weather dependent energy patterns we observe when analyzing buildings.
For all the examples, the x-axis represents outdoor air temperature in °C, and the y-axis shows the additional weather-related energy consumption in kW. The blue line indicates unoccupied regime consumption, while the red line represents occupied regime consumption.
Cooling dominated building
In Figure 1, we see a typical cooling-dominated building with well-managed operations. Notice how energy consumption rises with increasing temperatures only during the occupied regime. During unoccupied periods, the energy consumption remains flat, indicating that the cooling setback is functioning effectively. This is the desired behavior.
However, in Figure 2, we see a different scenario. While there is some distinction between the occupied and unoccupied regimes, the gap is not sufficient to indicate effective cooling setback. This suggests that cooling continues even when the building is unoccupied, revealing energy savings potential.
Heating dominated buildings
The same logic applies to heating-dominated buildings. Heating setbacks during unoccupied periods should be optimized to balance energy savings with thermal inertia. Overly aggressive reductions—such as complete weekend shutdowns—can delay Monday warm-up and strain HVAC systems during recovery. A practical target is an 80% heating setback. For example, if the heating-related load is 10kW, the unoccupied load should ideally be 8kW. Reducing the indoor temperature by just 1°C can lower the heating load by approximately 6%.
Figure 3 demonstrates a heating-dominated building with a well-implemented setback. In contrast, Figure 4 shows a building where heating setback is either nonexistent or poorly implemented, as indicated by the overlapping consumption patterns.
Buildings with Both Heating and Cooling Loads
Of course, a building doesn’t have to be just cooling or heating dominated. Many energy patterns resemble a “U” shape, where we have some heating-related energy consumption in colder months, minimal load during shoulder periods, and cooling-related consumption in warmer months. How should we interpret such patterns, and what should we focus on? Let’s look at a few examples.
In Figure 5, we see a building with both heating and cooling loads, but with almost no distinction between the occupied and unoccupied regimes. The slight reduction in cooling load during unoccupied hours is not sufficient to indicate effective setback implementation. Uncovering immediate savings opportunities can be as easy as reviewing existing equipment schedules and setpoints with no need for costly investment.
In Figure 6, we observe a more defined cooling setback. At 30°C, the unoccupied cooling load is approximately 4kW, while the occupied load is 10kW. However, the heating regime shows minimal differentiation, indicating a missed opportunity to adjust heating schedules and setpoints.
Finally, let’s look at a building that gets it right for both heating and cooling. In Figure 7, we see a clear reduction in the unoccupied regime for both heating and cooling loads. This is the desired behavior, demonstrating effective setbacks and indicating significant potential for savings through targeted schedule and setpoint adjustments.
How can we apply these insights in practice?
Identifying inefficiencies in weather-dependent load patterns provides a clear path to actionable savings. By fine-tuning setpoints and schedules, we can reduce unnecessary consumption, estimate potential savings, and prioritize buildings within a portfolio for targeted adjustments.
Next week, we’ll shift our focus to time-related load patterns and how they shape building energy use. Stay tuned!
