Written By: Jessica Renner, Catalyst Partners
When most people think of building energy models, two uses usually come to mind: predicting energy use intensity (EUI) and documenting compliance for energy code and certifications like LEED. While those are both important, an energy model can be much more than a compliance checkbox.
In fact, the richness of the data inside a model makes it an incredibly versatile tool. Here are a few powerful, but less talked about, ways energy models can be used.
1. Exterior Glass SHGC Sensitivity Analysis
The solar heat gain coefficient (SHGC) of exterior glass can sometimes dramatically affect both cooling and heating loads in a building. Instead of defaulting to your standard glass selection, an energy model (a computer-based simulation of how a building uses energy over time) allows you to test multiple SHGC scenarios and see how sensitive your building is to this variable.
By plotting SHGC values against the anticipated annual energy use generated by the energy model, you can quickly visualize the trade-offs and identify whether your project benefits more from higher solar gains (helping offset winter heating) or lower gains (reducing summer cooling demand). If reducing carbon emissions or the peak cooling load is more important to your particular project, consider directly comparing SHGC performance to those variables. See two very different real world examples of analysis output below:
Figure 1: New Construction High Rise Mixed-use building example. An energy model was used to create this SHGC sensitivity curve. The graph shows that the building benefits from exterior glass with lower SHGC (0.21-0.27). Reducing the summer cooling load is most impactful on the building’s annual utility costs.
Figure 2: New Construction Research and Design Facility example. Each dot on the graph represents a unique combination of energy conservation strategies, ranging from lighting to envelope to controls. A genetic algorithm was used to simultaneously generate and evaluate thousands of possible design solution combinations. The most effective strategy combinations, shown by the dots clustered in the lower left corner, are considered the “optimized solutions” for this building. The overall trend indicates that moderate SHGC values (0.30–0.40) produce the best-performing solution sets. Note that this analysis focuses on EUI and operational carbon, not energy cost.
This type of analysis can help the team justify glazing choices to building owners, potentially defending an upfront cost increase.
BONUS TIP: Not every building orientation has to have the same type of glass. Consider optimizing the glass SHGC by orientation to take advantage of seasonal changes in weather and sunlight.
2. Heat Recovery Chiller Sizing
Heat recovery chillers are becoming more common in buildings that have simultaneous heating and cooling demands. But right-sizing them is tricky without understanding how those loads will exactly play out once the building is in operation.
An energy model provides hourly heating and cooling output that can be compared side-by-side. By overlaying these profiles, you can identify the size and timing of overlapping loads, which is essential for sizing the heat recovery chiller correctly. If a heat recovery chiller is oversized, the project could experience:
Poor efficiency at part load: Heat recovery chillers are most efficient when operating near their design point. Oversized units spend more time cycling or running at very low part-load conditions, which wastes energy and reduces heat recovery effectiveness.
Higher upfront cost: Larger chillers and associated pumps, piping, and controls drive up first cost. If the building never needs that capacity, the investment is wasted.
Reduced system reliability: Short cycling from frequent start/stop operations can increase wear and tear on compressors, shortening equipment life and raising maintenance costs.
Instead of sizing based on rules of thumb, design around the actual anticipated building schedules and loads using the energy model.
3. Electricity Rate Selection
Utility rates can be just as important as equipment efficiency when it comes to long-term building operating costs. Energy models provide detailed load profiles that reveal not only how much electricity a building uses, but also when it uses it. That when is often called the peak load—the highest amount of demand a building places on the system during a given period. Peak loads matter because they not only determine equipment sizing but can also trigger expensive demand charges on utility bills.
With this information, you can compare different electricity rate structures (e.g., flat, time-of-use, or demand-based tariffs) to see which one best aligns with the building’s peak demand times.
For example, if the model shows peak loads occurring in the afternoon, a time-of-use rate with high afternoon charges may not be the best choice. On the other hand, if your building has relatively flat demand, a demand-based rate could be more economical.
This proactive approach can demonstrate significant operational savings over the life of the building before a utility bill even arrives.
BONUS TIP: By looking at electrical load profiles, you can identify opportunities for shifting energy use to cheaper off-peak hours by using batteries or thermal storage.
4. Resilience Under Extreme Weather
Designing for average weather conditions isn’t enough anymore, especially as climate change drives more frequent heat waves, polar vortexes, and heavy storm events. An energy model can be used to explore how a building reacts when conditions push beyond the “typical” design day.
By running simulations with extreme weather files, you can test questions such as:
Heat wave: Will cooling systems keep up during a week of consecutive 100°F days, or will indoor conditions creep beyond comfort limits?
Polar vortex: Does the heating plant have enough capacity to maintain setpoints during sustained subzero temperatures?
By testing against the extremes, design teams can identify vulnerabilities early and make targeted upgrades that improve occupant comfort, protect equipment, and extend building life.
In conclusion, energy models are often used as compliance tools, but their real value is demonstrated when project teams use them to guide early design decisions and future planning. By applying models in multiple ways, design teams can unlock value that would otherwise remain untapped.
Conclusion
In conclusion, energy models are often used as compliance tools, but their real value is demonstrated when project teams use them to guide early design decisions and future planning. By applying models in multiple ways, design teams can unlock value that would otherwise remain untapped.
Key Takeaways:
Smarter glazing selection: Instead of defaulting to what’s available or cheapest, project teams can use SHGC sensitivity analysis to justify glazing choices that balance aesthetics and energy performance.
Right-sized equipment: Use hourly data output to size heat recovery chillers and potentially avoid costly oversizing. This can ensure that equipment is matched to the building’s actual operating profile.
Lower utility costs: By comparing utility tariffs against modeled building load profiles, owners can select the electricity rate structure that minimizes operating costs from day one.
Resilience: Running the model against heat waves and extreme cold streaks can help a team understand how the building behaves when conditions push beyond the “typical.” This allows for thoughtful HVAC sizing, envelope upgrades, and other design choices that protect systems, improve occupant comfort, and make the building more durable for the future.
