How Thermal Energy Demand Intensity Impacts Building Design
The ways in which buildings use energy, particularly when it comes to efficiency, are an increasing area of focus when it comes to creating high-performance buildings that not only meet code requirements, but also go above and beyond in their performance achievements, including building in climate resiliency.
In September 2023, ASHRAE held their Building Performance Analysis conference in Austin, Texas. The theme of the conference was to take a holistic approach to building analysis and examine links between comfort, embodied carbon, and operational energy.
As part of this conference, RWDI’s own Aylin Ozkan, Technical Director, gave a presentation focused on thermal energy demand intensity (TEDI) and the major factors that influence it, as well as the overall impact TEDI can have on the design process.
We spoke to Aylin to get the most important takeaways from her presentation.
Q: What is thermal energy demand intensity (TEDI)?
Aylin: Thermal energy demand intensity, also known as TEDI, is the measure of energy in the form of heat (thermal energy) a building needs for both space conditioning and the conditions of ventilation air. TEDI only considers the heat load independent of the system type or heating equipment efficiency.
Q: How does TEDI impact the building design process?
A: Maintaining focus on TEDI during the creation of high-performance buildings, particularly while accounting for the effects of climate change and building in climate resilience, can be incredibly beneficial. For instance, the actions that help reduce TEDI most effectively, such as optimizing the building envelope, corridor pressurization, and energy recovery, help keep a building’s operational carbon low. Also, responsive orientation to the sun, optimum massing, and high-performance envelope will help buildings maintain habitable temperatures during power outages.
A holistic approach is key to effectively managing TEDI, and this starts quite early in the building design process. It typically means the integrated design process starts earlier, requires continuous coordination between various disciplines, and that building material suppliers need to be at the table during the early stages as well. Bringing suppliers to the table is particularly helpful, since it allows for a picture of what’s available in the market to make cost-effective and impactful building design decisions early.
Q: What major factors influence TEDI?
A: Passive design measures impact TEDI the most. This means when we want to reduce thermal demand, we must focus on building massing, orientation, and the building envelope. When it comes to the building envelope, for TEDI we are increasingly focused on how to apply detailed assemblies, including balcony design, glazing, and solutions to create a thermally efficient and airtight envelope.
Some building codes may have additional requirements that impact TEDI, such as the requirement of a detailed thermal bridge calculation. Corridor pressurization can also have a significant influence on TEDI, which is why it needs to be considered during the early stages of the design process.
Q: How do we achieve reductions in TEDI?
A: Achieving TEDI reductions requires a holistic approach, including making improvements not only to the active systems of the building, but to passive systems as well. This means optimizing massing and orientation, designing an airtight building that could help reduce the outdoor air needs for corridor pressurization, and many of the main influences on TEDI I mentioned previously.
Energy recovery ventilation units are vital to achieving TEDI reduction targets, and decisions must be made early on for these systems to achieve high efficiency. Some types of ERV systems require significant redesign if considered during later stages.
Q: How do we achieve reductions in the other main energy metrics? How do they impact TEDI?
A: In this case, we’re looking at total energy use intensity (TEUI) and greenhouse gas intensity (GHGI) as our other main energy metrics. To achieve TEUI reductions, we need to consider electrification and improving efficiencies. Common practices include reducing light density, choosing low-flow water fixtures, switching to heat pumps for space and DHW heating – and overall looking for strategies to improve the efficiency of heating and cooling systems. Meeting the GHGI target can be as straightforward as simply electrifying the building if the grid emission mix is favorable.
It should be noted, however, that while reducing TEUI helps manage GHGI (and vice versa), neither has a significant impact on achieving TEDI reductions. Managing TEDI, however, does have a significant impact on TEUI and GHGI, making them easier to manage.
Q: What is the number one takeaway from your presentation?
A: Creating high-performance buildings, especially ones focused on thermal resilience, requires impactful design choices. In many cases, this means acting on strategies to manage TEDI, including passive design measures like examining building massing, tightening the building envelope with strategic detailed assemblies to lower heat loss, and managing outdoor air rates for corridor pressurization.
It’s also worth noting that building codes and standards are beginning to pay more attention to thermal demand. The Toronto Green Standard, for example, is stringent when it comes to TEDI now. TEDI is commonly found in other building codes as a path you can follow, and while it may not be required in these codes yet, it is quite likely to become so in the future. Focusing on it now helps get building designers ahead of the curve.