Internal gains are a crucial yet often overlooked aspect of sustainable building design. While solar panels and green rooftops steal the spotlight, the thermal energy generated inside a building—from occupants, lighting, and equipment—can significantly optimize energy efficiency. These hidden heat sources are key to reducing reliance on external heating systems and creating greener, more sustainable spaces.
In this blog, we’ll delve into internal heat gains, how to calculate them, and their critical role in achieving sustainable design goals.
What Are Internal Heat Gains?
In every building, heat doesn’t just come from the sun. Inside, three primary sources contribute to internal heat gains:
- People
- Lighting
- Equipment
When calculated accurately, these sources release thermal energy that can influence energy usage and efficiency. Together with solar gains, internal heat gains form the foundation for designing energy-efficient buildings.
Calculating Heat from People
Our bodies naturally emit heat, which varies depending on activity levels. For example:
- A person working at a desk generates around 100 W of heat.
- Someone engaged in sports can release as much as 500 W.
To calculate this energy for a building:
- Determine the building’s purpose (e.g., office, gym, or home).
- Multiply the number of occupants by the thermal energy released per person.
- Factor in working hours per day and days per month for an accurate figure.
This calculation shows how a bustling office will have higher internal heat gains than a sparsely populated house. Reference tables, often found in building standards or guides, provide typical heat emission rates per person.
Lighting: A Dual Role
Lighting is essential for visibility and contributes to internal heat gain. The heat released depends on the installed power density, typically measured in W/m².
For example:
- Office buildings, where lights remain on for extended periods, will emit more heat compared to residential homes.
To calculate lighting heat gains:
- Identify the average installed power density for the building type.
- Multiply this value by the lit area and operational hours.
Modern lighting solutions, such as LEDs, can reduce energy consumption and heat emissions, making them a sustainable choice for green buildings.
Heat from Equipment
Computers, printers, kitchen appliances, and other devices contribute significantly to internal heat gains, especially in commercial spaces. Like lighting, the heat emitted by equipment depends on power usage and operational time.
For precise calculations:
- Use data from project designs or manufacturer specifications.
- Multiply the equipment’s thermal energy output by the hours it operates.
Again, this data is often expressed in W/m², making it easy to scale calculations based on the building’s size.
Total Heat Gains: A Holistic View
Once you’ve calculated the heat gains from people, lighting, and equipment, these are added to solar heat gains to find the total heat gains for the building. For example:
- Calculate the energy in kWh for each source.
- Sum these values for a monthly or annual total.
The result helps architects and engineers design energy-efficient HVAC systems, reducing energy waste and enhancing sustainability.
Why Internal Heat Gains Matter in Sustainable Design
Understanding internal heat gains isn’t just about numbers; it’s about optimizing energy use. By accurately predicting heat contributions:
- HVAC systems can be sized appropriately, reducing energy waste.
- Designers can leverage internal gains to offset heating needs in colder months.
- Combined with passive solar design, internal gains enhance overall energy efficiency.
For instance, studies show that internal heat gains can account for 10–20% of a building’s energy use, depending on its purpose and occupancy.
Conclusion
Internal heat gains are more than just a technical detail—they’re a powerful tool for energy efficiency in sustainable building design. By harnessing the heat generated by people, lighting, and equipment, architects can reduce reliance on external heating systems and create buildings that work smarter, not harder.
Ready to design greener, more efficient spaces? Start by integrating internal heat gains into your calculations—it’s simpler than you think, and the benefits are immense.
To deepen your understanding sustainable design, explore the following: Energy Modeling and Heat Transfer Calculation: Essential Tools for Sustainable Building Design
Top 11 Inspiring Green Building Types That Redefine Sustainability
