Understanding the Relationship Between Thermal Mass & HVAC Efficiency

From concrete to steel, commercial buildings are made up of a variety of materials that conduct heat at different rates. These speeds, known as U-values, are significant but not wholly accurate. Two walls can have the same U-value but consume different amounts of energy, thus affecting the overall performance of custom HVAC systems. Why? Because the materials that compose these walls have different thermal masses.

What Is Thermal Mass?

Thermal mass is the amount of heat energy a wall absorbs and stores through the process of conduction. It is calculated using the combined materials’ specific heat, density, and thickness. Here, specific heat refers to the amount of energy it takes to increase the temperature of one pound of the wall by one degree.

A significant amount of energy is needed to change the temperature of dense materials like tiles, concrete, and bricks. Therefore, these materials are said to have a high thermal mass. Thin, lightweight materials like timber, on the other hand, have low thermal mass.

How Does It Affect HVAC Efficiency?

Heat transfers occur only when a wall’s interior surface becomes warmer than the ambient air. Because materials with high thermal mass absorb more energy than those with a low thermal mass, this temperature increase occurs long after outside temperatures reach their peak. Therefore, thermal mass prevents temperature fluctuations by storing heat energy during the day and re-radiating it at night.

This phenomenon not only makes the building’s interior cooler and more comfortable, but it also helps your custom HVAC system operate more efficiently. On days with large temperature fluctuations, for example, the heat and solar energy absorbed by the walls may never reach the interior of your property. As a result, cooling equipment doesn’t need to work as hard, and the building uses less energy.

By understanding thermal mass, contractors and property managers can pick more efficient building materials as well as design better custom HVAC systems. Call us at (914) 668-4700 to learn more about this invaluable measurement.