Which factor has the most significant influence on HVAC systems in a building?

The factor that has the most significant influence on HVAC systems in a building is the changes to the building envelope. The building envelope refers to the physical barrier separating the interior of a building from the exterior environment. It includes elements such as walls, roofs, windows, and doors. When there are changes to this envelope—such as improvements in insulation, new windows, or modifications in structural designs—it can greatly impact the heating and cooling requirements of the HVAC system.

Changes in the building envelope can alter how heat enters or escapes the building, directly affecting energy consumption, efficiency, and comfort levels. For instance, improved insulation means that less energy is needed to maintain desired indoor temperatures, which can lead to significant operational cost savings and improved performance from HVAC systems. Additionally, the envelope can influence indoor air quality and humidity levels, further emphasizing its critical role in how HVAC systems function.

While outdoor temperature, indoor air quality, and device efficiency are all important factors influencing HVAC systems, they do not have the same broad and fundamental impact as changes in the building envelope, which provide the foundational structure to which the HVAC system responds and adapts.