What happens to the HVAC system when the distribution system operates outside the thermal envelope?

When the distribution system of an HVAC system operates outside the thermal envelope, the HVAC unit needs to exert more effort to maintain the desired indoor temperature. This happens because the air traveling through the ducts can lose or gain heat, depending on the surrounding environment outside the thermal envelope. As a result, more energy is required to heat or cool the air to the desired temperature before it is delivered indoors.

The increased workload directly impacts the efficiency of the HVAC system, as it has to work harder to compensate for the temperature variations. This can also lead to increased wear and tear on the system, potentially shortening its lifespan and increasing maintenance costs. Therefore, the correct understanding of this scenario is that the HVAC system indeed works harder when the distribution system is outside the thermal envelope.