In a single-duct constant-volume system without heat recovery, what happens to energy use?

In a single-duct constant-volume system without heat recovery, what happens to energy use?

• A. Energy use goes down.
• B. Fan energy consumption increases but coil energy stays the same.
• C. Ventilation requirements increase.
• D. Energy use goes up.

Answer: (D)

In a single-duct, constant-volume system with no heat recovery, increasing ventilation means more outdoor air must be conditioned to indoor conditions. Since there is no heat recovery, the energy used to heat, cool, and dehumidify that outdoor air cannot be reclaimed from exhaust air. The coil must handle a larger conditioning load, raising its energy consumption, and the overall energy use goes up. The fixed total air flow means you’re not reducing fan work, and while ventilation requirements rising is part of why energy goes up, the practical result is a higher total energy demand.

In a single-duct, constant-volume system with no heat recovery, increasing ventilation means more outdoor air must be conditioned to indoor conditions. Since there is no heat recovery, the energy used to heat, cool, and dehumidify that outdoor air cannot be reclaimed from exhaust air. The coil must handle a larger conditioning load, raising its energy consumption, and the overall energy use goes up. The fixed total air flow means you’re not reducing fan work, and while ventilation requirements rising is part of why energy goes up, the practical result is a higher total energy demand.