Understanding ERV Efficiency
An energy recovery ventilator moves stale indoor air outside. It also brings fresh outdoor air inside. The core transfers heat and moisture between both airstreams. This process reduces the load on heating and cooling equipment. Efficiency shows how much outdoor air was preconditioned before it reached the room.
Important Readings
A good calculation needs three sets of readings. Measure outdoor air before the core. Measure return air entering the exhaust side. Measure supply air leaving the core. Temperature gives sensible recovery. Humidity ratio gives latent recovery. Enthalpy gives total recovery. These values describe different parts of comfort and energy use.
Efficiency Types
Sensible efficiency compares the temperature change caused by the core. It is useful for dry climates and heating checks. Latent efficiency compares moisture change. It matters in humid climates and dehumidification work. Total efficiency compares enthalpy. It includes both heat and moisture in one result.
Mechanical Ventilation Impact
Mechanical ventilation systems can look efficient but still waste power. Fans, dirty filters, pressure drop, and unbalanced airflow reduce net benefit. This calculator includes airflow, pressure, fan power, bypass, and derate inputs. These options help compare measured recovery with operating savings.
Airflow Balance
Balanced airflow is important. If supply airflow is much higher than exhaust airflow, the core cannot recover energy from all incoming air. If exhaust airflow is higher, the building may lose conditioned air. The calculator uses the lower airflow for recovered energy. It also reports the balance ratio for review.
Field Accuracy
Field readings need care. Use steady operation. Keep doors and bypass dampers in normal positions. Place sensors away from sun, coils, and wet surfaces. Let readings stabilize before recording values. Small humidity errors can change latent and total efficiency.
Use Results Carefully
The results should be used as engineering estimates. They are not a certified rating. Manufacturers test equipment under controlled standards. Field results can differ because airflow, installation, frost control, leakage, and maintenance vary. Still, a careful calculation is useful. It can show poor setup, fouled cores, or weak fan performance.
Better Decisions
Use the output to improve decisions. Compare sensible, latent, and total values together. Then check the net recovered energy. A high efficiency with high fan power may save less than expected. A moderate efficiency with low pressure drop can perform better during daily operation.