The inputs you need first
Sizing starts with both airflows (m3/h), the supply and exhaust inlet temperatures, the efficiency target, the allowable pressure drop, and the physical space. Balanced airflows give the best recovery; large imbalances waste core capacity.
A simple recovered-energy calculation
Recovered power is roughly Q equals 0.33 times V times DeltaT, where V is airflow in m3/h and DeltaT is the temperature difference in Kelvin, giving Q in kW. For example 10,000 m3/h with a 20 K difference recovers about 66 kW - enough to cut heater or chiller load substantially.
Efficiency versus pressure drop
More heat-transfer surface raises efficiency but also fan energy. Counter-flow plates reach 80 to 90 percent; cross-flow plates settle around 60 to 70 percent. Pick the arrangement that meets the efficiency target without blowing the pressure-drop budget.