How to Size and Select Cross-Flow Plate Heat Exchangers for Recovery Units
This article shows how to size and select cross-flow plate heat exchangers for an air-to-air recovery unit, from airflow and effectiveness to pressure drop, frost and material choice.
Step 1: fix airflow and temperatures
Start with supply and exhaust airflow (m³/h) and the exhaust-to-supply temperature difference. These set the heat duty. A full workflow is in our sizing guide.
Step 2: choose effectiveness and NTU
Effectiveness ε = (T_in – T_out_supply) / (T_in – T_exhaust). For a cross-flow plate, effectiveness relates to NTU and the capacity ratio. Cross-flow is a few points below counter-flow at equal area — compare in plate comparisons.
Step 3: size plate area and face velocity
- Larger plate area and lower face velocity raise effectiveness but increase size and cost.
- Typical face velocities are 1.5–3.0 m/s; higher speeds raise pressure drop and fan energy.
- Balance against the efficiency targets you set.
Step 4: frost and condensation
In cold climates exhaust can fall below the dew point and frost on the core. Use bypass, preheat or a frost-stat. See gasketed vs brazed for serviceability when washdown is needed.
Step 5: material
- Aluminum — light, conductive, standard.
- Stainless steel — corrosive or hygienic air.
- Polymer — anti-fouling, easier to clean.
Our Heat Recovery Guide links the selection chain end to end.
Frequently asked questions
How do I size a cross-flow plate exchanger?
Fix airflow and temperatures, pick target effectiveness, then size plate area and face velocity so effectiveness is met at an acceptable pressure drop.
What face velocity is typical?
About 1.5 to 3.0 m/s is typical; higher speeds save size but raise fan energy and drop.
How do I avoid frost on the core?
Use summer bypass, inlet preheat or a frost thermostat so exhaust stays above the frost point in cold operation.
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