Selecting an air-to-air heat exchanger is a six-step loop: define the duty, pick a type, size it, check pressure drop, choose materials, then handle frost and maintenance. This guide walks through each.
Step 1 — Define the duty
- Airflows (both streams, m³/h or CFM). Exhaust and supply are usually similar.
- Temperatures — outdoor design, exhaust (room) temperature, desired supply temperature.
- Moisture — inlet/outlet humidity ratio if you need enthalpy recovery (ERV).
- Contaminants — dust, grease, solvents, acidity → drive material and cleanability choices.
Step 2 — Pick a type
Counter-flow plate for compact HVAC; rotary wheel for large airflows needing enthalpy recovery; heat pipe for freeze-safe retrofits; run-around coil when streams must stay isolated (toxic/explosive exhaust).
Step 3 — Size it (effectiveness–NTU or LMTD)
Start from the required effectiveness ε. For a counter-flow plate with balanced airflows:
ε ≈ NTU / (1 + NTU)
NTU = UA / Cmin, where U is overall conductance (W/m²·K), A the area, and Cmin = ṁ·cp of the smaller stream. Rearranging gives the needed area A for a target ε. More area = higher ε but bigger core and more fan power.
Step 4 — Pressure drop & fan power
Recovered energy is free; fan energy is not. Check the core's pressure drop at your airflow and add it to the system curve. A rule of thumb: keep total recovered energy at least 5–10× the extra fan power, or the payback collapses.
Step 5 — Materials & corrosion
- Aluminum — default, good for clean air.
- 316L stainless — coastal, mildly corrosive exhaust.
- Titanium / polymer — aggressive acids, chlorides.
- ERV membrane — for moisture transfer.
Step 6 — Frost & maintenance
Below about −5 °C exhaust, plan defrost (bypass/preheat). Specify accessible cores and a cleaning method (vacuum, wash, CIP) matched to your dust load. Fouling is the #1 cause of falling effectiveness in industry — see our notes on industrial drying and case studies.
Don't do it by hand
Use the interactive sizing calculator at en159.com for a first-pass selection, then confirm with the manufacturer. For units and datasheets visit cncsp.com.
HeatRecoveryHub is an independent knowledge base by Zibo Qiyu.