Retrofitting heat recovery into an existing building is different from designing new. Space, duct layout, and control integration usually drive the choice more than peak efficiency.
Step 1: Audit the Air Streams
- Confirm there is a dedicated exhaust and a matching supply.
- Measure airflow (m³/h or CFM) and temperature profiles.
- Note operating hours — recovery only pays where runtime is high.
Step 2: Pick a Form Factor
| Constraint | Best fit |
|---|---|
| Exhaust far from supply | Run-around coil |
| No cross-contamination allowed | Plate or heat pipe |
| Humidity control needed | Enthalpy wheel |
| Tight mechanical room | Heat pipe (compact) |
Step 3: Integrate Controls
- Add a bypass for mild-weather free cooling.
- Interlock with existing BMS via dry contacts or BACnet.
- Use variable-speed fans to follow load.
Step 4: Verify Savings
Before commissioning, baseline energy use. After 3–6 months, compare to confirm payback matches the model.
A retrofit succeeds on planning and verification as much as hardware. Phase the work to avoid shutting down occupied spaces, and confirm the existing duct static pressure before sizing any core so you do not inherit a high-pressure-drop system. Where the exhaust and supply are far apart, a run-around coil keeps the retrofit feasible without re-ducting. Use a measurement and verification plan based on a recognized protocol so the reported savings survive audit: baseline energy, then compare after a full season. Tie the recovery to the existing controls through dry contacts or a network link so it runs only when needed. Our psychrometric guide shows how recovery shifts the air state on the chart.
Frequently Asked Questions
Do I need to replace the AHU?
Usually not. Add-on cores or remote run-around coils can be fitted around existing equipment.
What is the biggest retrofit risk?
Undersized ducts causing high pressure drop; verify static pressure before specifying.