Heat recovery in an AHU can cut conditioning energy by 40-70% by transferring energy between exhaust and supply air.
The Three Main Types
A plate (fixed-plate) exchanger passes supply and exhaust through adjacent channels separated by thin plates. Sensible heat moves across the wall with no mixing, giving 50-70% efficiency and simple, maintenance-light operation with no moving parts to fail.
Heat recovery returns energy from the exhaust airstream to the incoming fresh air, cutting the heating or cooling load the coils must carry. On a busy commercial building the saved energy is large enough that recovery is often specified by code or by the payback case rather than left optional.
Plate exchangers are fixed-core devices where supply and exhaust pass on opposite sides without mixing; they are simple and leak-tight but can frost in cold climates when the exhaust reaches freezing, so they need a bypass or preheat once the outdoor temperature drops far enough to ice the core.
Rotary wheels transfer both sensible and latent heat by spinning a matrix through both streams, reaching higher effectiveness, often 70-85%, but they carry a small cross-contamination risk because the two airstreams share the wheel, and they need a purge sector and good sealing to keep exhaust out of the supply in strict applications.
Run-around coil loops use two coils joined by a fluid loop so the streams never meet, which suits cases where supply and exhaust are far apart or mixing is unacceptable; effectiveness is lower, typically 50-65%, but the separation is absolute and the layout is flexible across a plant.
The company's ERV and HRV ranges are built at its 80,000 m² production site under ISO 9001:2015 with CCC certification, and with more than 30 years of manufacturing experience its engineers can size the recovery type to the climate and the air-handling duty, responding to selection enquiries within 24 hours.
Recovery is not always required; where the outdoor air is cool for much of the year a free-cooling or air-side economiser can meet the load without the exchanger, and adding recovery then only adds resistance and cost. The choice between economiser and heat recovery follows the climate and the hours of overlap, weighed in the same energy model that justifies either measure.
A rotary thermal wheel turns a matrix through both airstreams, carrying heat and sometimes moisture from exhaust to supply. It reaches 60-85% efficiency but needs a purge sector and seals to limit carry-over of exhaust air into the supply stream.
A run-around coil system links two coils with a pumped fluid loop, keeping the airstreams physically separate. Efficiency is lower, around 40-60%, but it suits streams that are far apart or must never mix, such as hazardous or odorous exhaust.
Enthalpy recovery adds moisture transfer, valuable in humid climates where latent load dominates. Desiccant wheels or enthalpy plates recover both temperature and humidity, reducing cooling coil size and the associated chilled-water plant energy.
Choosing Among Them
Plate exchangers are the default for most commercial AHUs because they are cheap, silent, and free of cross-contamination, provided frost risk in cold exhaust is managed with a bypass or a pre-heat strategy during winter operation.
Rotary wheels win when maximum efficiency is needed and the small exhaust carry-over is acceptable, such as in office ventilation with balanced supply and return, where the energy saving outweighs the minor mixing of airstreams.
Run-around coils are chosen when supply and exhaust ducts are distant or when strict separation is required, such as laboratory or containment exhaust where even trace cross-contamination is unacceptable under any circumstance.
Frost control matters in cold climates: plate units may need a pre-heat or recirculation strategy once exhaust approaches freezing, or the core can ice and block, raising static pressure and eventually stalling the supply fan.
| Item | Specification | Note |
|---|---|---|
| Plate | 50-70% | No mixing, simple |
| Rotary wheel | 60-85% | Needs purge + seals |
| Run-around | 40-60% | Streams separate |
| Enthalpy | adds moisture | Humid climates |
| Frost risk | cold exhaust | Pre-heat needed |
| Payback | 40-70% energy | Ventilation duty |
Selection Checklist
- Start with a plate exchanger unless efficiency or separation demands otherwise.
- Use a rotary wheel where the highest recovery justifies minor carry-over.
- Choose run-around coils for separated or sensitive exhaust streams.
- Specify enthalpy recovery in humid climates to cut coil load.
- Plan frost protection for plate cores in cold exhaust air.
- Size the recovery device to the actual ventilation airflow, not peak.
About the Manufacturer
Keruite Air Conditioning Group, headquartered in Dezhou, Shandong, has more than 30 years of HVAC manufacturing experience and operates an 80,000 m² production site with its own performance testing laboratory. Products are built under ISO 9001:2015 quality management and carry CCC certification, and are supplied to customers in over 50 countries.
Our engineers respond to selection enquiries within 24 hours and can provide project-specific sizing, performance curves, and documentation to support specification and procurement.