Run-Around Coil vs Heat Pipe: Choosing Separated-Stream Recovery

Two ways to keep streams separate

When the two airstreams must never mix, rotary wheels are off the table. The two disciplined technologies are the run-around (loop) coil and the heat pipe, and they solve the same problem differently. This article helps you pick between them.

Both are detailed in Run-Around Coil and Desiccant Recovery and the heat-pipe overview at Heat Pipe Heat Exchangers.

Run-around coil

Two finned coils joined by a sealed pipe loop filled with water or glycol. The exhaust coil heats the fluid; the fluid warms the supply coil. Streams never meet; only fluid moves. Effectiveness is about 50 to 65 percent, plus a small pump and freeze-protected fluid. The big advantage is serviceability: coils sit in each airstream and can be cleaned or replaced independently, and the loop can span long distances between streams.

Heat pipe

A sealed tube that moves heat by phase change with no pump and no fluid loop. Effectiveness is about 50 to 70 percent sensible, but it requires a 3 to 5 degree slope with the condenser above the evaporator, and it works across a single assembly rather than between distant streams. It is the choice where power is scarce and access is hard, such as telecom shelters and remote sites.

How to choose

Use a heat pipe when you want passive, maintenance-free, separate-stream recovery across a wall and power is limited. Use a run-around coil when the streams are far apart, when you need easy coil service, or when you want to add a desiccant or water-loop tie-in. For pharmaceutical, laboratory, or hazardous exhaust, either is acceptable and the wheel is not. Our pharma recovery article shows the run-around layout in a containment context.

Trade and verify

Both trade some effectiveness for absolute separation. Size within each device's limits and confirm the gain against fan or pump power using our savings guide.

Bottom line

Run-around coil for distance and serviceability, heat pipe for passive duty: both keep streams separate and both beat a wheel where mixing is forbidden. Contact Qiyu engineering (15753355505) for a contained-recovery design.