The Separation Problem
Some sites cannot mix supply and exhaust air at all: cleanrooms, hospitals, and hazardous or corrosive environments. Rotary wheels and plate exchangers move energy through a shared surface, so engineers turn to technologies that keep the streams fully isolated.
Heat Pipes
A heat pipe is a sealed tube filled with a working fluid. Heat evaporates the fluid at the warm end and condenses it at the cool end, moving energy with no moving parts and no cross-contamination. Heat-pipe arrays sit in a single device spanning both airstreams, making them compact and maintenance-free.
Run-Around Coils
A run-around, or coupled coil, system uses two coils connected by a pumped fluid loop. One coil sits in the exhaust, the other in the supply; the fluid carries heat from one to the other. Because the only link is the external pipe loop, the airstreams are completely separate, and the coils can be far apart.
Which to Choose
- Heat pipes: best for moderate temperature recovery in a compact footprint, no pumps, very reliable.
- Run-around coils: best when streams are distant, when liquids or gases other than air are involved, or when very high separation is required.
Practical Notes
- Heat pipes are nearly passive; size them for the operating temperature band.
- Run-around loops need a pump and freeze protection in cold sites.
- Both avoid the leakage and contamination risks of wheels, which is why separated-stream recovery is common in mines, data centers, and pharmaceutical plants.
Outlook
As air-quality and contamination rules tighten, separated-stream recovery will keep growing. Heat pipes and run-around coils give engineers a clean way to recover energy without compromising isolation.