The Concept

A run-around coil system uses two coils - one in the exhaust stream, one in the supply stream - linked by a pumped fluid loop (water or water-glycol). Heat transfers from exhaust to supply through the fluid, with the airstreams completely separate.

Key Selection Parameters

• Coil size - larger coil surface raises transferred energy
• Loop fluid - water-glycol for freeze protection in cold climates
• Pump and loop length - shorter loops and correct pipe size cut pumping loss
• Fluid temperature - set the loop temperature to maximise the gradient

When to Choose Run-Around

• Airstreams are far apart or contaminated (kitchen, lab, industrial exhaust)
• Zero cross-contamination is required
• You want to recover heat without a shared core

Watch-outs

The pump uses energy, so net savings are lower than a direct exchanger. Size the loop to keep pumping power small, and insulate pipes to avoid losses.