Run-around Coil Heat Recovery Systems

A run-around coil heat recovery system uses two finned coils connected by a closed glycol loop. A pump circulates the fluid between the exhaust coil, where it picks up heat, and the supply coil, where it releases heat into the incoming air.

When to Use a Run-around Coil

This design is ideal when the supply and exhaust ducts are far apart or on different floors. Because the coils are separate and connected only by piping, installation flexibility is much higher than with plate or wheel exchangers.

System Components

• Exhaust air coil (finned tube)
• Supply air coil (finned tube)
• Circulation pump
• Expansion tank and glycol-water mixture
• Controls and temperature sensors

Pros and Cons

Pros:

• No risk of cross-contamination
• Works over long distances
• Easy to retrofit into existing ductwork
• Can recover heat from multiple exhaust points

Cons:

• Lower efficiency than counter-flow plate or rotary wheels (typically 40–60 %)
• Requires pump power and maintenance
• Glycol solution must be checked periodically

Common Applications

• Kitchen and laboratory exhaust
• Multi-zone commercial buildings
• Industrial processes with remote exhaust stacks
• Swimming pools and locker rooms

Controls and commissioning determine whether a run-around coil reaches its rated recovery. A variable-speed glycol pump trimmed to outdoor and exhaust temperatures lets the loop deliver more heat in winter and coast in mild weather, while a motorized bypass keeps supply temperature within setpoint. Integrate the pump and dampers with the building management system using dry contacts or a network link so the recovery runs only when the exhaust fan is on. During commissioning, balance flow to the design rate, confirm there are no air locks in the high points, and verify the expansion tank charge. Our heat recovery solutions include factory-tested coil bundles and control packages for retrofit projects.

Frequently Asked Questions

What glycol concentration is typical?
A 30–50 % propylene glycol solution is common, depending on freeze protection requirements.

Can run-around coils recover humidity?
No. They are sensible-only systems and do not transfer moisture.

Frequently Asked Questions

Pros:nnNo risk of cross-contaminationnWorks over long distancesnEasy to retrofit into existing ductworknCan recover heat from multiple exhaust pointsnnCons:nnLower efficiency than counter-flow plate or rotary wheels (typically 40–60 %)nRequires pump power and maintenancenGlycol solution must be checked periodicallynnnCommon ApplicationsnnKitchen and laboratory exhaustnMulti-zone commercial buildingsnIndustrial processes with remote exhaust stacksnSwimming pools and locker roomsnnnControls and commissioning determine whether a run-around coil reaches its rated recovery. A variable-speed glycol pump trimmed to outdoor and exhaust temperatures lets the loop deliver more heat in winter and coast in mild weather, while a motorized bypass keeps supply temperature within setpoint. Integrate the pump and dampers with the building management system using dry contacts or a network link so the recovery runs only when the exhaust fan is on. During commissioning, balance flow to the design rate, confirm there are no air locks in the high points, and verify the expansion tank charge. Our heat recovery solutions include factory-tested coil bundles and control packages for retrofit projects.nFrequently Asked QuestionsnWhat glycol concentration is typical?

A 30–50 % propylene glycol solution is common, depending on freeze protection requirements.

Can run-around coils recover humidity?

No. They are sensible-only systems and do not transfer moisture.