The Complete Handbook of Coils

Chapter 1: Understanding Coils

A coil is a length of tubing or wire wound in a tight loop or spiral, designed to transfer heat between two fluids, store electrical energy, or create a magnetic field. That simple definition conceals the engineering that makes a coil useful or worthless in any given application.

Coils show up in nearly every mechanical and electrical system you encounter. In your home or office, the air conditioning system has a cold coil (evaporator) indoors and a hot coil (condenser) outside. Industrial chillers, heat pumers, and process cooling equipment all use coils as their primary heat-transfer mechanism. Radiators in vehicles are coils. Heating systems—whether hydronic (hot water) or steam—rely on coils to move heat from the source into the air or water being heated. Electrical transformers, induction heating systems, and motor windings all use coils to store and convert energy. Despite this diversity, the fundamental principle remains consistent: a coil moves energy from one place or medium to another.

The reason coil choice matters has nothing to do with marketing or brand preference. It has everything to do with physics and materials science. A coil's ability to transfer heat efficiently depends on its surface area, the material it's made from, the quality of contact between its tubing and any fins attached to it, the diameter and wall thickness of the tubing, and the path the fluid inside takes as it moves through the coil. Change any of these variables and you change the performance, the pressure