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Mechanical / HVACaka: evaporator coilaka: DX coilaka: cooling coil

Evaporator

In Plain English

The part of a refrigeration system that absorbs heat from air or water to provide cooling.

Definition

The heat exchanger in a refrigeration system where low-pressure liquid refrigerant absorbs heat from the medium being cooled (air or water) and evaporates into a vapor. In direct-expansion (DX) cooling systems, the evaporator coil is located in the air stream; in water-cooled chillers, it is a shell-and-tube or plate heat exchanger that cools water. The evaporator is the cooling side of the refrigeration cycle.

Why It Matters in Bidding

On mechanical bids, the evaporator type drives equipment cost, piping scope, and coordination, so estimators must read the schedule to distinguish a DX coil from a chiller's shell-and-tube barrel. Misreading the cooling side leads to taking off the wrong refrigerant or chilled-water piping, a scope error that surfaces expensively during submittals.

Example

An HVAC estimator pricing a rooftop unit confirms the evaporator coil is factory-installed in the air handler, then prices only the supply ductwork and condensate drain rather than the field refrigerant piping a split system would require.

Related Terms

CompressorRefrigerantChillerCondensing Unit

Frequently Asked Questions

A direct-expansion evaporator coil sits in the airstream and needs refrigerant piping, while a chiller's evaporator cools water requiring chilled-water piping, pumps, and insulation. Each carries very different labor and material scope, so the estimator must match takeoff to the equipment schedule to avoid pricing the wrong system entirely.
Evaporator capacity sized in tons sets the equipment price, and the configuration dictates whether the bid includes refrigerant lines and charge or a full chilled-water distribution loop. Larger or specialized evaporators may extend lead times, which the estimator should flag because procurement timing affects schedule and cash flow on the job.
Beyond the coil or barrel itself, related scope includes condensate drainage and trapping, refrigerant or chilled-water piping and insulation, controls for the cooling stage, and access for coil cleaning. Estimators capture these as separate line items so the cooling side is fully covered rather than buried in a lump equipment number.

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