Moisture load and airflow
Return Air
回风
Return air is air removed from a space and routed back toward an air-handling, heating, cooling or ventilation system for recirculation or exhaust.
- Abbreviations
- RA
- Aliases
- return airstream
QUANTITY, SYMBOL AND UNIT
Quantity / objectReturn air
UnitNot applicable
Definition
Return air is air removed from a space and routed back toward an air-handling, heating, cooling or ventilation system for recirculation or exhaust.
Some or all of the return stream may be reused as supply air, while the remainder may be relieved or exhausted. Return-air temperature and humidity are often used for control, but they represent the mixture collected by that return path rather than every local zone condition.
Relations and distinctions
Return and recirculated air
Return air is all air extracted into the return path; recirculated air is only the portion reused as supply air.
Return air and room air
A return reading describes the collected mixture at its sensor location and may not capture gradients near crops, cold surfaces or remote enclosures.
Engineering meaning
- State the return sensor location and airflow path when using its humidity signal for equipment control.
- Account for exhaust, relief, outdoor-air mixing and leakage when closing the system air and moisture balance.
Common misconceptions
MisconceptionReturn-air RH is automatically the same as RH at every point in the room.
Accurate explanationThe return sensor sees the air collected by a particular path; stratification, short-circuiting and local loads can produce different conditions elsewhere.
Application boundaries
- Return air may be partially or completely exhausted rather than recirculated.
- A return-air reading cannot by itself diagnose hidden condensation or weak air distribution.
Supporting sources
-
ASHRAE / SRC-ASHRAE-TERMINOLOGY-RETURN
ASHRAE Terminology: Return Air ↗
Live terminology database / Entry: return air
Supports: Return air is removed or extracted from a space; Return air may be recirculated or exhausted; Only the reused portion is recirculated air
Maintenance record
Return Air
- Maintained by
- Yakeclimate Engineering Team
- Authoritative sources verified
- August 3, 2026
- Terminology checked
- August 3, 2026
- Last updated
- August 3, 2026
- Term ID
- EKS-HUM-061