EKS-HUM-014 / Moisture load and airflow

Moisture Generation Rate

产湿率

Moisture generation rate is the mass of water released as vapour by a source within a defined time interval.

Aliases: water-vapour generation rate

QUANTITY, SYMBOL AND UNIT

Quantity / objectMoisture generation rate

Symbolṁ_w,gen

SIkg/skilogram of water per second

Commonkg/hkilogram of water per hour

CommonL/daylitre of water per day: Requires an explicit water-density basis

Definition

Moisture generation rate is the mass of water released as vapour by a source within a defined time interval.

Sources can include occupants, open water, crops, wet products, cleaning, combustion or industrial processes. A useful design value states the source, operating mode, schedule and averaging period.

Formula and variables

ṁ_w,gen = Δm_w / Δt

Conditions: Average rate over the stated observation interval. The measured or estimated water mass and time interval must refer to the same source boundary.

Symbol	Meaning	Unit
`ṁ_w,gen`	moisture generation rate	kg/s or kg/h
`Δm_w`	water mass released as vapour	kg
`Δt`	observation interval	s or h

Relations and distinctions

Generation rate and moisture load

Generation rate describes one or more internal sources. Moisture load also includes boundary flows such as ventilation and infiltration.

Generation rate and RH rise

Generation is a mass rate. The resulting RH change also depends on temperature, volume, surfaces, air exchange and active moisture removal.

Engineering meaning

Separate continuous, intermittent and startup sources when building a load schedule.
Use measured project data when a process or crop source differs materially from published design conditions.

Common misconceptions

MisconceptionA source has one fixed moisture generation rate under all operating conditions.

Accurate explanationActivity, product condition, crop stage, temperature, airflow and schedule can change the rate.

Application boundaries

A published source rate must not be transferred to a different process without checking its basis.
Condensed liquid retained or drained inside the boundary is not automatically equal to vapour released to the air.

Supporting sources

ASHRAE / SRC-ASHRAE-F25-CH18

ASHRAE Handbook - Fundamentals, Chapter 18: Nonresidential Cooling and Heating Load Calculations ↗

2025 SI edition / Chapter 18, Section 1 and Section 2 internal heat gains
Supports: Occupants and equipment can emit moisture into a space; Moisture addition is a rate that contributes to latent load; Design data must be tied to activity and operating condition

Maintenance record