SectionsExtract air handling units
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Extract air handling units

An extract AHU removes air with a defined temperature and contaminant load. Its replacement-air path and discharge destination are part of the same design.

Principle and scope

An extract unit removes air from rooms or processes. Replacement air must enter through a designed supply or transfer path. Filters, materials and fan execution depend on the extracted contaminants and temperature.

Ordinary general-ventilation equipment is not automatically suitable for grease, corrosive fumes, explosive atmospheres or smoke extraction. Those duties require a separately specified system and evidence for the exact application.

Select the extract duty

Describe the extracted substance, concentration where known, temperature, moisture, operating schedule and permitted discharge. Determine replacement airflow and pressure relationships with adjacent spaces. Select casing and fan materials, filtration and cleaning access for the actual duty. A fan selection for clean room air cannot be transferred to contaminated process exhaust without review.

Related components: Fan

Calculate a stated temperature change in the extract stream. The result does not select an extract fan or establish a replacement-air path.

Calculate sensible air load

Sensible air load calculation

Calculate the heat rate associated with a specified temperature change in one air stream. Enter all five values for your stated operating conditions.

Mass flow ṁ = ρ × V̇ / 3600; temperature change ΔT = Tout − Tin; sensible heat rate Q̇ = ṁ × cp × ΔT. With the units below, the result is in kW. Positive Q̇ means heating; negative Q̇ means cooling. Zero flow or zero temperature difference gives zero sensible load.

For a steady, single-phase air stream with constant user-supplied properties. The balance excludes latent heat, moisture changes, phase change, shaft work and kinetic/potential energy changes. It does not select a fan, coil or complete AHU.

Topic for the local draft

Opening a page does not select anything. A topic choice records context only; no product or configuration is selected.

Operating inputs

Use density at the same state and volume basis as the entered airflow. Enter cp in kJ/(kg·K), not J/(kg·K). Density and cp are editable assumptions; no universal values are prefilled. Check that your temperatures and properties describe gas-phase air. This tool does not check phase boundaries or property-table consistency.

Interactive calculation requires JavaScript. The formula, units, scope and reference information remain available here for manual use.

Heat recovery

Extract air can be an energy source for a recovery system, provided contaminants, leakage and fouling are acceptable. A run-around liquid loop can connect physically separate supply and extract units. It does not remove the need to check corrosion, cleaning and freeze protection on the extract coil.

Related components: Liquid-to-air coil

Commissioning and service

Inspect deposits, corrosion and cleaning access at intervals suitable for the actual extracted air. Verify that replacement air is available in every operating mode. Retain the contaminant specification with the equipment record so later fan or filter replacement does not lose the original safety conditions.

Related components: Fan · Air filter

Back to section: Extract

A guide to equipment and selection; the final configuration and performance require project-specific confirmation.