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Supply air handling units

A supply AHU prepares air for delivery to rooms. Selection begins with the required outdoor-air supply and the complete path back out of the building.

Principle and scope

A supply unit draws in outdoor air and delivers it after the specified filtration and treatment. The building still needs an extract or relief path. Adding supply air without checking the return path can change room pressure and prevent the intended airflow.

Distinguish a unit handling only outdoor air from one mixing outdoor and recirculated air. The outdoor-air requirement, winter heating duty and frost protection must be checked for the actual intake conditions.

Select outdoor-air duty

For a 100% outdoor-air unit, use the outdoor winter and summer states at the intake. For mixing duty, state both the outdoor fraction and the resulting mixed-air condition. Specify the supply temperature, humidity duty, pressure and acceptable sound at the intended operating flow. The room load and the ventilation-air treatment load are different inputs.

Calculate the sensible temperature change of supply air. Filtration, outdoor-air requirements and fan/coil selection remain separate.

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.

Modular

A modular supply unit allows filtration and heating/cooling sections to be arranged around the outdoor-air duty. Its assembly still needs a defined extract or relief path elsewhere in the building. Select the final section order for frost protection, condensate management and service access.

Commissioning and service

At commissioning, measure the outdoor and delivered flows and test the heating frost sequence. During service, track intake obstruction, filter pressure and coil condition. Keep the selected duty, fan setting and heating-medium conditions with the unit documents.

Related components: Fan · Air filter · Air-treatment coil

UPGR sectional AHU with a partly withdrawn finned coil, copper headers and a removable access panel.

Access to a finned coil in a sectional AHU. Reserve space for removing the access panel and handling the coil; the actual removal procedure follows the equipment documentation.

Access opening
Provides access to the coil section.
Finned coil
The removable assembly must fit through the access opening and be handled with suitable support.
Headers and connections
Check disconnection requirements and available service space before removal.
Back to section: Supply

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