Air Balancing

The Air Balancing pane is where you balance each space’s airflows. It sits between Configuration and Layout in the System Design section.

Configuration works on central units and terminal units. Air Balancing works on spaces only, so it has no tab switcher and no diagram view: the sidebar lists every space in the project, and the pane always shows the floor plan. Pick the equipment mode in the selector at the top left of the plan before you edit, because design airflows are stored per mode.

Spaces come from the Building Model. Until the project has one, the sidebar shows No Spaces with a Create Spaces button that opens the Spaces pane.

Space Airflows

Select a space to balance its airflows in the Space Data panel. The Required column shows the calculator’s minimum. Most of the Design column is editable, and each edited cell resets back to its calculated value:

• Supply - Conditioned air the unit delivers to the space; defaults to the largest of the load-driven, code-driven (ACH/area), and ventilation requirements on a coupled terminal. A decoupled terminal takes its outdoor air directly, so ventilation does not raise its supply
• Return - Air drawn back from the space to be reconditioned
• Exhaust - Air discharged outdoors, driven by the space type’s exhaust requirement
• OA (VRP, Mixed) / OA (VRP, Direct) - Outdoor air required by the project ventilation standard. The label reads Mixed when outdoor air is blended into the supply at the unit, or Direct when a dedicated outdoor-air system (DOAS) delivers it straight to the space. Only Direct is editable; Mixed is calculated, and you raise it through the Supply row instead
• OA (IAQP, Mixed) / OA (IAQP, Direct) - Outdoor air from the ASHRAE 62.1 Indoor Air Quality Procedure, after crediting in-space air cleaning. This row appears only when the space has an IAQP outdoor air rate. It is hidden when that rate reads Not achievable or Not evaluable, and it is always read-only
• Transfer In and Transfer Out - Air moved to or from adjacent spaces
• Differential - Net balance: supply plus transfer in, minus return, exhaust, and transfer out. For a decoupled terminal, direct outside air also counts toward the plus side. A positive value pressurizes the space. This row is always calculated

HVAKR warns when a space is out of balance, and names the amount: adjust return, exhaust, or transfer air until supply (plus direct outside air, for a decoupled terminal) matches the air leaving the space.

Where the Supply Default Comes From

Above the Airflows table, the Space group shows the space’s Area and design Occupancy. Below the table, Supply Basis reports the values the Supply default is built from. All of them are read-only:

• Total Space Sensible - The space’s sensible load
• Sensible from Direct OA - The share of that load carried by direct outdoor air. Shown for a decoupled terminal only
• Load-determined Supply - Airflow needed to carry the sensible load at the unit’s supply air temperature
• Required Minimum Supply - The code-driven minimum: the larger of the space type’s Min. Supply Air Changes and Area Min. Supply

When the space has an IAQP result, an IAQP group adds Air Cleaners, Air Cleaning (Vc), Outdoor Air, and Controlling Requirement. The controlling requirement names the individual compound or mixture that sets the minimum IAQP airflow. Outdoor Air reads Not achievable or Not evaluable when the procedure cannot produce a rate.

Each placed air cleaner adds its Clean-Air Delivery Rate (CADR) to Air Cleaning (Vc). The CADR comes from a linked catalog product, or you enter it on the air cleaner in Layout. When a placed air cleaner has no CADR, the IAQP group warns: “Air cleaner placed with no clean-air delivery rate. Link a product or enter the airflow and efficiency on the air cleaner.”

Set Supply to a Fixed Rate or a CFM/ft² Rate

Use a space type minimum when supply may go higher, and a per-space override when supply must hold at an exact value:

• Minimum for every space of a type - In Basis of Design > Space Types, set Area Min. Supply or Min. Supply Air Changes. The minimum applies to every space of that type in every equipment mode and follows changes to space area. Load or ventilation can still raise supply above it
• Exact value for one space - In Air Balancing, pick the equipment mode, select the space, and enter the airflow in the Design column of the Supply row. For a per-area rate, multiply the Area in the Space group by the rate in matching units: ft² × CFM/ft² gives CFM, and m² × L/s/m² gives L/s. Convert a rate in the other unit system first. For example, 400 ft² × 0.25 CFM/ft² = 100 CFM. The override replaces the calculated supply in the selected mode only, so enter it in every equipment mode (for example cooling and heating). It does not follow later changes to space area. Reset the cell to return to the calculated value

The Space Data panel edits one space at a time. To set a Supply override on many spaces at once, ask AI Chat, for example: “Set supply to 0.25 CFM/ft² on every corridor in every equipment mode.”

Airflow Diagram and Psych Chart

Each selected space shows an airflow diagram above its data: supply entering on the left, return and exhaust leaving on the right, and the differential below. For a decoupled terminal, direct outside air also enters on the left.

Click the chart button (Open the airflow diagram and psych chart) in the panel header to open a larger dialog with the diagram and a psychrometric chart side by side. The chart plots the space type’s indoor setpoint against the supply air the serving equipment delivers, with the same comfort zones and Space SHR line the Configuration chart uses.