System Design Overview

The System Design section is where you configure your HVAC systems, balance space airflows, design duct layouts, and review the resulting schedules.

Sections

Configuration

Set up central unit and terminal unit equipment:

Components on each unit’s airflow diagram: outside air, ERV, return air, coils, and fan heat
Outside air method and supply air temperatures
Energy configuration for energy estimates
Design and required airflows at peak

Air Balancing

Balance each space’s airflows:

Design supply, return, and exhaust
Outdoor air delivered directly to the space
Transfer air in and out
The resulting differential, with a warning when the space is out of balance

Layout

Design the duct distribution system:

Register, terminal unit, and central unit placement
Duct and riser routing and sizing
Fitting loss coefficients: HVAKR places the fittings themselves
Critical path and pressure calculations

Schedules (β)

Review what the layout places, one table per schedule:

Central Units and Terminal Units: name, area served, components, sizing airflows, and cooling and heating capacities. Terminal units also show the system that serves them
Air Cleaners: the space, tag, linked product, manufacturer, model, description, and clean-air delivery rate (CADR). Change an air cleaner’s product or tag directly in the table. Selecting a product copies its tag; edit the tag for that unit, or clear it to remove the tag
Registers: identical registers grouped by tag, type, placement, manufacturer, model, description, face size, and neck size, with a quantity
Ducts & Fittings: length, fitting count, and sheet metal weight per duct type and size. Unsized ducts share one row per duct type, with no size, weight, or cost

Manufacturer, model, and description come from the linked catalog product and show its current values. A register without a catalog product shows the manufacturer and model of its register model, with no description.

A schedule with no items is hidden. Choose Costs in the header to show cost columns:

Enter a cost for each central unit, terminal unit, and air cleaner. Register rows take a unit cost that applies to every register in the row and is multiplied by the quantity. Costs save on each item.
Duct cost is calculated: the weight times the duct type’s Cost by Weight. Weight comes from the duct size, length, and the duct type’s Material and Wall Thickness, set under Basis of Design > System Types. Fittings are counted but not priced.

To export a schedule, select its rows and choose Download CSV in the selection toolbar.

Workflow

The typical system design workflow:

Configure - Set central unit and terminal parameters
Balance - Adjust per-space supply, return, exhaust, and transfer airflows
Layout - Route ducts and size components

Each step builds on the previous, so work through them in order.

System Configuration

Before designing ductwork:

Verify system loads are accurate
Set appropriate supply air temperature
Configure outdoor air requirements
Add the components each terminal unit has

Design Validation

Run the project Check to validate your design: ask AI Chat to “Check this project,” or run a check job via the REST POST /projects/{id}/jobs endpoint. Check’s design-quality checks include:

Airflow balance: central unit and terminal (zone) supply vs. return/exhaust
Equipment oversizing: coil capacity flagged when it’s more than 200% of peak load
CFM/ton ratio outside the expected 300–500 range
Duct heat gain coverage against the ceiling-plenum cooling load

Check skips the oversizing and CFM/ton checks for a system whose central unit supplies 100% outside air (a DOAS). That unit’s airflow and coil capacity follow the ventilation air, not the space load.

Best Practices

Finalize loads first - Complete building model before system design
Work system by system - Focus on one system at a time
Check air balance - Verify supply equals return plus exhaust
Validate equipment - Confirm selected equipment meets requirements
Document assumptions - Note design decisions for future reference