Duct Layout

The Layout pane is where you design the duct distribution system, including routing, sizing, and component selection.

Duct Routing

Creating Duct Runs

Duct routing lives in the sidebar’s Routing tab. Draw duct runs on the floor plan:

1. Open the Routing tab and pick a duct type from the Ducts palette
2. Click to place duct segments
3. Connect to terminal units and registers
4. Close loops where needed

Duct Types

Ducts are drawn with the duct types you defined in System Types — pick one from the Ducts palette before drawing. Each duct type carries its own sizing criteria (max velocity, max pressure drop, max height) and a display color, and HVAKR sizes every duct assigned to it against those criteria.

There is no fixed supply/return/exhaust “duct type” to choose here. A run’s airflow direction — supply, return, or exhaust — follows the registers and equipment it connects, not the duct type.

Routing Considerations

Plan duct routes to:

• Minimize total length
• Avoid obstructions
• Allow for insulation and access
• Fit within available plenum space

Duct Sizing

Sizing Criteria

Each duct is sized against the criteria of its duct type. HVAKR picks the smallest size that satisfies all of them at the duct’s design airflow:

Max Velocity

Caps air velocity for noise control:

• Higher limits = smaller ducts
• Lower limits = quieter system
• Typical: 1500-2000 FPM main, 800-1200 FPM branch

Max Pressure Drop

Caps the friction rate (pressure drop per 100 ft):

• Typical: 0.08-0.10 in. wg per 100 ft
• Keeps fan power reasonable on long runs

Max Height

Caps the duct height so it fits the available plenum space. Rectangular ducts get wider instead of taller once the limit is reached.

Automatic Sizing

HVAKR automatically sizes ducts:

1. Assign a duct type with the sizing criteria you want
2. HVAKR sizes each duct to meet all criteria
3. Review and adjust as needed

Fittings and Transitions

Fitting Types

HVAKR places fittings automatically wherever ducts meet or change size. Three fitting types are modeled:

• Elbow - A change in direction
• Transition - A size change, either an increase or a reduction
• WYE - A branch takeoff, either converging or diverging

Fitting Loss Coefficients

Each fitting type adds pressure loss through a configurable loss coefficient (Cʟ):

• Set Cʟ (Main) for every type, plus Cʟ (Branch) for WYEs, in the Fittings palette under the Routing tab
• HVAKR ships a default coefficient for each type that you can override per project
• The coefficient feeds each fitting’s contribution to the total pressure calculation

Reducing Losses

Minimize fitting losses:

• Use larger radius elbows
• Avoid abrupt transitions
• Use turning vanes where needed

Pressure Calculations

Pressure Graph

View the pressure profile through the system:

• Static pressure (SP) at each duct segment
• Velocity pressure (Vp) at each fitting
• Pressure drop (PD) across each element
• External static pressure (ESP) for the full path

Critical Path

Identify the critical path:

• Highest pressure drop path
• Determines fan sizing
• Other paths need balancing

Fan Sizing

The fan must overcome:

• Total duct pressure drop
• Terminal unit pressure drop
• Filter pressure drop
• Coil pressure drop

3D Visualization

View the duct layout in 3D:

• Rotate and zoom the model
• Check for interferences
• Verify routing and sizing

Best Practices

1. Route before sizing - Establish routing first
2. Use consistent duct types - Keep sizing criteria consistent within a run
3. Check velocities - Stay within acceptable ranges
4. Verify pressure drop - Within equipment capability
5. Document routing - For construction drawings