Ahu Design

Fan Arrangement

Section Sequence (Draw-Through)

Standard arrangement for draw-through configuration:

1. Outdoor Air Section (damper, louver)
2. Return Air Section (damper)
3. Mixing Section
4. Filter Section (pre-filter, final filter)
5. Preheat Coil (if required)
6. Cooling Coil
7. Fan Section
8. Reheat/Heating Coil (if required)
9. Humidifier (if required)
10. Supply Section

Section Sequence (Blow-Through)

For DX or specific applications:

1. Outdoor Air Section
2. Return Air Section
3. Mixing Section
4. Filter Section
5. Fan Section
6. Cooling Coil
7. Heating Coil
8. Supply Section

Sizing Calculations

Face Area

Face Area (ft²) = CFM / Face Velocity (fpm)

Target face velocities:
- Filters: 400-500 fpm
- Cooling coils: 450-550 fpm
- Heating coils: 500-700 fpm

Cabinet Sizing

Width = √(Face Area × Aspect Ratio)
Height = Face Area / Width

Standard aspect ratios: 1.0 to 1.5 (W:H)
Add clearances for:
- Access doors: +6" per side
- Drain pans: +4" height
- Insulation: +2" per face

Section Lengths

Application-Specific Considerations

Healthcare/Laboratory

• 100% outdoor air capability
• HEPA filtration provisions
• Redundant fans
• Enhanced access for cleaning

Data Center

• High sensible ratio
• Tight temperature control
• Redundancy requirements
• Energy efficiency focus

Manufacturing

• High outdoor air ratios
• Robust filtration
• Explosion-proof options
• Corrosion resistance

Commercial Office

• Energy recovery opportunity
• Variable volume capability
• Sound attenuation
• Standard efficiency

Input Requirements

Read from state files:

• state/request.json: Customer requirements
• state/constraints.json: Engineering constraints

Output Specification

Write to state/concept.json:

{
  "design_id": "AHU-{timestamp}",
  "version": 1,
  "configuration": {
    "type": "horizontal|vertical|stacked",
    "arrangement": "draw_through|blow_through",
    "orientation": "left_to_right|right_to_left"
  },
  "cabinet": {
    "width_in": 84,
    "height_in": 72,
    "total_length_in": 240,
    "face_area_sqft": 42
  },
  "sections": [
    {
      "position": 1,
      "type": "outdoor_air",
      "length_in": 24,
      "notes": "Motorized damper, birdscreen"
    }
  ],
  "preliminary_selections": {
    "fan_type": "plenum",
    "coil_rows_cooling": 6,
    "coil_rows_heating": 1,
    "filter_type": "MERV13"
  },
  "design_notes": [
    "Selected draw-through for improved coil dehumidification",
    "Fan plenum sized for low velocity discharge"
  ]
}

Validation Checks

Before outputting:

1. Total length fits envelope constraint
2. Face velocity within acceptable range
3. Section access provisions adequate
4. All required sections included