HVAC System Design Skill Skill

HVAC System Design Skill

Purpose

The HVAC System Design skill provides comprehensive capabilities for heating, ventilation, and air conditioning system design according to ASHRAE standards, enabling systematic load calculations, equipment selection, ductwork design, and energy efficiency analysis for commercial and industrial buildings.

Capabilities

Heating and cooling load calculations
Psychrometric analysis and chart calculations
Equipment selection (AHU, chillers, boilers)
Duct and piping system sizing
Energy efficiency analysis (ASHRAE 90.1)
Indoor air quality assessment (ASHRAE 62.1)
System simulation and optimization
Control system specification

Usage Guidelines

Load Calculations

Cooling Load Components

External Loads
- Solar radiation through windows (SHGC consideration)
- Conduction through envelope (walls, roof, floor)
- Infiltration and ventilation air
Internal Loads
- People: 250 Btu/h sensible, 200 Btu/h latent (typical office)
- Lighting: Use installed wattage with diversity
- Equipment: Plug loads with usage factors
Calculation Methods
- CLTD/CLF method: Manual calculations
- RTS (Radiant Time Series): More accurate
- Heat Balance Method: Full simulation

Heating Load

Design Conditions
- Use ASHRAE 99.6% or 99% design temperature
- No solar credit for heating design
- Full infiltration at design conditions
Load Components
- Envelope conduction (U × A × ΔT)
- Infiltration/ventilation (1.08 × CFM × ΔT)
- No internal gains credited

Psychrometric Analysis

Key Properties
- Dry-bulb and wet-bulb temperatures
- Relative humidity and humidity ratio
- Enthalpy and specific volume
- Dew point temperature
Process Calculations | Process | Constant Property | |---------|------------------| | Sensible heating/cooling | Humidity ratio | | Humidification | Enthalpy (adiabatic) | | Dehumidification | Saturation curve | | Mixing | Mass-weighted average |

Coil Processes

Sensible Heat Ratio (SHR) = Qs / Qt

Bypass Factor (BF) = (T_leaving - T_ADP) / (T_entering - T_ADP)

Equipment Selection

Air Handling Units

Coil Sizing
- Entering/leaving air conditions
- Water temperatures (chilled water: 44/54°F typical)
- Face velocity: 400-550 fpm
Fan Selection
- Total static pressure requirements
- Fan efficiency and motor sizing
- Variable speed considerations

Chillers

Types and Selection
- Reciprocating: < 200 tons
- Scroll: 20-400 tons
- Screw: 100-1500 tons
- Centrifugal: > 300 tons
Efficiency Metrics
- COP (Coefficient of Performance)
- kW/ton: 0.5-0.8 typical range
- IPLV: Part-load efficiency

Duct Design

Sizing Methods
- Equal friction: Constant pressure drop per 100 ft
- Static regain: Constant velocity pressure
- Velocity method: Noise-controlled
Pressure Drop
- Typical systems: 0.08-0.1 in.w.g./100 ft
- Low velocity: < 0.08 in.w.g./100 ft
- High velocity: > 0.1 in.w.g./100 ft
Fitting Losses
- Express as equivalent length or C coefficient
- Use ASHRAE duct fitting database

Energy Efficiency

ASHRAE 90.1 Compliance
- Envelope requirements (U-values, SHGC)
- HVAC efficiency minimums
- Lighting power density limits
- Energy cost budget method
Energy Conservation Measures
- Economizer operation
- Heat recovery
- Variable speed drives
- Demand-controlled ventilation

Process Integration

ME-013: HVAC System Design

Input Schema

{
  "building": {
    "location": "string",
    "type": "office|retail|healthcare|industrial",
    "gross_area": "number (ft2)",
    "floors": "number"
  },
  "design_criteria": {
    "indoor_summer": {
      "temp": "number (F)",
      "rh": "number (%)"
    },
    "indoor_winter": {
      "temp": "number (F)"
    },
    "ventilation_standard": "ASHRAE 62.1|local code"
  },
  "internal_loads": {
    "occupancy": "number (people)",
    "lighting": "number (W/ft2)",
    "equipment": "number (W/ft2)"
  }
}

Output Schema

{
  "loads": {
    "peak_cooling": "number (tons)",
    "peak_heating": "number (MBH)",
    "ventilation": "number (CFM)"
  },
  "equipment": {
    "ahu": [{
      "designation": "string",
      "supply_cfm": "number",
      "cooling_tons": "number",
      "heating_mbh": "number"
    }],
    "chiller": {
      "type": "string",
      "capacity": "number (tons)",
      "efficiency": "number (kW/ton)"
    },
    "boiler": {
      "type": "string",
      "capacity": "number (MBH)",
      "efficiency": "number (%)"
    }
  },
  "energy_analysis": {
    "annual_cooling": "number (kWh)",
    "annual_heating": "number (therms)",
    "eui": "number (kBtu/ft2/yr)"
  }
}

Best Practices

Use ASHRAE weather data for design conditions
Apply appropriate safety factors (10-15% typical)
Consider zone diversity for central equipment
Verify ventilation rates meet ASHRAE 62.1
Model energy performance before finalizing design
Coordinate with architectural and structural disciplines

Integration Points

Connects with CFD Analysis for airflow modeling
Feeds into Thermal Analysis for component design
Supports Building Energy Simulation for annual performance
Integrates with Control System Design for automation

Agent Skills: HVAC System Design Skill

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