Hvac Design

1. External Loads

   • Solar radiation through windows (SHGC consideration)
   • Conduction through envelope (walls, roof, floor)
   • Infiltration and ventilation air

2. 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

3. Calculation Methods

   • CLTD/CLF method: Manual calculations
   • RTS (Radiant Time Series): More accurate
   • Heat Balance Method: Full simulation

Heating Load

1. Design Conditions

   • Use ASHRAE 99.6% or 99% design temperature
   • No solar credit for heating design
   • Full infiltration at design conditions

2. Load Components

   • Envelope conduction (U × A × ΔT)
   • Infiltration/ventilation (1.08 × CFM × ΔT)
   • No internal gains credited

Psychrometric Analysis

1. Key Properties

   • Dry-bulb and wet-bulb temperatures
   • Relative humidity and humidity ratio
   • Enthalpy and specific volume
   • Dew point temperature

2. Process Calculations

   Process	Constant Property
   Sensible heating/cooling	Humidity ratio
   Humidification	Enthalpy (adiabatic)
   Dehumidification	Saturation curve
   Mixing	Mass-weighted average

3. Coil Processes

   Sensible Heat Ratio (SHR) = Qs / Qt
   
   Bypass Factor (BF) = (T_leaving - T_ADP) / (T_entering - T_ADP)
   

Equipment Selection

Air Handling Units

1. Coil Sizing

   • Entering/leaving air conditions
   • Water temperatures (chilled water: 44/54°F typical)
   • Face velocity: 400-550 fpm

2. Fan Selection

   • Total static pressure requirements
   • Fan efficiency and motor sizing
   • Variable speed considerations

Chillers

1. Types and Selection

   • Reciprocating: < 200 tons
   • Scroll: 20-400 tons
   • Screw: 100-1500 tons
   • Centrifugal: > 300 tons

2. Efficiency Metrics

   • COP (Coefficient of Performance)
   • kW/ton: 0.5-0.8 typical range
   • IPLV: Part-load efficiency

Duct Design

1. Sizing Methods

   • Equal friction: Constant pressure drop per 100 ft
   • Static regain: Constant velocity pressure
   • Velocity method: Noise-controlled

2. 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

3. Fitting Losses

   • Express as equivalent length or C coefficient
   • Use ASHRAE duct fitting database

Energy Efficiency

1. ASHRAE 90.1 Compliance

   • Envelope requirements (U-values, SHGC)
   • HVAC efficiency minimums
   • Lighting power density limits
   • Energy cost budget method

2. 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

1. Use ASHRAE weather data for design conditions
2. Apply appropriate safety factors (10-15% typical)
3. Consider zone diversity for central equipment
4. Verify ventilation rates meet ASHRAE 62.1
5. Model energy performance before finalizing design
6. 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