HVAC Network Simulation

This project simulates HVAC components, including VAV boxes, Air Handling Units (AHUs), and complete buildings.

Components

• VAV Box: Variable Air Volume terminal unit with optional reheat capability

  • Modulates airflow in cooling mode
  • Controls reheat valve in heating mode
  • Maintains minimum airflow in deadband mode
  • Calculates energy usage
  • Models thermal behavior with occupancy and solar heat gain
  • Supports time-of-day simulation

• Air Handling Unit (AHU): Central unit that supplies conditioned air to multiple VAV boxes

  • Controls supply air temperature
  • Coordinates multiple VAV boxes
  • Manages cooling and heating coil valve positions
  • Calculates total system energy usage
  • Optional supply air temperature reset for energy savings
  • Supports both chilled water and DX (direct expansion) cooling
  • Calculates chilled water flow rates for hydronic systems
  • Models multi-stage compressor operation for DX systems

• Building: Top-level container for HVAC equipment and building-wide data

  • Manages multiple AHUs and zones
  • Tracks outdoor weather conditions (temperature, humidity, wind, solar)
  • Calculates solar position based on time and location
  • Models building-wide energy usage
  • Generates energy reports by equipment and energy type
  • Supports time-based simulation with weather data inputs

• Cooling Tower: Evaporative heat rejection for water-cooled chillers

  • Models part-load performance based on wet bulb and load conditions
  • Calculates approach temperature and efficiency
  • Simulates variable-speed fan control
  • Predicts water consumption from evaporation, drift, and blowdown
  • Supports multiple cells with load-based staging

• Chiller: Produces chilled water for cooling coils

  • Supports both water-cooled and air-cooled configurations
  • Models COP and capacity based on part-load ratio and temperatures
  • Integrates with cooling tower for water-cooled operation
  • Calculates energy consumption based on operating conditions
  • Allows for setpoint adjustment with efficiency impacts

• Boiler: Produces hot water for heating coils

  • Supports both gas-fired and electric configurations
  • Models condensing boiler efficiency variation with return water temperature
  • Simulates realistic cycling behavior with minimum run times
  • Calculates fuel consumption with appropriate units
  • Provides detailed energy analysis for different operating modes

Getting Started

# Run the tests
python -m unittest discover tests

# Run single VAV box simulation (requires matplotlib)
python example_simulation.py

# Run thermal simulation with solar gain and occupancy (requires matplotlib)
python example_thermal_simulation.py

# Run AHU with multiple VAV boxes simulation (requires matplotlib)
python example_ahu_simulation.py

# Compare chilled water and DX cooling types (requires matplotlib)
python example_cooling_types.py

# Run complete building simulation with weather data (requires matplotlib)
python example_building_simulation.py

# Run comprehensive system simulation with all equipment types (requires matplotlib)
python example_complete_system.py

# Run BACnet integration with accelerated VAV simulation (requires BAC0)
python example_bacnet_simulation.py

Features

• Realistic PID control for damper and reheat valve modulation
• Deadband operation to prevent short cycling
• Energy usage calculation for all system components
• Supply air temperature reset based on zone demands
• Dynamic thermal modeling of zone temperatures
• Support for both heating and cooling modes
• Time-of-day based solar heat gain calculation
• Occupancy-based thermal load modeling
• Window orientation effects on zone temperature
• Thermal mass and building envelope heat transfer
• Multiple cooling system types:
  • Chilled water systems with valve modulation and flow calculation
  • DX (direct expansion) systems with multi-stage compressor control
  • Different efficiency models based on system type and conditions
• Central plant equipment:
  • Cooling towers with variable-speed fans and approach temperature modeling
  • Chillers with performance curves and condenser temperature effects
  • Boilers with condensing operation and fuel consumption tracking
  • Primary/secondary equipment integration (chiller + cooling tower)
• Whole-building simulation capabilities:
  • Integration of multiple HVAC systems
  • Building-level energy analysis and reporting
  • Weather data processing
  • Solar position calculation based on time and location
  • Time-based simulation with variable conditions

Example Simulations

Single VAV Box Simulation

The example_simulation.py script demonstrates a single VAV box behavior over a 24-hour period with:

• Varying zone temperature based on time of day
• Automatic mode switching between heating, cooling, and deadband
• Visualization of temperatures, airflow, valve positions, and energy usage
• Color-coded operating modes

Thermal Simulation with Solar and Occupancy

The example_thermal_simulation.py script demonstrates thermal behavior of VAV zones with:

• East-facing and west-facing office zones for comparison
• Time-of-day effects on solar heat gain through windows
• Scheduled occupancy with appropriate heat gain from people
• Building envelope heat transfer based on outdoor temperatures
• Detailed thermal modeling showing how zones respond differently throughout the day
• Comparison of HVAC system response to different solar load profiles

AHU Simulation

The example_ahu_simulation.py script demonstrates an AHU controlling multiple VAV boxes:

• Models a small building with office, conference room, and lobby zones
• Realistic occupancy patterns for each zone
• Dynamic thermal model accounting for outdoor conditions and internal loads
• Visualization of all zone temperatures, airflows, and system energy usage
• Supply air temperature reset based on zone demands

Cooling Types Comparison

The example_cooling_types.py script compares different cooling system types:

• Side-by-side comparison of chilled water and DX cooling performance
• Response to varying outdoor temperatures and cooling loads
• Chilled water flow rate calculation based on cooling demand
• DX compressor staging based on load requirements
• Energy efficiency differences between system types
• Impact of outdoor temperature on system performance

Complete Building Simulation

The example_building_simulation.py script demonstrates a whole-building simulation:

• Models a complete 2-story office building with multiple HVAC systems
• 5 thermal zones with different setpoints and orientations
• Mixed equipment types (chilled water and DX cooling systems)
• 24-hour simulation with realistic weather data
• Solar position calculation based on time, date, and location
• Comprehensive energy reporting and visualization
• Analysis of energy consumption by equipment type and category

Comprehensive System Simulation

The example_complete_system.py script demonstrates a complete HVAC system with all equipment types:

• Models a mixed-use 4-story building with multiple HVAC systems
• Includes 14 zones across different space types (office, retail, conference, lobby)
• Multiple AHUs with both chilled water and DX cooling
• Diverse central plant equipment:
  • Water-cooled and air-cooled chillers
  • Cooling towers with variable-speed fans
  • Gas-fired condensing and electric boilers
• Load distribution between parallel equipment
• Performance monitoring of all system components
• Analysis of efficiency under varying conditions
• Detailed visualization of key performance metrics

BACnet Integration Simulation

The example_bacnet_simulation.py script demonstrates BACnet integration with our HVAC simulation:

• Creates a simulated VAV box with realistic behavior
• Automatically generates BACnet points from process variable metadata
• Maps Python data types to appropriate BACnet object types
• Establishes a BAC0.lite() network for BACnet/IP communication
• Runs an accelerated simulation (1 hour per minute) with dynamic behavior
• Continuously updates BACnet points with current simulation state
• Makes the simulated HVAC equipment discoverable by any BACnet client
• Proper conversion of state variables (like modes) to BACnet multi-state values

Process Variables and Metadata

All equipment classes in the simulation provide standardized access to their state through:

1. get_process_variables() - Instance method that returns a dictionary of all current state variables
2. get_process_variables_metadata() - Class method that returns metadata for all process variables

The metadata includes:

• Type information (float, int, bool, str, etc.)
• Human-readable labels
• Detailed descriptions
• Units (°F, CFM, BTU/hr, etc.)
• Enumeration options for state variables

This standardized interface enables:

• Consistent access to equipment state across the simulation
• Self-describing HVAC equipment models
• Automatic BACnet point generation with appropriate data types
• Future extension for other protocols and interfaces

BACnet Integration

The simulation framework includes BACnet integration using the BAC0 library. To use this feature:

1. Install BAC0:

   pip install BAC0

2. Run the BACnet integration example:

   python example_bacnet_simulation.py

You can then use any BACnet client to discover and interact with the simulated HVAC equipment, including:

• BAC0's built-in script functionality
• Yabe (Yet Another BACnet Explorer)
• Proprietary BMS systems with BACnet/IP discovery

The BACnet integration enables:

• Testing BACnet interfaces without physical equipment
• Developing and debugging BACnet applications
• Creating hybrid systems with real and simulated equipment
• Training purposes for building automation