The beating heart of Building Performance Simulation

Building Performance Simulation

With origins reaching back over 25 years, the technology originally dubbed ‘APplication for Air-Conditioning and Heating Engineers‘ has evolved into a user-interface, rules processor and the best whole-building energy simulation engine in the world. 

APACHE has become the beating heart of IES Virtual Environment.

APACHE’s Graphical User Interface and API


The APACHE Application in IESVE Software is an easy-to-use graphical user interface (GUI) for the APACHE engine and provides access to the following:

  • 3D model engagement (assign/edit/customize)
  • Assignment of constructions, gains, ventilation to room(s) or group model selections
  • Editing of assigned room template data in Tabular spreadsheet mode. Includes functionality for Copy/paste/import/export.
  • Customization of energy meters, renewable energy technologies, profiles and controls
  • Simulation control for loads calculations or energy modeling


The IES Virtual Environment software provides a VE-Scripts dialog, which is a Python-based Application Programming Interface (API). The API allows for additional custom APACHE simulation controls and auto-creation of results & reports from APACHE’s results.  Click below for detailed guidance when using the Python API.

APACHE for Heating & Cooling Loads Calculations

Loads calculations with the world-renowned APACHE engine allows for easy-to-use access to the most robust industry methods, which require (sub)-hourly calculations that account for the storage and thermal mass of construction materials. 

APACHE for Energy Simulation

Widely regarded as the best whole-building energy simulation engine in the world, the powerful APACHE engine used in the IES Virtual Environment software has unrivalled flexibility and features.

  • Integration: 1-way and 2-way model simulation links with other IESVE Applications & simulation engines for solar, daylight, airflow and HVAC. 
  • Captures building performance metrics for energy, water, carbon, cost, comfort, loads and more.
  • Extensive range of predictive simulation results variables for buildings, systems, zones, room and surfaces.
  • Simulation results available for annual, monthly, hourly, and sub-hourly analysis. 1-minute simulation time-step available.
  • Assess thermodynamic performance of active and passive systems, with the ability to perform multiple simultaneous simulations in parallel using the Parallel Simulation Manager.
  • ASHRAE 140 Validated and EPAct Approved
  • Electrification and Decarbonization design alternatives available
apache diagram

APACHE for HVAC Optimization

The ApacheHVAC Application in the IES Virtual Environment software allows for detailed HVAC design and optimization for airside systems, waterside plant loops, isolated HVAC equipment or for a large campus of buildings with one central plant.  External metered BAS/BMS hourly time-series data sources can be imported into ApacheHVAC to consider new design or control scenarios, all without any 3D model building representation. These plant-only simulation in ApacheHVAC can be coupled with energy generation from PV + Battery Storage within IESVE Software.

APACHE for Energy Code Compliance

APACHE automates the creation of energy code baseline models for compliance comparisons by interpreting the rules associated with local building energy codes, regulations, standards and rating systems. E.g. ASHRAE 90.1, Part L, NECB, Title 24, IECC, etc.

APACHE for Occupant Thermal Comfort

During a simulation, APACHE accounts for thermal mass and records the surface temperatures in rooms and airflow rates through openings on a sub-hourly basis. Those results can be used to confirm occupant comfort for each hour of the year or those results can be exported to MicroFlo as boundary conditions for detailed CFD analysis.

Hourly Comfort Simulation

  • Set occupant Clothing (CLO) and Metabolic Rate (MET).
  • Vary occupant clothing levels based on comfort parameters.
  • Establish nominal and elevated air speeds with air circulation fans; or engage operable windows..
  • Include factors for short-wave radiation to the space occupants based on occupant orientation and posture.
  • Perform comfort analysis for hundreds of rooms during thousands of hours, with one simulation. E.g. 8,760 hours.
  • Analyze operative temperatures, PMV, PPD, standard effective temperatures and more.
  • Comply with ASHRAE Standard 55 or CIBSE TM52

CFD Comfort Simulation

APACHE accounts for surface temperatures in rooms and airflow rates through openings. Export results to MicroFlo as boundary conditions for detailed CFD analysis.

  • Set occupant Clothing (CLO) and Activity level (MET).
  • Calculate mean radiant temperatures by numerical integration or area-weighted surface temperature
  • Analyze Comfort metrics such as (dry-resultant) operative temperatures, PMV, PPD and more.

Got a question?

Contact our team to find out more about APACHE.