Questions to Ask Before Choosing HVAC Design Software
10 Essential criteria to look for in a modern HVAC loads and design software.
Effortless Code Compliance
Does the software effortlessly meet ASHRAE Standard 183 in a real project workflow, not just in theory? Standard 183 is now referenced in both ASHRAE 90.1 and IECC as the minimum requirement for load calculations to meet energy code. It lays out criteria for peak cooling and heating load calculations in all but low-rise residential buildings. Omitting or estimating key elements such as internal surface effects can result in non-compliance.
Compliance by design, not by effort. IESVE is positioned to support all key minimum ASHRAE Standard 183 requirements through its 3D geometry, physics-based thermal simulation and ASHRAE Heat Balance approach, while reducing the amount of manual rework needed. The software captures internal gains against heating loads and facilitates psychrometric documentation of system interactions, which is difficult in tools that don't model HVAC as a network of components.
Calculation Method Matters
Does the tool use the ASHRAE Heat Balance Method? ASHRAE Standard 183 leaves the choice of calculation method to the engineer, but the mathematical rigor and capabilities of those methods differ. Heat Balance is only method the ASHRAE Handbook of Fundamentals endorses for resolving all heat gains and thermal mass calculations without approximation or use of weighting-factors such as used in the RTS or TETD-TA and CLTD/CLF/SCL methods.
The most accurate method for determining loads and reducing professional risk. IESVE uses the ASHRAE Heat Balance Method in the Apache engine, which is ASHRAE 140 validated. It can deliver full hourly simulation of load behavior as it supports time-based heat transfer calculations through all construction layers without approximations. This is especially significant in systems where timing and interactions matter such as heat pumps, thermal storage or heat recovery systems.
Stress-Free Solar Radiation
Does the tool facilitate quick and easily modeling of hourly solar radiation across all room surfaces, including interior walls, floors, ceilings, and partitions, as required by Standard 183? Most tools technically meet this requirement, but the level of effort required can differ hugely due to a lack of 3D geometry. If the process is prohibitively time-consuming, it’s prone to simplification which often results in required interior surfaces and assemblies being omitted in practice, causing non-compliance with Standard 183.
Solar radiation calculations without any extra user effort. IESVE represents every room surface explicitly in its 3D model. This enables in-built calculation and understanding of solar distribution across all interior surfaces, including the effects of blinds, shades and drapes. Meaning that solar radiation is applied to every relevant surface automatically and that short- and long-wave radiation is accurately captured.
System-Level Impacts
Does the software represent the HVAC system as a network of real components (coils, fans, pumps, ducts, pipes, heat exchangers), rather than an abstract system block? This allows loads, capacities, and energy use to be calculated accurately within the HVAC system design, improving confidence in equipment selection and plant sizing. While also supporting the Standard 183 requirement for reporting system-level impacts, including duct losses, fan heat, and air-side processes such as mixing and reheat.
Full component-level HVAC modeling. ApacheHVAC models the complete system as a network of components with an explicit psychrometric state at each node, enabling IESVE loads reports to drill down into system-level impacts. The IESVE approach also enables dynamic, part‑load simulation of individual components to reflect real HVAC system operation without relying on fixed efficiency assumptions.
Unbroken HVAC Workflow
Do peak loads results feed directly into a full HVAC system design workflow or is there manual re-entry between steps? Can the engineer move from climate assessment to peak loads to sized equipment with a detailed control strategy all within one environment? This helps ensure sizing results remain fully traceable back to the underlying load model and carry forward into detailed design and control strategy optimization.
Climate-to-HVAC design in one unbroken workflow. IESVE delivers a Climate Assessment Report with ASHRAE Design Day Data in seconds before any model is built. Then ASHRAELoads calculates peak loads via the Heat Balance Method, following which an engineer can move directly into ApacheHVAC for system sizing and dynamic load calculations with no manual re-entry as room and zone data flows straight in. Finally, detailed design and control strategy customization can be refined, all from the same model.
Built-In Scenario Testing
Can you quickly and systematically vary one or more design parameters, such as HVAC system type, climate or envelope construction, and automatically run multiple scenarios with side-by-side comparisons? This enables a quick review of what works best and supports early design conversations without rebuilding the model from scratch, helping to keep mechanical scope responsive to early architectural changes.
Rapid scenario testing built in. The Parametric simulation module in IESVE enables fast comparison of HVAC strategies against the same load set or enables you to test against future climate extremes, for example. This is particularly valuable at early-stage decision making or when under value engineering pressure as it enables you to quickly deliver clear evidence for selecting one HVAC strategy over another.
BIM/CAD Connectivity
Is the tool locked to a single BIM/CAD platform (e.g. Revit)? Or does it support multiple authoring environments to fit the firm's actual workflows – Revit, Rhino, SketchUp, AutoCAD?
The broadest BIM/CAD ecosystem on the market. A Pollination plugin offers native IESVE .GEM interoperability with Revit and Rhino, eliminating geometry errors and cutting model import time by up to 40%. IESVE also supports gbXML, SketchUp, AutoCAD, and ArchiCAD transfer (via IFC), with a BIM Navigator that consolidates all import settings into a single step-by-step workflow.
Modern HVAC Systems
Does the tool cover the full range of typical and innovative HVAC systems, including low-carbon and electrification strategies, with customisable control sequences? Mechanical Engineers today need to configure, simulate and optimize the full spectrum of systems, including VRV/VRF systems, air, ground and water source heat pumps (ASHP/GSHP/WSHP), chilled beams, radiant systems, DOAS, thermal energy storage and evaporative cooling.
The most comprehensive coverage across HVAC system types, from Variable Refrigerant Flow (VRF) and Dedicated Outdoor Air Systems (DOAS) to Chilled Beams, Radiant Systems, Heat Pumps, and Thermal Energy Storage (TES). IESVE supports end‑to‑end HVAC modelling using a library of hundreds of predefined, fully configurable system prototypes alongside a flexible, component‑based approach. This allows users to model the broadest range of conventional and advanced HVAC systems on the market, while retaining full transparency and engineering control. All accurately sized using the industry-validated ASHRAE Heat Balance method.
Defensible & Transparent Results
Can outputs be traced and interrogated at the building, room, zone, system, and component level, for internal QA, permit documentation, and defending the design against contractor equipment substitutions?
Visual QA/QC checking from a whole-building perspective right down to the HVAC component level. VistaPro enables interrogation of results at any level (room, zone, system, component). Extremely useful when you need to defend your system choices to a contractor during value engineering, or for producing client-ready 3D visuals which support design communication.
Energy Modeling Capabilities
Some traditional HVAC tools do not provide meaningful energy modeling capabilities, even as the market shifts from stand-alone HVAC Design toward integrated load, system, and energy analysis. Peak-load calculations remain essential, but systems must still be capable of meeting design conditions. However, most buildings rarely operate at or near their peak load, which is where evaluating performance across an entire year of operation using an 8,760-hour thermal simulation is powerful for understanding load ranges over the course of a year.
30 years of continuous development. The APACHE engine is fully owned and developed in-house by IES, so the team can directly support every modelling detail. While IESVE has a continuous innovation roadmap aligned to emerging HVAC Design, energy code and electrification trends.
