Validation Standards for Building Simulation Software

Validation standards such as ASHRAE Standard 140, EN 15255/15265, EN 13791 and CIBSE TM 33 verify the correct implementation of physical algorithms in building simulation software using defined test cases with reference results. For summer thermal protection in Germany, EN 13791 and DIN 4108-2 are the decisive standards; internationally, ASHRAE 140 is the minimum requirement. A program’s published validation documentation is a key selection criterion for engineers and designers.

Why validation?

A dynamic building simulation program solves complex physical equations — heat conduction, radiation, convection, ventilation, HVAC control. Errors in the implementation lead to erroneous results that are hard to detect in practice. Validation standards provide an objective basis for checking the correct implementation of the physical algorithms. They do not replace the user’s plausibility check, but they do give the assurance that the computational core is working correctly.

ASHRAE Standard 140

Background

ASHRAE Standard 140 (Standard Method of Test for the Evaluation of Building Energy Analysis Computer Programs) is the most widely used validation standard internationally. It was first published in 2001 and is updated regularly. The standard originates from the BESTEST procedure (Building Energy Simulation Test), developed in the 1990s within the framework of the IEA (International Energy Agency).

Test cases

The standard comprises several test series:

• Building Thermal Envelope: Test cases with a simple single-zone building under various boundary conditions — opaque components, glazings, solar shading, internal loads, night ventilation, ground coupling. The results (heating and cooling energy demand, peak loads) are compared with reference results from several validated programs.
• HVAC systems: Test cases for mechanical cooling and heating, including capacity control and part-load behaviour.
• Ground-coupled heat transfer: Since the 2017 extension, additional test cases for heat transfer via ground-coupled components.

Evaluation

There is no rigid pass-or-fail criterion. The results of a program are compared with the spread of the reference programs. If a result falls outside this spread, an investigation is required — there may be an error in the program, but there may also be a legitimate modelling approach that differs from the reference programs.

Software with ASHRAE 140 validation

EnergyPlus, IDA ICE, TRNSYS, ESP-r, VICUS Buildings (via NANDRAD/SimQuality) and many other programs have run through ASHRAE 140 test cases and publish the results.

EN 15255 and EN 15265

Background

The European standards EN 15255 and EN 15265 are part of the EPBD set of standards (Energy Performance of Buildings Directive) and define validation test cases for simulation programs used in the context of European energy-saving legislation.

• EN 15255 (Energy performance of buildings — Sensible room cooling load calculation — General criteria and validation procedures): Defines test cases for calculating the sensible cooling load of a room. The test cases check the correct representation of solar radiation, internal loads and thermal mass.
• EN 15265 (Energy performance of buildings — Calculation of energy needs for space heating and cooling using dynamic methods — General criteria and validation procedures): Defines test cases for calculating the heating and cooling energy demand using dynamic methods. The standard comprises 12 test cases with a single-zone building under systematically varied boundary conditions (orientation, glazing, shading, internal loads, ventilation, control).

Significance

EN 15255 and EN 15265 are particularly relevant for the European market, as they form the basis for the recognition of dynamic simulation methods within the framework of national energy-saving regulations. In Germany, dynamic simulation is permitted as a verification method for summer thermal protection in accordance with DIN 4108-2 — the underlying software should have passed the EN validation.

Software with EN 15255/15265 validation

IDA ICE has published the validation in accordance with EN 15265 and is thus one of the few programs that cover both ASHRAE 140 and the European standards. EnergyPlus and TRNSYS are also tested against these standards, but do not always publish the results explicitly.

EN 13791

Background

EN 13791 (Thermal performance of buildings — Calculation of internal temperatures of a room in summer without mechanical cooling — General criteria and validation procedures) defines test cases for calculating summer room temperatures without active cooling. The standard is particularly relevant for the verification of summer thermal protection.

Test cases

The standard comprises four validation test cases:

1. Test case 1: Single-zone room with constant outdoor temperature and defined internal loads — tests the steady-state heat balance.
2. Test case 2: Single-zone room with periodically varying outdoor temperature — tests the representation of thermal mass.
3. Test case 3: Single-zone room with realistic climate and solar radiation — tests the overall representation of summer behaviour.
4. Test case 4: Multi-zone model with heat transfer between rooms.

Significance

EN 13791 is the definitive validation standard for the verification of summer thermal protection in Europe. Programs used for the simulation-based verification in accordance with DIN 4108-2 should have passed this validation.

IEA SHC Task 34 / EBC Annex 43

Background

IEA SHC Task 34 (Testing and Validation of Building Energy Simulation Tools) was an international research project of the International Energy Agency (Solar Heating and Cooling Programme) that ran from 2003 to 2008. It was carried out jointly with EBC Annex 43 (Testing and Validation of Building Energy Simulation Tools) of the Energy in Buildings and Communities Programme.

Contents

The project went beyond the existing BESTEST test cases and developed additional validation procedures:

• Multi-zone models: Test cases for buildings with several thermally coupled zones, including heat transfer through interior walls.
• Ground coupling: Extended test cases for ground-coupled components, which were later incorporated into ASHRAE 140.
• Mechanical systems: Test cases for HVAC components and their control.
• Empirical validation: Comparison of simulation results with measurement data from real buildings and test cells.

Significance

IEA SHC Task 34 significantly advanced the validation methodology for building simulation. Many of the developed test cases have been incorporated into subsequent revisions of the standards. The empirical validation — the comparison with real measurement data, such as those generated for a digital twin — complements the analytical validation of the other standards and significantly increases their expressiveness.

Participating software

Software participating in the project included EnergyPlus, ESP-r, IDA ICE, TRNSYS and VA114, among others. IDA ICE published extensive validation results within the framework of Task 34, especially for multi-zone models and empirical test cases.

CIBSE TM 33

Background

CIBSE TM 33 (Tests for Software Accreditation and Verification) was developed by the Chartered Institution of Building Services Engineers (CIBSE) in the United Kingdom. It defines test cases for the accreditation of simulation software in the context of British building regulations (Building Regulations Part L).

Test cases

TM 33 comprises a series of test cases that focus on calculations relevant in British practice:

• Heating and cooling energy calculation
• Daylight calculation
• Overheating risk (summer thermal protection)
• CO₂ emissions calculation

Significance

TM 33 is particularly relevant for projects in the United Kingdom. CIBSE accreditation is in many cases a prerequisite for the use of simulation software within the framework of British energy efficiency regulations.

Software with TM 33 validation

IDA ICE is accredited in accordance with CIBSE TM 33 and can therefore be used for verifications under the British Building Regulations. DesignBuilder (via EnergyPlus) and TAS are also CIBSE-accredited.

Comparison table: validation standards by software

As of April 2026. ”–” means: not published or not carried out.

IDA ICE in detail

IDA ICE (Indoor Climate and Energy) from EQUA Simulation AB has one of the most extensive validation histories on the market. The software has completed and published the following validations:

• ASHRAE 140: Complete test series for building envelope and HVAC systems.
• EN 15265: All 12 test cases passed; the results lie within the reference spread.
• EN 15255: Cooling load calculation validated.
• EN 13791: All four test cases for summer room temperatures passed.
• IEA SHC Task 34 / Annex 43: Active participation in the research project with results for multi-zone models and empirical validation.
• CIBSE TM 33: Accredited for use within the framework of the British Building Regulations.

This broad validation base makes IDA ICE one of the best-validated commercial simulation programs. For projects that require formal validation in accordance with European standards, this is a relevant advantage.

VICUS Buildings and SimQuality

VICUS Buildings uses the simulation engine NANDRAD, which was validated within the framework of the SimQuality project. SimQuality is a German research project that has developed specific validation test cases for building simulation software. The test cases are based on ASHRAE 140 but supplement it with additional practice-oriented scenarios. Beyond this, NANDRAD has been tested against ASHRAE 140 test cases.

Validation in accordance with EN 15255, EN 15265 and EN 13791 is in preparation. For the verification of summer thermal protection in accordance with DIN 4108-2, VICUS Buildings can already be used.

Which standard for which purpose?

Conclusion

Validation is not a one-off seal of quality, but an ongoing process. Every new program version should be tested against the relevant standards. For users, the published validation documentation is an important selection criterion for the software comparison — it shows not only that a program calculates correctly, but also that the vendor provides transparency about the capabilities of its software.

When selecting a simulation software, the validation should be evaluated in the context of the use case: for summer thermal protection in Germany, EN 13791 and DIN 4108-2 are decisive. For international projects, ASHRAE 140 is the standard. For the British market, CIBSE TM 33 is relevant. VICUS Buildings covers the core validation through SimQuality and ASHRAE 140 and is progressively extending this with the European standards.

Further reading: Dynamic Building Simulation — what gets validated: the simulation method itself, Building Simulation Software Comparison — the tools being tested and their validation coverage, Summer Thermal Protection in Accordance with DIN 4108-2 — a practical application where validated software is essential.

References and Standards

• ASHRAE Standard 140 — Standard Method of Test for the Evaluation of Building Energy Analysis Computer Programs
• VDI 6020 — Requirements on methods of calculation to thermal and energy simulation of buildings and plants
• Judkoff, R.; Neymark, J. (1995): International Energy Agency Building Energy Simulation Test (BESTEST) and Diagnostic Method. NREL/TP-472-6231.