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EnergyFront V3.5 Validation and Testing Report

1. What EnergyFront does and what was tested

EnergyFront does not compute building physics itself. It writes an EnergyPlus input file (IDF) from the inputs of its interface, runs EnergyPlus 9.4 and reads back the results. The tests therefore answer three questions: (1) does EnergyFront write the same model as a reference IDF, so that EnergyPlus gives the same results; (2) when an existing IDF is opened in EnergyFront, what is kept, what is approximated and what is lost, and is every loss reported to the user; (3) do the inputs of the interface reach the IDF as intended. The accuracy of the physics itself is that of EnergyPlus 9.4 and is documented by its developers.

• Method A, generation fidelity: ASHRAE Standard 140-2020 envelope cases entered in EnergyFront; the EnergyFront IDF and the reference IDF run with the same weather file and compared.
• Method B, round trip of an IDF: HVAC BESTEST, Furnace BESTEST and EnergyPlus 9.4 example files opened with File > Open IDF 9.4, written again by EnergyFront and run.
• Method C, software tests: automated tests of inputs, rules, units, interface, tagging for PareVia and EPCalibration, and traceability of every input to the IDF objects it changes.

2. ASHRAE Standard 140-2020 envelope cases (Method A)

Cases 600 and 900 (low and high mass, south windows), their variants 610 to 650 and 910 to 950 (overhang, east and west windows, shading fins, thermostat setback, night ventilation) and the free-floating cases 600FF, 650FF, 900FF and 950FF. Weather file 725650TYCST.epw (Denver) of the Standard. The example results of the Standard (informative Annex B8) are ranges of other programs, not pass/fail criteria.

* 13 of 48 results lie outside the range of the example results of the Standard. In every such row the reference IDF run directly in EnergyPlus 9.4 gives the same value, so the departure belongs to the reference model with EnergyPlus 9.4 and not to the translation by EnergyFront. The heating of cases 640 and 940 is explained below; the other departures have not yet been investigated further.

Cases 640 and 940, heating. In the reference IDF of these two cases the heating setback ends as a step: 10 °C until 07:00 and 20 °C from 07:00. ASHRAE Standard 140-2020 specifies a linear recovery from 10 °C at 07:00 to 20 °C at 08:00. With an ideal heating system of unlimited capacity, the step puts the whole recovery into the first time step after 07:00, which raises the hourly peak and the annual heating. The reference IDF was run again with the recovery of the Standard (steps of 1.67 K every 10 minutes from 07:00 to 08:00), all other inputs unchanged:

With the recovery of the Standard both cases lie within the example ranges, so the departure comes from the setback input, not from EnergyPlus 9.4 or from EnergyFront. The schedules of EnergyFront have hourly values, so a recovery within the hour cannot be entered: EnergyFront models these two cases with the step, as the reference IDF in the table above.

Result. In all 48 comparisons the EnergyFront model gives the same annual and peak loads as the reference IDF within 0.02 %, and the same free-floating temperatures (0.00 K). This shows that the interface inputs of EnergyFront can express these cases completely and that EnergyFront writes them as the reference does. It does not by itself show that EnergyPlus is within the ranges of the Standard.

3. HVAC BESTEST and Furnace BESTEST (Method B)

Result. The thermal loads of the zone are reproduced within 0.02 %. HVAC equipment energy is not the same, because EnergyFront writes its own HVAC systems and does not keep the component curves of an imported IDF. The HVAC equipment models of EnergyFront have not been validated against the HVAC BESTEST performance cases.

4. EnergyPlus 9.4 example files (Method B)

47 example files of EnergyPlus 9.4, including the 16 DOE commercial reference buildings, were opened in EnergyFront, written again and run (annual, Chicago TMY3). The purpose is to check the importer: a difference is acceptable only when the import report names its cause. The per-file results and causes are in the report and in the package.

Class	Meaning	Files
A match	Areas, lighting and equipment within 3 %, zone loads within 5 %, mean temperature within 0.5 K	3
B explained	Every difference is named in the import report of EnergyFront (approximated or not converted)	41
B test artifact	Artificial test geometry (an open zone) that EnergyFront closes; not reported	1
C not imported	Not imported, with a clear message (simple surface objects)	2

5. Automated software tests (Method C)

• Inputs and rules: 170 checks passed. Units and generator: 514 checks passed. Interface: 488 checks passed. Tagged IDF and CSV for PareVia and EPCalibration: 47 checks passed.
• Traceability: 307 inputs in 30 buildings; each change must change the IDF objects listed in the traceability matrix.
• Verification report: one known open item (ground temperature of an imported layered construction).
• Every run of EnergyFront writes a verification report (Results > Verification) that lists the inputs next to what EnergyPlus reports back. It is a check of each model, not of the tool in general.

6. Known limitations (summary)

The full list is in Section 8 of the report and is part of the Licence Agreement. Results in these areas need independent checking.

• Engine: EnergyPlus 9.4.0 only; its physics, numerical methods and known issues apply.
• Geometry: flat roofs only; plenums and attics are not zones; a floor mixing zones with different multipliers is modelled once; zones taller than one storey get one storey; imported IDFs must use detailed surfaces.
• Constructions and ground: Window5 data-file glazing, complex fenestration (BSDF), C-factor / F-factor constructions, fixed convection coefficients, two-dimensional ground models and skylights are not converted on import.
• Loads and schedules: schedules have hourly values, so a setpoint change within the hour (such as the 1-hour setback recovery of ASHRAE 140 cases 640 and 940) cannot be entered; holidays of an imported IDF are not kept; gas equipment, refrigeration and exterior lighting are not converted.
• HVAC: EnergyFront writes its own systems; components, curves, loops and controls of an imported IDF are not kept; equipment energy can differ substantially; HVAC equipment models are not validated against the HVAC BESTEST performance cases (CE300 and above).
• Results: zone variables are not multiplied by zone or floor multipliers; central HVAC energy cannot be split by floor; Ideal loads report thermal energy converted with a constant COP on the Results page only.
• Process: the report was prepared by the developer and has not yet been reviewed independently; no empirical validation against a measured building has been done yet.

7. Your responsibility

Before relying on any result, check it for your project: review the verification report of the run, the EnergyPlus error file (eplusout.err) and, for an opened IDF, the import report; compare with hand calculations, benchmarks, measured data or another simulation program; and have the results reviewed by a suitably qualified professional (Licence Agreement, Section 9). Do not describe EnergyFront or your results as certified, approved or validated by ASHRAE, or as compliant with ASHRAE Standard 140.

8. Public validation package

The public validation package (ZIP) lets you repeat the tests: the report (PDF), the results tables (CSV) of the Standard 140 cases, HVAC BESTEST, Furnace BESTEST and the example files, and the EnergyFront projects (*.json) of the Standard 140 cases. Open a project in EnergyFront, choose the weather file of the Standard (725650TYCST.epw, not included) and run it. The Standard, its weather file and the reference input files are not included.

9. References

1. ANSI/ASHRAE Standard 140-2020, Standard Method of Test for the Evaluation of Building Energy Analysis Computer Programs. ASHRAE, Atlanta.
2. NREL, BESTEST-GSR: Building Energy Simulation Test Generation, Simulation and Reporting. github.com/NREL/BESTEST-GSR
3. US Department of Energy, EnergyPlus version 9.4.0. energyplus.net

This page summarises the EnergyFront V3.5 Validation and Testing Report; if they differ, the PDF report prevails. It describes the stated version, test cases and conditions only. EnergyPlus is a trademark of the US Department of Energy. ASHRAE Standard 140 is referred to by name only. EnergyFront is not affiliated with, sponsored by or endorsed by the US Department of Energy, NREL or ASHRAE.