Validation

Tested against instruments in the street, against Radiance and EnergyPlus, and against CFD.

Last updated 30 Oct 2026

Radiant heat, Gothenburg Street instruments

4.5 K

K means kelvin, a step of one degree. In Gothenburg, our radiant heat (Tmrt) result is typically 4.5 K away from what the instruments in the street measured.

We tested three more sites: Phoenix (11.1 K against 14.3 K), Melbourne (11.8 K against 12.5 K) and Guelph (9.7 K against 12.3 K). Each pair is our error against SOLWEIG, a widely used research model, on the same input. Gothenburg is on par. At Guelph, a site we held out when we built the engine, our error is 21 % lower.

Perceived heat, Guelph Held-out

3.9 K

Perceived heat (UTCI) is within about 4 K of the street measurements.

Radiant heat, Melbourne Held-out

11.8 K

A site we did not use to build the engine. 989 points in 3 courtyards.

Sun against Radiance

2.6 %

Median difference in solar radiation against Radiance, on a real Vienna tile.

Buildings against EnergyPlus

0.98

Rank correlation with EnergyPlus on the BESTEST buildings. Design options come out in the same order.

Wind against CFD

0.988

Index of Agreement. Mean absolute error 0.31 m/s against high-fidelity CFD.

Speed

44 s

Perceived heat (UTCI) for 400 km² of Berlin at 1 m, end to end.

What we test

Perceived heat (UTCI) on a 1 m grid over a district in Singapore, from the platform — Perceived heat (UTCI) on a 1 m grid, Singapore case study.

infrared.city is a fast solver for screening many options. We test every kind of result it gives.

Perceived heat: we compare radiant heat (Tmrt) with street instruments in four cities, and run SOLWEIG, a widely used research model, on the same input. Sun and light: we compare with Radiance. Building energy: we compare with EnergyPlus. Wind: we compare with high-fidelity CFD.

When to use which tool: compare infrared.city with ENVI-met, SOLWEIG, PALM-4U and Orbital Stack

Speed

Run time from 1 km² to 400 km².

1 km²Vienna · 6,904 buildings · geometry already uploaded 5 s

9 km²Vienna · 28,714 buildings 24 s

100 km²Hamburg · 59,883 buildings 37 s

400 km²Berlin · 318,856 buildings 44 s

Perceived heat (UTCI) for one summer day, 08 to 18 h, on a 1 m grid, on our production cloud. 1 km²: geometry already uploaded, measured 24 Oct 2026 (first run with upload about 17 s). 9 to 400 km²: end to end, building data and upload included, measured 23 Oct 2026. Berlin ran as four 100 km² runs at the same time.

All sites and method

Every number above, with the full context.

Perceived heat: four citiesRadiant heat (Tmrt) against street instruments, and the reference data

Radiant heat (Tmrt)

Typical error (RMSE) in K against field instruments. Lower is better.

InfraredSOLWEIG, research model Source: infrared.city internal validation report (Oct 2026), available on request. Same points, weather and 3D scene for both models. Lighter bars: in-sample sites.

Phoenix and Gothenburg are in-sample: we used the data while we built the engine. Melbourne and Guelph are held-out sites: we changed no setting for them. Method: Thermal model method.

The reference data

Site	Instrument	Sample
Gothenburg, Sweden	Six-direction sensors	3 sites, 85 hours
Phoenix / Tempe, USA	MaRTy cart (six-direction sensors)	One park, 438 points, summer days
Melbourne, Australia	Globe thermometers	3 courtyards, 989 points
Guelph, Canada	MaRTy cart	9 sites, 140 points

For each measured point and hour, we read the model cell at that place. The weather is the measured weather of the test days. Error is model minus measured. We report the typical error (RMSE). The Gothenburg value is a mix of three sites. We tested the engine as it was on 23 October 2026.

Sun and light: against RadianceSolar radiation, sky view, sun hours and daylight

We compare our results point by point with Radiance 6.1, the open-source lighting simulation from Lawrence Berkeley National Laboratory and a standard tool for light and solar studies. Both tools get the same geometry, materials, sky and sun positions.

Model	Test scenes	Result
Solar radiation	Street canyons (height to width 0.5 to 3), a courtyard, an open square with a tall bright tower, a low building, real tiles of Vienna and Hong Kong. Glass, white render, dark brick and concrete facades. Radiance with 8 reflections	Median difference 2.6 % (Vienna) and 4.5 % (Hong Kong). Per street case 0.1 to 7 %, deep sunny canyons 2 to 7 %
Sky view factor	Street canyons and a Vienna tile with 119 points. Cosine-weighted, the same definition in both tools	Median difference 0.6 to 0.7 points, correlation 0.997
Direct sun hours	One June day and one June month, Vienna and Hong Kong latitudes, 20 points per case	The same hours at all 20 test points of each case
Daylight availability	The same scenes and periods as direct sun hours	Matches Radiance on the same scenes and sun positions
Daylight factor	CIE overcast sky. Side-lit 4 × 6 m room and deep 4 × 12 m room, wall reflectance 0.5 and 0.7. Radiance with 6 reflections	Median difference 0.3 to 0.4 percentage points. Side-lit rooms read slightly high: 3.7 % against 3.2 %

Facade materials set the light that walls reflect onto the street. We also check the energy balance: the light that arrives, is absorbed and leaves adds up (ratio 0.98 to 1.00). For scale: a good field pyranometer has an uncertainty of about ±4 %, a typical weather file 5 to 10 %. Tests run 27 to 29 October 2026.

Buildings: against EnergyPlusRank correlation 0.98 to 0.99 on the BESTEST buildings

We compare the building energy model with EnergyPlus, the reference tool of the US Department of Energy, on the standard BESTEST test buildings, and test it to the European standard EN 15265.

Design variants rank in the same order as in EnergyPlus: rank correlation 0.98 to 0.99. That is what early design decisions need. Absolute heating plus cooling is 8 to 15 % above EnergyPlus. To EN 15265 the model reaches level C or better in 4 of 4 continuous and 3 of 8 intermittent cases. The monthly method follows ISO 13790 and reproduces all 12 monthly values of its worked example (Annex J) exactly; ISO 52016-1 keeps the same monthly structure. Tests run in September 2026.

Wind: the AI modelIndex of Agreement 0.988, mean absolute error 0.31 m/s

The wind model is an AI model that we trained on CFD results. We tested it against high-fidelity CFD simulations of many urban shapes: Index of Agreement 0.988 (1.0 is a perfect match) and a mean absolute error of 0.31 m/s. The full text is in the article Wind model validation.

3D CFD on request for strong-wind cases. If a project needs more than screening, talk to us.

Model cards

What each of the 12 models computes, how, and the standards it follows.

Wind speed

Computes: Wind speed in m/s at pedestrian level, for one wind direction.
How: An AI model, trained on CFD results, estimates the wind field from the urban shape. It does not run CFD for each request.
Tested: 0.988 Index of Agreement vs CFD
Aligned with: VDI 3787-4

Pedestrian wind comfort

Computes: Comfort and safety classes on a ground grid, over a wind climate.
How: The wind model gives 16 directional wind fields. We combine them with the local wind climate and classify every place to the established criteria: Lawson, NEN 8100, Davenport and VDI 3787.
Aligned with: Lawson (LDDC), NEN 8100, VDI 3787-4

Thermal comfort

Computes: Percent of the chosen time that each ground cell is in the UTCI comfort band.
How: Ray tracing gives sky view and solar radiation. Mean radiant temperature comes from surface temperature, solar and sky view. UTCI combines it with air temperature, humidity and wind: the weather-file wind, or local wind for each cell from the AI wind model as an option.
Tested: 4 cities radiant heat measured in the street
Aligned with: UTCI, Bröde et al. 2012, VDI 3787-2, VDI 3785-1

Heat stress

Computes: Percent of the chosen time that each ground cell is above the UTCI heat-stress threshold.
How: The same UTCI engine as thermal comfort. A statistics step counts the hours above the threshold.
Tested: 4 cities radiant heat measured in the street
Aligned with: UTCI, Bröde et al. 2012, VDI 3787-2

Cold stress

Computes: Percent of the chosen time that each ground cell is below the UTCI cold-stress threshold.
How: The same UTCI engine as thermal comfort. A statistics step counts the hours below the threshold.
Tested: 4 cities radiant heat measured in the street
Aligned with: UTCI, Bröde et al. 2012, VDI 3787-2

Microclimate (UTCI)

Computes: UTCI in degrees C on a ground grid, at a chosen time or time window.
How: Ray tracing gives the radiation. Mean radiant temperature and the weather data give the UTCI value.
Tested: 4 cities radiant heat measured in the street
Aligned with: UTCI, Bröde et al. 2012, VDI 3787-2, VDI 3787-8

Daylight availability

Computes: A direct-sun score from 0 to 100 percent, for a point or a surface.
How: Ray tracing follows the sun positions that nothing blocks. The score reaches 100 percent at half of the maximum possible sun access.
Tested: Same values as Radiance
Aligned with: Perez all-weather sky, EN 17037

Sky view factors

Computes: The visible sky, from 0 to 100 percent, at each point or surface.
How: A hemispherical ray trace samples the sky directions that are visible.
Tested: 0.7 pt median difference vs Radiance
Aligned with: VDI 3787-1

Direct sun hours

Computes: Hours of direct sun at each point or surface, over a chosen period.
How: Ray tracing checks each chosen sun position for shade and adds up the hours.
Tested: Same hours as Radiance, at every test point
Aligned with: EN 17037 sunlight exposure

Solar radiation

Computes: Solar energy in kWh/m2 on ground, facade and roof surfaces.
How: A sky matrix built from the direct and diffuse radiation of the weather file. Ray tracing finds the shade and the sky exposure of each surface, and the light that facades reflect, from each building's material.
Tested: 2.6 % median difference vs Radiance
Aligned with: ISO 52010-1, VDI 3789-2, Perez all-weather sky

Interior daylight factor

Computes: Daylight factor in percent at points inside a room.
How: A CIE standard overcast sky. Ray tracing follows the light through the openings.
Tested: 0.4 pt median difference vs Radiance
Aligned with: CIE standard sky (ISO 15469), EN 17037

Energy balance

Computes: Monthly heating and cooling need, and the annual energy use intensity in kWh/m2 per year.
How: A monthly energy-need calculation to ISO 13790, with zones and solar gains.
Tested: 0.98 rank correlation with EnergyPlus
Aligned with: ISO 13790 monthly method, ISO 52016-1, EN 15265 test cases, ASHRAE 140 (BESTEST), ISO 6946, ISO 13370