Over the last few summers, many cities have had a preview of their climate future: dangerous heat, strained healthcare systems, and outdoor workers pushed to their limits. Heat is a silent hazard, and one of the biggest challenges is that we still don't measure it very well where people actually live, work and move.
If you want to know whether a particular street, schoolyard or construction site is unsafe, you need more than just the air temperature from a distant airport. You need a way to capture how sun, humidity and wind combine at that specific location to create heat stress on the human body. That is exactly the gap the Trofic instrument is designed by us to fill.
Trofic (Temperatuur, Radiatie en OmgevingsFactoren Index‑Constructie) is a new, passively ventilated sensor housing that measures shaded air temperature, humidity and black‑globe temperature in one compact unit, without fans or mains power. It's designed for dense networks in cities, remote regions and low‑resource settings where conventional heat‑stress stations are too expensive or too hard to maintain.
Why conventional measurements miss heat stress
Most automatic weather stations, including many official networks, only measure standard air temperature and humidity. To assess heat stress, a widely used metric is the Wet Bulb Globe Temperature (WBGT), which combines three separate temperatures: dry‑bulb (shaded air), wet‑bulb (humidity and evaporative cooling) and black‑globe (sun and radiant heat). In practice, the wet‑bulb and black‑globe components are often missing and have to be modelled from other data.
This introduces two problems:
- If the basic measurements used to drive the model are biased, the WBGT estimate will also be biased.
- WBGT varies sharply over short distances because of buildings, trees, paving and shading, so a single reference station cannot describe the heat stress pattern across a whole city.
Consumer all‑in‑one (AiO) weather stations haven't solved this problem. Their small, passive radiation shields often allow sensors to overheat in strong sun and light winds, creating daytime temperature errors of 1–4 °C or more. Even the World Meteorological Organization notes that poorly shielded sensors can over‑read by more than 4 °C under strong irradiance. Those errors matter most precisely when people are at highest risk.
Trofic starts from a simple question: can we design a low‑cost instrument that keeps shaded air temperature accurate under strong sun, and at the same time measures black‑globe temperature directly, in the very locations where people are exposed?
How Trofic works: a solar chimney for temperature sensors
At the heart of Trofic is a black‑painted copper tube that acts as a solar chimney. When the sun heats the outside of the tube, that heat transfers to the air inside, which becomes warmer and rises. This buoyancy‑driven flow pulls cooler ambient air past the shaded temperature and humidity sensors mounted below the chimney, ventilating them without any fan or mains electricity.
The instrument integrates three key elements:
- A shaded dry‑bulb thermometer in a passively ventilated housing.
- A co‑located capacitive humidity sensor.
- A 15 cm diameter black‑globe thermometer to capture radiant heat load.
Together, these measurements allow more accurate calculation of WBGT and related indices than standard AiO stations that lack a black‑globe and suffer from solar heating bias.
Numerical simulations of the chimney show daytime upward airflow speeds of around 0.3–0.8 m s⁻¹, depending on wind conditions. Under strong sun, the copper tube surface warms by roughly 5–15 °C above ambient air, driving robust natural convection through the chimney. At night, the radiative balance reverses: the tube can cool below the surrounding air, which can slightly reduce nighttime temperatures in calm, clear conditions. For heat‑stress applications, which focus on daytime extremes, this nocturnal limitation is of minor practical importance.
What the tests show: accuracy without fans
Trofic has been evaluated through a combination of theoretical modelling, laboratory experiments and a short field deployment.
In the laboratory, a prototype Trofic unit and two consumer AiO stations were exposed to a calibrated solar simulator delivering around 1000 W m⁻² of shortwave radiation, with ambient air at 21.3 °C. Under these high‑radiation conditions:
| Instrument | Over-read vs ambient | Reduction vs AiO |
|---|---|---|
| Trofic | +0.8 °C | Reference |
| AiO Station 1 | +1.9 °C | 58% error reduction |
| AiO Station 2 | +3.9 °C | 79% error reduction |
In other words, Trofic reduced solar‑induced temperature errors by roughly 58–79% compared with conventional passive shields. That's similar to the improvement you would expect from an actively ventilated screen, but achieved passively, with no fans or power supply.
A short‑term field trial then compared Trofic with a nearby reference‑grade automatic weather station operated by the national meteorological service. Trofic's dry‑bulb temperatures closely tracked the reference station, with similar diurnal cycles and almost identical mean values. The measured black‑globe temperature showed realistic responses to solar radiation and consistently higher daily peaks than the modelled values derived from the reference station, suggesting that the model underestimates peak radiant heat during strong sun.
Designed for low cost, low maintenance and local manufacture
Beyond the physics, Trofic is designed to be something cities, researchers and communities can actually deploy at scale. Several design choices support that goal:
- LoRaWAN connectivity and low power — Trofic is intended to be paired with off‑the‑shelf LoRaWAN edge devices, which can run for multiple years on a single battery pack. This avoids mains power, SIM cards and data plans.
- No moving parts — the passive ventilation means no fans to fail or clog. Routine servicing is reduced to occasional inspection and battery replacement over multi‑year periods.
- 3D‑printed housing — the enclosure is designed for additive manufacturing using common materials such as PETG, with around 400 g of plastic and simple copper components. This allows the instrument to be printed locally from open design files.
- Recyclable and repairable — at end‑of‑life, the copper chimney and PETG housing can be separated using basic hand tools, allowing both materials to be recycled without contamination.
A techno‑economic assessment suggests that Trofic units can be produced and operated at less than one‑fifth of the total lifecycle cost of typical WBGT or AiO weather stations that rely on cellular connectivity. With that cost structure, it becomes realistic to deploy an order of magnitude more measurement points in many urban or low‑ and middle‑income settings.
Where Trofic fits: from cities to low-resource settings
Trofic is not meant to replace every instrument in a national network. Instead, it fills a specific niche: dense, low‑maintenance heat‑stress monitoring in places where people are most exposed and infrastructure is limited. Examples include:
- Urban neighbourhoods with vulnerable populations, where micro‑scale differences in shading and surface materials drive large WBGT differences.
- Schoolyards, sports facilities and playgrounds, where children are active during the hottest parts of the day.
- Outdoor work environments such as construction sites, ports or informal markets, where continuous power and IT support are often lacking.
- Low‑ and middle‑income regions where import costs, servicing and spare parts make conventional WBGT stations impractical.
A step towards equitable heat intelligence
As heatwaves grow in frequency and intensity, it will no longer be enough to know that "the city" is hot. Decision makers will need to know which streets, schools and job sites are unsafe, and when interventions — closing a playground, shifting work hours, opening a cooling centre — are necessary.
Trofic is one example of how instrument design can evolve to meet that challenge: using basic physics to deliver more accurate measurements when and where they matter, while keeping costs and maintenance low enough for widespread deployment. By improving two of the three WBGT components and enabling dense, off‑grid networks, Trofic aims to make high‑quality heat‑stress data accessible not just to a handful of research sites, but to communities and cities everywhere.
If you are interested in piloting Trofic in your city, organisation or research project, get in touch to explore deployment options and data integration with existing networks.
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