Black Globe Temperature Meter: Measuring Radiant Heat
In most indoor and outdoor comfort assessments, temperature is the first parameter engineers look at. However, temperature alone doesn’t always explain why a space feels hot or uncomfortable. Often, the missing piece is radiant heat—the heat we feel directly from surrounding surfaces or sunlight. To measure this accurately, professionals use a specialized instrument called the Black Globe Temperature Meter.
What is a Black Globe Temperature Meter?
A Black Globe Temperature Meter is a device used to measure the combined effects of radiant heat, air temperature, and air movement on the human body. It consists of a temperature sensor (typically a thermocouple or thermistor) placed inside a matte black, hollow copper sphere—usually 150 mm in diameter. The black coating absorbs radiant energy from all directions, allowing the sensor to reach an equilibrium temperature that reflects both the air and the surrounding thermal radiation.
This “globe temperature” is one of the three parameters used in calculating the Wet Bulb Globe Temperature (WBGT) index—a standard measure of heat stress and thermal comfort used in workplaces, outdoor events, and building environments.
Radiant Heat and Why It Matters
Radiant heat is the transfer of thermal energy through electromagnetic waves, primarily in the infrared spectrum. Unlike convection or conduction, radiant heat doesn’t require air movement or direct contact. It travels straight from warm surfaces to cooler ones—like the heat you feel when standing near a window on a sunny day, even if the air is cool.
In buildings, radiant heat can come from:
Sunlight transmitted through glass windows and skylights
Heated walls, roofs, and floors exposed to the sun
High-temperature lighting or electrical equipment
Nearby hot surfaces (e.g., machinery, ovens, or poorly insulated ducts)
Because radiant heat acts independently of air temperature, a space may appear thermally “normal” when measured with a standard thermometer or thermohygrometer, yet occupants still feel discomfort due to radiation asymmetry.
Understanding Radiant Heat — The Cave Analogy
Radiant heat works both ways — it can make you feel warmer or cooler depending on the temperature of the surrounding surfaces. A classic example is the feeling of coolness inside a cave. Even if the air temperature inside the cave is not very low, you still feel cool because the cave walls are much colder than your body. Your body radiates heat toward these cooler surfaces, losing thermal energy through radiant heat transfer.
This phenomenon is called radiant cooling — your body cools not because the air is cold, but because it is losing heat to the cooler surroundings. The same principle applies in buildings: if interior surfaces like walls, ceilings, or windows are warm, occupants feel hotter even if the air is conditioned; but if those surfaces are cool, the space feels more comfortable. The black globe temperature meter helps quantify this radiant effect, providing a complete picture of thermal comfort beyond just air temperature.
How Radiant Heat Measurement Differs from Regular Heat Measurements
Most standard temperature measurements—like those from thermometers, thermostats, or HVAC sensors—only detect air temperature. These instruments measure the convective heat transfer between air and the sensor, completely overlooking the influence of radiant energy from surrounding surfaces.
The Black Globe Thermometer, however, captures the combined effect of:
Air Temperature (Convective Heat Transfer)
Radiant Temperature (Infrared Radiation from Surroundings)
Air Velocity (Rate of Heat Loss from the Globe)
This makes globe temperature a far more realistic representation of what occupants actually experience.
For example:
If a room has cool air but sunlight streaming through a window, the air temperature might read 24°C, while the black globe temperature could read 30°C—revealing the radiant load.
Conversely, in an evenly shaded area, both readings might match closely, confirming uniform comfort conditions.
Applications in Building Performance and HVAC
At Stout Energy, we often use black globe temperature measurements during thermal comfort studies, energy health checks, and post-installation audits. These readings help us identify hidden radiant loads that air sensors alone cannot detect.
Typical use cases include:
Assessing solar heat gain through glazing or skylights
Evaluating thermal comfort in offices, galleries, or lobbies
Diagnosing uneven heat distribution in large spaces with exposed roofs or ducts
Validating insulation performance and envelope heat gain in sustainable building designs
By combining globe temperature with air temperature, relative humidity, and air velocity data, our engineers can compute the Mean Radiant Temperature (MRT)—a critical input for ASHRAE Standard 55 thermal comfort analysis.
Why It Matters for Sustainable Building Design
In sustainable HVAC design, understanding radiant effects is essential for minimizing energy waste and improving occupant comfort. By accurately measuring radiant heat, designers can:
Optimize glazing and shading strategies
Improve duct and roof insulation
Refine air distribution for better occupant comfort
Prevent overcooling, reducing unnecessary chiller load and energy consumption
In short, the Black Globe Temperature Meter helps bridge the gap between measured comfort and felt comfort, enabling smarter, more energy-efficient building design.
Conclusion
While regular temperature sensors only tell part of the story, the black globe temperature meter reveals how radiation affects real-world comfort. At Stout Energy, we integrate this level of precision into our HVAC performance assessments and sustainability audits—ensuring that every degree of cooling truly contributes to comfort, not just numbers on a thermostat.