Thermal comfort is one of the main challenges for building owners, since there are technical and subjective factors interacting. Variables like temperature and humidity can be measured and controlled, but thermal comfort also depends on individual preferences, clothing and metabolism. For these reasons, finding a temperature that makes everyone in a building comfortable is practically impossible.
To maximize thermal comfort in commercial buildings, an effective strategy is dividing indoor spaces into many temperature zones with independent controls. To complement this HVAC design approach, companies can let employees sit where they feel the most comfortable, instead of having a fixed desk.
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Scientific studies differ slightly in their results. However, the ideal temperature for human comfort and productivity is in the approximate range of 20°C to 25°C (68°F to 77°F). As the indoor temperature deviates from this range, there is a negative impact on productivity and comfort.
Companies often underestimate the financial impact of losing productivity; a well-designed energy efficiency project does not save energy at the expense of wellness. For example, a building could simply reduce its ventilation rate to save on HVAC, but the loss of air quality can make employees less productive. If the measure saves $2,000/month, but the productivity loss is $5,000/month, there is a net loss even when energy is saved.
Main Factors that Influence Thermal Comfort
The WELL Building Standard is a certification system similar to LEED, but more focused on human health and wellness. Thermal comfort is one of the main performance categories in the WELL standard. Six main factors that influence thermal comfort have been identified, and also several secondary factors.
Thermal Comfort, 6 Main Factors
Psychological factors have also been linked with thermal comfort. For example, persons who are experiencing negative emotions may feel less comfortable in conditions where they normally feel comfortable.
Of the six main factors that influence thermal comfort, three can be controlled directly by an HVAC system: dry-bulb temperature, relative humidity and air speed. Radiant HVAC systems in particular can also control the temperature of some indoor surfaces, such as walls and floors. Occupants can gain more control over their clothing insulation if companies adopt a flexible dress code.
To account for differences in metabolic rate and secondary comfort factors, the best solution is giving occupants control over their immediate surroundings. This can be combined with the mobility to use different workspaces.
Air humidity has a significant impact on thermal comfort. However, controlling relative humidity is less subjective than controlling air temperature, since there are negative effects at both humidity extremes - dry and humid.
- Low humidity causes particles to stay airborne for longer, and this includes allergens and viruses. Even if harmful particles are controlled, low humidity can irritate the skin, eyes and respiratory system. In addition, low humidity causes static electricity to accumulate, and discharges can damage electronic equipment.
- High humidity stimulates the reproduction of harmful organisms like bacteria, mold and dust mites - all of them cause health problems.
- Both humidity extremes tend to worsen the discomfort caused by high and low temperatures.
ASHRAE recommends keeping relative humidity within a range of 30% and 60%, and ideally between 40% and 50%. This prevents the negative effects of high and low humidity, while improving thermal comfort
Using Technology to Improve Thermal Comfort
When a large indoor area uses a single temperature zone and a single thermostat, there is less control over thermal conditions. For example, occupants close to HVAC diffusers may feel the air speed is too high, while occupants close to windows may be affected more by the outdoor temperature.
To achieve better control over indoor temperatures, built environments can be divided into a larger number of thermal zones. The WELL building standard recommends one thermal zone per 320 ft2 or per 5 occupants, whichever results in less zones. In addition, temperature sensors should be placed at least 3.3 feet away from sources of cold or heat, to ensure a correct reading.
Building occupants can be provided with a mobile application that accomplishes the two following functions:
- Controlling temperature and air speed in their immediate surroundings.
- A temperature map of all workspaces, so they can choose where they want to sit.
The application can keep a temperature record of the locations chosen by each occupant. This information can then be used to suggest spots where they will feel comfortable, based on the temperature distribution measured.