Thermal comfort is one of the main challenges for building owners, as there are technical and subjective factors that interact. 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 comfortable in a building is practically impossible.
To maximize thermal comfort in commercial buildings, an effective strategy is to divide interior spaces into several temperature zones with independent controls. To complement this HVAC design approach, companies can allow employees to sit wherever they feel most comfortable, rather than having a stationary 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 indoor temperatures deviate from this range, there is a negative impact on productivity and comfort.
Companies often underestimate the financial impact of lost productivity; A well-designed energy efficiency project does not save energy at the expense of well-being. For example, a building could simply reduce its ventilation rate to save on HVAC, but the loss of air quality could make employees less productive. If the measure saves $2,000/month but the productivity loss is $5,000/month, there will be a net loss even when there are energy savings.
Main Factors that Influence Thermal Comfort
The WELL Building Standard is a certification system similar to LEED, but more focused on human health and well-being. Thermal comfort is one of the main performance categories of the WELL standard. Six main factors that influence thermal comfort were identified, as well as several secondary factors.
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Thermal comfort, 6 main factors |
Secondary Factors |
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Psychological factors have also been associated with thermal comfort. For example, people who experience 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 directly controlled by an HVAC system: dry bulb temperature, relative humidity and air velocity. Radiant HVAC systems, in particular, can also control the temperature of some interior surfaces, such as walls and floors. Occupants can gain more control over the insulation of their clothing if companies adopt a flexible dress code.
To account for differences in metabolic rate and secondary comfort factors, the best solution is to give occupants control over their immediate environment. This can be combined with 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, as there are negative effects at both extremes of humidity – dry and humid.
- Low humidity causes particles to stay in the air longer, and this includes allergens and viruses. Even if harmful particles are controlled, low humidity can irritate the skin, eyes and respiratory system. Additionally, low humidity causes static electricity to build up and discharges can damage electronic equipment.
- High humidity encourages the reproduction of harmful organisms like bacteria, mold and dust mites – all of which cause health problems.
- Both extremes of humidity tend to aggravate the discomfort caused by high and low temperatures.
ASHRAE recommends maintaining relative humidity between 30% and 60%, and ideally between 40% and 50%. This avoids 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 near HVAC vents may feel that the air velocity is too high, while occupants near windows may be more affected by the outside temperature.
To achieve better control of internal temperatures, built environments can be divided into a greater number of thermal zones. The WELL building standard recommends one thermal zone per 320 ft2 or per 5 occupants, whichever results in fewer zones. Furthermore, temperature sensors must be placed at least 1 meter away from sources of cold or heat to ensure a correct reading.
Building occupants can receive a mobile application that performs the following two functions:
- Control the temperature and speed of the air in your immediate surroundings.
- A temperature map of all workspaces, so you can choose where you 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 places where they will feel comfortable, based on the measured temperature distribution.
