Energy efficiency in buildings is almost always a top priority for building owners and contractors alike. However, it is not fully effective when occupants are uncomfortable with the indoor environment. If an occupant is too warm or too cold in a space, he or she will take alternative routes of heating or cooling their area, such as with space heaters, fans, or window-mounted air conditioners. And those could be substantially worse for the building’s efficiency than typical heating, ventilation, and air conditioning (HVAC) systems.
What is thermal comfort?
Thermal comfort can also be referred to as human comfort. In this industry, thermal comfort is often defined as the occupant’s overall satisfaction with his or her indoor thermal environment, which is often assessed by subjective evaluation. In other words, it is the occupant’s satisfaction with his or her temperature surroundings. Because thermal temperature and comfort is so important to occupants, they’re important to consider when designing human-occupied structures.
How is thermal comfort calculated?
Before calculating human comfort, six factors need to be taken into consideration when in the design process. There is a mix of both personal and environmental factors, which include:
● Metabolic rate: The energy generated from the human body
● Clothing insulation: The thermal insulation the person is wearing
● Air temperature: The temperature of the air around the person
● Radiant temperature: The average of all the temperatures from surfaces around the person
● Air velocity: The rate of air movement given distance over time
● Relative humidity: The percentage of water vapor in the air
Personal factors are metabolic rate and clothing, whereas the environmental factors include air temperature, radiant temperature, relative humidity, and air velocity.
A widely utilized method of calculating thermal comfort is referred to is the Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD). The PMV refers to thermal scale that runs from hot (+3) to cold (-3) and was the result of a study conducted to verify comfort sensations based on temperature. The result was an average, universal thermal comfort between -0.5 and +0.5 for an interior space. The PPD is the prediction of the percent of occupants who will be dissatisfied with the thermal conditions. As the PMV number moves further from zero, the PPD increases. The idea is that you can never please 100 percent of building occupants at all times, however, the goal will always be to have a less than 10 percent of the occupants dissatisfied for an interior space.
Gausman & Moore mechanical engineers utilize software to predict and calculate thermal conditions in the buildings we help design. Inlet and outlet vanes sizes and positions are optimized to minimize a structure’s energy costs while utilizing innovative building systems. For more information about our HVAC services in buildings or other mechanical engineering services, visit our Mechanical Engineering page or call us at 651-639-9606.