The indoor environment and microclimate of a building is one of the most important factors that will come to define the success of the building being used for its designed purpose. A modern multi-story office building is of no use for its intents and purposes if it cannot sustain a relative degree of comfort for its human occupants.
Humans, by nature, are incredibly sensitive to their environment and because of this, the indoor climate of a building is a directly determining factor of workplace productivity and health. However, achieving a level of thermal comfort that functions as a sustainable means of keeping human occupants satisfied with their environment and able to work and function optimally is highly complex. Here’s a closer look at thermal comfort and how to design for it.
What is Thermal Comfort?
Firstly, a definition of thermal comfort as being, “that condition of mind which expresses satisfaction with the thermal environment and is assessed by subjective evaluation,” means that there is no blanketed measure of relative temperature ranges to measure people’s comfort levels with their thermal environment. It’s a subjective experience that depends on a number of variables in itself.
Indoor climate regulators like traditional heating, ventilation and air conditioning (HVAC) systems and radiant cooling solutions are not designed for varying individual response to environmental conditions. That’s why it’s generally accepted that thermal comfort is the measure of a relationship between surveyed satisfaction vs. dissatisfaction with individuals’ environment e.g. an 80% overall satisfaction with the thermal environment would be a positive indicator of satisfactory thermal conditions being maintained in the building.
For the individual, thermal comfort variables include their own metabolic rate as well as the level of insulation that they apply to their body with clothing. These factors then influence individuals’ sensitivity to their immediate indoor environmental conditions, which are a result of the combination of air temperature, radiant temperature and relative humidity.
The challenge for architects and designers then becomes to keep a focus on sustainable design elements for their green building – at the same time ensuring that important thermal comfort factors have been considered in the implementation of indoor climate regulation solutions.
Designing for Thermal Comfort
The focus for designers when designing with thermal comfort in mind should be on HVAC or radiant cooling system design that can achieve the dual purpose of sustainable energy efficiency and a balanced thermal environment. According to an excerpt from the Requirements for Building Thermal Conditions, “the object of energy conservation is to use the minimal amount of energy necessary to perform the required work in a safe and efficient manner,” and not, to paraphrase, to freeze in the dark.
The table below from USACE Engineer Research and Development Center, shows the requirements for dry bulb temperature and relative humidity for occupied and unoccupied facilities to reduce the risk of moisture-related problems:
Thankfully, designers and architects don’t need to be left in the dark when it comes to calculating the energy efficiency of a proposed indoor temperature regulating system. From a workplace design perspective, it may be helpful to understand models such as the adaptive model and behaviour model of thermal comfort design. From a structural perspective, analysis of existing thermal scales when applied to buildings of a similar size and in similar climatic zones can also be very helpful in designing for thermal comfort. The research is out there and will benefit the planning and implementation of a thermal comfort solution that fits into a green design goal.
When employing green design measures for buildings specific to South East Asia, the humidity of the region is perhaps the most important factor when choosing between a more traditional HVAC system or radiant cooling solution for indoor climate control. It is worth noting that, in this case, radiant cooling solutions do not have the capacity for dehumidification. While a radiant cooling system will still prove an energy efficient means of temperature regulation, it will have to be employed in conjunction with a dedicated outdoor air system (DOAS), for dehumidification and ventilation if thermal comfort is to be achieved.
With the complexities of achieving both thermal comfort and energy efficiency in sustainable building design, it may just be a hybrid solution that is best able to meet both of those important demands.