Attributes of the Space Influencing Comfort
As you can see, six attributes of the space influence comfort: thermal, air quality, acoustical, lighting, physical, and psychosocial. Of these, only the thermal conditions and air quality can be directly controlled by the HVAC system. The acoustical (noise) environment may be influenced to some extent. The lighting and architectural aspects are another field, but these can influence how the HVAC is perceived. The psychosocial environment (how people interact sociably, or unsociably!) in the space is largely dependent on the occupants, rather than the design of the space.
We will briefly consider these six aspects of the space and their influence on comfort.
1. Thermal conditions include more than simply the air temperature. If the air speed is very high, the space will be considered drafty. If there is no air movement, occupants may consider the space ‘stuffy’. The air velocity in a mechanically conditioned space is largely controlled by the design of the system.
On the other hand, suppose the occupants are seated by a large un- shaded window. If the air temperature stays constant, they will feel very warm when the sun is shining on them and cooler when clouds hide the sun. This is a situation where the architectural design of the space affects the thermal comfort of the occupant, independently of the temperature of the space.
2. The air quality in a space is affected by pollution from the occupants and other contents of the space. This pollution is, to a greater or lesser extent, reduced by the amount of outside air brought into the space to dilute the pollutants. Typically, densely occupied spaces, like movie theatres, and heavy polluting activities, such as cooking, require a much higher amount of outside air than an office building or a residence.
3. The acoustical environment may be affected by outside traffic noise, other occupants, equipment, and the HVAC system. Design requirements are dictated by the space. A designer may have to be very careful to design a virtually silent system for a recording studio. On the other hand, the design for a noisy foundry may not require any acoustical design consideration.
4. The lighting influences the HVAC design, since all lights give off heat. The lighting also influences the occupants’ perception of comfort. If the lights are much too bright, the occupants may feel uncomfortable.
5. The physical aspects of the space that have an influence on the occupants include both the architectural design aspects of the space, and the interior design. Issues like chair comfort, the height of computer keyboards, or reflections off computer screens have no relation to the HVAC design, however they may affect how occupants perceive the overall comfort of the space.
6. The psychosocial situation, the interaction between people in the space, is not a design issue but can create strong feelings about the comfort of the space.
Characteristics of the Individual that Influence Comfort
Now let us consider the characteristics of the occupants of the space. All people bring with them health, vulnerabilities and expectations.
Their health may be excellent and they may not even notice the draft from the air conditioning. On the other hand if the occupants are patients in a doctor’s waiting room, they could perceive a cold draft as very uncomfortable and distressing.
The occupants can also vary in vulnerability. For example, cool floors will likely not affect an active adult who is wearing shoes. The same floor may be uncomfortably cold for the baby who is crawling around on it.
Lastly the occupants bring their expectations. When we enter a prestigious hotel, we expect it to be comfortable. When we enter an air-conditioned build- ing in summer, we expect it to be cool. The expectations may be based on pre- vious experience in the space or based on the visual perception of the space. For example, when you enter the changing room in the gym, you expect it to be smelly, and your expectations make you more tolerant of the reality.
Clothing and Activity as a function of Individual Comfort
The third group of factors influencing comfort is the amount of clothing and the activity level of the individual. If we are wearing light clothing, the space needs to be warmer for comfort than if we are heavily clothed. Similarly, when we are involved in strenuous activity, we generate considerable body heat and are comfortable with a lower space temperature.
In the summer, in many business offices, managers wear suits with shirts and jackets while staff members may have bare arms, and light clothing. The same space may be thermally comfortable to one group and uncomfortable to the other.
There is much more to comfort than most people realize. These various aspects of comfort will be covered in more detail in later chapters.
The Next Step
Chapter 2 introduces the concept of an air-conditioning system. We will then consider characteristics of systems and how various parameters influence system choice. Chapter 2 is broad in scope and will introduce you the content and value of the other ASHRAE Self-Study Courses.