ASHRAE-Standard-55 - Page 045
Extracted Content
information regarding the comfort requirements of children, the disabled, or the infirm. It is acceptable to apply the information in this standard to these types of occupants if it is applied judiciously to groups of occupants, such as those found in classroom situations.
E7. NATURALLY CONDITIONED SPACES
Section 5.3 contains the methodology that should be used for most applications. The conditions required for thermal comfort in spaces that are naturally conditioned are not necessarily the same as those conditions required for other indoor spaces. Field experiments have shown that in naturally conditioned spaces where occupants have control of operable windows, the subjective notion of comfort is different because of different thermal experiences, availability of control, and resulting shifts in occupant expectations. Section 5.4 specifies criteria required for a space to be considered naturally conditioned. The methods of Section 5.4 may, as an option, be applied to spaces that meet these criteria. The methods of Section 5.4 may not be applied to other spaces.
E8. SPACE DESIGN FOR OCCUPANTS IN THERMAL TRANSITION
E8.1 Problem. People arriving in buildings have different activity levels, body temperatures, and skin wetness from those who have been indoors longer, and they may experience discomfort during the transition. These transitions occur in outdoor-to-indoor transitional spaces, such as lobbies, retail stores, and transit centers, but they also continue in interior destination spaces such as offices, conference rooms, classrooms, and restaurants. It is challenging to condition such spaces to suit the comfort requirements of all the occupants, some of whom may not be experiencing the transition. There are energy and economic consequences to the methods employed.
On the positive side, there are possible comfort benefits to the occupant from experiencing a transition from a cold or hot environment toward a neutral one. A favorable body or skin temperature gradient is perceived as pleasant at a significantly higher intensity than is experienced in steady-state comfort; this is termed alliesthesia . It affects both temperature gradients occurring over time and among different parts of the body. These temperature gradients may involve thermal stimuli from the environment that are above what is allowed in the standard for steady-state conditions.
Winter situation: In cold seasons, the body heat deficits from outdoor exposure (exposed body surfaces and extremities might be cold upon entering the building) can take a long time to warm up. They can be targeted and corrected by hot air curtains, focused or local radiant heaters, and by direct thermal contact with warmed surfaces in active seats and desk furniture. There is at this point insufficient information about transient comfort in warming transitions to suggest specific design solutions for winter.
Summer situation: In hot conditions, people
a. Enter buildings with elevated body temperature acquired in the outdoor environment and from the meta bolic exertion of walking b. Change from walking to sitting activity, during which their metabolic rate decreases
When people enter buildings, the elevated body heat from outdoor exposure and walking has to be removed from the skin before it can cause discomfort indoors. Unfortunately, the outdoor wind levels and the self-generated wind from walking disappear when one enters a building and becomes stationary. This causes a spike in a person’s skin temperature and sweat rate as the body compensates for the lost convective cooling. The resulting discomfort can persist for over an hour. During this period the occupant may feel the need to complain or to reset the room thermostat to a cooler set point. The resulting cooler space temperature then persists well beyond the occupant’s period of thermal transition, and may overcool multiple occupants while increasing the building’s cooling energy.
In addition, there are spaces in which some occupants are continuously at higher metabolic rates than others and require different levels of cooling. An example might be diners and waiters at restaurants, or clerks and shoppers in stores. Their variation in cooling requirements takes place across short distances or (from the perspective of a moving occupant) short time steps.
The environmental control options for removing body heat differ greatly in their effectiveness. Current research shows that elevating indoor air movement is far more effective than reducing indoor temperature, both for maintaining comfort throughout transitions from outdoors to indoors, and during the metabolic downstep when a person sits down. When the indoor operative temperature alone is used to remove body heat, both subjective comfort votes and physiological responses respond much more slowly.
This finding about occupant cooling has important practical implications for the design and operation of buildings, one related to comfort and one to energy efficiency:
ANSI/ASHRAE Standard 55-2023 43