Human Response to Air Movement-Evaluation of ASHRAE's Draft Criteria (RP-843)

Jørn Toftum
Arsen Melikov
Agnieszka Tynel
Marcin Bruzda
P. Ole Fanger

The aim of this study was to evaluate the present ASHRAE Standard 55-1992 draft criteria and to describe how air movement is perceived at thermal sensations slightly cooler and slightly warmer than neutral. At temperatures 18°C, 20°C, 23°C, 26°C, and 28°C (64.4°F, 68°F, 73.4°F, 78.8°F, and 82.4°F), 40 subjects at slightly cool, neutral, and slightly warm overall thermal sensation were exposed to air velocities that were increased step-by-step from less than 0.1 m/s to 0.8 m/s (19.7 fpm to 157.5 fpm). Subjects who felt cool or slightly cool perceived air movement as being uncomfortable at lower air velocities than did subjects feeling neutral or warmer. No difference in draft sensitivity between subjects feeling neutral, slightly warm, or warm was observed. A smaller percentage of subjects were dissatisfied due to draft than prescribed by ASHRAE Standard 55 guidelines on air movement. The discrepancy could be explained by the effect of thermal sensation and activity level on draft sensitivity. Permissible mean air velocities as recommended by the standard thus provide a conservative upper limit for air velocity that protects occupants who are sensitive to air movement, occupants who feel cooler than neutral, or occupants who are occupied mostly with sedentary work. To accommodate all occupants in a given indoor environment, therefore, it is recommended that air movement generated by the HVAC system be designed according to the criteria in the current Standard 55 to minimize complaints of draft. To provide comfort for occupants who prefer more air movement, local air movement under individual control is easy to generate, e.g., by a desk fan.

Thermal Comfort Models and “Call Out” (Complaint) Frequencies (RP-1129)

C. Federspiel

Previous research describes a model that can be used to assign economic cost to thermal discomfort. This is a subject of unquestionable importance to ASHRAE. More research is needed to establish the accuracy of this model so that it may gain acceptance as an economic analysis tool.

The results of this research will impact ASHRAE Standard 55 as follows. The model can be used to optimize building temperature to either minimizing total cost (energy plus service call cost) or to minimizing complaint frequency. These two temperatures could be used as a new basis for the upper and lower limits of the comfort zone. Unlike the existing upper and lower limits, these limits would have an economic basis.

The objective of this research project is to evaluate the accuracy of the complaint model recently proposed.

Experimental Determination of the Limiting Criteria for Human Exposure to Low Winter Humidity Indoors (RP-1160)

David P. Wyon, PhD, Member ASHRAE
Lei Fang, PhD
Love Lagercrantz
P. Ole Fanger, DSc, Fellow/Life Member ASHRAE

The 2005 ASHRAE Handbook—Fundamentals (ASHRAE 2005) states that Liviana et al. (1988) found that eye discomfort increases with time if the dew-point temperature is less than 2°C (35.6°F). This was the basis for the minimum RH that appeared in the thermal comfort zones that were until recently recommended in ASHRAE Standard 55 (ASHRAE 1992, 1995). They prescribed a lower humidity ratio limit of 4.5 g/kg (31.5 gr/lb), corresponding to 30% RH at 20.5°C (68.9°F). This lower limit is no longer recommended in the latest version of the same standard (ASHRAE 2004). According to section 5.2.2, “Humidity Limits” (ASHRAE 2004), “There are no established lower humidity limits for thermal comfort; consequently, this standard does not specify a minimum humidity level. However, non-thermal comfort factors such as skin drying, irritation of mucus membranes, may place limits on the acceptability of very low humidity environments.” ANSI/ASHRAE Standard 62-1989 (ASHRAE 1989) recommended an optimum indoor humidity range of 30% to 60% RH, while later revisions (Standards 62.1 and 62.2) no longer recommend a lower humidity limit. The low relative humidity limits originally prescribed in both of these ASHRAE standards may have been intended to minimize dry skin, eye irritation, respiratory infections, allergy and asthma, viability and virulence of bacteria and viruses, ozone production, etc.

Operable Windows, Personal Control, and Occupant Comfort (RP-1161)

Gail S. Brager
Gwelen Paliaga
Richard de Dear

Past research (ASHRAE RP-884) demonstrated that occupants of naturally ventilated buildings are comfortable in a wider range of temperatures than occupants of buildings with centrally controlled HVAC systems. However, the exact influence of personal control in explaining these differences could only be hypothesized because of the limits of the existing field study data that formed the basis of that research. The objective of ASHRAE RP-1161 was to quantitatively investigate how personal control of operable windows in office settings influences local thermal conditions and occupant comfort. We conducted a field study in a naturally ventilated building where occupants had varying degrees of control over the windows. Utilizing continuous measurement of each subject’s workstation microclimate, plus a Web-based survey that subjects took several times a day and was cross-linked to concurrent physical assessments of workstation microclimatic conditions, we collected over 1000 survey responses in each of the two main seasons. The data show that occupants with different degrees of personal control had significantly diverse thermal responses, even when they experienced the same thermal environments and clothing and activity levels. Our findings offer further empirical support for the role of shifting expectations in the adaptive model of thermal comfort.