Devonshire and Sayer (2003) performed an experiment designed to address some of these
issues. Four otherwise identical sedans had infrared-reflective (IRR) film applied to differing
sections of the cars’ glazing. Two independent variables were manipulated: A/C output (two
different settings) and IRR film placement (windshield and front side windows, windshield only,
front side windows only, and no IRR film applied). Dependent variables included subjective
assessments of thermal comfort as well as objective measures of skin temperature and cabin air
temperature. Consistent with past research, presence of the film significantly decreased interior
air temperatures during both a static soak and dynamic cool-down of the cars. As expected, the
magnitude of this effect was larger in those conditions in which larger surface areas of film were
applied. Presence of the film was also associated with a significant increase in subjective
assessments of thermal comfort during a vehicle cool-down, an increase that appeared to be at
least partly independent of the air temperature inside the vehicle. That is, for any given air
temperature, subjective ratings of thermal comfort were better in those conditions in which the
IRR film was applied.
This last finding is consistent with well established models of thermal comfort that
include factors other than air temperature, and points in particular to the possible role of radiant
heat in influencing ratings of comfort in an automobile. However, the study included no direct
measure of radiant energy, making it difficult to quantify a relationship between air temperature
and radiant heat. Further, the study examined subjective ratings of comfort in transient cooldown
conditions (in which subjects entered a hot car and immediately turned on the A/C), but
not in steady-state conditions (i.e., conditions resembling driving on the road, in which the
climate remains relatively unchanged).
The present study, designed as a follow-up to Devonshire & Sayer (2003), investigated
the relationships among air temperature, radiant heat, and subjective ratings of comfort in both
transient and steady-state conditions when an IRR treatment is used. The study had two phases:
Phase 1: Establish a relationship between radiant heat and subjective comfort ratings.
Hypothesis: When air temperature is held constant, subjects will find an IRR-treated
condition more comfortable than an untreated condition.
Phase 2: Quantify the relationship.
Hypothesis: Subjects will require a lower air temperature in the untreated condition vs. the
treated condition to maintain the same level of comfort.