Measurements
Heat Index/Humidex
Heat Index/Humidex
The Heat Index is determined using the dry bulb temperature and relative humidity. Based upon
charts available from the U.S. National Weather Service, Heat Index represents how an average
person feels relative to climate conditions. For a given temperature, the higher the humidity, the
higher the heat index.
The Heat Index is defined over a temperature range of 70F – 120F (21C – 49C) and a relative
humidity range of 30% - 99%. Outside of this range, the instrument will show dashes in the display
for the Heat Index.
The Humidex, used primarily in Canada, functions similar to the Heat Index concept. The values are
slightly different. The Humidex is defined over a temperature range of 70F – 109F (21C – 43C)
and a relative humidity range of 20% – 99%. Outside of this range, the instrument will show dashes
in the display for the Humidex.
Air Flow
The QUESTemp 36 measures air flow if the Air Probe accessory is used. The Air Probe uses an
omni-directional anemometer sensor that measures air flow between 0 and 20 meters per second in
0.1 m/s increments. See “Air Flow Functionality,” for more details.
Thermal Comfort (QUESTempº 36 model only)
Thermal comfort readings for indoor environments are a benefit of DMS software and are not
displayed or printed from the instrument directly. Readings are derived from the dry bulb, relative
humidity, mean radiant temperature, air flow, and user entered parameters of clothing, metabolic rate
and external work.
Thermal comfort indices, Predicted Mean Vote (PMV) and Predicted Percent Dissatisfied (PPD), help
predict the thermal satisfaction level of a person with their indoor environment. The PMV is a rating
scale of +3 to -3 where +3 is much too warm, -3 is much too cool, and 0 is thermally neutral. The
PPD reflects what percent of people in a given location would be dissatisfied with their thermal
surroundings.
The formulas used by DMS software to derive the PMV and PPD come from the international
standard ISO 7730 “Moderate thermal environments - Determination of the PMV and PPD indices
and specification of the conditions for thermal comfort.”
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General