U.S. Weather Bureau
D.I = 0.4(wet-bulb temperature + dry-bulb temperature) - 15.
public response hearings
It was superceded in the 1970's by the more sophisticated heat index.
E. C. Thom.
The discomfort index.
Weatherwise, vol 12, pages 57-60 (1959)
During the spring of 1959 the U.S. Weather Bureau announced that it would make public values of the Discomfort Index for certain cities. This useful Index is the subject of this and two subsequent Reference Data sheets.
During the nineteen-twenties the American Society of Heating and Ventilating Engineers developed its Effective Temperature scale. By extensive laboratory tests "effective temperature values" were established for each group of separate simultaneous dry bulb temperature and relative humidity (or wet bulb temperature) readings which gave equivalent feelings of comfort.
Although Effective Temperature has been widely used by heating and air conditioning engineers, it was not widely known by non-engineers. More recently, J. F. Bosen of the Office of Climatology of the Weather Bureau reduced Effective Temperature to a formula:
DI = 0.4 (td + tw) + 15
where DI = the Discomfort Index,
td = dry bulb temperature,
tw, = wet bulb temperature.
The value and the usefulness of the Discomfort Index is due to its direct relationship with the degree of discomfort experienced. It is known that a few people in summer will be uncomfortable from heat and humidity by the time the Discomfort Index reaches 70; half or more of the people will be uncomfortable by the time the Discomfort Index reaches 75; everyone will be looking for relief by the time the Discomfort Index reaches 79, and discomfort will become more acute as the Index climbs still higher. Infrequently, Discomfort Index values reach 90, and 92 is the highest noted so far in the sampling of United States data.
The efficiency of workers decreases noticeably with higher Discomfort Index values. This is recognized in the Washington, D.C., area, for example, where government workers in non-airconditioned buildings may be dismissed when conditions are such that the Discomfort Index exceeds 85.
The Discomfort Index.
Air Conditioning, Heating and Ventiliating, vol. 56, page 99 (June, 1959).
The optimum line for summer on the ASHAE comfort chart coincides with 71 F effective temperature and along this line corresponding values of the Discomfort Index range from 70 to 71.8 F. There is consequently no disagreement with the general premise that, as D.I. values rise appreciably above 70 F, discomfort can be anticipated. However, Discomfort Index appears to be little more than a simple formulation relating the comfort of the individual to an outdoor environment.
Discomfort Index may thus have utility in expressing weather information, but as far as air conditioning is concerned, it contributes nothing new to information which has been at our disposal for many years. The quite unfortunate thing is that the Discomfort Index can be extremely misleading to uninformed individuals who, from an analysis of dry-bulb and wet-bulb temperatures, might gain the impression that no discomfort problems arise if outside temperatures are such that the D.I. values remain below 70 F. Unfortunately, with humans living in buildings, nothing could be further from the truth, as the only people in a building whose comfort would even be approximated by this formula would be those who spend their time on building patios, in penthouses, or in the peripheral rooms of a building with no human, lighting or solar loads and with all windows open. These conditions are rarely reached.
Burgess I. Jennings
ASHRAE Journal, vol 1, page 66 (April 1959).
'DISCOMFORT INDEX' draws protests from tourist industry. Many substitute names suggested. Weather Bureau bows.
According to many in the tourist trade, the Discomfort Index in their localities never exceeds 75. For at that point more than half the people feel uncomfortable, a fact no more permissable to state than that a certain woman is "old."
The secret of eternal spring is to mask the weather with a pleasant euphemism, such as "Comfort Index", a suggested substitute for "Discomfort Index". The Weather Bureau in Washington, D.C., bowing to complaints, has adopted the noncommital "Temperature-Humidity Index", but has left the decision on name change up to the individual weather stations. Next summer the Bureau will adopt one name to be used nationally, if it is decided to continue the index at all.
In add1tion to the pressure from business groups in several resort areas, the Weather Bureau admitted, several critical newspaper editorials were reponsible for its switch of name. Public interest in the Discomfort Index will be evaluated by the Bureau in the fall. Twenty-four weather stations now compute the daily index. If the program is continued next year, it is expected that all stations will do likewise.
Other suggested names received by the Bureau include Heat Moisture Index, Cooling Degree Index, Humitemp, Thermidity, Air Conditioning Value, Effective Heat Index, Human Reaction Scale, and Toler-Rate.
Some sectors of the air conditioning industry see the Discomfort Index as an aid to sales. Allied Appliance Company, a Boston distr1butor of Fedders air cond1tioning units, for instance, has issueda blanket order to city newspapers and TV stations to run its Discomfort Index ad whenever the DI goes above 75. The Du Pont Company's Freon Products Division has published a chart of maximum DI values for selected stations during July, 1956.
Air Conditioning, Heating and Ventilating. Page 10 (July 1959).
In the field of heating, ventilating and air conditioning, a figure of merit for indoor environment.
In economics and financial studies, another name for the misery index.
In South Africa, an index calculated by the South African Weather Service using the equation:
Discomfort Index = (2 x T) + ( Rh/100 x T) + 24,
where T is the dry-bulb or air temperature in degrees Celsius and RH is the percentage relative humidity.
This index gives the following degrees of discomfort: 90-100 - very uncomfortable 100-110 - extremely uncomfortable 110+ - hazardous to health
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