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1950-51 Theatre Catalog, 9th Edition, Page 369 (347)

1950-51 Theatre Catalog, 9th Edition
1950-51 Theatre Catalog
1950-51 Theatre Catalog, 9th Edition, Page 369
Page 369

1950-51 Theatre Catalog, 9th Edition, Page 369

In the cooling or washing chamber, a certain amount of water is evaporated, due to the intimate contact between air and water droplets. The heat necessary to accomplish this operation must come from the air itself, and, as a result, the dry-bulb or measurable temperature, as seen on the conventional thermometer, is reduced. Fig. 1 illustrates that on the ordinary system it is reduced from a temperature of 900 to a temperature of 750. The wet-bulb temperature of 700 in this particular case remains the same, however, indicating that no actual addition or subtraction of heat has taken placeemerely a transfer of the form of heat. In other words, the sensible or ordinary thermometer-measuring temperature has been reduced, while the latent heat (that amount represented by water in the air) has been increased. The total heat, however, has remained the same.

The amount of such dry-bulb temperature reduction varies considerably with entering air conditions. While Fig. 1 shows a temperature of 900 dry-bulb and 700 wet-bulb with a resulting or leaving temperature of 750 dry-bulb and 7'0o wet-bulb, this is but one case among thousands. The ordinary evaporative cooling system will reduce the dry-bulb temperature approximately 75% of the difference between the entering dry-bulb and wetebulb. Thus, if the entering temperature had been 800 dry-bulb and '700


wet-bulb, the temperature would only have been reduced 71/2L7 for a leaving condition of 721/20 dry-bulb and 700 wet-bulb.

Some further reduction in what is known as effective temperature is also accomplished in the system, due to air motion inducing a cooling effect upon the people in the audience. This effective temperature is not measurable upon the ordinary thermometer. It is, however, the temperature which the body actually feels when all factors of temperature, moisture content, and air motion are applied. Several additional degrees of such effective temperature cooling are usually obtainable through air motion in the evaporative cooling system.


The equipment required for an evaporative cooling system in any theatre is usually quite simple and the parts readily identifiable. Fig. 2, for example, shows the heart of a typical system with a blower, pent house, hydraulic drive, motor, evaporative pad type washer, etc. Among these parts, the blower and washer are perhaps most deserving of further attention.


The ventilating fan or blower moves the air around and draws it into the

cooling chamber. Thousands of blowers, such as the one illustrated in Fig. 3, are employed in theatre ventilation and cooling.

It is a serious mistake, in determining the size of a blower or blowers on a certain installation, to decide on a unit that is too small or to operate it at too high a speed. For instance, a 36" blower equipped with a five horsepower motor may deliver enough air, but a 42" blower driven with the same motor will deliver more air and do so more quietly. The additional cost of the larger blower Will actually be absorbed in savings of power operating costs over a period of years.

The following table shows what many engineers consider the minimum cubic feet of air per minute per seat required to cool a theatre properly during the high excessive temperature months for each area (see Fig. 10). All blowers should be equipped with hydraulic drives or multi-speed motors, so the blower speed can be adjusted to fit temperature conditions:

Areas with 650 to 700 designed

Wet-BulF65 c.f.m. per seat

Areas with 700 to 737 designed

Wet-BulF7O c.f.m. per seat Areas with 730 to 740 designed

Wet-Bulb-75 c.f.m. per seat Areas with 750 to 760 designed

Web-Bulb-80 c.f.m. per seat

FIGURE Ze'l'ypicul evaporative cooling unit (Photograph courtesy of National Engineering &: Manufacturing Co.).
1950-51 Theatre Catalog, 9th Edition, Page 369