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Re: Are Roof Top Units considered Dead or Live Loads?

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Paul Ransom wrote:
From: "Dennis S. Wish, PE" <dennis.wish(--nospam--at)>
I've never considered a roof top A/C or Swamp Cooler to be a dead load.
What's a swamp cooler?

An evaporative cooler used here in the desert during the summer. I discovered that during the depression era people lived in submarine homes - wood shacks covered with canvas with a dripping water pipe located at the peak of the roof. The canvas became the roof and walls. The water saturated the canvas and the hot dry air in the summer evaporated lowering the temperature by more than 30-degrees.
Evaporative coolers are still used in low humidity areas were water is run through a filter and a strong fan draws air through the filter. The evaporation of the water cools the air down depending on the relative humidity. In a region where the humidity may be 10% you can get as much as a 30-degree (F) difference between outside and in. A mister is the current evolution of evaporative coolers.
The system weighs very little and is inexpensive as it works on the strength of the motor and a rotating drum that pulls the air into the ducts.
Many people still rely upon them as the main source of cooling in the desert, we have two systems using the evaporative cooler until it gets above 110-degrees, then we switch to a conventional central A/C.

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