DA-76-08-1 -- The Air Washer -- An Old Tool Sharpened by New Ideas ✓ Most Recent

Let us assume you are an air-conditioning systems designer and you want to specify a system using a very efficient, trouble free and economically operating primary heat transfer means. You want it to be virtually an ideal device and you might describe such a heat transfer device as follows.

It should be capable of cooling, humidifying, dehumidifying, air-cleaning and heating. It should do all these things without any finned tube surfaces such as cooling or heating coils--as a matter of fact it should have no fixed heat transfer surfaces at all. It should make possible the use not only of the usual economy cycle of full fresh air but it should provide an additional economy cycle beyond that. Its maintenance should be practically automatic and it should have a long and reliable operating life. It should be subject to precise automatic control and various versions of the unit should be capable of operating at air velocities up to 1,500 fpm so as to occupy a minimum of space.

If you were to specify such a device as might meet the above description without naming or describing the hardware one might accuse you of dreaming or calling for some fantastic new spin-off of space age science. Not so at all! You would merely be asking for the heat transfer means that gave birth to the air-conditioning industry early in the century. You would be talking about a spray-type air washer. In fact the term "air-conditioning" was coined by an engineer, Stuart W. Cramer of Charlotte, North Carolina in connection with his work with air washers. He introduced this term formally in an address to a convention of the American Cotton Manufacturers Association in May 1906. Dr. Willis Carrier's early experiments and installations of about the same vintage used air washers.

The air washers of today, in the highly refined forms available from a number of commercial sources, will in fact perform all of the functions and have all of the characteristics described in early paragraphs. The new needs that have sharpened this old tool for new and broader uses are the conservation of energy, requirements for air cleanliness and the need for precise humidity control in more and more industrial air conditioning jobs. Designers of large industrial air-conditioning systems have never abandoned the use of these direct spray type heat exchangers and more engineers are leaning toward their use every day.

Before going further into the applications and characteristics of air washers, let us examine what is and what is not an air washer. While an air washer is a highly efficient evaporative cooling device, all evaporative coolers are not air washers in the strict sense of the generic term. Units using wetted pads or flooded fills are very efficient evaporative coolers but they do not handle enough water to provide the water-to-air contact required to use refrigeration in the form of chilled water. To put it simply, all "air washers" are "evaporative coolers" but all "evaporative coolers" are not "air washers". Therefore, for the purposes of this paper let us consider that an "Iair washer" is a device consisting of a proper housing over a basin, with the housing containing from one to four banks of sprays and with some means of eliminating droplets of free moisture from the airstream after it passes through the sprays.

We will now take a look at modern air washers by way of explanation of how they fit the preceding description of their functions and characteristics.

Lest this paper might be construed as a commercial inflllence toward use of some proprietary product, it should be stated here that air washers with the characteristics mentioned are available from a number of manufacturers and are not the proprietary products of one or two.