A modern day refrigeration system is based on a “closed-loop” concept, in which a refrigerant gas is continuously recirculated. The three basic components within this loop are a compressor to pressurize and circulate the fluid; an evaporator to absorb heat from the area surrounding it; and a condenser, to get rid of the heat taken on by the evaporator. As with any refrigeration system, each of these three basic components is found in a water cooler.

Compressors are sophisticated and relatively expensive devices, which in most cases incorporate an electric motor and pump within a sealed housing. The size of the compressor used is one of the common bases for determining the capacity of chilled water per hour provided (we'll explain more about that factor shortly). Generally, the compressors used in pressurized coolers today come in fractional-horsepower designations ranging from 1/6 to 1/3 (compressors for bottle units can be as small as 1/10 horsepower).

There are two basic ways the heat in a cooler's refrigeration system is carried off: it can be transferred to the air around the cooler, or it can be carried off by water. The component terms involved in these two options are the air-cooled condenser and the water-cooled condenser.

The condenser on an air-cooled type is made with a great number of metal fins projecting from a serpentine pattern of refrigerant tubing (same basic principle here as in the case of a radiator). Heat from the refrigerant is transferred to the outside surfaces of the fins, and air drawn over these surfaces by a fan carries off that heat into the area surrounding the cooler (often referred to as the “ambient” surrounding).

In the case of a water-cooled condenser, the refrigerant coil is immersed in a pipe or chamber through which supply water is channeled. Being lower in temperature than the gas in the refrigerant line, this water absorbs the heat and sends it down the drain. (The operation of a fan or flow of condenser water takes place only during the approximate “on” cycle of the compressor - they don't run all the time.)

One final point of clarification in regard to condensers: many bottle-type water coolers do not require a fan. The capacity requirements of such models are so low, that a simple wire-like grid - called a static condenser - mounted on the back of the cabinet is able to disperse the heat to the surrounding air without need for a fan.

With this basic refrigeration concept established, we now can better comprehend one of the primary criteria in categorizing water coolers -capacity. On the surface, capacity refers to the number of gallons per hour (gph) of 50°F water that a cooler will deliver. Capacity in this sense can range from as low as 2 or 3 gph to as much as 20, depending on the design.

But what makes one model a low-capacity unit, and another high? It has to do with those components of the refrigeration system we mentioned - the compressor, evaporator, and condenser. To put it simply, more powerful compressors and higher capacity evaporator and condenser designs are able to cool a greater amount of water during a given period than smaller types.

There is one additional device used to increase capacity that you should be aware of: the pre-cooler, which removes some of the heat from the incoming water before it enters the basic evaporation region of the system. Pre-cooling is accomplished by simply winding the incoming copper water line around the tailpiece of the drain leading down from the basin. This way, excess water, which splashes onto the basin and flows down the drain when the cooler is in use, can actually be employed to reduce the temperature of water coming into the system. (There is no actual contact between incoming and outgoing water - the transfer of heat takes place between the metal walls that separate the two.) The addition of this pre-cooler component can boost the capacity of a cooler substantially - for instance, from 8 gph to 14 gph, using the same basic refrigeration components. Capacity is one of the most basic criteria in specifying a water cooler for a particular location - so basic in fact, that many manufacturers incorporate the capacity rate right into their model number. Most manufacturers also provide guidelines concerning the number of persons that can be served per hour by each model offered.

Specific Water Cooler Models:

• Floor: This type is available in the traditional adult-height designs, as well as low-level versions for children. In addition, there are models, referred to as “two-level” or “bi-level,” which combine an adult-height floor unit with a wall version hung at a lower level to the side for use by children. While most floor models permit installation flush against the wall, there are certain models, called “free-standing” types, which don't.

• Wall: Designed to mount onto the wall (occupying no actual floor space), this style has become extremely popular because it eliminates obstructions to floor care. As a point of clarification, there are a number of water-cooler models that mount in the wall; but the type normally termed “wall” or “wall-hung” mounts on the wall, not in it. Such models are available in a number of shapes and sizes, offering a great deal of flexibility in terms of positioning height. In other words, the same basic model can be installed as either an adult unit or a children's model by simple placement level on the wall. There are two-level models available in wall types, too, usually made possible by the combining of a model built with a short housing with a model using a longer one. (Two-level models typically employ only one refrigeration system, by the way, meaning that one of the housings is just a “dummy” shell.)

• Recessed: Next, we have the recessed types that install into the wall to varying degrees. The fully recessed type goes almost totally within the wall, providing a formed alcove with ample head clearance for drinking. Unlike most other models, this type is vented from the front, through a louvered panel (this means that air blown over the condenser comes out the front). There is also a popular hybrid design, called the “semi-recessed” cooler, in which there is a basic housing hung on the wall surface, with a backsplash extension of the basin recessing a short distance into the wall. An offshoot of this is the “simulated semi-recessed” design, which provides the same basic function except that the backsplash lays against the wall surface, rather than recessing into it.

• ADA: The fastest growing category in the last decade has been the handicapped accessible cooler. The Americans with Disabilities Act (ADA) has dictated the design characteristics of these units to allow clearance for wheelchairs under the unit. Today, ADA units account for more than half of all sold. There are units with the mechanical components both above and below the plane of the basin. In some units, the mechanical systems are recessed into the wall leaving only the basins projecting forward. The other key design feature of these units is the actuation. Actuation must be at or near the front of the unit and must not require grasping or twisting. This is accomplished by push bar, pushbuttons or electronic control. The force required to operate the push bar or pushbutton is prescribed at less than five foot-pounds.

• Specialty Models: Beyond these basic models we have described, there are a few other, more specialized types, including those with heavy-duty cabinets for certain industrial applications, and models with explosion-proof electrical provision. There is also a sub-category of design called the “remote chiller,” which provides just the refrigeration mechanics without a cabinet, basin or bubbler. A chiller can be used in an under-counter location of a kitchen, for instance, to feed an outlet mounted on the sink above. Likewise, such a package can be linked to drinking fountains, to provide cold water to those locations. In addition, remote chillers are often used to meet industrial and medical needs for chilled water or other fluids.

• Bottle: Now that we've pretty well covered the subject of pressurized water coolers, let's look briefly at the bottle variety. Such versions differ from pressure models in several ways, beginning with the source of water involved. Since bottle-cooler designs receive water from a bottle rather than from a building supply, and since the user takes this water in a cup (meaning there is little or no splash or wasted water), there is no need for either supply or drain connections. In other words, you simply put the unit where you want it, set the bottle on top, and plug in the cooler.