Trane SYS-APM001-EN Air-cooled condenser, Air-cooled versus water-cooled condensers, Maintenance

Primary System Components

Packaged or Split System?

A number of different options are available for packaging and splitting the components of an air-cooled chiller. There is an excellent discussion in Chilled-Water Systems, part of the Air Conditioning Clinic Systems Series (TRG-TRC016-EN).

While they found that some of the internally-enhanced tubes fouled in the long term, they concluded:

Because of the high hardness and low water velocity used in these tests, we do not believe that the fouling experienced is typical of that expected in commercial installations. With use of good maintenance practices and water quality control, all of the tubes tested are probably suitable for long-term-fouling applications.

It is important to remember that a chiller selected for low flow does not necessarily have low velocity through its tubes, as discussed in the chapter “System Design Options” on page 27. If tube fouling is a major concern, consider the use of smooth, rather than internally-enhanced, tubes in the condenser for ease of cleaning.

Air-cooled condenser

Air-cooled chillers do not use condenser-water, since they reject their heat by passing ambient air across refrigerant-to-air heat exchangers. In packaged air-cooled chillers, the manufacturers improve performance by staging fans in response to chiller load and ambient, dry-bulb temperature. Air-cooled chillers can also be split apart. One technique is to use an indoor remote evaporator with a packaged air-cooled condensing unit outdoors. Another technique is to locate the compressor(s) and the evaporator indoors (also known as a condenserless chiller) with an air-cooled condenser outdoors. It is also possible to have an indoor air-cooled condenser.

Air-cooled versus water-cooled condensers

One of the most distinctive differences in chiller heat exchangers continues to be the type of condenser selected—air-cooled versus water-cooled. When comparing air-cooled and water-cooled chillers, available capacity is the first distinguishing characteristic. Air-cooled condensers are typically available in packaged chillers ranging from 7.5 to 500 tons [25 to 1,580 kW]. Packaged water-cooled chillers are typically available from 10 to nearly 4,000 tons [35 to 14,000 kW].

Maintenance

A major advantage of using an air-cooled chiller is the elimination of the cooling tower. This eliminates the concerns and maintenance requirements associated with water treatment, chiller condenser-tube cleaning, tower mechanical maintenance, freeze protection, and the availability and quality of makeup water. This reduced maintenance requirement is particularly attractive to building owners because it can substantially reduce operating costs. However, see “Energy efficiency” below.

Systems that use an open cooling tower must have a water treatment program. Lack of tower-water treatment results in contaminants such as bacteria and algae. Fouled or corroded tubes can reduce chiller efficiency and lead to premature equipment failure.

SYS-APM001-EN Chiller System Design and Control 5