A Versatile, Economical, Clean Energy

Engineered Systems, Oct, 1999

Whether you're looking at installation in a new facility or replacement of existing equipment, natural gas cooling technologies offer you an unbeatable combination: a luxury of choice with an economy of operation. But natural gas cooling is more than versatile and economical, it's clean - much cleaner than the coal and oil used to generate electricity. So it helps to protect and preserve our environment.

Natural gas air conditioning, dehumidification, and refrigeration equipment have made dramatic strides during the last decade. Today, high-efficiency natural gas cooling equipment is readily available for hospitals, nursing homes, hotels, office buildings, warehouses, supermarkets, quick-serve restaurants, industrial facilities, schools, theaters, ice rinks, etc.

The availability of a new generation of more efficient and reliable gas cooling products from a significant number of U.S. manufacturers is only one reason for the interest in gas cooling. Other recent developments contributing to the momentum toward natural gas cooling include:

* Ability to take advantage of low natural gas prices

* Desire to cut energy costs and eliminate electric peak demand charges

* Realization of lower operating and maintenance costs that offset first-cost premiums and create quicker payback on capital investments

* Debut of alternative financing programs offering creative approaches to equipment acquisition

* Need to improve indoor air quality (IAQ) economically

* Response to political calls to use an abundant fuel such as natural gas, 95% of which is produced domestically

* Establishment of a hedge against the uncertainties of energy deregulation

* Dramatic efficiency improvements of Combined Cooling, Heating and Power (CCHP) Systems (for more information about CCHP Systems, see page 4).

There are three basic types of gas cooling equipment on the market today: engine-driven chillers, desiccant dehumidifiers, and absorption chillers.

Each type is available from multiple vendors in standard packaged equipment that has proven reliable in a variety of applications. Most manufacturers will provide larger units or special custom configurations tailored to meet the needs of virtually any application. Absorption and desiccant equipment is particularly amenable to being packaged with cogeneration systems, which provide the heat needed to power these systems. Engine chillers can also be combined with absorption chillers or desiccant dehumidifiers, using the heat rejected by the chiller engine to power the other equipment.

Engine-Driven Systems.

Heavy-duty workhorses.

Natural gas engine-driven cooling systems employ a mechanical process similar to electric cooling systems. The difference lies in what drives their reciprocating, rotary screw, or centrifugal compressors -- a high-efficiency natural gas engine instead of an electric motor. Furthermore, the gas cooling chiller's engine and exhaust heat can be recovered to efficiently generate high-temperature domestic hot water or process steam, or to regenerate desiccant dehumidifiers or power absorption chillers.

Gas engine-driven cooling, heating and cooling, and heat pump systems reduce electricity consumption and peak demand. They also offer very efficient part-load performance.

Installations with several hundred to several thousand tons of cooling capacity -- such as those serving hospitals, office complexes, and industrial plants -- may use industrial natural gas engines and combustion or steam turbines to power centrifugal and screw compressor chillers in central plants.

Commercial and industrial customers -- such as breweries, and meat-packing plants -- can find heavy-duty natural gas cooling equipment available to meet their cold storage and process needs in the 250 to 2,100-ton range. Customers with smaller cooling needs may turn to industrial, automotive, or marine-derivative engines in neatly packaged, compact units with capacities ranging from 15 to 800 tons.

Desiccant Systems.

The low, low humidity choice.

The primary functions of a commercial air conditioning system are to reduce the humidity of an air stream (latent cooling) and to lower the temperature (sensible cooling). Most conventional air conditioners perform latent and sensible cooling simultaneously by cooling the air stream until sufficient moisture condenses out. Typically, if humidity control is a priority, after the air has been dehumidified, it is then reheated to bring it to a comfortable level temperature before it is sent into the conditioned space.

Desiccant dehumidifiers, in contrast, can directly remove moisture from the air without cooling it. This process allows for the separate control of temperature and humidity. This makes desiccant system dehumidifiers well-suited for sites requiring low humidity levels or those with high dehumidification loads, such as medical facilities, supermarkets, health spas, hotels, offices, and restaurants.

Benefits of desiccant dehumidification equipment:

* Permits the downsizing of chillers and ducts in new construction by separating latent and sensible loads, which can yield significant cost savings -- in many cases, making the first cost equal to or less than that of conventional electric cooling systems.