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NATURAL GAS COOLING
High Efficiency Alternative to Conventional Electric Cooling
OPTION 1:
NATURAL GAS ENGINE-DRIVEN COOLING
Commercially proven vapor-compression (engine-driven) cooling systems from 25 to 4,000 tons cooling capacity are
available today. These include engine-driven cooling systems suitable for commercial or industrial use.
FEATURES & BENEFITS
Benefits relative to conventional electric chillers include:
•
Lower operating cost
•
Release of electrical capacity for other applications
•
Supplemental heat source
DEFINITION
Engine-driven systems are cooling systems in which a natural gas-fueled reciprocating internal-combustion engine, often
driving a screw compressor, replaces the traditional electric motor as the energy source. The screw compressors respond
well to variable speeds and have good turndown ratios—which improve engine efficiency under part-load conditions.
Centrifugal rather than screw compressors may be used in larger systems.
INTRODUCTION
Engine-driven systems are cooling systems represented by a thermodynamic cycle in which the refrigerant is compressed,
cooled at constant pressure, condensed, and throttled in the conventional vapor-compression refrigerating cycle. The
natural gas-fueled compressor engine is the energy source.
HOW ENGINE-DRIVEN SYSTEMS WORK
The traditional vapor-compression cycle
The diagram on the right illustrates the vapor-compression refrigeration
cycle. Shaft work is supplied to the compressor by either an electric
motor, natural gas engine, or turbine. Refrigerant vapor is
thus compressed to higher pressure (and temperature).
The vapor must condense to liquid at this higher pressure
and temperature. Because the temperature is greater than
ambient, heat is rejected from the system and flows into
ambient air.
Vapor Compression
Schematic
The high-pressure liquid then passes through a throttling
valve that reduces its pressure, which reduces its boiling
point to approximately 40˚F at design conditions. The lowpressure liquid then passes into the evaporator and is
boiled or vaporized at this lower temperature and pressure.
Because the boiling temperature is now lower than the
temperature of the conditioned air, heat moves from the
conditioned air stream into the evaporator and causes the
liquid to boil. Removing heat from the air in this manner
cools it, fulfilling the purpose of the vapor-compression
cooling system.
LOCAL INSTALLATIONS
Customer
Carriage House
Hockey Outlet
Wilson Greatbatch
Equipment
Energen Technologies
Energen Technologies
Tecochill
Size (HP)
250
150
300
ENGINE-DRIVEN CHILLER VENDORS
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Carrier Corp.
•
Century Corp.
•
Energen Technologies
•
McQuay International (Sanyo)
•
Tecochill
•
Trane Co.
•
York International Corp.
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Location
Fredonia
Wheatfield
Clarence
OPTION 2: NATURAL GAS ABSORPTION COOLING
Commercially proven absorption cooling systems of from 3 to 1,700 tons cooling capacity, throughout the residential,
commercial and industrial cooling capacity ranges, are available today.
FEATURES & BENEFITS
Benefits of absorption cooling include:
•
Lower operating cost
•
No ozone-damaging refrigerants—only water required
•
Safer, quieter operation
•
Lower-pressure or vacuum systems; no large rotating components
•
Less space required than electric chiller with separate boiler
•
Higher reliability
•
Lower maintenance
DEFINITION
Absorption systems are cooling systems where a refrigerant is allowed to evaporate due to its physical property of having
an affinity for an absorbent. It is during this evaporation process where heat is also absorbed, thereby creating a cooling
effect. Once the absorbent becomes saturated with refrigerant and can absorb no more, the solution needs to be
separated or regenerated, so that it may be used again. Direct heat from a natural gas flame or indirect heat in the form
of steam can be used to regenerate the absorbent and refrigerant solution. The heat absorbed during this process is then
rejected in the condenser, along with the heat that was absorbed during the evaporation process (see diagram below).
INTRODUCTION
Absorption cooling systems represent a thermodynamic
cycle that is driven by heat energy rather than by
mechanical energy. Absorption chillers are either lithium
bromide and water (LiBr/H2O) or ammonia and water
systems. The LiBr/H2O system uses lithium bromide as
the absorber and water as the refrigerant. The ammoniawater system uses water as the absorber and ammonia
as the refrigerant.
HOW ABSORPTION SYSTEMS WORK
The single-effect absorption cycle
Absorption chillers operate on the principle that some
materials will absorb others—even when both are in
liquid form. For example, ordinary table salt (sodium
chloride) pulls water vapor out of the air, absorbing it
and making the salt damp, coagulated, and hard to pour.
For absorption cycle purposes, lithium bromide water solution, a liquid that absorbs water vapor, is used.
A major difference between the conventional vapor compression cycle and the absorption cycle is the refrigerant used.
Chlorofluorocarbons (CFCs) have been the most popular refrigerants for mechanical refrigeration systems for decades;
however, distilled water is an adequate refrigerant in most large commercial absorption systems. Unlike mechanical
compression systems, absorption cycles need a second fluid, lithium bromide water solution, which is non-toxic. Because
lithium bromide (the absorbent) does not boil, water (the refrigerant) is easily separated from it by adding heat.
Two variations of the absorption cycle that are more efficient and effective in certain conditions are the Double-Effect and
Generator Absorber heat eXchanger (GAX) absorption technology.
LOCAL INSTALLATIONS
Customer
Canisius College
Mod Pac
Equipment
Hitachi
York
ABSORPTION CHILLER VENDORS
•
Carrier Corp.
•
Century Corp.
•
Hitachi
•
McQuay International (Sanyo)
Size (Tons)
250
200
•
•
•
•
Location
Buffalo
Buffalo
Servel (Robur Corp.)
Trane Co.
Yazaki Energy Systems, Inc.
York International Corp.
FOR FURTHER INFORMATION
•
National Fuel Gas Distribution Corp., 6363 Main St., Williamsville NY 14221-5887; phone (716) 857-7776 or
http://www.nationalfuelgas.com/.
•
Energy Solutions Center Inc. 400 N. Capitol St., NW, 4th Floor, Washington DC 20001; phone (202) 824-7150; or
http://www.energysolutionscenter.org/
NATIONAL FUEL STATEMENT
At National Fuel, we believe in providing information on natural gas technologies, enabling our customers to make
informed decisions on their energy needs. This information covers existing technologies, new technical developments,
emerging breakthroughs in energy use, and energy-saving ideas still in development.
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