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TRG-TRC012-EN 33
period five
Application Considerations
notes
and temperatures that the air-cooled chiller. Generally, air-cooled chillers last 15
to 20 years, while water-cooled chillers last 20 to 25 years.
To summarize the comparison of air-cooled and water-cooled helical-rotary
chillers, air-cooled chiller advantages include lower maintenance cost, a pre-
packaged system for easier design and installation, and better low ambient
operation. Water-cooled chiller advantages include greater energy efficiency (at
least at design conditions) and longer equipment life.
Condensing Temperature Control
All chillers require a minimum pressure difference between the evaporator and
condenser to ensure proper management of oil and refrigerant. This minimum
pressure difference depends on the chiller design and controls. The most
common method of maintaining this pressure difference at the various load
conditions is to control the condensing temperature by varying the temperature
or flow rate of water (or air) flowing through the condenser. By controlling the
condensing temperature, most helical-rotary water chillers can start and
operate over a wide range of conditions.
Controlling condensing temperature: 1) maintains chiller efficiency, 2)
maintains the required pressure differential between the evaporator and
condenser for controlled flow through the refrigerant metering system, and 3)
prevents the pressure imbalance that could cause oil loss problems.
Controlling the refrigerant pressure difference between the evaporator and
condenser of an air-cooled chiller is accomplished by varying the flow rate of
the air flowing through the condenser coils. This control is an integral part of
the chiller design.
cooling tower
cooling tower
condenser
condenser
water
water
pump
pump
condenser
condenser
Condensing Temperature Control
Figure 48