Civil Engineering Reference
In-Depth Information
12.8
Energy Saving and Computer Control
The coefficient of performance is the index commonly used to compare refrigeration
systems.
As explained in Sect.
12.2
, the upper limit is related to the Carnot cycle in which
the COP index depends only on the cold- and warm-region temperatures (
T
C
,
T
H
).
The need for a difference between the evaporation and condensation
temperatures and those of the cold and warm regions (which are the
T
c
and
T
H
limiting temperatures of the Carnot cycle) together with the losses inside the
components of the systems makes the real cycle less efficient than the ideal one.
In order to obtain operating conditions with the best COP, and so to ensure
significant energy saving, the following suggestions can be made for both plant
management and capital investment:
Plant management
• The evaporation temperature must be the highest permitted by the needs of the
users. This can be achieved by setting the temperature control of the fluid to be
cooled or of the suction pressure of the valve.
• The condensation temperature must be the lowest permitted by the cooling
system and by the warm-region temperature.
• The load rate of the single compressors must be kept as high as possible by
taking out the single machines in sequence in order to avoid low efficiency
occurring at low rate.
Capital investment
• Installing a floating point for the control of the evaporating temperature
according to external conditions and user needs
• Improving the efficiency of the cooling equipment to allow lower condensation
temperatures
• Installing a variable-speed drive to regulate the refrigerant flow without
dissipation
• Installing centralized computer control
Costs and energy can also be saved by installing cold storage systems, such as
ice or cold-water or eutectic storage, to shift the energy consumption from peak
hours to low-rate hours and to smooth load demand and so the system power profile
(see Sect.
4.9
).
Heat recovery from the hot water of the condenser cooling circuit is always
possible. The maximum recoverable heat equals the heat to be subtracted from the
refrigerant in the condenser; actual values are lower (roughly 50 %) depending on
the temperatures of potential end users. Typical uses are space heating, sanitary hot
water, and cleaning.
Heat recovery from the lubricant oil-cooling system allows higher temperatures
than recovery from the condensation phase.
For high-power systems, drivers such as steam or gas turbines can be used in a
cogeneration cycle.
