Efficiency is dependent both on the efficiency of the equipment and the
efficiency of the system. A system designed with efficient equipment that is
used inefficiently makes for an inefficient system.
Capacity is typically expressed in kW of refrigeration in SI units and in tons
of refrigeration in US customary units.
The coefficient of performance or COP is the ratio of refrigeration capacity
to compressor power.
In the US, EER and SEER may also be used to express efficiency. It is
better to use SEER when choosing equipment.
The options of using central plants versus distributed equipment should be
compared. Smaller units may provide more flexibility in managing variable
loads and future changes.
Different types of compressor technology are used depending on the
required capacity. Centrifugal compressors are most efficient for large
applications. Absorption chillers are the least efficient, but may be able to
run from a free source of waste heat.
Water cooled equipment is more efficient than air cooled equipment.
Geothermal heat pumps and earth tubes can improve the efficiency of
systems.
In cooling towers, fan hub and blade tip seals can improve efficiency.
Equipment should be correctly sized. Downsizing may be required in some
cases.
Consider two smaller chillers or boilers rather than one large one. A
separate system may be beneficial for 24/7 loads.
Consider replacing aging units with more efficient ones, including premium
efficiency motors.
Replace constant volume systems with variable air volume.
Variable speed drives can save energy with chillers, fans, pumps and
cooling towers.
Consider economizer cycles to use free cooling when outdoor air enthalpy
is low.
Avoid pressure drops in air handling and pumping systems
Adjust the thermal lift between the condensing temperature and the
evaporating temperature to reduce the energy consumed.
Direct digital controls provide effective automation for energy efficiency.
Energy recovery may be possible using equipment such as plate and frame
heat exchangers or heat wheels.
Supply and exhaust air should be effectively controlled.
Hydronic balancing is necessary in water-based systems.
Fix building envelopes and pipes and ducts and insulation to reduce HVAC
loads.