Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.
Air conditioning installations are typically designed with
enough cooling capacity to satisfy the desired minimum
temperature under the heaviest load. Since heat loads tend to be
less than the maximum designed loads, the system will most
often be working under part-load rather than full-load
conditions. Operating at these part-load conditions at fixed
capacity will be more expensive than if the capacity were able
to match the required load. Varying capacity air conditioning
systems, which make use of inverter technology, have been
developed in order to track the required cooling load more
closely. These high quality air conditioners are advertised as
consuming around 30 per cent less energy than conventional
systems.
This experimental investigation looked into the steady state
performance and start-up power requirements of an inverter
driven refrigeration unit versus fixed speed operation. A three
phase (745 W motor) air conditioning laboratory setup was
used in direct-on-line (fixed speed) mode and also with a
variable frequency drive (inverter). The results obtained
showed that the cooling coefficient of performance increased as
the operating frequency was reduced. This means that an
improved performance can be achieved at lower operating
frequencies. A reduced start-up power was required for the
inverter driven system, however the additional power
requirements for the inverter resulted in the mains driven
system being more efficient at full-load conditions. The
improved coefficient of performance at lower frequencies
resulted in an improved performance for the inverter driven
system when compared to a conventional system at part-load
conditions.
