Feature
Continued from page 19
A diffuser converts this energy into pressure energy and
discharges into the condenser. The pumping efficiency increases
with speed; hence this type of compressor is designed to operate
at high speed.
The main advantage of a centrifugal compressor is that there
are no valves, pistons or cylinders. The wearing parts that need
monitoring are the main bearings.
Centrifugal compressors are available in larger capacities
needed for larger air conditioning systems like district cooling,
hotels, shopping malls, larger office complex, etc.
“Digital Scroll and Semi hermetic compressors, Variable speed
compressors are being considered by many end users,” says
Vadivelan Kannan, director technical services at Emerson.
CHOOSING THE RIGHT COMPRESSORS
Engineers and HVAC contractors have a few options to choose
from. Kannan says, “The application plays a major role in selecting
the type of compressor. The type of compressor depends on the
specific application and the capacity.”
Kannan unpacks each application and type:
Residential Application: Hermetic compressors are generally
used for residential applications like refrigerators and airconditioners
as the load variations and installation complications
of these type of applications are limited enabling the use standard
hermetic compressors.
Commercial Application: Though Semi Hermetic
compressors were popular in these applications due to their
perceived repairability and reliability, of late, more and more
customers are shifting to hermetic scroll compressors which have
advantages of better efficiency, competitive prices, simplicity and
higher reliability.
Industrial Application: Depending on the capacity, many
types of compressors are being used for this application. Screw
compressors are used for larger capacity whereas Semi hermetic
compressors are used for medium capacity and Hermetic Scroll
compressors are being used for smaller capacity requirements.
“Compressor capacity modulation has become popular as its
saves lot of energy and at the same time reduces temperature
fluctuation inside the conditioned space,” Kannan says.
Additionally, most of the compressors used for commercial
and industrial applications now come with sophisticated
electronics which protects the compressor by using the
compressor itself as a sensor. “This helps the service engineers
to trouble shoot better and quicker. This even enables remote
trouble shooting possibilities,” Kannan explains.
Bell adds that “several design criteria would also need to be
considered to ensure that a compressor runs optimally. These
IMD
include the compressor selection, refrigerant type, system
components and evaporator and condenser selection. An
engineer would be looking at information like the isentropic
efficiency and volumetric efficiency of a refrigeration
compressor which are very important for system operations
including the COP.”
Additionally, most of the
compressors used for commercial
and industrial applications now
come with sophisticated electronics.
ENSURING LONGEVITY
“Matching of system components with correct operating
condition are essential to get the maximum capacity and
efficiency from the compressors. Periodic maintenance of
heat exchangers is very critical for maintaining the capacity
and efficiency of the compressors and the system. Customers
should consider total lifetime cost rather than focusing on initial
Continued on page 23
The reliability
of the system
is drastically
improved with
minimum
shutdown time.
www.hvacronline.co.za RACA Journal I August 2020 21