24-01-2013, 11:19 AM
Comparative assessment of environment-friendly alternatives to R134a in domestic refrigerators
1Comparative assessment.pdf (Size: 198.09 KB / Downloads: 26)
Abstract
In the present work, the possibility of using
R152a and hydrocarbon refrigerants (such as R290,
R1270, R600a, and R600) as alternatives to R134a in
domestic refrigerators has been assessed theoretically.
The refrigerants are assessed over wider range condensing
and evaporator temperatures. The assessment
was done with standard parameters such as pressure
ratio, volumetric cooling capacity (VCC), coefficient
of performance (COP), compressor input power,
compressor discharge temperature, and total equivalent
warming impact (TEWI). The results obtained showed
that pure hydrocarbon refrigerants are not suitable to be
used as alternatives to R134a due to its mismatch in
VCC. R152a has approximately the same VCC with
about 9% higher COP and lower values of operating
pressure and compressor input power. The discharge
temperature of R152a was higher than that of R134a
by about 14–26 K.
Introduction
In India, about 80% of the domestic refrigerators use
R134a as the refrigerant due to its excellent thermodynamic
and thermophysical properties. However, R134a
is known to have high global warming potential (GWP)
of 1,300. Kyoto Protocol of United Nations Framework
Convention on Climate Change (UNFCCC) called for
the reduction in emissions of six categories of greenhouse
gases including hydrofluorocarbon (HFC) refrigerants
(Wen-Tien 2005). From the environmental, ecological,
and health point of view, there is urgent need to find a
better substitute for the HFC refrigerants (Johnson 1998).
According to the Kyoto protocol, governments around
the world are voluntarily committed to reduce the green
house gas emissions to the atmosphere. To meet the
objectives of the Kyoto protocol and satisfy the growing
demand for domestic refrigerator needs, it is essential to
identify a long-term energy-efficient and environmentfriendly
alternative to R134a.
Effect of condensing temperature
Figure 2 shows the performance characteristics of the
domestic refrigerator at different condensing temperatures
form 40°C to 60°C with −15°C evaporator
temperature. The pressure ratio of R600 and R1270
yield the highest and lowest pressure ratio, respectively.
All the alternatives except R600 have lower pressure
ratio across the considered range of condensing temperatures.
The increase in pressure ratio will reduce the
volumetric efficiency of the compressor.
Conclusion
A comparative assessment was performed theoretically
with R134a and its alternatives (R152a and hydrocarbon
refrigerants) in a domestic refrigerator and the
following conclusions are drawn.
& Except for flammability, R152a, R600, and R600a
with negligible GWP compared to R134a are
found to be the best long-term alternative option.
& R290 and R1270 cannot be used as alternatives due
to their high operating pressures compared to R134a.
& R600a and R600 offer many desirable characteristics
such as low operating pressure, mass flow
rate, and discharge temperature, and high COP
and specific volume, but it requires a compressor
design change.
& R152a offer many desirable characteristics such as
low operating pressure, mass flow rate, and higher
COP by about 9%, 40% and 7–9%, respectively.
& R152a has approximately the same VCC.
& The pressure ratios at 40, 50 and 60°C condensing
temperature are found to be approximately the
same.