22 May 2008

A NOVEL COOLING CONCEPT AND SYSTEM WITH ZERO OZONE DEPLETION POTENTIAL AND NEAR ZERO GREEN HOUSE GAS EMISSIONS


The use of hydrofluorocarbons (HFCs) in the compression refrigeration has significant
advantage over hydrochlorofloro carbons (HCFCs) in terms of ozone depletion potential (ODP)
but offers very high global warming potential (GWP). The other demits of HFCs are the
requirement of stringent regulatory mechanism to control the manufacture, distribution, usage
and disposal of these refrigerants which have a GWP ranging from 120 to 14,800. According to
Montreal Protocol these regulations are essential to minimise the green house effects due to
HFCs. Besides HFCs there is very limited number of refrigerants available for the compression
cycle. These are ammonia, carbon dioxide or butane based compression cycle systems.
Ammonia and carbon dioxide systems operate at very high pressure and these refrigerants
could be used only with certain specific alloys and materials due to their corrosive nature. Heat
driven absorption system also offers zero ozone depletion and global warming potentials.
Amongst these the water-lithium bromide absorption systems are popular but require frequent
maintenance due to lithium bromide corrosion and vacuum loss. Adsorption systems based on
water-silica gel are designed to address some of these corrosion problems but these systems
also suffer from a frequent vacuum loss problem which requires continuous operation of vacuum
pumps. All waste heat driven systems claim to have a COP of 0.7 to 1.5 depending on the
number of evaporations and heat recovery stages used but practically a maximum COP of 0.3 to
1.0 is achievable due to the loss of vacuum particularly after 1-2 years of operation. The sludge
generated from the lithium bromide chillers could also be an environmental nuisance and may
require safe disposal. In order to address these energy efficiency and environmental issues
particularly those related to ozone layer depletion and global warming due to refrigerant
emissions, CSIRO Energy Technology has developed a novel cooling concept which could be
operated with waste heat, solar energy, gas or electricity. The concept offers a far superior
performance in terms of design, maintenance requirements and overall energy saving. This
paper describes the novel cooling concept, a laboratory demonstration system and some
important performance results.