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.