Potential energy savings when using saline water for cooling chillers in Malta

Abstract

Several cooling systems found in facilities on the coast of St. Julian's were found to be making use of chillers whose condensers are cooled with saline water as opposed to air. The former practice is advantageous since it results in better chiller performance which can be explained through thermodynamic principles. The principle of operation of water-cooled chillers is to reject heat from the condenser to saline groundwater obtained from boreholes through a heat exchanger. The higher temperature saline ground water is then rejected to the sea. Chillers cooled with saline groundwater are subject to the Borehole Drilling and Excavation Works within the Saturated Zone Regulations and to the Protection of Groundwater against Pollution and Deterioration Regulations. Under both the Energy End-Use Efficiency and Energy Services Regulations and the Promotion of Energy from Renewable Sources Regulations, Ground Source Heat Pump systems can contribute to the set targets. Chillers configured to have their condensers cooled by saline groundwater qualify as Ground Source Heat Pump systems. Heat pumps and district heating and cooling are both regarded as adequate means for improving the energy performance of buildings under the Energy Performance of Buildings Regulations. By using the principles of the standard vapour-compression cycle, the system Coefficient of Performance of an air-cooled chiller system was found to be 4.0 while that of a water-cooled chiller system was found to be 5.9. This translates into an energy saving potential of 63.3 GWh of electricity per year and a total of 55,733 tonnes of carbon dioxide emissions avoided per year. 63.3 GWh represents approximately 2.85% of the generated electricity in Malta per year.