Heat driven cooling in district energy systems

Abstract: Abstract The threat of global warming, caused by increasingemissions of carbon dioxide (CO2), is one reason why cooling supply systems mustwork more efficiently in the world today. An increasing share,currently between 10 and 20%, of the global output ofelectricity is consumed to produce cooling. The majority of thecoming increase in electricity production will be based on theconsumption of fossil fuels, implying everincreasing CO2-emissions. Vapor compressor chillers are currentlythe predominant provider of cooling and consume large amountsof electricity as well as leak refrigerants that harm theenvironment.This thesis focuses on the production of cooling from adistrict energy system perspective, with focus on heat-drivencooling. Cooling technologies, CHP production and thermalstorage are discussed in order to find a cost effective andenvironmentally sound way to meet today?s increasingcooling demand. Heat-driven cooling technologies withenvironmentally friendly refrigerants can give a net output ofelectricity if used in combination with combined heat and power(CHP) production. There is a net electricity output from asystem including heat-driven cooling. Also fuel is saved forthe production of cooling since heat-driven cooling is moreeffective as compared to vapor compressor chillers that consumeelectricity.It is found that cost effective solutions for district heatdriven chillers and/or the combined production of electricityand district cooling can be found in all climates with a highenough density of heating and cooling demands. In dry climates,with low latent cooling loads, district cooling has a largepotential and absorption cooling will give a high fuelutilization, as seen from a system perspective. District heatdriven chillers are believed to be very energy efficient inwarm and humid climates since desiccant systems are aneffective way of handling latent cooling loads. The choicebetween district heat driven chillers and district coolingdepends very much on the availability of a cost effective heatsink and the available space that can be used for coolingequipment.Low cost heat, a requirement for heat-driven cooling, can besupplied e.g. from CHP (back-pressure steam turbine), wasteincineration or from flue gas condensation. Inlethumidification in combination with enhanced latent flue gasheat recovery is found to be energy effective both for thesupply of heat and cooling using absorption chillers.Thermal storage can improve the performance, lower thecapacity requirements (cost of capital), and increase theseasonal efficiency of cooling equipment. CHP, coolingproduction and thermal storage are three fields in the districtenergy system that need to be integrated and adapted to localconditions in order to find a cost and energy effectivesolution to meet the increasing cooling demand of today.Key words:District heating, district cooling, thermalstorage, humidified gas turbines, combined heat and power,cooling