New Possibilities with Old Technique : a Feasibility Study of Absorption Cooling in Örebro District Cooling Network

Abstract: E.ON Värme in Örebro produces electricity and delivers heat and cooling to customers in the region. The Åby Plant operates as a combined heat and power (CHP) plant and runs mostly on different biofuels. A new boiler and turbine is projected for the plant and will start operating fully during year 2012. This creates new possibilities for the existing small scale district cooling production. The number of cooling subscribers is today low and the power output is approximately 7.7 MW but has a great potential of growing in the future. Higher electricity prices, due to the deregulated electricity market and growing environmental concerns motivate the use of district cooling. Cooling production at E.ON Värme in Örebro today comes from modified heat pumps with low efficiency and free cooling. The idea is to replace the heat pumps with either new compression cooling machines, absorption cooling machines (ACM) or a mixture of both. This thesis analyzes possible benefits with the use of heat driven cooling i.e. absorption cooling compared with conventional compression cooling. Excess heat from electricity generation in CHP plants is often a problem during the warm period of the year. Normally most of the heat is distributed to industries and households for heating. However, during the summer, the demand for district heating is low which constrain electricity production. The absorption technique utilizes heat as fuel and increases electricity generation during warm periods. This together with a decrease in electricity consumption has positive effects on the environment since it reduces electricity produced in plants controlling margin production. Those plants are most often coal condense plants with high emissions of fossil CO2. Most scientists believe that CO2 emissions from human activities are the main cause to the increasing greenhouse effect. The importance of reducing CO2 emissions is therefore high and is one of the motives for district cooling based on ACM that replaces small local electricity driven chillers. Since the Åby plant uses mostly biofuels the contribution of fossil CO2 is low. ACM utilizes heat as fuel, therefore the positive effects related to ACM are fairly obvious when the electricity price and the demand for cooling are high. To analyze and optimize the energy system in Örebro, a model was created in the program MODEST, which is software developed at Linköping Institute of Technology. Optimizations with different cooling demands and electricity prices have been made. The cooling production mix is split up in two scenarios, a visionary scenario where no restrictions are considered and a restricted scenario with restricted ACM capacity. The results have been gathered and analyzed and supports the common statements about absorption cooling. A simulation of the visionary scenario with unrestricted ACM capacity together with the highest cooling demand (20 MW) and the highest electricity prices (European prices), gave an annual decrease in global CO2 emissions of 9 400 tonnes compared to a scenario with only compression cooling machines. Furthermore, the system running cost was almost 9 MSEK lower on an annual basis. In the restricted scenario, a pay-off analysis shows that the additional costs due to ACM is covered by the lower system cost in less than 3 years when the electricity prices are as forecasted for 2012-2015. All the simulations where absorption cooling was a part of the energy system gave positive results both from an economical and environmental point of view.