Integrated energy modelling to support district cooling optimisation: Methodological approach

In a district cooling system different kinds of cooling production can be combined (e.g., vapour compression chillers, absorption chillers, and free cooling). Controlling those systems in an efficient way is a complex problem: the cooling demand is much more difficult to predict than the heat demand and, as for absorption chillers, heat sources such as the solar energy and the waste heat are not predetermined by the designers. The EU project INDIGO deals with the improvement of District Cooling (DC) systems. Its main goal is the development of a more efficient, intelligent, and cheaper generation of DC systems. The results of INDIGO will include the development of: predictive controllers; system management algorithms; an open-source planning tool. To validate the results, the consortium is analysing some case studies. The proposed solutions for DC systems will be installed in the Basurto Hospital campus in Bilbao. Different parts of models that regard the buildings and all the relevant components of the DC system are being developed: 1. generation systems; 2. distribution and storage systems; 3. HVAC systems; 4. thermal behaviour of the buildings, considering also internal loads and building use. The first three parts are being simulated by means of Modelica, an open-source object-oriented modeling language that provides dynamic simulation models for building energy and control systems. The fourth part is being modelled with EnergyPlus. They are going to be integrated through the Functional Mock-up Interface (FMI) for co-simulation. The models of some building envelope elements are being validated considering experimental measurements (heat flow rates, temperatures, entering solar radiation). Component models for the air handlers and for the fan-coils found in the studied buildings are developed in Modelica. Different kinds of chillers are modelled. Particular attention is paid to the distribution system, where thermal and hydraulic effects must be considered jointly. All the developed models will be validated, both independently and considering the integration, using data acquired at the test-site. The validated models will be considered a reference point for the development of the innovative controllers, of the management strategy, and of the planning tool. The new models developed in Modelica will be part of a District cooling open-source library (DCOL).