In this project a new methodology in energyPRO that allows modelling energy systems with simultaneous production and consumption of heat at different temperatures has been developed.
Using this methodology, it is e.g., possible to model a heat pump that simultaneously cool and heat the return water from the district heating grid. This can be modelled in combination with a thermal storage tank, where the heat pump consumes water from the middle of the storage, cools the bottom of the storage and produce hot water to be delivered to the top of the storage or directly to the district heating grid. The cooled water can be used to increase the efficiency of temperature dependent energy conversion units such as flat plate solar collectors or woodchip boilers.
energyPRO is thereby capable of modelling and optimizing the operation of such energy systems, using a new state-of-the-art mixed-integer linear programming (MILP) method. In the project the methodology is used to analyse the business-economic potential of operating the heat pump using internal heat sources in addition to an external heat source at a typical Danish district heating plant.
The concept is explored in combination with respectively a woodchip boiler and solar collector. The analysis shows that operation of the heat pump with internal heat sources has the potential to reduce the operation costs of the plant. This is especially true in combination with solar heating, where the solar fraction is increased from 22% to 30%. This added solar collector production is occurring throughout almost the entire year and allows substantial increases in production during the colder part of the year.