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Grid Flexible Control of Heat Pumps Markus Lindahl, Sweden Within the EU project Flexible Heat and Power (FHP), RISE Research Institutes of Sweden has, together with the other project partners, evaluated the possibilities and limitations for external control of today’s and tomorrow’s heat pumps. This in order to control the power consumption, as well as providing demand response. Both indirect control, via temperature sensor override, and direct control of the compressor speed has been evaluated by laboratory tests of a ground source heat pump. Direct control gives the best accuracy, while indi- rect control works on more or less all heat pumps. TOPICAL ARTICLE Introduction The European power system is undergoing a major transformation driven by a steadily increasing share of power from renewable intermittent energy sources, such as wind and sun. Heat pumps, with their possibility to convert power to heat, can support the transforma- tion of the power system. Making use of the building’s thermal inertia in combination with controlling the heat pump ́s power consumption makes it possible to also provide demand response. The EU project Flexible Heat and Power (FHP) was com- pleted during fall 2019, and included partners from seven different research institutes and companies in Europe. RISE Research Institutes of Sweden has, together with the other project partners, evaluated the possibili- ties and limitations for external control of today’s and tomorrow’s heat pumps, with focus on space heating of buildings. By external control of the heat pumps and their power consumption, demand response can be offered to the power grid. The term “demand response” includes controlling the power consumption to better match the consumption with the power supply. Demand response can be used to avoid power peaks, balance the power consumption, avoiding curtailment of power production from intermittent renewable sources, etc. The aim of the FHP-project is to use demand response to secure that electricity from intermittent, renewable sources, such as wind and sun, can be used. In the FHP project this is done by making dynamic clusters of heat pumps, giving higher flexibility when controlled together. The Flexible Heat and Power project Within the FHP project, the demand response possibili- ties of heat pumps have been investigated. The benefit with heat pumps, when it comes to demand response, is their possibility to transform power to heat. In combi- nation with the thermal inertia in buildings, or thermal storages, it gives a possibility to control, within certain limits, when the building needs to be heated and still ma- Download and share this article intain a good indoor climate. By controlling the power consumption of the heat pump, it is possible to help balancing the power systems variations in supply and demand. However, controlling the power output from a single heat pump gives low flexibility to the grid, so in order to provide a useful scale of demand response, a coalition of heat pumps needs to be controlled. In order to do this in an efficient and functional way, several steps are needed. The first step is to calculate the available thermal flex- ibility from the individual buildings. This is done by dynamic thermal models, calibrated with data from ex- isting buildings, using machine learning. The models are used to create a plan, a so called “Flex Graph”, including when and how much power the heat pump will need for heating the building. It also shows available flexibility for heating. The “Flex Graphs” for each individual buil- ding are sent to a central “Dynamic Coalition Manager” used for gathering the available flexibility for a number of heat pumps in a community or a neighbourhood. The aggregated plan can for example be used in collabora- tion with the local Distribution System Operator (DSO) in order to avoid local grid problems or in cooperation with the Balance Responsible Party (BRP) to offering balancing services. Finally, the selected control of the heat pump coalition will be disaggregated and dis- patched to the individual heat pumps, where the contri- bution from each single heat pump, most probably, will vary over time, based on the local situation at the mo- ment. This is done by an iterative process made by a dist- ributed optimization algorithm called ADMM. Control of heat pumps One important step in the chain to provide demand re- sponse is to be able to control the heat pump based on external signals in order to make the heat pump use the amount of electricity asked for, in this case the power consumption “negotiated” by the ADMM-algorithm. The heat pumps on the market today are developed to give VOL.38 NO 1/2020 HPT MAGAZINE 31PDF Image | Integration of Heat Pumps into the Future Energy
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