Modelling of Wax Actuators in Underfloor Heating Manifolds

Finding sources for power grid balancing has become increasingly important with more renewables used for production. In buildings, heat pumps could be utilized among other electrical appliances. The heat pumps would work at full power to balance the overproduction in the grid. However, short-term grid flexibility announces the consumption need up to 5 minutes in advance, which can prove a problem to control. When there is no current energy need in the building, all valves are closed. That means that when a heat pump with overridden control starts working at the maximum frequency, its full power heats up the local circuit very fast, especially when there is no storage tank. Whether the heat pump overheats and cannot be used for balancing the grid or the whole system opens for heating depends on the regulating valves and their opening speed. For underfloor heating systems, the valve opening speed is slower than for other systems as wax actuators are used. This paper focuses on how to model these wax actuators and determine the opening time to provide input for further studies on flexibility. A physical and a linear segment model are parameterized and the results show that the wax actuator fully opens the valve in six minutes.