The “Hardware-in-the loop” approach for the experimental test of an innovative dual-source heat pump

In this paper the lay-out and the main operative features of the new climatic room of the Applied Thermal Engineering Laboratory of the University of Bologna designed for experimental tests on small and medium commercial and innovative heat pumps following the “Hardware in the loop” approach are described and discussed. After the description of the main components of the test rig and its control loop, the main characteristics of the climatic room are presented by means of a series of dynamic simulations obtained by using both TRNSYS 17 and SIMULINK. The double-modelling enables to make a more precise prediction of the behaviour of the thermal loop during dynamic working conditions. The climatic chamber is a room with a volume of 60 m³ and reduced heat losses where commercial or innovative heat pumps having a nominal thermal power lower than 15 kW can be tested under operative conditions which reproduce the real behaviour of a thermal plant. The heat pump can work between two external thermal reservoirs (i.e. air and ground) which can vary their temperature in time reproducing the evolution of the real climatic data (i.e. external air) or of the ground (by means of a vertical borehole heat exchanger) and one internal reservoir (i.e water) which varies its temperature on the basis of the trend of the building loads (i.e. return water). The hydronic loop of the climatic room is designed in order to reproduce exactly the time dependent trend of the external air during a specific day in a specific site and the trend of the return water temperature due to the instantaneous building loads, obtained with the help of a dynamic simulation software applied to a specific building. In this way the room allows to test the heat pump under realistic conditions in order to obtain information about its performances adopting a specific control logic. As an example, this paper shows in which way the climatic room will be used in the frame of the HEGOS project for the optimisation of the control system adopted for a heat pump able to use two external thermal reservoirs (i.e. air and ground).