A new climate chamber for air-source and ground-source heat pump testing based on the Hardware-in-the Loop approach: Design and cross validation

The present paper describes a new test bench, designed for experimental tests on small-and medium-sized air-source and ground-source heat pumps, built at the University of Bologna (Italy). The test rig is based on the "Hardware-in-the-Loop" approach and is mainly composed of a test room (i.e. the climate chamber), in which the tested heat pump is placed, a borehole heat exchanger field for tests on ground-source units, the hydraulic loop and the building emulator. The test rig allows to test commercial and prototypal heat pumps under dynamic operating conditions, in order to reproduce the real behavior of a heat-pump based heating system and assess the heat pump effective energy performance. According to the Hardware-in-the-Loop approach, the hydraulic circuit of the facility is designed to reproduce exactly the time-dependent variations of the weather data during a series of representative days in a chosen site and the building thermal load given to the heat pump, calculated by a dynamic simulation software (i.e., the building emulator). In this paper, main components of the experimental facility are presented and the outcomes of a series of numerical simulations carried out with different software, such as Trnsys, Matlab-Simulink and STAR-CCM+, to define the system operative range and the effective behavior of the test bench under dynamic conditions are reported. Numerical models have been validated with experimental data, obtained from a trial test carried out on an air-source heat pump according to current technical standards. Comparison between numerical data and experimental results point out an excellent agreement and, for this reason, numerical models can be used to assess the optimal position of the tested heat pump within the chamber or to define the test bench operating conditions. The cross-validation methodology between experimental data and numerical results from different software, applied in this paper to a test bench for heat pumps, can be employed for the sizing of other test facilities.