Non-Intrusive Performance Assessment Method For Heat Pumps: Experimental Validation And Robustness Evaluation Facing Faults

Thanks to their high theoretical efficiency, residential heat pumps (HP) are a promising technology when attempting to reduce the energy consumption of heating in dwellings. Evaluation of their real performances on-field is thus crucial to promote their development and deployment. However, measuring accurately real heating capacity of air-to-air HP is not easy, since measuring air enthalpy and mass flow rate is challenging. A previously developed non-intrusive internal method based on the compressor energy balance has been improved. It can calculate the coefficient of performance (COP) of different HP types, including air-to-air, on field, thanks to real-time measurements, without interfering with normal operation of the system, and without technical data of the specific heat pump. In this study, a complete validation of this method has been led on a test bench, using an air-to-water HP in order to compare the results of the method with the water-side measurements. This internal refrigerant method was tested for various climatic conditions and heating needs, in stationary and dynamic conditions, including starting and defrosting phases. Different faults were simulated to analyse the behaviour of the method in these conditions, including refrigerant undercharging and exchanger fouling. The analysis also extends to identifying which parameters need to be observed to early detect these faults. The method proves to be robust and its uncertainty to remain low, although it varies with the different working phases. The precise knowledge of real-time performances obtained with this method can help to assess the performance impact of faults and thus to improve associated fault detection and diagnostic methods. On a longer-term scale, the comparison of measured field performances and performances obtained via simplified models, such as regulatory models for instance, could give interesting indications to improve these models

Performance Comparison Of Round Tubes Finned Heat Exchangers And Macro Micro-Channel Heat Exchangers In A Low Capacity Heat Pump

Micro-channel heat exchangers (MCHE) are used in automobile applications due to their low weight and high compactness. Those MCHE are just gaining interest in stationary application and they have a great potential for low heating capacity heat pumps to be installed in “passive houses” where the heating demand is 3 to 5 times lower than in the current new individual houses built in European countries. In this paper, a low capacity integrated air to air heat pump prototype is used to perform an experimental comparison of both a round finned tube and a MCHE used as an evaporator. The MCHE is a prototype one using flat fins. The comparison is based on a constant face surface criterion and an equivalent cooling capacity for different inlet temperature and air flow rate conditions. R-134a is the refrigerant used in the heat pump. First, both evaporators performances are compared experimentally and the results show a clear advantage for the MCHE. In a second step, the behavior of the MCHE evaporator is studied under frosting conditions. The frosting kinetics and the defrosting behavior are analyzed. The results show a behavior similar to round tube finned heat exchangers, with frosting cycle higher than 45 min and a defrosting, using ventilation exhaust air, in less than 10 min