AbstractsEngineering

A significant part of the environmental impact of a heat pump isgenerally related to the direct emission of the refrigerant fluid during thelife time of the machine. Although the Montreal Protocol has alreadylargely secured its status as a success story by cutting the ozone deplentationrefrigerants drastically, we still have to deal with the challengesresulting from climate change.Natural refrigerants such as Propane permits to design more ecofriendlysystem without sacrificing the performance of the machine. Thethesis work is part of a European project called Next Generation of HeatPumps working with Natural fluids (NxtHPG) whose primary aim is thedevelopment of heat pumps working with Natural refrigerant that aresafe, reliable, with high efficiency and high capacity. Royal Institute oftechnology (KTH) is one of the partner of the project and responsiblefor the experimental campaign of two large propane heat pumps: an airsource heat pump (Case 1 ) and a ground source heat pump suitablefor boreholes (Case 2 ). Few cases in literature report on studies aboutlarge capacity heat pumps using propane as refrigerant.This thesis project focuses on the experimental evaluation of theCase 2 from an energy point view. The safety issues about the use of flammable refrigerant, i.e propane, are briefly reported; however theyare not considered strictly part of the thesis work since they are coveredin other phases of NxtHPG project. Experimental tests for Case 1 werenot conducted during this thesis work because of delays in the prototypedelivery from the manufacturer. However, concerns about the hydraulicloop of the test rig of both the heat pumps was identified and a newdesign was suggested and implemented.During the experimental campaign for Case 2 a significant numberof tests were performed according to a specific text matrix definedfrom the EN 14285 standard. A simple heat pump model has beenused to evaluate the overall performance of the machine from the directmeasurements. The heat pump components (compressors, condenser,evaporator, expansion valve) have been analysed in details by definingspecific analysis model for each one. The results have been comparedwith the manufacture expectation.The prototypes demonstrated to have potentially very good performance,since in the first set of tests the machine behaved as expectedby the IMST-ART software. On the other hand, a drop of the unitefficiency and capacity have been registered during the experimentalcampaign for similar working condition. Two different explanations areinvestigated to clarify the strange phenomenon. The first hypothesisconsiders minor internal damage in the compressor, as check valve leakage;consequence of the use of the compressor in a tandem layout. Itgenerates a back-flow in the non working compressor. The second explanationregards inert gas infiltration in the system. On the otherhand they are not able to explain entirely the system issues and theyneed to be confirmed by the manufacturer analysis of the open compressor.The further improvements, proposed and…