Using an inverter-driven compressor in variable capacity heat pump systems has a main drawback, which is the extra loss in the inverter. The present experimental study aims to recover the inverter losses by using brine-cooled and water-cooled inverters, thereby improving the total efficiency of the heat pump system. In order to achieve this goal, a test rig with the air-cooled, water-cooled and brine-cooled inverters is designed and built, and a comparative analysis of the recovered heat, inverter losses and system performance is conducted when the compressor is driven by the water-cooled, brine-cooled and air-cooled inverters at three different switching frequencies for each inverter. The experimental results show that the inverter losses as a magnitude and as a ratio of the total consumed power are lowest in the brine-cooled inverter and highest in the air-cooled one at all the compressor speeds and all the inverter switching frequencies. Moreover, the recovered energy varies between 45 and 125 (W) in the water-cooled inverter, which corresponds to 63 and 69 (%) of the inverter losses; while it varies between 61 and 139 (W) in the brine-cooled inverter, which corresponds to 79 and 90 (%) of the inverter losses. It is also proved that the improvement of the system coefficient of performance (COPsys) is almost the same when the water-cooled or the brine-cooled inverter is used and varies between 0.54 and 3 (%) in comparison with using the air-cooled one. Indeed, the total isentropic efficiency of the compressor is improved slightly when using the water-cooled inverter and little more when using the brine-cooled one at the same running conditions. In addition, the total isentropic efficiency of the compressor is improved by increasing the inverter switching frequency when any of the inverters is used. The experimental results also show that cooling the inverter by the water, which comes out from the condenser, increases the maximum temperature of the base plate of the inverter about 10 °C which could cause a two-fold deterioration in the inverter median life in comparison with cooling the inverter by air. On the contrary, using the brine for cooling the inverter decreases the maximum temperature of the base plate of the inverter about 30 °C which could cause about a six-fold improvement in the inverter median life. / Capacity-controlled Ground Source Heat Pump single-family dwellings

An electrical distribution network supplies power to many households at a time. Each house has various types of electrical appliances which consume different levels of power depending on its function and the load it supplies. An ideal case would be when no appliances cause power disturbances, however, in reality, many electrical appliances (e.g. refrigerators, computers, heat pumps, etc.), due to their inherent characteristics. The distribution network is now fed back with non-sinusoidal power, called harmonics, causing inefficiencies and potential failure in other appliances connected to the same network. Harmonics are the additional frequency components to the fundamental sinusoidal voltage or current (e.g. 50Hz fundamental frequency in Europe). To avoid the malfunction of the network, each electrical appliance in any household has to comply with the standard IEC 61000-3-2 (current rating $<$16A) defined by the International Electrotechnical Commission (IEC). According to these standards, current harmonics have been observed up to 40th harmonics. If the fundamental frequency is 50 Hz, then harmonic currents up to 2000 Hz have to be considered. Usually, the harmonics are quantified by the measurement when the appliance has been constructed at which point changes are costly and time-consuming.  This thesis investigates the possibility to model these appliances at an early stage of development enabling cost-effective and quick improvements. The model is achieved by reducing a heat pump into a set of chokes, an EMI filter, a rectifier, and a load represented by a variable current source to simulate the compressor which draws the majority of power the system uses. The state-of-the-art, referred to as white box modeling, uses schematics to model these components while this thesis presents a methodology to model without schematics, referred to as black box modeling.  For the black box model, impedance of the components is measured and equivalent circuits are modeled accordingly in Simulink to simulate the harmonics. The validity of a black box simulation model from the equivalent circuit extracted by the impedance measurements is investigated in this thesis. The black box modeling is compared with the white box modeling and measurements for the purpose of verification.   The result is good but more work is needed. The black box model is verified using two different systems which are similarly accurate. Simulating harmonics at a higher power level yields better results. The black box model is more accurate than the white box model, mainly due to the inclusion of parasitics in the EMI filter. Possible additional harmonics generation in unmodeled components is investigated and found to be insignificant.