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Digital model of a heat pump operation for indoor space heating using the rejected heat of a photovoltaic panel

Nikoloudakis Nikolaos

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Summary

In the era we live in, the ever-increasing need to cover heating (and cooling) needs, indoors, requires an increase in the energy produced. The environmental footprint of energy production (gas/oil power plants) is very large, which exacerbates the problem of the climate and energy crisis. At this point, it is important to find ways to save energy, as well as to improve systems that will be more efficient, i.e., they will need less energy for their operation and will be able to satisfactorily cover these needs. A system that can help in this matter is the heat pump.In this thesis, a theoretical study was made for the operation of a heat pump that uses the photovoltaic panel as the vaporizer of the system. An absorbent copper plate is attached to the back of the panel to which the pipes where the fluid circulates are attached. The fluid used is R134-A refrigerant, which directly absorbs heat from the panel to change phase and turn into vapor. Photovoltaic panels were defined as monocrystalline type which have a total surface area of ​​4 m2 and an electrical energy conversion efficiency equal to 0.15 (15%). For the realization of the study, meteorological data were taken for the year 2016 in the area of ​​the Technical University of Crete. From these data, the ambient temperature and solar radiation data were used. Heat losses were then calculated for an interior space of dimensions 4 x 4 x 3 (L-W-H) for which the heat pump had to cover these losses.The operation of the heat pump system was based on the vapor compression refrigeration cycle, with constant vaporizing and condensing pressures. Then the theoretical model and the code in python programming language were used to calculate the thermodynamic values, where the coefficient of performance (COP) of the heat pump, the input work of the compressor (Wc), the heat rejected to the indoor space (Qcond) were calculated, as well as panel outlet temperature (T1) and condensation temperature (T3).The heat losses of the interior space for the operating hours of the heat pump were equal to 3,74 kWh. The heat pump was operating in the pressure range of 1,639 kPa and 6 kPa, with temperature T1 equal to -15⁰C and temperature Τ3 equal to 21,5⁰C. In this particular pressure range the heat pump produced 2,79 kWh of heat that was dumped into the interior space, covering at a percentage of 75% the heat demand of the space. The coefficient of performance was also calculated and was equal to 6,9. The electricity consumption of the heat pump was equal to 0,42 kWh, while the PV panels produced 0,87 kWh of electricity for the same amount of time. Thus, the PV panels can cover the electricity demand of the heat pump. In correspond to a split unit air conditioner of 12000 Btu that would consume 2,68 kWh of electricity for the same operating hours, the heat pump only needed the 15% of that electricity to cover the heat demands. Finally, the conversion efficiency of the pv panel, due to cooling from the heat pump’s evaporator, increased at 25,8%, while the pv panels without the evaporator had a conversion efficiency equal to 19,4%.

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