OSTIM Technical University and Critical Thinking Institute-Polar Project and Technology
Heat Pumps or Heat Pipes for the Fifth-Generation District Heating and Cooling Systems?
Heat pumps are touted as one of the key instruments of decarbonization to meet the goals of the Paris
Agreement. Heat pumps, demanding electrical power, are responsible for carbon dioxide emissions due to two reasons. The first emission source emanates from the fact that they cause an exergy deficit between the low-exergy thermal power they supply and the high-exergy electrical power input. The second reason is direct carbon dioxide emissions from the power plants with a mix of renewables and fossil fuels in the energy stock of a particular region or country. The break even-point for their heating coefficient of performance (COP) is above ten, which is not feasible with single-stage heat pumps. Therefore, the industry and the energy sector claim that this issue may be resolved by cascading multiple heat pumps and the necessary temperature lift, and their COP will increase. This presentation shows that this claim does not hold true, and the contribution of heat pumps remains limited to the decarbonization issue, and the total electrification of the heating ad cooling sector with heat pumps will remain a sweet dream that will never come true. This is also true for 100% renewable case because renewables such as solar electricity from photo-voltaic panels carry their own carbon dioxide emissions responsibility because they destroy the thermal exergy that could be recovered for useful work, say for district heating. The European Union has developed a road map to utilize solar heat and waste energy at temperatures as low as 35oC for the fifth-generation district heating. Because the temperature peaking by the cascaded heat pump for satisfying the higher temperature demand of existing heating equipment is not a proper solution, as will be shown in this presentation, the only sustainable solution is to eliminate the temperature gap from the equipment side with low-temperature heating and high-temperature cooling radiant panels using heat pipes. The same technology may be used in solar photo-voltaic-thermal (PVT) panels, providing supply temperatures around 35oC. This perfect temperature fit on the supply and demand side eliminates the need for temperature peaking and minimizes heat pumps until innovations bring to the market heat pumps with design COP values well above ten. This presentation will show a solar prosumer house with the phase-change material type of thermal storage, heat-piped thermal exchangers, heat-piped radiators for heating, heat-piped ceiling cooling panels, heat piped, next-generation solar PVT panels, all of which eliminate the major pumping demand with electricity, minimize exergy destructions, and eliminate heat pumps. The presentation also shows that rather than large district energy systems, local district energy loops will be more feasible while reducing large district pumps in fifth-generation district heating systems and cooling, in which exergy destructions are even more critical in district cooling.
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