Abstract
The heating and cooling sector, responsible for a large fraction of greenhouse emissions, may have a large scale impact on the energy system evolution contributing to smart industrial and domestic electrification; at the same time the recent increase of renewable energy sources installation, posing a threat in terms of grid stability, makes available a considerable amount of clean and cheap electrical energy during peak hours production. Power to heat technologies constitute a promising solution to face both these issues reducing the electric demand variability and decarbonizing the heat production. Large vapor compression heat pumps are a reliable technology able to compete, under the economic point of view, with the heat-only-boilers in order to serve district heating networks. Performance and economic profitability of a compression cycle is strongly dependent on available thermal source and the temperature of water delivered to the network. The present work explores and compares performance and economic indicators under different installation conditions, considering compression heat pumps employing four different fluids: a traditional HCF (R134a) and three natural fluids, ammonia (R717), butane (R600), and propane (R290), often preferred nowadays to HCFs due to the lower global warming potential.
Highlights
The use of large size Heat Pump, HP, in Europe as generators of District Heating, DH, dates back to the 1980s, when they were exploited in Sweden to balance newly installed nuclear capacity
The present analysis considers three fluid presenting reduced environmental impact: Ammonia (R717) and two hydrocarbon fluid butane(R600) and propane (R290), whose performances are benchmarked against the standard R134a, today avoided because of its high Global Warming Potential
Looking at the hydrocarbon fluid, R600 present the widest domain of applicability, thanks to the ability to reach high temperatures at relatively low pressure, on the other hand R290 is strongly limited by the maximum pressure, and it is not able to provide heat at temperatures higher than 77°C
Summary
The use of large size Heat Pump, HP, in Europe as generators of District Heating, DH, dates back to the 1980s, when they were exploited in Sweden to balance newly installed nuclear capacity. With the heating and cooling sector using half of the total energy consumed in Europe [2], the HP technology was estimate to supply the 25-30% of the total DH production in 2050 [3], with a subsequent reduction of the global greenhouse gas emission impact from fossil fuelled combustion plants. A. David et al, presented a survey of the existing capacity of electric large-scale heat, highlighting as most of the new projects, that were commissioned after 2006, registered an increase of the use of natural refrigerants, about the 20% of their survey data base [5]. HPs with hydrocarbons and ammonia are considered commercially available, with performance similar to a heat pump using HFCs, while carbon dioxide are still at lower Technology Readiness Level [7] and will be not addressed in this work. Butane, R600, has the capability to extend even further the maximum supply temperature thanks to its higher critical temperature
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