Abstract
In this paper two solar electric-driven air conditioning systems are compared and analyzed from an energy and environmental point of view. Both systems satisfy the electricity, space heating and cooling needs of an existing multi-purpose, multi-story building that is simulated with TRNSYS 17. The first one, considered as reference system, is based on a centralized electric heat pump coupled with a conventional photovoltaic plant installed 10 years ago. The second one, hereinafter proposed system, has a hybrid configuration, consisting of a ground-source heat pump, a low temperature thermal network and a series of electric heat pumps, one per apartment. In addition, the plant is connected to a high-performance commercial photovoltaic system equipped with a solar tracking system to the panels. Five different solutions realized with vertical, two horizontal orientations, polar and two-axis trackers are taken into account and compared with the standard fixed configuration. The last hybrid configuration can be seen as an upgrade of an existing decentralized air conditioning system in which the local electric heat pumps are converted in water-to-water devices that interact with the thermal grid representing the heat source/sink for them. In both solar electric heating and cooling plants the photovoltaic system is installed on the building roof and it produces electricity to feed the heat pumps and end-users. The electricity surplus or the load not covered by solar field is fed to/taken from power grid. The energy and environmental analyses have been performed by considering both average annual and monthly values of power grid efficiency and CO2 emission factor for electricity. By comparing reference system and proposed one equipped with a two-axis tracker system a primary fossil energy saving of 101.67% is achieved in summer period and 28.10% in winter period. These percentages are the highest values recorded, even if, for all configurations the energy analysis rewards the proposed system. The results of environmental analysis demonstrate that the reference system has the worst performances compared to proposed system with all solar tracker systems selected guarantying positive values for avoided carbon dioxide index up to 45.86%.
Highlights
The total final energy consumption in the EU-28 amounted to 13,414 TWh in 2017
Plant coupled with a ground source heat pumps (GSHPs), a low temperature TG and a series of water-to-water EHPsPS located at each apartment (Figure 4). This configuration is an upgrade of an existing decentralized air conditioning system in which the local electric heat pumps are converted in water-to-water devices interacting with the thermal grid (TG) representing the heat source/sink for them
It can be noticed that the borehole temperature rises during the cooling period that represents the charging phase and it decreases during heating operations
Summary
The total final energy consumption in the EU-28 amounted to 13,414 TWh in 2017. Buildings (residential and tertiary sector) made a substantial contribution to European countries energy consumption. 37.5% (5028 TWh) of final energy demand in EU-28 was due to buildings in 2017 [1]. In the same year, the energy consumption for heating, cooling and domestic hot water accounted for 79% of total EU-28 total energy demand. Cooling requests have experienced a growing trend in the civil sector during last decade due to the increase of indoor comfort. Energies 2020, 13, 3585 expectations and the climate change resulting in environmental temperature rises [2].
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