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Dual Source Solar Assisted Heat Pump Model Development, Validation and Comparison to Conventional Systems

pubblicazioni - Memoria

Dual Source Solar Assisted Heat Pump Model Development, Validation and Comparison to Conventional Systems

Questo articolo presenta un nuovo sistema SAHP (pompa di calore elio-assistita) integrato con pannelli ibridi fotovoltaico/termico (PVT).

The 2010 Energy Performance of Buildings Directive gives to European Member States mandate to draw up national plans to increase the number of nearly zero-energy buildings (NZEBs). Residential energy consumption has to be significantly reduced in terms of space heating, space cooling and by providing domestic hot water (DHW). As itresults from the International Energy Agency (IEA) Task 44 “Solar and Heat Pump Systems”, combining solar energy and heat pumps (HPs) to build a Solar Assisted Heat Pump (SAHP) system is a promising solution.Can it be interesting and sustainable also for yearly building energy needs (space heating and cooling, DHW production) in Mediterranean area? This paper presents a new SAHP system integrated with hybrid photovoltaic/ thermal panels (PVT).

When building thermal energy request increases with the decrease of external air temperature, standard air-to-water heat pumps (AWHP) lose efficiency in heating mode. In summer, the high temperature reached by PV cells brings to a reduction in panels electricity generation. These are the main reasons which lead optimal configuration and control strategy choice, together with years of experimental know-how and data on HP studies collected in RSE research centre and Politecnico di Milano University.Main components are a dual-source HP, PVT panels and two storage tanks (one for DHW and one, from now called “cold” tank, between solar panels and the heat pump). Solar heat absorbed by PVT is directly stored for DHW if water reaches the set temperature, otherwise it is sent to the cold one.

In both cases photovoltaic cells are cooled so their electricity generation increases. By having two different heat exchangers on source side, the investigated configuration can switch from air to the cold tank, with cold weather, increasing system’s performances.In this work the developed system were compared with two conventional systems: an AWHP integrated with standard photovoltaic panels; an AWHP integrated with hybrid PVT panels for DHW production only. Those systems were investigated for a single family house, through one year simulation in the TRNSYS software. The main componentsof the models (HP, Storage tanks, PVT) were validated with experimental data.Control strategy, size of the tanks and number of panels were investigated with parametric studies. With 12 PVT panels solar field and a 0.9 m3 cold storage, the combined system decreased the total electric energy consumption by 12% and the withdrawal from the grid by 34% in Milan, compared to a conventional AWHP combined with 12 standard photovoltaic panels. Relating the same systems with simulations in Rome, a decreased electric energy consumption of 18% was obtained together with an increased electric energy surplus of 76%. The studied system’s performance was compared also to a conventional AWHP, with in addition 12 PVT panels for DHW production only.

The results showed a decreased electric energy consumption of 6% in Milan and of 12% in Rome, and a decreased grid consumption by, respectively, 29% and 71%. Thanks to these results an experimental prototype has been designed and built in December 2016. Data observed from first trial monitoring campaign highlighted better performances than expected. After a season of investigation and data analysis for the system, new findings will be illustrate.

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