The advantage of running a direct expansion CO&lt;sub&gt;2&lt;/sub&gt; heat pump with solar-and-air simultaneous heat sources: experimental and numerical investigation

Conte, Riccardo; Zanetti, E.; Tancon, Marco; Azzolin, Marco; Girotto, Sergio; Del Col, Davide

doi:10.1016/j.apenergy.2024.123478

The advantage of running a direct expansion CO₂ heat pump with solar-and-air simultaneous heat sources

Title

The advantage of running a direct expansion CO₂ heat pump with solar-and-air simultaneous heat sources: experimental and numerical investigation

Author

Conte, Riccardo (Università degli Studi di Padova)
Zanetti, E. (TU Delft Heat Transformation Technology; Università degli Studi di Padova)
Tancon, Marco (Università degli Studi di Padova)
Azzolin, Marco (Università degli Studi di Padova)
Girotto, Sergio (ENEX S.r.l.)
Del Col, Davide (Università degli Studi di Padova)

Date

2024

Abstract

Dual-source solar-air heat pumps represent a promising solution for overcoming the limitations associated with single-source utilization, thereby enhancing heat pump performance. However, running the heat pump by alternatively employing the more advantageous source requires the integration of a controller capable of continuously monitoring and predicting the heat pump's performance in response to dynamic environmental and operational variables. Even so, a selective alternate operation does not allow to get the maximum possible performance from the use of the two heat sources. A different approach to address this challenge is the simultaneous utilization of the two sources, by properly combining two evaporators in the CO₂ circuit. This paper presents an experimental investigation of a dual-source heat pump using CO₂ as refrigerant, which can operate in three different evaporation modes: air-mode (using a finned-coil evaporator), solar-mode (using a photovoltaic-thermal PV-T evaporator), and simultaneous-mode (using both the evaporators simultaneously). The novel solution presented here does not require to split the refrigerant flow rate between the two evaporators and at the same time it solves the problem of possible maldistribution at the inlet of the evaporators. Experimental data indicate that the heat pump operating in simultaneous-mode allows to increase the evaporation pressure and the coefficient of performance compared to operation in air-mode or solar-mode. The measurements have been employed for validating a model of the system, capable of predicting steady-state and dynamic performance under various environmental and operational conditions. Simulation results show that the simultaneous-mode operation can be outperformed by the solar-mode only at high irradiance and low air temperature, when the evaporation temperature gets higher than the air temperature. Finally, the impact of the number of PV-T collectors and solar irradiance on the heat pump performance has been simulated and discussed. On this regard, the simultaneous use of the two heat sources adds more flexibility to the system and its design, because even the availability of a small solar area can contribute enhancing the performance over the mere air source heat pump.

Subject

Air source
Carbon dioxide
Direct expansion
Dual-source heat pump
Flooded evaporator
PV-T

To reference this document use:

http://resolver.tudelft.nl/uuid:f1fe5489-9a10-4e76-b103-114df403a871

DOI

https://doi.org/10.1016/j.apenergy.2024.123478

ISSN

0306-2619

Source

Applied Energy, 369

Part of collection

Institutional Repository