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.2021 Feb:164:472-490.
doi: 10.1016/j.renene.2020.09.098. Epub 2020 Sep 21.

The potential role of trans-critical CO2 heat pumps within a solar cooling system for building services: The hybridised system energy analysis by a dynamic simulation model

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The potential role of trans-critical CO2 heat pumps within a solar cooling system for building services: The hybridised system energy analysis by a dynamic simulation model

Gianluigi Lo Basso et al. Renew Energy.2021 Feb.

Abstract

The rotary desiccant wheels application in the air conditioning systems are used for the air dehumidification by means of hygroscopic layers for water vapor adsorption. Nevertheless, external heat sources are required for water desorption to close the air treatment cycle. This paper investigates on the possibility to integrate in that cycle a new component, such as thetrans-critical CO2 heat pump, to reduce the contribution of external thermal sources. In so doing, the high temperature waste heat discharged by the heat pump hot sink can be fruitfully exploited. Additionally, a PV array has been added to the typical layout based on the solar collectors, in order to assure the heat pump electrical driving. The energy analysis is carried out by calculating the energy performance indicators of the whole cooling system, simulating it by a dynamic model built in the MATLAB SIMULINK environment. Specifically, an air handling unit has been properly sized to supply cooling load to a reference conference hall of 1200 m3, with changes in boundary conditions (i.e. solar radiation, daily temperature and relative humidity variations). Indeed, three different cities representing the most typical Italian climatic zones, have been considered for assessing the proposed technical option suitability.

Keywords: CO2; Desiccant cooling; HVAC energy Efficiency; Hybrid systems; Solar cooling; Trans-critical heat pump.

© 2020 Elsevier Ltd. All rights reserved.

PubMed Disclaimer

Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
DEC functional scheme and potential external heat sources: a) CHP engines; b) HPs; c) Flat solar collectors; d) Vacuum solar collectors; e) Parabolic trough solar collectors; f) Waste heat from other processes.
Fig. 2
Fig. 2
P-h diagram Carbon Dioxide Refrigerant [R744] (Source: Emerson Climate Technologies [57]).
Fig. 3
Fig. 3
Basic layout oftrans-critical CO2 HP.
Fig. 4
Fig. 4
Potential modifications related to evaporation, compression and expansion phases. a) Auxiliary loop system; b); c).
Fig. 5
Fig. 5
Expansion Turbine integration for mechanical work recovery. a) indirect low-pressure drive with optimised intermediate pressure; b) direct high-pressure drive; c) Direct low-pressure drive.
Fig. 6
Fig. 6
Energy scenarios: plant layouts and reference outdoor conditions.
Fig. 7
Fig. 7
Temperature (on the left) and absolute humidity (on the right) over the simulation time: Milan, Rome, Palermo (from the top to the bottom). The red lines represent the supply absolute humidity. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
Fig. 8
Fig. 8
a) CO2 outlet temperature from the gas cooler and optimal pressure vs. recovery heat exchanger effectiveness; b) COP and electric work vs. recovery heat exchanger effectiveness.
Fig. 9
Fig. 9
Trans-critical CO2 HP Coefficient of Performance vs. Gas cooler pressure with changes in geographic area and optimised CO2 outlet temperature from the gas cooler.
Fig. 10
Fig. 10
Milan case study: Regeneration power and cooling power over May.
Fig. 11
Fig. 11
Milan case study: Regeneration power and cooling power over August.
Fig. 12
Fig. 12
Rome case study: Regeneration power and cooling power over May.
Fig. 13
Fig. 13
Rome case study: Regeneration power and cooling power over August.
Fig. 14
Fig. 14
Palermo case study: Regeneration power and cooling power over May.
Fig. 15
Fig. 15
Palermo case study: Regeneration power and cooling power over August.
Fig. 16
Fig. 16
Thermodynamic transformations on psychrometric diagram for solar cooling system control strategy.
Fig. 17
Fig. 17
Control strategy scheme for Solar cooling plant.
Fig. 18
Fig. 18
Energy balance of reference solar cooling system over five months simulation time-period.
Fig. 19
Fig. 19
Energy balance of hybrid solar cooling system over five months simulation time-period.
Fig. 20
Fig. 20
a) Thermal solar fraction values for three different cities; b) required PV receiving surface normalised by unit of air flow rate.
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References

    1. Statistics | eurostat.https://ec.europa.eu/eurostat/databrowser/view/ten00124/default/table?la... (n.d.) accessed May 5, 2020.
    1. Mancini F., Nastasi B. Energy retrofitting effects on the energy flexibility of dwellings. Energies. 2019;12:2788. doi: 10.3390/en12142788. - DOI
    1. Lo Basso G., Nastasi B., Salata F., Golasi I. Energy retrofitting of residential buildings—how to couple Combined Heat and Power (CHP) and Heat Pump (HP) for thermal management and off-design operation. Energy Build. 2017;151:293–305. doi: 10.1016/j.enbuild.2017.06.060. - DOI
    1. Lo Basso G., Rosa F., Astiaso Garcia D., Cumo F. Hybrid systems adoption for lowering historic buildings PFEC (primary fossil energy consumption) - a comparative energy analysis. Renew. Energy. 2018;117:414–433. doi: 10.1016/j.renene.2017.10.099. - DOI
    1. De Santoli L., Lo Basso G., Spiridigliozzi G., Garcia D.A. Proc. - 2018 IEEE Int. Conf. Environ. Electr. Eng. 2018 IEEE Ind. Commer. Power Syst. Eur. EEEIC/I CPS Eur. 2018. 2018. Innovative hybrid energy systems for heading towards NZEB qualification for existing buildings. - DOI

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