Energy Analysis and Cost-Effective Design Solutions for a Dual-Source Heat Pump System in Representative Climates in Europe

[EN] Ground-source heat pumps are an efficient technology for heating and cooling in buildings. However, the main limitation of their widespread application is the borehole heat exchanger's (BHE) high investment cost. Hybridizing GSHP systems may overcome this limitation. This research work analyzes the long-term energy performance of a dual-source heat pump (DSHP) system, which uses the air or the ground as external heat/sink sources, in three representative European climates. First, a BHE cost-effective design solution is proposed for each climatology; then, a complete energy analysis is carried out, and the optimal source control parameters that best enhance the system performance in each climate are determined with the use of a complete dynamic model of the DSHP system developed in TRNSYS. Simulations were carried out for a 25-year operation period. Results show that the DSHP maintains the efficiency during the simulated period, with deviations lower than 1.7% in all cases. Finally, the source control optimization method results in only slight efficiency gains (<0.35%) but with a stronger effect on the ground/air use ratio (up to 25% use of air in cold climates), reducing the thermal imbalance of the ground and leading to a consequent BHE size length and cost reduction.This research was partly funded by the European Commission, grant number 656889.Milanowski, M.; Cazorla-Marín, A.; Montagud- Montalvá, C. (2022). Energy Analysis and Cost-Effective Design Solutions for a Dual-Source Heat Pump System in Representative Climates in Europe. Energies. 15(22):1-30. https://doi.org/10.3390/en15228460130152

A novel TRNSYS type of a coaxial borehole heat exchanger for both short and mid term simulations: B2G model

[EN] A dynamic model of a ground source heat pump system is a very useful tool in order to optimize its design and operation. In order to fairly predict the performance of such a system, the dynamic evolution of the fluid entering the heat pump and coming from the borehole heat exchanger (BHE) must be accurately reproduced not only in the long term but also in the short-mid term operating conditions, as it directly affects the coefficient of performance of the heat pump unit. In this context, the B2G model was developed to reproduce the short-term dynamic evolution of the fluid temperature inside the BHE. This work presents the new upgraded version of the B2G dynamic model for a coaxial BHE, which includes several new features to better reproduce not only the short-term but also the mid-term behaviour of the BHE. For that purpose, the model of the surrounding ground has been improved: vertical heat conduction in the grout and ground, heterogenous ground with different layers, and a higher number of ground nodes in the thermal network considered in the model were added, which are automatically located by means of polynomial correlations for any type of ground, geometry and operating conditions. This novel approach has been implemented in TRNSYS for accurately modelling the dynamic behaviour of a coaxial BHE with low computational cost (2.5¿s for a 24¿h simulation period in a modern computer). The model has been validated against experimental data from a dual source heat pump installation in Tribano (Padua, Italy) and has proven capable of accurately reproducing the short-mid term (up to five days) behaviour of the BHE, with a deviation lower than 0.12¿K.The present work has been supported by the European Community Horizon 2020 Program for European Research and Technological Development (2014-2020) inside the framework of the project 656889 –GEOTeCH (Geothermal Technology for Economic Cooling and Heating) and by the Generalitat Valenciana inside the program “Ayudas para la contratación de personal investigador en formación de carácter predoctoral (ACIF/2016/131)”.Cazorla-Marín, A.; Montagud- Montalvá, C.; Tinti, F.; Corberán, JM. (2019). A novel TRNSYS type of a coaxial borehole heat exchanger for both short and mid term simulations: B2G model. Applied Thermal Engineering. 164(114500):1-15. https://doi.org/10.1016/j.applthermaleng.2019.114500S11516411450

Sizing of the buffer tank in chilled water distribution air-conditioning systems

[♪EN] This paper presents a sizing study of the buffer tank in chilled water A/C systems. In order to find out the adequate sizing criteria for buffer tanks in these kind of installations, a review of different manufacturers' guidelines was carried out and it was concluded that there are three main operation parameters affected by the volume of the tank: the ON cycle time, the OFF cycle time, and the number of starts per hour of the chiller compressor. In order to better understand the influence of each parameter, a theoretical analysis was carried out where the impact of the building thermal load in different design criteria was also studied. After a thorough analysis of all the studied criteria, it was concluded that the minimum ON cycle time which is necessary to ensure that the oil returns to the compressor is the most critical criterion. Finally, a design guideline is proposed by the authors in order to determine the minimum volume of the buffer tank, mainly depending on the capacity of the chiller and the temperature deadband of the thermostat control.This work was supported by the "Programa de Ayudas de Investigacion y Desarrollo (PAID)" of the Universitat Politecnica de Valencia. This work was also supported under the FP7 programme "Advanced ground source heat pump systems for heating and cooling in Mediterranean climate" (GROUND-MED project).Cervera Vázquez, J.; Montagud Montalvá, CI.; Corberán Salvador, JM. (2016). Sizing of the buffer tank in chilled water distribution air-conditioning systems. Science and Technology for the Built Environment. 22(3):290-298. https://doi.org/10.1080/23744731.2016.1131569S29029822

Evaluation of Alternatives for Energy Supply from fuel Cells in Compact Cities in the Mediterranean Climate. Case Study: City of Valencia

[EN] A study of energy supply alternatives was carried out based on a cogeneration fuel cell system fed from the natural gas network of compact Mediterranean cities. As a case study it was applied to the residential energy demands of the L'Illa Perduda neighbourhood, located in the east of the city of Valencia and consisting of 4194 residential cells. In total, eight different alternatives were studied according to the load curve, the power of the system, the mode of operation and the distribution of the fuel cells. In this way, the advantages and disadvantages of each configuration were found. This information, together with the previous study of the energy characteristics of the neighbourhood, enabled selection of the most promising configuration and to decide whether or not to recommend investment. The chosen configuration was a centralised system of phosphoric acid fuel cells in cogeneration, with approximately 4 MW of thermal power and an operating mode that varied according to the outside temperature. In this way, when heating is required, the plant adjusts its production to the thermal demand, and when cooling is required, the plant follows the electrical demand. This configuration presented the best energy results, as it achieved good coverage of thermal (62.5%) and electrical (88.1%) demands with good primary energy savings (28.36 GWh/year). However, due to the high power of the system and low maturity (i.e., high costs) of this technology, would be necessary to make a large initial economic investment of 15.2 Meuro.This research was funded by Catedra de Transicion Energetica Urbana (UPV-Las NavesFVCiE). Grant number 20210096. This work was supported by a grant of the Cátedra de Transición Energética Urbana UPV-Las Naves-FVCiE, which is chair at Universitat Politència de València (UPV) in collaboration with the city hall of Valencia. (Grant number: 20220027).Martínez Reverte, I.; Gómez-Navarro, T.; Sánchez-Diaz, C.; Montagud- Montalvá, C. (2022). Evaluation of Alternatives for Energy Supply from fuel Cells in Compact Cities in the Mediterranean Climate. Case Study: City of Valencia. Energies. 15(12):1-30. https://doi.org/10.3390/en15124502130151

Advances in the determination of the thermal ground properties for the design of borehole heat exchangers using thermal response tests

In order to correctly design a Borehole Heat Exchanger (BHE), it is necessary to have a precise determination of the thermal properties of the ground. Reliable values of the effective thermal conductivity of the soil, the BHE thermal resistance, and the temperature of the undisturbed soil allow to properly size the length, geometry and distribution of the BHEs field. In-situ Thermal Response Tests (TRTs) were developed with this objective. With time, computerized tools have been developed to allow rapid estimation of the properties based on a set of data acquired in short-term tests. This contribution illustrates the use of one tool, implemented in TRNSYS and based on the B2G model, for estimating the ground properties in a BHE located at the Polytechnic University of Valencia. Additionally, the impact of groundwater flow on the results obtained with the conventional analysis methodology of a TRT in the same BHE is analysed

Hot sanitary water production with CO2 heat pumps: Effect of control strategy on system performance and stratification inside the storage tank

[EN] In this work three different control strategies for the production of sanitary hot water by means of an electric heat pump working with CO2 are investigated. The heat pump is a prototype, here modelled in the vapour-compression software package IMST-ART. By simulating this model, the performance of the heat pump is correlated to the boundary conditions and is scaled to different sizes, namely 1, 1.5, and 2 times larger than the reference system. After having chosen an application for which the load profile of sanitary hot water during the year is known, these heat pumps are simulated in a TRNSYS16 model where the production of sanitary hot water and the consumption are buffered by the presence of a tank. Key parameter in guaranteeing comfort and good performance of the system is the stratification inside the storage tank. The size of the tank necessary to keep a certain level of comfort at the user is then determined through a parametric analysis for each size of the heat pump. The energetic performance is also evaluated for each system in terms of seasonal performance factor. Then, the results obtained are compared with a different system where the heat pump is equipped with an inverter and the circulation pump follows a different control logic. The size of the tank and the seasonal performance factor are therefore determined in this case too. Moreover, a night&day control logic is compared to these first two options to have a baseline of comparison in terms of volume of storage needed to guarantee a same level of comfort and performance. To provide information also on the running costs, a parametric analysis was run varying the type of control, the heat pump and the tank sizes for different load profiles. The results show that the size of the heat pump has a significant effect on the comfort of the user, which usually leads to oversizing of the storage tank when the load profile is unknown. With regard to this, the results obtained for the alternative control system show a 20% reduction of the volume of the tank, given a certain level of comfort, and is therefore useful to reduce the size of the storage tank.The study related to thiswork has been partially supported by the FP7 European project ‘Next Generation of Heat Pumpsworkingwith Natural fluids’ (NxtHPG) Grant agreement no: 307169. The work of M. Tammaro on electric heat pumps is financially supported by Universita degli Studi di Napoli Federico II throughthe FP7 European project 'Next Generation of Heat Pumps working with Natural fluids' (NxtHPG).Tammaro, M.; Mauro, AW.; Montagud Montalvá, CI.; Corberán Salvador, JM.; Mastrullo, R. (2016). Hot sanitary water production with CO2 heat pumps: Effect of control strategy on system performance and stratification inside the storage tank. Applied Thermal Engineering. 101:730-740. https://doi.org/10.1016/j.applthermaleng.2016.01.094S73074010

Improvement of transversal professional skills through cooperative work and group dynamics in the UPV Master's Degree in Energy Technologies for Sustainable Development (MUTEDS)

[EN] This article presents an updating of the structure, methodology and evaluation results after 4 years of teaching (courses 2015-2016, 2016-2017, 2017-18 and 2018-19) of a subject entitled Applied energy technology - Project course belonging to MUTEDS (Master's Degree in Energy Technology for Sustainable Development) at the Universitat Politècnica de València). The presented subject is mainly focused on improvement of professional skills as multidisciplinary teamwork and leadership, lifelong learning, competitiveness, planning and managing of time and effective communication in English. To work these competences students have to do, in 8 sessions, the exercise of creating a company (including name and logo) where there are 4 -6 students randomly selected and with different roles, this company evaluates technical-economical-environmental feasibility of an energy project (related with energy efficiency and renewable sources in and specific location) during 8 technical session (in which roles change in each session), and present the project proposal in a public competitive event where the students vote the best work according to their point of view. In parallel, competences and academic quality of the reports are evaluated by the professors.Alfonso Solar, D.; Vargas Salgado, CA.; Montagud Montalvá, CI.; Corberán Salvador, JM. (2020). Improvement of transversal professional skills through cooperative work and group dynamics in the UPV Master's Degree in Energy Technologies for Sustainable Development (MUTEDS). Editorial Universitat Politècnica de València. 239-248. https://doi.org/10.4995/INN2019.2019.10134OCS23924

A novel TRNSYS type for short-term borehole heat exchanger simulation: B2G model

[EN] Models of ground source heat pump (GSHP) systems are used as an aid for the correct design and optimization of the system. For this purpose, it is necessary to develop models which correctly reproduce the dynamic thermal behavior of each component in a short-term basis. Since the borehole heat exchanger (BHE) is one of the main components, special attention should be paid to ensuring a good accuracy on the prediction of the short-term response of the boreholes. The BHE models found in literature which are suitable for short-term simulations usually present high computational costs. In this work, a novel TRNSYS type implementing a borehole-to-ground (B2G) model, developed for modeling the short-term dynamic performance of a BHE with low computational cost, is presented. The model has been validated against experimental data from a GSHP system located at Universitat Politecnica de Valencia, Spain. Validation results show the ability of the model to reproduce the short-term behavior of the borehole, both for a step-test and under normal operating conditions. (C) 2015 Elsevier Ltd. All rights reserved.The present work has been supported by the FP7 European project Advanced ground source heat pump systems for heating and cooling in Mediterranean climate (GROUND-MED).De Rosa, M.; Ruiz Calvo, F.; Corberán Salvador, JM.; Montagud Montalvá, CI.; Tagliafico, L. (2015). A novel TRNSYS type for short-term borehole heat exchanger simulation: B2G model. Energy Conversion and Management. 100:347-357. https://doi.org/10.1016/j.enconman.2015.05.021S34735710

Diagnosis of the building stock using Energy Performance Certificates for urban energy planning in Mediterranean compact cities. Case of study: The city of València in Spain.

[EN] This research aims to diagnose the energy performance of buildings in València and identify areas where energy efficiency can be improved. The energy performance results of all 129,487 EPCs in the city were mapped and compared to socioeconomic variables to gain insights into the reasons behind the results. The study reveals that the city¿s building stock has poor energy performance, attributed to the lack of building standards during the city¿s expansion in the 1960s and 1970s. The worst energy performances are observed in the peripheral districts, particularly in the city¿s northern half, where low-income and low-renting rates are common, resulting in reduced investment capacity for individuals to retrofit their homes. To promote quick dissemination of measures to retrofit households, they must be adequate, economical, and replicable, avoiding social, administrative, and economic barriers. The study highlights the importance of EPCs as an objective tool to diagnose the energy efficiency of a city¿s building stock. Policymakers can use the findings to identify areas that require improvements and evaluate the appropriate actions to improve the building stock¿s energy performance. This study presents significant potential to reduce buildings¿ energy demand and achieve climate goals through EPCs.This article is an extended and updated version of a paper originally presented at the 17th Conference on Sustainable Development of Energy, Water and Environment Systems (SDEWES 2022) held in Paphos, Cyprus, over the period 6th to 10th November 2022 (denoted then as paper SDEWES2022.00306 Assessment of Buildings¿ Energy Efficiency over the Years at a City-wide Level: the Case of Valencia). This project has received funding from the European Union¿s Horizon Europe research and innovation programme under Grant Agreement No. 101075582. The Spanish public administration partly supported this work under the grant PURPOSED project (ref: PID2021-128822OB-I00), financed by the Spanish State Investigation Agency. The Catedra ¿ de Transicion ¿ Energ¿etica Urbana (Las Naves-VCiE-UPV) also supported this work. Thanks to Mireia Roncero Tarazona for creating the maps in this article.Manso-Burgos, Á.; Ribó-Pérez, DG.; Van As, J.; Montagud- Montalvá, C.; Royo, R. (2023). Diagnosis of the building stock using Energy Performance Certificates for urban energy planning in Mediterranean compact cities. Case of study: The city of València in Spain. Energy Conversion and Management: X. 20:1-18. https://doi.org/10.1016/j.ecmx.2023.1004501182

Energy and techno-economic assessment of the effect of the coupling between an air source heat pump and the storage tank for sanitary hot water production

[EN] Heat pumps are proved to be a highly efficient technology for sanitary hot water production. However, when installing them coupled with the storage tank, an inefficiency up to 30% can be introduced in the system since this coupling cannot be direct according to EN 1717:2000; in order to prevent from any potential pollution of potable water in case of a refrigerant leakage. This research work evaluates three types of indirect coupling in the case of an air source heat pump system for sanitary hot water production: a coil heat exchanger inside the storage tank (CC), an intermediate heat exchanger between the tank and the heat pump (EHXC) and a double wall condenser (DWCC). A techno-economic assessment was carried out for the representative climate conditions around Europe. Results show that the DWCC is always the most efficient and cost-effective solution with a 3.66% lower energy efficiency than the direct coupling (Base Case), whereas the CC is not only the less efficient solution (27.1% lower than the Base Case) but also the less cost-effective, with a 50% lower net present value than the DWCC.The authors acknowledge the financial support provided by the project "ENE2017-83665-C2-1-P" and the programme 'Formation de Profesorado Universitario (FPU15/03476)', funded by the "Ministerio de Ciencia, Innovation y Universidades" of Spain.Masip, X.; Cazorla-Marín, A.; Montagud- Montalvá, C.; Marchante-Avellaneda, J.; Barceló Ruescas, F.; Corberán, JM. (2019). Energy and techno-economic assessment of the effect of the coupling between an air source heat pump and the storage tank for sanitary hot water production. Applied Thermal Engineering. 159(113853):1-8. https://doi.org/10.1016/j.applthermaleng.2019.113853S1815911385