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Renewable Energy Communities have been recently introduced in European legislation to promote distributed generation from renewable energy sources. In fact, they allow to produce and consume energy from shared local power plants. Low temperature district heating and cooling networks with distributed heat pumps have demonstrated their capability to exploit renewable and waste heat sources in the urban environment. Therefore, they are considered a promising infrastructure to help decarbonize the building sector. As their main operating cost is the electricity purchased by the utility for heat pumps and circulation pumps, this work investigates whether a Renewable Energy Community could help mitigate such cost by sharing electricity produced by local photovoltaic (PV) systems. The research relies on computer simulations performed with both physical and statistical models for the evaluation of electrical load profiles at the district level. Results show that due to the different seasonality between heating demand and PV production, the increase in self-consumption due to the distributed heat pumps is lower than 10%. The use of batteries does not seem convenient for the same reason. The environmental benefit of the proposed system is evident, with CO2 emissions reduced by 72–80% compared to the current situation depending on PV power installed. It also emerged that PV sharing significantly improves the self-consumption at the district level, in particular when the installed PV power is limited (+45%). In conclusion, results suggest that current incentives on PV-sharing make Renewable Energy Communities a viable option to improve the techno-economic performance of fifth-generation district heating and cooling networks. [ABSTRACT FROM AUTHOR]

Following the 2016 central Italy earthquakes, the high seismic vulnerability of existing buildings is once again at the center of the debate. Indeed, the majority of the Italian building stock (around 60%) was built before adopting the first seismic provisions (1974) and in a territory entirely characterized by medium to high levels of seismic hazard. On the other hand, the first provisions addressing thermal performance criteria were introduced in 1976 but with limited impact. A consistent reduction in energy consumption was further achieved in 1991, when even more buildings were erected. As a consequence, the Italian building stock is characterized by reduced seismic capacity and poor energy efficiency and, to optimize the available resources, combined retrofit interventions approaches are required. In this context, a synergic strategy for the seismic and energy retrofit of a unreinforced masonry (URM) building was proposed. The former Courthouse in Fabriano (Ancona, Marche), a strategic, three-story, unreinforced masonry building in the network of permanent monitoring systems of the Italian Department of Civil Protection, was selected as a case study. The overall effectiveness of various solutions of combined structural refurbishment and energy retrofit interventions, having different levels of invasiveness on the building, was assessed. In addition, a common methodology based on the expected annual losses allowed evaluating the financial feasibility of the proposed integrated interventions and estimating the changes in the return of the retrofitting investment in various seismic and climate zones. The results also show how the payback period could be significantly reduced by incentives and regulatory frameworks that currently favour the execution of integrated interventions. [ABSTRACT FROM AUTHOR]

Energy communities (ECs) are becoming increasingly common entities in power distribution networks. To promote local consumption of renewable energy sources, governments are supporting members of ECs with strong incentives on shared electricity. This policy encourages investments in the residential sector for building retrofit interventions and technical equipment renovations. In this paper, a general EC is modeled as an energy hub, which is deemed as a multi-energy system where different energy carriers are converted or stored to meet the building energy needs. Following the standardized matrix modeling approach, this paper introduces a novel methodology that aims at jointly identifying both optimal investments (planning) and optimal management strategies (operation) to supply the EC's energy demand in the most convenient way under the current economic framework and policies. Optimal planning and operating results of five refurbishment cases for a real multi-family building are found and discussed, both in terms of overall cost and environmental impact. Simulation results verify that investing in building thermal efficiency leads to progressive electrification of end uses. It is demonstrated that the combination of improvements on building envelope thermal performances, photovoltaic (PV) generation, and heat pump results to be the most convenient refurbishment investment, allowing a 28% overall cost reduction compared to the benchmark scenario. Furthermore, incentives on shared electricity prove to stimulate higher renewable energy source (RES) penetration, reaching a significant reduction of emissions due to decreased net energy import. [ABSTRACT FROM AUTHOR]

Ground coupled heat pumps are a notoriously efficient system for heating and cooling buildings. Sometimes the characteristics of the building and the user's needs are such that the amount of heat extracted from the ground during the winter season can be considerably different from the amount injected in summer. This situation can cause a progressive cooling or heating of the ground with a negative effect on the energy efficiency and correct operation of the system. In these cases, an accurate sizing has to be done. In systems already built, it could be necessary to intervene a posteriori to remedy an excessive ground thermal drift due to the energy unbalance. In this work, such a situation relating to a real office building in Italy is investigated and several solutions are examined, one of which has been then implemented. In particular, a hybrid heat pump using as heat sink both the ground and external air is compared with common solutions through computer simulations using a dedicated numerical model, which has also been compared with monitoring data. As a result, the hybrid heat pump shows better performance and limits the thermal drift of the ground temperature. [ABSTRACT FROM AUTHOR]

The energy-saving potential of heat pump technology is widely recognized in the building sector. In retrofit applications, especially in old and historic buildings, it may be difficult to replace the existing distribution and high-temperature emission systems. Often, historical buildings, especially the listed ones, cannot be thermally insulated; this leads to high temperatures of the heat carrier fluid for heating. In these cases, the main limits are related, on the one hand, to the reaching of the required temperatures, and on the other hand, to the obtaining of good performance even at high temperatures. To address these problems, a suitable solution can be a two-stage heat pump. In this work, a novel concept of a two-stage heat pump is proposed, based on a transcritical cycle that uses the natural fluid R744 (carbon dioxide) with an ejector system. The second refrigerant present in the heat pump and used for the high-temperature stage is the R1234ze, which is an HFO (hydrofluoro-olefin) fluid. This work aims to present the effective energy performance based on real data obtained in operating conditions in a monitoring campaign. The heat pump prototype used in this application is part of the H2020 Cheap-GSHP project, which was concluded in 2019. [ABSTRACT FROM AUTHOR]

In the European Union (EU), buildings are responsible for about 40% of the total final energy consumption, and 36% of the European global CO2 emissions. The European Commission released directives to push for the enhancement of the buildings energy performance and identified, beside the retrofit of the current building stock, Heating, Ventilation, and Air Conditioning (HVAC) systems as the other main way to increase renewable energy sharing and overall building energy efficiency. For this purpose, Ground Source Heat Pumps (GSHPs) represent one of the most interesting technologies to provide energy for heating, cooling, and domestic water production in residential applications, ensuring a significant reduction (e.g., up to 44% compared with air-source heat pumps) of energy consumption and the corresponding emissions. At present, GSHPs mainly employ the refrigerant R410A as the working fluid, which has a Global Warming Potential (GWP) of 2087. However, following the EU Regulation No. 517/2014 on fluorinated greenhouse gases, this high GWP refrigerant will have to be substituted for residential applications in the next years. Thus, to increase the sustainability of GSHPs, it is necessary to identify short time alternative fluids with lower GWP, before finding medium-long term solutions characterized by very low GWP. This is one of the tasks of the UE project "Most Easy, Efficient, and Low-Cost Geothermal Systems for Retrofitting Civil and Historical Buildings" (acronym GEO4CIVHIC). Here, a thorough thermodynamic analysis, based on both energy and exergy analysis, will be presented to perform a comparison between different fluids as substitutes for R410A, considered as the benchmark for GSHP applications. These fluids have been selected considering their lower flammability with respect to hydrocarbons (mainly R290), that is one of the main concerns for the companies. A parametric analysis has been performed, for a reversible GSHP cycle, at various heat source and sink conditions, with the aim to identify the fluid giving the best energetic performance and to evaluate the distribution of the irreversibilities along the cycle. Considering all these factors, R454B turned out to be the most suitable fluid to use in a ground source heat pump, working at given conditions. Special attention has been paid to the compression phase and the heat transfer in evaporator and condenser. [ABSTRACT FROM AUTHOR]

The design of ground source heat pumps is a fundamental step to ensure the high energy efficiency of heat pump systems throughout their operating years. To enhance the diffusion of ground source heat pump systems, two different tools are developed in the H2020 research project named, "Cheap GSHPs": A design tool and a decision support system. In both cases, the energy demand of the buildings may not be calculated by the user. The main input data, to evaluate the size of the borehole heat exchangers, is the building energy demand. This paper presents a methodology to correlate energy demand, building typologies, and climatic conditions for different types of residential buildings. Rather than envelope properties, three insulation levels have been considered in different climatic conditions to set up a database of energy profiles. Analyzing European climatic test reference years, 23 locations have been considered. For each location, the overall energy and the mean hourly monthly energy profiles for heating and cooling have been calculated. Pre-calculated profiles are needed to size generation systems and, in particular, ground source heat pumps. For this reason, correlations based on the degree days for heating and cooling demand have been found in order to generalize the results for different buildings. These correlations depend on the Köppen–Geiger climate scale. [ABSTRACT FROM AUTHOR]

In this study, the thermal behavior of the coaxial and double U borehole heat exchangers was investigated using numerical simulations in both the long- and short-term. As a reference for borehole heat exchanger specifications, the existing coaxial and double U probes of a geothermal heat pump installed within the Horizon 2020 research project named "Cheap GSHPs" were considered. Nine years of simulations revealed that when borehole heat exchangers are subjected to a balanced thermal load, and intermittent operating modes of the ground source heat pump system are set, the coaxial pipes' configuration provides better thermal performance due to the higher thermal capacitance of the heat-carrier fluid and the lower borehole thermal resistance. The analysis was conducted considering two different types of ground with different thermal conductivity values. As result, the more conductive ground type highlights the higher yield of the coaxial probe. [ABSTRACT FROM AUTHOR]

Ventilation systems are necessary to ensure a good indoor air quality, especially in buildings characterized by high energy performance. An all-air system could be more flexible than radiant systems that need to be combined with other systems to provide fresh air and control latent loads. In this work, a multi-zone all-air system has been compared with a radiant floor integrated with mechanical controlled ventilation and an isothermal dehumidifier. All the systems have been modeled in TRNSYS considering a residential building and three different locations (Helsinki, Milan and Rome). The comparison has been performed in terms of both indoor conditions and energy consumption. The results outline that the two systems are able to maintain the desired indoor conditions. For the energy consumption, an air-to-water heat pump and all the auxiliaries have been considered. Under the same indoor conditions, in heating the electrical energy consumption of the all-air system is lower than that of the radiant floor (−19% in Helsinki, −32% in Milan and −74% in Rome); also in cooling the electrical energy consumed by the all-air system is lower in Milan and Rome (−14% and −29% respectively), whereas in Helsinki the difference is less than 5%. [ABSTRACT FROM AUTHOR]

The development of heat pump technology in the residential sector can lead, and has led to a reduction in greenhouse emissions and enhanced exploitation of renewable energy sources, including solar energy which represents the renewable source for excellence. The current study examines a multi-source energy system equipped with photovoltaic thermal hybrid solar collectors, two storage tanks for the heat source and the domestic hot water respectively and heat pumps for the space heating and domestic hot water production of a single-family dwelling located in North East Italy. Air, solar, and ground source heat pumps were analysed. Some configurations were investigated utilizing computer simulations based on a mathematical model developed to evaluate the electrical and thermal performances of hybrid solar collectors. A smart control unit capable of identifying the best heat source for the heat pump and of considering the possibility of injecting heat harvested by solar collectors into the ground during the summer period was analysed. The investigation uncovered that the multi-energy source systems were responsible for increasing the energy efficiency by 16–25% with respect to an ordinary air to water heat pump system. The simulations also revealed that the energy efficiency of the air-solar source system was slightly lower than that linked to the other configurations including a ground source heat pump. [ABSTRACT FROM AUTHOR]

A simulation model of ground source heat pump systems has been used to investigate to what extent a variable flow of the heat-carrier fluid of the ground loop affects the energy efficiency of the entire system. The model contemporaneously considers the borehole heat exchangers, the heat pump, the building load, and the control strategies for the circulation pumps of the ground loop. A constant speed of the circulation pumps of the ground loop was compared with a variable flow controlled by means of a constant temperature difference across the heat pump on the ground side considering the load profile of an office building located in North Italy. The analysis was carried out for a single U-tube, double U-tube and coaxial pipe heat exchangers. The control strategies adopted to manage the flow rate of the heat-carrier fluid of the ground loop affect both the heat exchange rate of the borehole field and the heat pump’s long-term energy efficiency. The simulations show considerable differences in the system’s seasonal energy efficiency. The constant speed of the circulation pumps leads to the best results as far as the heat pump’s energy performance was concerned, but this advantage was lost because of the greater amount of electrical energy used by the circulation pumps; this, of course, affects the energy efficiency of the entire system. The optimal solution appears then to be a constant temperature difference in the heat-carrier fluid across the heat pump. [ABSTRACT FROM AUTHOR]

The popularity of ground source heat pump systems for both heating and cooling has grown significantly over recent years. Ground heat exchangers are usually buried in the ground either vertically in boreholes or horizontally in trenches. Antifreeze fluids in closed-loop systems are commonly used in these plants to protect them from freezing phenomena and also to reduce the total length of the ground exchangers. In fact, the use of antifreeze fluid allows the system to work below 0 °C which implies higher temperature difference between the heat-carrier fluid and the undisturbed ground, consequently the heat flux increases and the total length of the boreholes can be reduced. This study has been set out to investigate three types of layout system: two conventional heat pumps using pure water and water-glycol respectively as the secondary fluid and an innovative heat pump with a flooded evaporator using pure water. The results demonstrated that, for conventional heat pumps with dry evaporator, the use of anti-freeze additives in mild climates is convenient only in grid-shaped borehole fields with a heating-dominant thermal load. In all other cases, the use of pure water decreases the overall operating costs. In addition, flooded evaporator heat pumps using pure water as a secondary fluid on the ground loop proved to be the most cost-effective solution. [ABSTRACT FROM AUTHOR]

The European building sector is responsible for approximately 40% of total energy consumption and for 36% of greenhouse gas emissions. Identifying technological solutions capable of reducing energy consumption and greenhouse gas emissions is one of the main objectives of the European Commission. Ground source heat pumps (GSHPs) are of particular interest for this purpose, promising a considerable reduction in greenhouse gas emissions of HVAC systems. This paper reports the results of the energetic analysis carried out within the EU research project GEO4CIVHIC about the performance of geothermal heat pumps working with low-GWP refrigerants as alternatives for R134a and R410A. The work has been carried out through computer simulations based on base and regenerative reverse cycles. Several heat sink and heat source temperature conditions have been considered in order to evaluate the GSHPs' performance in the whole range of real conditions that can be found in Europe. Particular attention has been paid to the evaluation of compression isentropic efficiency and its influence on the overall cycle performance when dealing with steady-state heat pump simulations. To do so, five different scenarios of isentropic efficiency calculation have been studied and discussed. [ABSTRACT FROM AUTHOR]

The buildings sector requires more than 40% from the total energy consumptionin Europe. In order to obtain the European energetic goals of decreasing the fossil fuel dependency by 2020 and beyond to 2050, new and efficient strategies concerning renewable energy should be integrated in buildings. In this study a comparative dynamic numerical analysis of the cooling energy performance of a façade building integrated with semitransparent PV cells inside the façade cavity is presented. The comparison included three main items, façade cavity ventilation system, façade inner layer glazed composition and three different climatic conditions. An Optimization between hybrid and natural ventilation system for the cavity is clarified. Putting forward an innovative idea to cool the cavity from indoor air to increase the conversion efficiency of PV modules installed inside the cavity. The energy analysis has been carried out by TRNSYS and the validation of the numerical model has been elucidated. [ABSTRACT FROM AUTHOR]

Exploiting renewable energy sources for air-conditioning has been extensively investigated over recent years, and many countries have been working to promote the use of renewable energy to decrease energy consumption and CO 2 emissions. Electrical heat pumps currently represent the most promising technology to reduce fossil fuel usage. While ground source heat pumps, which use free heat sources, have been taking significant steps forward and despite the fact that their energy performance is better than that of air source heat pumps, their development has been limited by their high initial investment cost. An alternative solution is one that uses solar thermal collectors coupled with a ground source heat pump in a so-called solar assisted ground source heat pump. A ground source heat pump system, used to heat environments located in a cold climate, was investigated in this study. The solar assisted ground source heat pump extracted heat from the ground by means of borehole heat exchangers and it injected excess solar thermal energy into the ground. Building load profiles are usually heating dominated in cold climates, but when common ground source heat pump systems are used only for heating, their performance decreases due to an unbalanced ground load. Solar thermal collectors can help to ensure that systems installed in cold zones perform more efficiently. Computer simulations using a Transient System Simulation (TRNSYS) tool were carried out in six cold locations in order to investigate solar assisted ground source heat pumps. The effect of the borehole length on the energy efficiency of the heat pump was, in particular, analyzed. Finally, a suitable control strategy was implemented to manage both the solar thermal collectors and the borehole heat exchangers. [ABSTRACT FROM AUTHOR]

An important consideration with regard to ground source heat pump (GSHP) systems is ensuring high energy efficiency performance throughout the years. Multi-year analyses are thus exceedingly important to evaluate the seasonal oscillations in the ground temperature and its long-term drift. As only a limited number of results based on real cases are available in the literature, this work aims to address this paucity of information. Seasonal and long-term computer simulations were conducted in order to investigate the thermal performance of two office buildings in Italy with unbalanced load profiles. The study focuses on the evaluation of ground temperature drift which was essentially due to an imbalance of the buildings’ load profile. An analysis, which was compared to two analytical approaches available in the literature, was carried out using a detailed numerical model. The effects of improved load balancing of the ground load profile and of a higher number of boreholes on seasonal oscillations and on the thermal drift were investigated. The results showed that rebalancing the ratio between the heat extracted from and injected into the ground led to better results from an energetic viewpoint almost certainly synonymous with an energetic-economic optimization. [ABSTRACT FROM AUTHOR]

Cool supply air flowing through the underfloor plenum is exposed to heat gain from both the concrete slab (conducted from the warm return air on the adjacent floor below the slab) and the raised floor panels (conducted from the warmer room above). The magnitude of this heat gain can be quite high, resulting in undesirable loss of control of the supply air temperature from the plenum into the occupied space. These warmer supply air temperatures can make it more difficult to maintain comfort in the occupied space (without increasing airflow rates), particularly in perimeter zones where cooling loads reach their highest levels. How to predict plenum thermal performance is one of the key design issues facing practicing engineers – evidence from completed projects indicates that excessive temperature rise in the plenum can be a problem. One of the recommended strategies for addressing temperature rise in UFAD systems is the use of ductwork (flexible or rigid) within the underfloor plenum to deliver cool air preferentially to perimeter zones or other critical areas of high cooling demand. Several experiments were carried out in a full-scale underfloor plenum test facility, in order to characterize all the phenomena that take place in an underfloor plenum equipped with a fabric or metal duct. Experimental data were collected for validation of a computational fluid dynamics (CFD) model of the plenum. This paper describes the first part of a more comprehensive work, whose aim is to use the validated CFD plenum model to conduct simulations of a broader range of plenum design and operational parameters. This work proves that using ductwork within the underfloor plenum reduce the temperature rise in the plenum. [ABSTRACT FROM AUTHOR]

Abstract: There is a rising interest in heating and cooling systems based on renewable energy sources. Air heating or cooling with earth-to-air heat exchangers (EAHE) is one approach for reducing ventilation heat losses and improving thermal comfort in buildings. A literature research was performed in order to analyze the design, characteristics of earth-to-air heat exchangers and whether they could be coupled with HVAC system coupling. A range of projects was compared in order to collect and summarize design suggestions. [Copyright &y& Elsevier]

Highlights: [•] Short helical shaped pipe and double U-tube heat exchangers are compared. [•] The thermal behaviour in both long and short terms is investigated. [•] The models consider the interaction between the ground and the environment. [•] The axial heat conduction affects the fluid heat carrier temperature. [•] The helical heat exchanger has better thermal performance than the double U-tube. [ABSTRACT FROM AUTHOR]

In the European Union, 40% of the overall final energy consumption is attributable to the buildings sector. A reason for such data may be found considering that the great majority of the building stock is more than 40 years old. According to the European Commission, an interesting potential lies in the refurbishment of the building sector, and heat pump technology has been recognized as one of the most cost-effective solutions to tackle the environmental issue of this sector. Regarding heat pump technology, ground-source heat pumps (GSHPs) have been proven to be the most efficient solution on equal boundary conditions. Despite this, in most EU states' markets, GSHPs hold only a small market share with respect to air-source heat pumps. In this paper, the state of art and possible future developments of GSHP technology have been reviewed together with a focus on the potential of such technology, most of all on the refurbishment of existing buildings, and on the obstacles to its spread. The state of art of borehole heat exchangers has been studied, focusing on the parameters characterizing the outside pipe and the pipe itself, i.e., pipe and grout materials. Moreover, an overview on the last developments involving refrigerants and secondary fluids is given. Finally, the design and control strategies of GSHPs have been reviewed. [ABSTRACT FROM AUTHOR]

A promising district heating concept consists of distributing the heat at temperatures below 45 °C and using booster heat pumps at the customers' substations to provide the appropriate temperature needed for space heating and domestic hot water production. As such, thermal networks would be able to abate heat losses and substantially increase the number of recoverable heat sources. At the same time, the supply temperature from the booster heat pumps can be tailored to the building supplied instead of being based on the most critical consumer. This work investigates the performance of booster heat pumps assuming network supply temperatures in the range between 15 °C and 45 °C. The impact of supply and return temperature on the levelized cost of heat for different end users was assessed. The parametric study shows the importance of the nominal network temperature difference in the design phase of the system in order to reach a good trade-off between initial investment and operating costs. The economic analysis shows that the system is already competitive with individual gas boilers provided that a local low-temperature heat source can be recovered with minor marginal costs. [ABSTRACT FROM AUTHOR]

Ground-coupled heat pumps are increasingly being utilized to heat and cool buildings. Although it is difficult to size and to predict their behavior and performance, their design can be optimized via simulations. EnergyPlus is a popular energy simulation program for modeling building heating and other energy flows and, since it is organized to consider borehole heat exchangers via the well-known g-functions approach, it can be used advantageously for that purpose. The Capacity Resistance Model is another recent numerical simulation tool devoted to ground and borehole heat exchangers. In this work, two methods to calculate the g-fucntions were analyzed, using as case-study a real office building, whose imbalance between the heat extracted and injected into the ground was found to be appreciable. The energy imbalance involves a ground temperature drift affecting the system efficiency. The results of the EnergyPlus g-functions and the Capacity Resistance Model model approaches were compared. The capacity of the two methodologies to accurately simulate this phenomenon were analysed also with reference to the available building's long-term monitoring data. The analysis showed the importance of using g-functions suitable to reflect the layout of the borehole field, in order to correctly evaluate the energy performance of the entire ground source heat pump system. [ABSTRACT FROM AUTHOR]

Simple, reliable building models have been receiving quite a bit of attention recently particularly with regard to diverse applications, such as building design for inexpert energy modellers, simulation of neighbourhood or city districts and model predictive control. The International Standard ISO 13790 and the German Guideline VDI 6007 use two different lumped-capacitance models (5R1C and 7R2C, respectively) based on deterministic, analytical procedures to identify their parameters. The current work investigates the suitability of these models in calculating peak loads and seasonal energy needs and their accuracy in estimating buildings’ dynamic behaviour. A room and an apartment were thus simulated using simplified models and with the benchmarked software TRNSYS. Four reference envelopes with different thermal insulation and heat capacities were examined in four climatic conditions. Each of the models was able to estimate quite precisely energy needs in both the heating and cooling modes, although the 7R2C model was slightly more accurate. The 5R1C model was, however, unable to follow the thermal response of the buildings during the cooling season, which in turn implied a systematic underestimation of the cooling peak load. The 7R2C model identified a significant reduction in the root mean squared error (RMSE) both in the indoor air temperature and in the heating/cooling loads with respect to the reference profiles. That model would seem then more suitable for the dynamic simulation of single thermal zones with hourly time steps in both heating and cooling modes. [ABSTRACT FROM AUTHOR]

The design phase of ground source heat pump systems is an extremely important one as many of the decisions made at that time can affect the system's energy performance as well as installation and operating costs. The current study examined the interpretation of thermal response testing measurements used to evaluate the equivalent ground thermal conductivity and thus to design the system. All the measurements were taken at the same geological site located in Molinella, Bologna (Italy) where a variety of borehole heat exchangers (BHEs) had been installed and investigated within the project Cheap-GSHPs (Cheap and efficient application of reliable Ground Source Heat exchangers and Pumps) of the European Union's Horizon 2020 research and innovation program. The measurements were initially analyzed in accordance with the common interpretation based on the first-order approximation of the solution for the infinite line source model and then by utilizing the complete solutions of both the infinite line and cylinder source models. An inverse numerical approach based on a detailed model that considers the current geometry of the BHE and the axial heat transfer as well as the effect of weather on the ground surface was also used. Study findings revealed that the best result was generally obtained using the inverse numerical interpretation. [ABSTRACT FROM AUTHOR]

Energy foundation piles can be an efficient cost-effective solution for ground source heat pump applications. As they are very different from standard ground heat exchangers, numerical or analytical models usually used to investigate their thermal performance must be carefully analysed before they can be applied. The total length of ground heat exchangers is a critically important factor in the overall design of a ground source heat pump. Ground thermal properties are the primary parameters affecting the size of ground heat exchangers. The thermal response test is the most commonly used procedure to determine the ground’s thermal conductivity. The current study investigated a thermal response test on a 20 m long energy foundation pile equipped with a double U-tube circuit. The test measurements were interpreted using both the infinite line source model and inverse numerical analysis by means of a detailed model that was able to consider both the actual geometry of the pile and the axial heat transfer. The results indicated an approximately 50% difference between the two values of ground thermal conductivity. The effect of this evaluation on the calculation of the energy piles’ total length was first investigated utilizing a method outlined in the literature. The consequences on the long term energy performance of a ground source heat pump system were then investigated using numerical simulations and taking into consideration the effect of the spacing between the foundation piles. It was found that the total length calculated using the result based on the infinite line source model was about 20% lower than that obtained using the inverse numerical approach. An approximately 10% difference in the heat pump’s seasonal energy efficiency was also found. [ABSTRACT FROM AUTHOR]

An empirical method aimed at generating maps of potential of geothermal energy exchange for shallow vertical closed-loop systems is proposed here. The method uses both geological and technological information. In particular, the ground parameters that mainly influence the heat transfer in borehole heat exchangers, the energetic parameters driving efficient operations of geothermal systems and heating and cooling requirements of a typical residential building are taken into account. Spatial modeling is carried out in a Geographic Information System leading to an effective and easy-to-use digital cartographic tool. An application of the method to four regions of southern Italy is also shown. [ABSTRACT FROM AUTHOR]

This work analyses the feasibility and sustainability of closed-loop heat-exchangers, also known as Borehole Heat Exchangers (BHEs), in shallow geothermal areas. By circulating a carrier fluid in a closed-loop of pipes installed vertically in a deep well, there is no fluid exchange between the BHEs and hot thermal groundwater, but only heat transfer. The BHEs absorb heat when in contact with the warmer subsoil, and release it to buildings. It is designed that heating is provided through a free-heating system, avoiding the need to use a Ground Source Heat Pump system or other thermal energy device. An actual application of such technique in a public building located in an important thermal area in north–east Italy is analysed in terms of its thermal impact on underground and groundwater temperature. The test area is part of the so called Euganean Thermal Basin (ETB), which is the most important thermal district in northern Italy. The ETB is located in the eastern Po river plain and is one of the most important thermal and mud-therapeutic spas in the world. More than 250 hotels offer hospitality to more than 3 million tourists every year. Almost every hotel and spa owns a well to extract thermal water at a temperature in the range 60–87 °C from the fractured carbonatic bedrock found at a depth of about 50–200 m below ground level. To preserve this fundamental resource, the local legislation does not allow extracted thermal water to be used for purposes other than therapeutic ones. Several spas and thermal wells are present in the surroundings of the concerned building and it must be verified that heat extraction by the BHE-array during its operation does not hinder the temperature of thermal wells. The analysis is carried out using a finite elements analysis code (FEFlow 6.1), simulating mass and heat transfer inside porous media. Various array configurations are simulated and it is found that an array of 4 BHEs 240 m deep provide enough thermal energy to the building decreasing by less than 2 °C the temperature of the closest well's extracted water. A feasibility analysis of a more widespread District Heating scheme in the Euganean Thermal Basin area should therefore be carried out. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ground source heat pump in geothermal basins is investigated. [•] TRT has been done to describe the ground properties. [•] Improvement of the heat pump performance is found. [•] GHE directly coupled with building is the best case in term of primary energy need. [Copyright &y& Elsevier]

Geothermal energy has the potential to contribute significantly to the CO 2 reduction targets as a renewable source for building heating and cooling but is yet under exploited, mostly due to its high initial investment cost. A lot of research is being carried out to optimise Ground Source Heat Pump (GSHP) systems' design, but a good control strategy is also fundamental to achieve long-term performance and reduced payback time. GSHP control optimisation is a non-linear dynamic optimisation problem that is influenced by multiple parameters. It can thus not be fully optimised with traditional methods. Artificial Intelligence, and in particular Machine Learning, is suited for this type of optimisation as it can learn implicit relations between parameters and can address non-linearity. This paper reviews the challenges of GSHP control and the strategies for control optimisation found in the literature, from basic rule-based system to artificial neural network-based strategies. Two principal uses of Artificial Intelligence for ground source heat pump control are identified: building a predictive model of the system that reflects its real performances and optimising the control decision in real time. However, the examples found in the literature are limited and the need to further explore the benefits of Machine Learning is identified. The latest developments in the field are reviewed to explore their potential to further improve GSHP control. The challenges of the full implementation of such algorithms are also discussed. • A review of GSHP control from rule-based systems to deep reinforcement learning. • Artificial intelligence for control predictive models and decision-making. • Recommendations on reporting of GSHP control research for benchmarking. [ABSTRACT FROM AUTHOR]

• A multi-objective MILP model is applied to the Italian and Swiss case studies. • Better overall performance of exergy upon primary energy in low-carbon contexts. • Energy Hub demand simulation is integrated with the supply side optimization. • Several energy and subsidies policies are evaluated. • Optimal operation strategies show smart trade-offs between exergy and cost. With growing concerns on global warming, exergy-based design methods for energy hubs (EHs) in the urban context have been recently investigated to promote more rational and efficient use of energy sources. This study aims to compare exergy-based multi-objective optimization for energy hubs with two primary energy-based methods. The comparison has been performed for Italy and Switzerland, two countries with diverse markets and national electricity production mixes, to indicate the generalizability of our findings. An apartment building in Vevey, Switzerland, was selected to provide domestic hot water demand and structural data to the space heating demand dynamic simulation, for which different TRY weather data have been used for the two countries. Once a superstructure for the energy supply system had been defined, a MILP framework was developed, minimizing a weighted sum of exergy and cost. Using different weights for the two objectives, a Pareto frontier was obtained for each scenario, defining the best possible trade-off solutions between economic and exergetic objectives. The same optimization methodology was performed using total or non-renewable primary energy as an objective. The use of a boiler and PV panels is preferred when primary energy-based methods are applied, while the use of heat pumps and solar thermal panels is preferred when exergy-based method is applied. As a result, the exergy-based method seems to be the most effective as the carbon intensity of the electricity decreases, providing solutions with lower CO 2 emissions and reasonable costs in the future when national electricity production will be gradually decarbonized. In addition, a sensitivity analysis of the exergy method was carried out to analyze the influence of key parameters such as energy prices and energy demand variation on the optimized energy system. In addition, the renovation scenarios of the case study building were presented, revealing different optimal setups of the energy hub as the weight of investment costs increases. [ABSTRACT FROM AUTHOR]

• A fruitful economic agreement between a mining industry and food production company. • The mine geological setting creates favorable condition for underground warehouses. • The dolomitic rock mass thermal behavior is described by a Finite Element Model. • The model is based on direct thermal conductivity measurements and monitoring data. • Compared to a surface deposit, the savings of specific energy consumption is 22% Underground food storage represents an interesting solution to the increasing demand for new food storage space, combining this demand with sustainable land exploitation. It also reduces the energy demand for food conservation, therefore limiting storage costs and greenhouse gas emissions. Moreover, atmospheric conditions can be easily controlled in underground warehouses, ensuring optimal long-term maintenance of the stored food. This paper presents a case study located in the Western Dolomites (Val Di Non, Trento, Italy), where mining activity is followed by the creation of storage space not only for food, but also for groundwater and a data hosting center. After the extraction of the dolomitic rock used in construction, underground excavated spaces are converted into warehouses, whose storage capability is improved once the inner surfaces have been protected by a gas-proof mineral hydraulic lime material, developed for this purpose. The thermal behavior of the rock mass over the first few years is analyzed by means of a Finite Element Model and compared with on-site monitoring data. Laboratory measurements of the thermal properties of the dolomite rock and the temperature data registered in the field permitted the development of a preliminary numerical model, in order to describe the heat exchange between the cavern and the rock mass and supply data to support future developments. Finally, the specific energetic consumption is compared with the one required by an aboveground deposit. [ABSTRACT FROM AUTHOR]

• Use of solar energy source in ground source heat pump applications. • Comparison of solar thermal collectors and photovoltaic hybrid panels. • Effects of climate on thermal and energy behaviour of the SAGSHP system. • The use of PVT panels increases the global COP of the system. • The multi-source energy system increases RES exploitation. The use of multi-source energy systems is a promising technical solution for the reduction of greenhouse gases emissions and, at the meantime, for enhancing the exploitation of renewable energy sources. The present paper analyses a Solar Assisted Ground Source Heat Pump system and tries to fill the gap in the literature, where a direct comparison between the consolidated solar thermal technology and the emerging and widely discussed photovoltaic thermal technology is missing. Indeed, the two different devices for the exploitation of solar energy have been analysed through dynamic simulations carried out in TRNSYS environment. Through this approach, it is possible to investigate and predict in detail the thermal and electrical behaviour of the energy system, composed by a water-to-water heat pump, which withdraws from two thermal reservoirs that are connected to a solar loop, composed either of solar thermal collectors or of photovoltaic thermal panels and to a ground loop. The heat pump is used to provide space cooling and space heating to a residential building, through fan coil terminal units or radiant floor system. Furthermore, the heat pump system assists the solar field in the production of domestic hot water. This study looks at the development of a flexible system able to work in different operating conditions. The model's boundary conditions can be changed for simulating a variety of case studies as the weather condition, the building load and the domestic hot water profile can be easily changed, together with specific components' parameters. The control strategy makes it possible to vary the setpoint temperatures for simulating different operating conditions and management choices. In this way, the user can easily adapt the model functions to a specific plant system. The operating conditions of the two systems layouts have been compared and the energy performances evaluated for three case studies characterised by the weather conditions of the European cities of Berlin (mild-cold climate), Venice (mild climate) and Barcelona (mild-warm climate), and the corresponding thermal load profile of a two-storey building with a useful floor area of 170 m2. The study shows the possibility to directly exploit the solar energy for the domestic hot water production and as a heat source for the heat pump. The results from the comparison between the two systems' configurations, with photovoltaic thermal panels and with solar thermal collectors, prove that there is the possibility to obtain a relevant improvement in the efficiency of the heat pump using photovoltaic thermal panels. The investigated multi-source energy system, moreover, allows an optimal employment of the available renewable heat sources and could easily be applied to case studies characterized by different boundary conditions. [ABSTRACT FROM AUTHOR]

• The design of a new GSHP system cannot disregard local ground thermal properties. • The ground thermal properties also affect the system long-term energetic performances. • A thermal properties database is proposed for both rocks and unconsolidated sediments. • It integrates and compares literature data with more than 400 direct measurements. When a new ground source heat exchanger field is planned, underground thermal properties input data are necessary for the correct sizing of the geo-exchange system. To support the design, the EU founded Cheap-GSHPs project developed a Decision Support System, that comprises a new database of thermal properties for both rocks and unconsolidated sediments. The thermal properties database has been developed by integrating and comparing data (1) provided by the most important international guidelines, (2) acquired from a wide literature review and (3) obtained from more than 400 direct measurements. The data are mainly thermal conductivity data, hence the convective contribution provided by groundwater flow to heat transfer is not included. This paper presents and analyses the collected database. [ABSTRACT FROM AUTHOR]