Testing of a dual-source heat pump coupled with flat-panel ground heat exchangers

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Enhancement of shallow ground heat exchanger with phase change material

Heat pumps perform better when coupled with ground as thermal source than with air. In literature, several studies and applications suggest and analyse the use of phase change materials (PCMs) coupled with single or double U-tube vertical borehole heat exchangers (BHEs). Usually, PCMs are mixed with the grouting material during the installation. An alternative solution to vertical BHEs is the use of horizontal ground heat exchangers (HGHEs). The present work investigates the possibility of coupling PCMs with a flat-panel HGHE installed inside a trench 2 m under the ground surface. The study analyses the case in which PCMs are adjacent to the HGHE, taking a cue from alternative coupling technologies which have PCMs added to the backfilling material of the trench where the HGHE is installed. The analysis has been conducted with COMSOL software tool. A simulation model of the system was developed to carry out a parametric analysis. The objective of the simulations is the investigation of the thermal behaviour of the HGHE patent pending coupled with PCMs under cycles of operation which represent how the heat pump could work in GSHP system. The results show the meaningful difference of using the PCM in direct contact with the HGHE

Energy Analysis of a Dual-Source Heat Pump Coupled with Phase Change Materials

Installation costs of ground heat exchangers (GHEs) make the technology based on ground-coupled heat pumps (GCHPs) less competitive than air source heat pumps for space heating and cooling in mild climates. A smart solution is the dual source heat pump (DSHP) which switches between the air and ground to reduce frosting issues and save the system against extreme temperatures affecting air-mode. This work analyses the coupling of DSHP with a flat-panel (FP) horizontal GHE (HGHE) and a mixture of sand and phase change materials (PCMs). From numerical simulations and considering the energy demand of a real building in Northern Italy, different combinations of heat pumps (HPs) and trench backfill material were compared. The results show that PCMs always improve the performance of the systems, allowing a further reduction of the size of the geothermal facility. Annual average heat flux at FP is four times higher when coupled with the DSHP system, due to the lower exploitation. Furthermore, the enhanced dual systems are able to perform well during extreme weather conditions for which a sole air source heat pump (ASHP) system would be unable either to work or perform efficiently. Thus, the DSHP and HGHE with PCMs are robust and resilient alternatives for air conditioning

Study on thermal performance of a PCM enhanced hydronic radiant floor heating system

Abstract Radiant floor systems enhanced with Phase Change Materials (PCMs) could achieve significant energy savings while improving the thermal comfort of occupants in lightweight buildings. Effective integration of PCMs typically requires customised solutions based on a comprehensive analysis due to their complex nature. The objective of the present study is the experimental and numerical investigation of a hydronic radiant floor heating system integrated with macroencapsulated PCM. Experimental tests were carried out on a laboratory-scale by the University of Ferrara, Italy, within the H2020 European project IDEAS. A 2D model was then implemented in COMSOL Multiphysics and calibrated in steady as well as in transient state according to the experimental tests. The behaviour of the system, including temperature distribution and heat flux, were analysed under different conditions. The impact of using dry and wet sand, as well as the effect of the position of PCM – above or under heating pipes – on thermal performance, were investigated. Results showed that the use of high thermal conduction in mortar increases much faster the overall performance of the PCM integrated underfloor heating system. Furthermore, the coupling technology with PCM containers installed under piping significantly enhances the positive effect of wet sand

Role of phase change materials in backfilling of flat-panels ground heat exchanger

The behaviour of a multi-source heat pump system coupled with phase change materials (PCMs) is discussed in this manuscript, as based on selected data collected during one-year testing at the TekneHub Laboratory of the University of Ferrara (Italy), as a synergic prototype setup of two European projects: IDEAS, an H2020 project, and CLIWAX, an EFDR project. Three geothermal loops of novel shallow FlatPanels ground heat exchangers (GHX) provide the coupling of a water-to-water heat pump with the ground, as backfilled with sand, a mixture of sand and granules with paraffins and containers filled in with hydrated salts. Furthermore, two hybrid photovoltaic panels and a dry-cooler complete the exploitable thermal sources landscape. Finally, a control unit manages all the elements for the exploitation of the different thermal sources. How the increased underground thermal energy storage is driven by PCMs has been investigated by means of specific tests, and compared with the standard case of backfilling sand. Results confirm that PCMs can compensate peak loads occurring during hard weather conditions. Good performances of the multi-source heat pump were found, with a winter coefficient of performance always higher than 5. Finally, the application of PCM in summer should be preferred in climatic zones with hot summers and cold winters, With evidence, latent heat, thermal conductivity and melting point of PCMs should be tuned accordingly to the energy requirements and the local ground thermal conditions. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

Modelling of shaded and unshaded shallow-ground heat pump system for a residential building block in a Mediterranean climate

Heat pumps may be coupled to shallow-ground geothermal fields and used for the purpose of space heating and cooling of buildings. However, quite often it is not possible to locate the geothermal field in cleared grounds, especially in cities where building density is high and land has a high premium. This leads to the possibility of burying the geothermal field under the basement of new building blocks, before construction of the building. In the present work, the shaded-unshaded arrangement is numerically studied by coupling the software DesignBuilder-EnergyPlus to assess the building's energy requirement with the software FEFLOW to solve the heat transfer equation in porous media. Assuming a standard residential building block, the coupling between the two software is performed by assigning the thermal energy requirement for air conditioning, as calculated by EnergyPlus, to a flat-panel typology of ground heat exchanger simplified in a 2D FEFLOW's domain. The results show that it is necessary to opt for a dual-source heat pump (air/geothermal) system to ensure that the ground is not frozen or over-heated at peak times and to improve the overall performance of the system.peer-reviewe

Field behaviour of a flat panel ground heat exchanger

An experimental plant has been devised to investigate the behaviour of a novel type of horizontal ground heat exchanger (GHX), aiming to improve the performance of ground-source heat pumps for space heating and cooling. The GHX system is composed by hollow flat panels, which have been installed edgeways in shallow trenches two meters deep in soil. The hydraulic closed loop and the surrounding soil have been equipped with several digital sensors to monitor the ground temperature distribution and the plant in real-time. The behaviour has been tested for two years in several operating carried out especially in summertime. The specific power of heat transfer for surface-unit achieves considerable values, and no over-heating conditions were measured at the soil surface. Moreover, the GHX showed to be able to involve a large soil volume, and this behaviour enables high energy performance, at least in cooling mode. After few months of inactivity, the natural ground heat transfer erased the memory of the energy exploitation carried out by the GHX. Thus, unlike with the vertical systems, long-term subsurface thermal energy build-up or depletion wouldn’t be expecting by shallow GHXs.Alternative Technologies Ltd., Energy Investment Ltd, JMV Vibro Blocks Ltd., Solar Engineering Ltd. and Solar Solutions Ltd.peer-reviewe

Solar gain mitigation in ventilated tiled roofs by using phase change materials

Several passive cooling design techniques are known for reducing solar heat gain through building envelope in summer season. These include the use of phase change materials (PCM), which has received an increased attention over the last years, and the strategy of increasing the above-sheathing ventilation (ASV) in ventilated roofs. However, few studies combine both technologies to maximise the building resilience in hot season. The effect of including a PCM layer into a ventilated roof is numerically analysed here in two different configurations: firstly, laid on the roof deck (PCM1 case) and, secondly, suspended in the middle of the ASV channel (PCM2 case). A computational fluid dynamics model was implemented to simulate airflow and heat transfer around and through the building envelope, under 3 days of extreme hot conditions in summer with high temperatures and low wind speed. Results showed slight differences in terms of mean temperatures at the different roof layers, although temperature fluctuations at deck in the PCM1 case were smaller than half of those estimated for the benchmark case. However, PCM2 configuration achieved a daily reduction of about 10 Wh/m(2) (18%) in building energy load with respect to the benchmark case, whilst PCM1 got only 4% due to the lower ventilation at night time. Therefore, a suspended PCM layer in the ASV channel would be a better measure in terms of energy performance than laid on the deck surface, although this last option significantly decreases thermal stress of the insulation layer

Experimental performance of a dual-source heat pump coupled with shallow horizontal ground heat exchangers

The present paper analyses the preliminary results about the performance of a dual-source heat pump (DSHP), able to switch between air and ground according to operating rules for the air-conditioning system. The prototype is composed by a common air-to-air heat pump whose refrigerant circuit has been modified for coupling through a plate heat exchanger with a geothermal closed loop, laid horizontally and edgeways into a shallow trench. As ground heat exchanger (GHE), the Flat-Panel solution has been chosen due to its higher performance in comparison with similar GHEs, that makes this solution suitable for the issue. To over/underload the GHE system according the air conditioning energy load, the closed loop can be reduced by means of valves. The switching between air and ground is then automatized with a control unit which controls valves according to rules based on air and ground temperature, air humidity, and frosting conditions at the evaporator. The prototype is fully monitored in terms of temperatures, pressures, flow rate and electricity supply, both at the refrigerant circuit and the closed loop. Moreover, a dedicated monitoring system collects data about weather conditions, ground temperature at several depths and distances from the Flat-Panels, and finally their heat flux. The heating performance of the DSHP is taken in comparison with the standard air-source solution, with evidence of the better behaviour, even for a closed loop drastically partialized.peer-reviewe

Phase Change Material Evolution in Thermal Energy Storage Systems for the Building Sector, with a Focus on Ground-Coupled Heat Pumps

The building sector is responsible for a third of the global energy consumption and a quarter of greenhouse gas emissions. Phase change materials (PCMs) have shown high potential for latent thermal energy storage (LTES) through their integration in building materials, with the aim of enhancing the efficient use of energy. Although research on PCMs began decades ago, this technology is still far from being widespread. This work analyses the main contributions to the employment of PCMs in the building sector, to better understand the motivations behind the restricted employment of PCM-based LTES technologies. The main research and review studies are critically discussed, focusing on: strategies used to regulate indoor thermal conditions, the variation of mechanical properties in PCMs-based mortars and cements, and applications with ground-coupled heat pumps. The employment of materials obtained from wastes and natural sources was also taken in account as a possible key to developing composite materials with good performance and sustainability at the same time. As a result, the integration of PCMs in LTES is still in its early stages, but reveals high potential for employment in the building sector, thanks to the continuous design improvement and optimization driven by high-performance materials and a new way of coupling with tailored envelopes