Search Results (10)

Decarbonizing building energy use requires efficient heat pumps and low-impact geothermal exchangers. A novel standalone TRNSYS Type was developed for a patented shallow horizontal ground heat exchanger (HGHE), called flat-panel (FP), designed at the University of Ferrara. Beyond simulating the FP in isolation, the Type enables coupling with other components within heat-pump configurations, allowing performance assessments that reflect realistic operating conditions. The Type was implemented in TRNSYS models of a ground-source heat pump (GSHP) and of a dual air and ground source heat pump (DSHP) to verify Type reliability and evaluate potential DSHP advantages over GSHP in terms of efficiency and ground-loop downsizing. The performance of the system was analyzed under varying HGHE lengths and DSHP control strategies, which were based on onset temperature differential $DT$. The results highlighted that shorter HGHE lines yielded higher specific HGHE performance, while higher $DT$ reduced HGHE operating time. Concurrently, the total energy extracted from the ground decreased with increasing $DT$ and reduced length, thus supporting long-term thermal preservation and allowing HGHE to operate under more favorable conditions. Exploiting air as an alternative or supplemental source to the ground allows significant reduction of the HGHE length and the related installation costs, without compromising the system performance. Full article

Geothermal heat pump systems (GHPSs) offer a sustainable and energy-efficient solution for heating and cooling buildings. Ground heat exchanger (GHE) design and configuration significantly impact on the overall performance and installation expenses of geothermal heat pump systems. This paper presents a comprehensive analysis of GHPSs, focusing on their advantages, disadvantages, key components, types, and particularly the various closed-loop GHE configurations. Detailed comparisons highlight how different designs affect thermal performance and installation costs. The findings reveal that helical GHEs offer superior thermal efficiency with reduced drilling requirements and cost savings, while coaxial GHEs, especially those using steel tubes, enhance heat transfer and enable shorter boreholes. Cost-effective options like W-type GHEs provide performance comparable to more complex systems. Additionally, triple U-tube and spiral configurations balance high efficiency with economic feasibility. The single and double U-tube remain the most common borehole geometry, though coaxial designs present distinct advantages in targeted scenarios. These insights support the optimization of vertical GHEs, advancing system performance, cost-effectiveness, and long-term sustainability in GHPS applications. Full article

Among the various approaches to agriculture, urban greenhouse farming has gained attention for its ability to address food security and disruptions to global food supply chains. However, the increasing impact of climate change and global warming necessitates sustainable methods for heating and cooling these greenhouses. In this study, we focused on the potential of slinky-coil horizontal ground heat exchangers (HGHEs) to meet the energy demands of urban greenhouses, assuming they are installed beneath the greenhouse to optimize space utilization. Climate data, an energy consumption profile for a greenhouse being designed in La Pocatière (Québec, Canada) and in-situ ground thermal properties assessments were used to build numerical models using FEFLOW and to evaluate the performance of the HGHEs simulated. Four scenarios were simulated and compared to a base case, considering the greenhouse’s maintenance of a constant temperature above an HGHE limited to the greenhouse’s dimensions. Our findings reveal that a minimum of 7.1% and 26.5% of the total heating and cooling loads of a small greenhouse (133 m² area) can be covered by HGHEs installed at a 1.5 m depth when there is no greenhouse above. When installed under a greenhouse with a constant inside temperature of 21 °C, the coverage for heating loads increases to 22.8%, while cooling loads decrease to 24.2%. Sensitivity analysis demonstrates that the constant temperature in the greenhouse reduces the system’s reliance on surface temperature fluctuations for both heating and cooling, albeit with reduced efficiency for cooling. Full article

Human interference with the Earth’s climate cannot be ignored any longer. Renewable energy sources need utmost attention in all energy sectors. For buildings, geothermal energy for heating, cooling, and domestic hot water is a sustainable solution. Horizontal ground heat exchangers (HGHE) demonstrate promising results with low installation costs. Research is focused on increasing their thermal performances by structural improvements and ground thermal proprieties improvements, with little research on using auxiliary heat to increase their performances. A numerical model for an HGHE was established to investigate the effects of auxiliary heat sources on the performances of the HGHE. The results demonstrate that heat transfer into the HGHE increases the overall ground temperature at the end of the heating season by 138.50% compared with no heat transfer from auxiliary heat sources. The ground freezing period decreased by approximately 24.74% by having a heated basement, approximately 40.20% by transferring heat with solar thermal panels, and approximately 62.88% by using both auxiliary heat sources. The difference between the undisturbed ground temperature and the ground temperature with no auxiliary heat sources at the end of the season was 3.45 °C. The difference between the undisturbed ground temperature and the ground temperature with all auxiliary heat sources resulted in 0.92 °C. Full article

Many regions in Poland face the problem of air pollution. These regions include, though are not exclusive, to health resorts, an important element of the healthcare industry. Poor air quality is mainly associated with the domestic sector, which is dominated by individual solid fuel and coal boilers. One option for reducing emissions is to use alternative energy sources for heating purposes. Therefore, the paper presents an analysis into the possibility of using low enthalpy (low temperature) geothermal energy in health resort areas. The main purpose of the article is to estimate the potential of soil and water as the lower source for a heat pump. The article presents analyses of geological and hydrogeological conditions based on which the thermal parameters of the rock mass were determined, which were thermal conductivity and unit heat output for 1800 operating hours per year. The calculated values were used to perform a spatial analysis of the data and create maps of the average thermal conductivity for horizontal ground heat exchangers (HGHE) to a depth of 2 and 10 m and vertical ground heat exchangers (VGHE) in depth ranges up to 30, 60, and 90 m. The heating power of the intakes, located in the research area, were estimated using empirical formulas. In addition, a detailed analysis of the physicochemical parameters of groundwater in terms of the requirements indicated by four heat pump manufacturers is presented. The results of the presented research makes it possible to assess the potential of low-temperature geothermal energy and to characterize the suitability of the selected location for the use of HGHE, VGHE, and wells. As a result, the discussed area was found to have a high potential for the use of ground source heat pumps and a moderate potential for the use of low-temperature systems based on groundwater. Full article

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. Full article

The efficiency of a heat pump energy system is significantly influenced by its low-temperature heat source. This paper presents the results of operational monitoring, analysis and comparison of heat transfer fluid temperatures, outputs and extracted energies at the most widely used low temperature heat sources within 218 days of a heating period. The monitoring involved horizontal ground heat exchangers (HGHEs) of linear and Slinky type, vertical ground heat exchangers (VGHEs) with single and double U-tube exchanger as well as the ambient air. The results of the verification indicated that it was not possible to specify clearly the most advantageous low-temperature heat source that meets the requirements of the efficiency of the heat pump operation. The highest average heat transfer fluid temperatures were achieved at linear HGHE (8.13 ± 4.50 °C) and double U-tube VGHE (8.13 ± 3.12 °C). The highest average specific heat output 59.97 ± 41.80 W/m² and specific energy extracted from the ground mass 2723.40 ± 1785.58 kJ/m²·day were recorded at single U-tube VGHE. The lowest thermal resistance value of 0.07 K·m²/W, specifying the efficiency of the heat transfer process between the ground mass and the heat transfer fluid, was monitored at linear HGHE. The use of ambient air as a low-temperature heat pump source was considered to be the least advantageous in terms of its temperature parameters. Full article

The paper deals with an analysis of temperatures of ground masses in the proximities of linear and slinky-type HGHE (horizontal ground heat exchanger). It evaluates and compares the potentials of HGHEs and ambient air. The reason and aim of the verification was to gain knowledge of the temperature course of the monitored low-temperature heat pump energy sources during heating periods and periods of stagnation and to analyse the knowledge in terms of the potential to use those sources for heat pumps. The study was conducted in the years 2012–2015 during three heating periods and three periods of HGHEs stagnation. The results revealed that linear HGHE had the highest temperature potential of the observed low-temperature heat pump energy sources. The average daily temperatures of the ground mass surrounding the linear HGHE were the highest ranging from 7.08 °C to 9.20 °C during the heating periods, and having the lowest temperature variation range of 12.62–15.14 K, the relative frequency of the average daily temperatures of the ground mass being the highest at 22.64% in the temperature range containing the mode of all monitored temperatures in a recorded interval of [4.10, 6.00] °C. Ambient air had lower temperature potential than the monitored HGHEs. Full article

This paper highlights the thermal performance of reclined (parallel to ground surface) and standing (perpendicular to ground surface) slinky horizontal ground heat exchangers (HGHEs) with different water mass flow rates in the heating mode of continuous and intermittent operations. A copper tube with an outer surface protected with low-density polyethylene was selected as the tube material of the ground heat exchanger. Effects on ground temperature around the reclined slinky HGHE due to heat extraction and the effect of variation of ground temperatures on reclined HGHE performance are discussed. A higher heat exchange rate was experienced in standing HGHE than in reclined HGHE. The standing HGHE was affected by deeper ground temperature and also a greater amount of backfilled sand in standing HGHE (4.20 m³) than reclined HGHE (1.58 m³), which has higher thermal conductivity than site soil. For mass flow rate of 1 L/min with inlet water temperature 7 °C, the 4-day average heat extraction rates increased 45.3% and 127.3%, respectively, when the initial average ground temperatures at 1.5 m depth around reclined HGHE increased from 10.4 °C to 11.7 °C and 10.4 °C to 13.7 °C. In the case of intermittent operation, which boosted the thermal performance, a short time interval of intermittent operation is better than a long time interval of intermittent operation. Furthermore, from the viewpoint of power consumption by the circulating pump, the intermittent operation is more efficient than continuous operation. Full article

The objective of this work was to monitor and analyse temperature changes in the ground with installed linear and Slinky-type horizontal ground heat exchangers (HGHEs), used as low-potential heat pump energy sources. Specific heat flows and specific energies extracted from the ground during the heating season were also measured and compared. The verification results showed that the average daily ground temperatures with the two HGHEs are primarily affected by the temperature of the ambient environment. The ground temperatures were higher than ambient temperature during most of the heating season, were only seldom below zero, and were higher by an average 1.97 ± 0.77 K in the ground with the linear HGHE than in the ground with the Slinky-type HGHE. Additionally, the specific thermal output extracted from the ground by the HGHE was higher by 8.45 ± 16.57 W/m² with the linear system than with the Slinky system. The specific energies extracted from the ground over the whole heating season were 110.15 kWh/m² and 57.85 kWh/m² for the linear and Slinky-type HGHEs, respectively. Full article