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17 pages, 5421 KiB

Open AccessArticle

Thermal Characteristics of Slinky-Coil Ground Heat Exchanger with Discrete Double Inclined Ribs

by Teguh Hady Ariwibowo and Akio Miyara

Resources 2020, 9(9), 105; https://doi.org/10.3390/resources9090105 - 30 Aug 2020

Cited by 9 | Viewed by 4172

The slinky ground heat exchanger (GHE) is the most widely utilized horizontal-type GHE, however, this GHE has a low curvature coil. The GHE has poor thermal mixing, especially at a low flowrate. At this flowrate, the coil heat exchanger has similar performance to a straight tube heat exchanger. Discrete double-inclined ribs (DDIR) are well known for their good thermal mixing by generating a vortex in straight tubes. In this paper, a numerical analysis of thermal performance for the plain coil and DDIR coil is discussed. It was found that the thermal performance of the DDIR coil was slightly higher than that of the plain coil in laminar flow. In turbulent flow, the DDIR coil was superior to the plain coil only in the first 149-min operation. The first 60-min analysis shows that in laminar flow, the average heat transfer rate in the plain coil is 59 W/m and in the DDIR coil is 60.1 W/m. In turbulent flow, the average heat transfer rate is 62 W/m, and the plain coil is 62.3 W/m. The copper DDIR coil material produced a better heat transfer rate than that of the composite and High-Density Polyethylene (HDPE). Sandy clay has the highest heat transfer rate. The influence of ground thermal conductivity on the performance of the GHE is more dominant than convection in the DDIR coil. Full article

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14 pages, 2382 KiB

Open AccessArticle

Analysis and Comparison of Some Low-Temperature Heat Sources for Heat Pumps

by Pavel Neuberger and Radomír Adamovský

Energies 2019, 12(10), 1853; https://doi.org/10.3390/en12101853 - 15 May 2019

Cited by 7 | Viewed by 3067

Abstract

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

(This article belongs to the Special Issue Sustainable Energy Reviews)

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14 pages, 2402 KiB

Open AccessArticle

Analysis of the Potential of Low-Temperature Heat Pump Energy Sources

by Pavel Neuberger and Radomír Adamovský

Energies 2017, 10(11), 1922; https://doi.org/10.3390/en10111922 - 21 Nov 2017

Cited by 7 | Viewed by 3947

Abstract

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 article belongs to the Section L: Energy Sources)

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13 pages, 2837 KiB

Open AccessArticle

Monitoring and Analysing Changes in Temperature and Energy in the Ground with Installed Horizontal Ground Heat Exchangers

by Pavel Pauli, Pavel Neuberger and Radomír Adamovský

Energies 2016, 9(8), 555; https://doi.org/10.3390/en9080555 - 28 Jul 2016

Cited by 9 | Viewed by 4172

Abstract

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

(This article belongs to the Special Issue Advanced Heating and Cooling Techniques)

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17 pages, 1515 KiB

Open AccessArticle

Analysis of Short Time Period of Operation of Horizontal Ground Heat Exchangers

by Salsuwanda Selamat, Akio Miyara and Keishi Kariya

Resources 2015, 4(3), 507-523; https://doi.org/10.3390/resources4030507 - 13 Jul 2015

Cited by 13 | Viewed by 5251

Abstract

Ground source heat pump (GSHP) systems have been proven to have higher efficiency compared to conventional air source heat pump systems for space heating and cooling applications. While vertical ground heat exchangers (GHE) are favorable in GSHP installation, this type of configuration requires higher capital costs as opposed to horizontal configuration. Numerical simulation has been used to accurately predict the thermal performance of GHE. In this paper, numerical analysis of thermal performance for slinky horizontal GHE loops in different orientations and operation modes is discussed. It was found that the loop orientation is not so important due to the little effect it has on thermal performance. While the mean heat exchange rate of copper loop increases 48% compared to HDPE loop, the analysis supports the common claim that heat exchange rate is predominantly limited by the thermal conductivity of the ground. With the same amount of circulation work, the mean heat exchange rate increases by 83%–162% when operated in parallel loops operations. The performance in these operations can be further optimized to 10%–14% increase when spacing between adjacent loops was provided. The spacing helps to minimize interference of heat flow that would penalize the overall thermal performance. Full article

(This article belongs to the Special Issue Alternative Energy Sources in Developing and Developed Regions)

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16 pages, 558 KiB

Open AccessArticle

Temperatures and Heat Flows in a Soil Enclosing a Slinky Horizontal Heat Exchanger

by Pavel Neuberger, Radomír Adamovský and Michaela Šeďová

Energies 2014, 7(2), 972-987; https://doi.org/10.3390/en7020972 - 24 Feb 2014

Cited by 37 | Viewed by 7019

Abstract

Temperature changes and heat flows in soils that host “slinky”-type horizontal heat exchangers are complex, but need to be understood if robust quantification of the thermal energy available to a ground-source heat pump is to be achieved. Of particular interest is the capacity of the thermal energy content of the soil to regenerate when the heat exchangers are not operating. Analysis of specific heat flows and the specific thermal energy regime within the soil, including that captured by the heat-exchangers, has been characterised by meticulous measurements. These reveal that high concentrations of antifreeze mix in the heat-transfer fluid of the heat exchanger have an adverse impact on heat flows discharged into the soil. Full article

(This article belongs to the Special Issue Geothermal Energy: Delivering on the Global Potential)

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