Monitoring and Analysing Changes in Temperature and Energy in the Ground with Installed Horizontal Ground Heat Exchangers
Abstract
:1. Introduction
- Analyse temperature changes in the ground with a linear HGHE and a Slinky-type exchanger during the heating season;
- Assess the effect of the HGHE configuration on the temperature values and distribution in the ground;
- Assess the effect of the HGHE configuration on the specific heat flows and specific energies extracted from the ground.
- (a)
- The ground temperatures will be largely above zero during the heating season for both exchanger types. The ground temperatures in the exchanger area will be rarely below zero;
- (b)
- The temperatures of the ground with the linear HGHE will be higher than those with the Slinky-type exchanger;
- (c)
- The specific heat flows and specific energies extracted from the ground by the HGHE will be higher for the linear HGHE type than for the Slinky type.
2. Materials and Methods
2.1. Measurement Methods
2.2. Method to Determine the Development of the Average Daily Temperatures
- = ground temperature (°C)
- = mean ground temperature (°C)
- = oscillation amplitude around the temperature (K)
- τ = number of days from the start of measurement (day)
- ϕ = initial phase of oscillation (rad)
- Ω = angular velocity (2π/365 rad/day)
3. Results and Discussion
3.1. Basic Ground Heat Parameters
3.2. Ground Temperatures During the Heating Season
3.3. Heat Flows and Specific Energies Extracted from the Ground
4. Conclusions
- The average daily ground temperature was primarily influenced by the ambient temperature te irrespective of the HGHE type. The average daily ground temperatures above the HGHEs during the heating season decreased toward the ground surface. Ground sensitivity to short-time ambient temperature changes has been noticed by Hepburn et al. [15], Popiel et al. [12], Inalli, Esen [5], and Zarrella and De Carli [17];
- The ground temperature near the HGHE was higher than ambient temperature te during 68.8% (linear HGHE) and 53.6% (Slinky-type HGHE) of the heating season. Ambient temperature was higher than the ground temperature particularly towards the end of the heating season. The importance of higher temperatures of a low-potential source for a heat pump has been pointed to by De Swardt, Meyer [11], as well as by Hepburn et al. [15];
- The average daily ground temperatures within the HGHE area were below zero only in the setting with the Slinky-type HGHE, and this was particularly toward the end of the heating season. Hypothesis a) formulated at the beginning of this paper was thereby confirmed;
- The average daily ground temperature within the HGHE area was 1.97 ± 0.77 K higher in the setting with the linear HGHE than in the setting with the Slinky-type HGHE. The minimum daily ground temperatures were also higher in the former setting than in the latter setting. Hypothesis b) was thereby confirmed;
- The reference average daily ground temperature beyond the HGHE area during the heating season was only 2.22 ± 1.23 K (linear HGHE) and 3.05 ± 1.41 K (Slinky-type HGHE) higher than that within the HGHE area. The differences between the reference ground temperatures and the temperatures within the HGHE areas are in accordance with the VDI recommendations [18];
- The specific energies extracted from the ground during a day of the heating season qd were higher by an average 239.91 ± 198.35 Wh/(m2·day) in the setting with the linear HGHE than in the setting with the Slinky-type HGHE. The specific energies extracted from the ground during the entire heating season were 110.15 kWh/m2 for the linear HGHE and 57.85 kWh/m2 for the Slinky-type HGHE. Hypothesis c) was thereby confirmed;
- The average specific thermal outputs qL extracted from the ground by the HGHE were 8.45 ± 16.57 W/m2 higher in the setting with the linear HGHE than in the setting with the Slinky-type HGHE. Hypothesis c) was thereby confirmed. Similar thermal output levels were reported by Wu et al. [20];
- Incident solar radiation plays an important role in the ground energy potential. The average incident solar radiation intensity during the heating season was Is.r. = 66.27 ± 55.35 W/m2. The total energies of solar radiation hitting the ground surface during the heating season were IΣd,s.r. = 350 kWh/m2. The data obtained by Hepburn et al. [15] and Wu et al. [19] were similar.
Author Contributions
Conflicts of Interest
Nomenclature
Abbreviations
HGHE | Horizontal Ground Heat Exchanger |
VGHE | Vertical Ground Heat Exchanger |
GSHP | Ground Source Heat Pump |
COP | coefficient of performance |
EHPA | European Heat Pump Association |
λ | thermal conductivity coefficient (/W/m·K) |
C | specific heat capacity (MJ/m3·K) |
a | temperature conductivity coefficient (m2/s) |
t | temperature (°C) |
mean temperature (°C) | |
w | volumetric moisture (%) |
ΔtA | oscillation amplitude around the temperature (K) |
τ | number of days from the start of measurement (day) |
ϕ | initial phase of oscillation (rad) |
Ω | angular velocity (2·π/365 rad/day) |
determination index (-) | |
Is.r. | solar radiation intensity (W/m2) |
q | specific thermal output (W/m2) |
qd | specific energy (Wh/m2) |
Substript
L | linear HGHE |
S | Slinky-type HGHE |
e | ambient air |
G | ground |
R | regression function |
d | day |
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Depth (m) | t (°C) | w (%) | λ (W/m·K) | C (MJ/m3·K) | a (m2/s) |
---|---|---|---|---|---|
0.22 | 12.36 | 26.20 | 1.28 | 2.14 | 6.00 × 10−7 |
0.30 | 11.31 | 30.30 | 1.38 | 2.24 | 6.17 × 10−7 |
0.60 | 11.90 | 27.29 | 1.15 | 1.73 | 6.66 × 10−7 |
0.90 | 12.16 | 32.30 | 1.41 | 2.12 | 6.67 × 10−7 |
1.20 | 12.29 | 34.9 | 1.50 | 1.99 | 7.55 × 10−7 |
1.50 | 13.37 | 40.50 | 1.76 | 2.40 | 7.33 × 10−7 |
1.60 | 13.68 | 37.50 | 1.65 | 2.27 | 7.24 × 10−7 |
Temp. (°C) | Average (°C) | Min. (°C) | Max. (°C) | ΔtA (K) | ϕ (rad) | (°C) | (-) |
---|---|---|---|---|---|---|---|
tLR1 | 8.04 ± 4.74 | 2.68 | 17.08 | 6.706 | 1.755 | 9.617 | 0.977 |
tLR2 | 7.08 ± 4.76 | 2.00 | 17.14 | 7.207 | 1.922 | 9.290 | 0.978 |
tLR3 | 7.23 ± 4.78 | 1.26 | 18.01 | 7.312 | 1.948 | 9.551 | 0.972 |
tLR5 | 6.55 ± 4.57 | 1.61 | 17.43 | 7.429 | 2.085 | 9.290 | 0.950 |
tLR7 | 6.06 ± 4.20 | 1.71 | 17.33 | 7.243 | 2.225 | 9.057 | 0.903 |
tLR8 | 5.94 ± 4.39 | 0.66 | 17.32 | 7.627 | 2.238 | 9.126 | 0.904 |
tLR9 | 5.86 ± 4.55 | 0.72 | 17.29 | 8.024 | 2.302 | 9.355 | 0.855 |
tLR11 | 9.30 ± 3.74 | 5.23 | 16.74 | 5.337 | 1.772 | 10.591 | 0.984 |
Temp. (°C) | Average (°C) | Min. (°C) | Max. (°C) | ΔtA (K) | ϕ (rad) | (°C) | (-) |
---|---|---|---|---|---|---|---|
tSR1 | 5.64 ± 4.76 | 0.84 | 16.51 | 7.397 | 1.987 | 8.096 | 0.969 |
tSR2 | 5.11 ± 4.94 | −0.19 | 16.54 | 7.736 | 2.022 | 7.783 | 0.946 |
tSR3 | 5.64 ± 4.82 | 0.99 | 16.71 | 7.788 | 2.057 | 8.435 | 0.969 |
tSR4 | 5.17 ± 4.92 | 0.36 | 17.08 | 8.095 | 2.096 | 8.187 | 0.961 |
tSR5 | 5.10 ± 4.95 | 0.13 | 17.16 | 8.110 | 2.091 | 8.108 | 0.958 |
tSR6 | 5.23 ± 4.75 | 0.60 | 17.03 | 8.034 | 2.154 | 8.374 | 0.949 |
tSR8 | 4.96 ± 4.57 | 0.41 | 16.91 | 8.198 | 2.285 | 8.493 | 0.905 |
tSR9 | 4.71 ± 4.51 | 0.31 | 16.80 | 8.421 | 2.376 | 8.531 | 0.804 |
tSR10 | 8.16 ± 4.05 | 3.87 | 16.51 | 5.947 | 1.845 | 9.790 | 0.983 |
Physical Quantity | Min. | Average | Max. |
---|---|---|---|
te (°C) | −9.15 | 5.44 ± 5.57 | 19.99 |
qL (W/m2) | 1.36 | 38.49 ± 19.74 | 84.17 |
qS (W/m2) | 0.00 | 30.08 ± 18.47 | 76.21 |
qd,L (kWh/m2·day) | 2.22 | 0.51 ± 0.33 | 1.66 |
qd,S (kWh/m2·day) | 0.00 | 0.27 ± 0.20 | 1.09 |
Is.r. (W/m2) | 3.52 | 66.27 ± 55.35 | 270.29 |
Id,s.r. (kWh/m2·day) | 0.085 | 1.61 ± 1.35 | 6.49 |
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Pauli, P.; Neuberger, P.; Adamovský, R. Monitoring and Analysing Changes in Temperature and Energy in the Ground with Installed Horizontal Ground Heat Exchangers. Energies 2016, 9, 555. https://doi.org/10.3390/en9080555
Pauli P, Neuberger P, Adamovský R. Monitoring and Analysing Changes in Temperature and Energy in the Ground with Installed Horizontal Ground Heat Exchangers. Energies. 2016; 9(8):555. https://doi.org/10.3390/en9080555
Chicago/Turabian StylePauli, Pavel, Pavel Neuberger, and Radomír Adamovský. 2016. "Monitoring and Analysing Changes in Temperature and Energy in the Ground with Installed Horizontal Ground Heat Exchangers" Energies 9, no. 8: 555. https://doi.org/10.3390/en9080555