Numerical Investigation on Auxiliary Heat Sources for Horizontal Ground Heat Exchangers
Abstract
:1. Introduction
2. Numerical Method
2.1. Geometric Model
- the system is simulated for the heating season;
- the ground is considered homogenous with constant thermos-physical proprieties;
- the HGHE pipes are considered one-dimensional lines with heat flux input;
- the surface heat transfer is approximated into mean temperatures of the exterior air;
- the heat transfer solved with COMSOL Multiphysics is only for solids.
2.2. Initial and Boundary Conditions
2.3. Validation of the Numerical Model
3. Results
- Case 1: HGHE with no auxiliary heat sources;
- Case 2: HGHE with heated basement;
- Case 3: HGHE with heat from solar thermal panels;
- Case 4: HGHE with heat from the heated basement and solar thermal panels combined.
- Exterior temperature;
- Heat extracted and transferred inside the HGHE;
- All physical geometry-related parameters.
3.1. Case 1: HGHE with No Auxiliary Heat Sources
3.2. Case 2: HGHE Heated Basement
3.3. Case 3: HGHE with Heat from Solar Thermal Panels
3.4. Case 4: HGHE with Heat from Heated Basement and Solar Thermal Panels Combined
4. Discussion
5. Conclusions
- Heat transfer inside the HGHE from auxiliary heat sources increases the overall HGHE temperature at the end of the heating season, with 1.11 °C for case 2 (heated basement), 1.53 °C for case 3 (solar thermal panels), 2.53 °C for case 4 (both auxiliary heat sources).
- The ground freezing period decreased by 24.74% in the case of a heated basement, 40.20% by transferring heat inside the HGHE from thermal solar panels, and 62.88% by using both auxiliary sources combined.
- At pipe depth (1.2 m) in case 1, without auxiliary heat sources, the ground froze for 30 days, and for case 2, with a heated basement, the ground froze for 21 days. This indicates that by only positioning the HGHE near a heated basement, the freezing period at pipe depth can decrease by approximately 30%.
- With the use of auxiliary heat sources, the mean temperature at pipe depth can stop the temperature decrease under the freezing point for the entire heating season. In this study, for cases 3 and 4, the ground at a pipe depth of 1.2 m did not freeze for the entire duration of 181 days of the heating season.
- Transferring heat inside the HGHE contributes to stabilizing the overall temperature inside the HGHE heat reservoir for the duration of the heating season, thus reducing the negative effects that exterior temperature variation has on the ground at the surface.
- Due to the extreme variation of daily and seasonal exterior temperature, some quantity of heat from the heat transferred inside the HGHE is lost to the environment, from the ground surface to the exterior air. Residual heat is lost all the time, so smart positioning of the HGHE near residual auxiliary heat sources, such as heated basements, needs to be considered when designing heat pump systems using HGHEs.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Material | Parameter | Value | Unit |
---|---|---|---|
Density | 1742 | kg/m3 | |
Soil | Thermal conductivity | 1.5 | W/m·K |
Specific heat capacity | 1175 | J/kg·K | |
Density | 2300 | kg/m3 | |
Basement wall/slab | Thermal conductivity | 1.8 | W/m·K |
Specific heat capacity | 880 | J/kg·K | |
Pipe length | 50 | m | |
Pipe step | 50 | cm | |
Polyethylene pipe | Pipe depth | 1.2 | m |
Outer diameter | 20 | mm | |
Thermal conductivity | 0.4 | W/m·K |
Location on Geometric Model | Boundary Condition Type |
---|---|
Exterior ground surface | Temperature |
Bottom ground surface | Heat flux |
Basement wall/slab surface | Heat flux |
Pipe | Heat flux |
All other surfaces | Periodic |
Corresponding Day | Case 1 [°C] | Case 2 [°C] | Case 3 [°C] | Case 4 [°C] |
---|---|---|---|---|
Mid-October | 12.45 | 12.45 | 12.45 | 12.45 |
Mid-November | 7.68 | 8.41 | 8.73 | 8.93 |
Mid-December | 2.19 | 3.49 | 4.41 | 5.20 |
Mid-January | −2.10 | −0.80 | 1.12 | 2.91 |
Mid-February | 1.38 | 2.37 | 3.59 | 4.69 |
Mid-March | 4.63 | 5.33 | 6.35 | 7.24 |
Mid-April | 6.49 | 6.98 | 8.50 | 9.10 |
Case | Start | End | Days | Freeze Depth |
---|---|---|---|---|
1–no auxiliary heat source | 21 November | 25 February | 97 | ~1.40 m |
2–heated basement | 6 December | 16 February | 73 | ~1.20 m |
3–solar thermal panels | 10 December | 5 February | 58 | ~1.13 m |
4–both auxiliary heat sources | 14 December | 18 January | 36 | ~0.92 m |
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Share and Cite
Bulmez, A.-M.; Ciofoaia, V.; Năstase, G.; Dragomir, G.; Brezeanu, A.-I.; Iordan, N.-F.; Bolocan, S.-I.; Fratu, M.; Pleșcan, C.; Cazacu, C.E.; et al. Numerical Investigation on Auxiliary Heat Sources for Horizontal Ground Heat Exchangers. Buildings 2022, 12, 1259. https://doi.org/10.3390/buildings12081259
Bulmez A-M, Ciofoaia V, Năstase G, Dragomir G, Brezeanu A-I, Iordan N-F, Bolocan S-I, Fratu M, Pleșcan C, Cazacu CE, et al. Numerical Investigation on Auxiliary Heat Sources for Horizontal Ground Heat Exchangers. Buildings. 2022; 12(8):1259. https://doi.org/10.3390/buildings12081259
Chicago/Turabian StyleBulmez, Alexandru-Mihai, Vasile Ciofoaia, Gabriel Năstase, George Dragomir, Alin-Ionuț Brezeanu, Nicolae-Fani Iordan, Sorin-Ionuț Bolocan, Mariana Fratu, Costel Pleșcan, Christiana Emilia Cazacu, and et al. 2022. "Numerical Investigation on Auxiliary Heat Sources for Horizontal Ground Heat Exchangers" Buildings 12, no. 8: 1259. https://doi.org/10.3390/buildings12081259