# Energy Pile Field Simulation in Large Buildings: Validation of Surface Boundary Assumptions

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## Abstract

**:**

## 1. Introduction

## 2. Validation of a COMSOL Model for a Single Pile against Measured Data

#### 2.1. Method

#### 2.2. Results

## 3. Ground Surface Boundary Analysis in COMSOL

#### 3.1. Method

#### Brine Flow Modelling

#### 3.2. Results

## 4. IDA-ICE Borehole Model Validation against COMSOL

#### 4.1. Method

#### 4.2. Results

## 5. Impact of Boundary Conditions on Energy Efficiency Calculations

#### 5.1. Method

#### 5.2. Results

## 6. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## Abbreviations

GHE | Ground Heat Exchangers |

FEM | Finite Element Method |

FDM | Finite Difference Method |

b.c. | Boundary Conditions |

Nomenclature | |

$\rho $ | Density [kg/m${}^{3}$] |

${c}_{p}$ | Specific heat at constant pressure [kJ/(kgK)] |

T | Temperature [°C] |

$\lambda $ | Thermal conductivity [W/(mK)] |

$\mathsf{\Delta}t$ | Time step [h] |

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**Figure 1.**Energy piles (circles) and monitoring layout (undisturbed T monitored at the isolated triangle) [53].

**Figure 3.**COMSOL simulation for the Innova office building reference pile. (

**Left**) the pile geometry (sensor T31 in red). (

**Right**) the result after t = 4800 h.

**Figure 4.**Measured (dashed) vs. COMSOL simulated (solid) temperatures for a single pile, sensors at 0.5 m and 4.5 m. Surface temperature in small dashes.

**Figure 8.**2D COMSOL result after 2400 hrs for (

**left**) (a) only floor and (

**right**) (b) floor + soil as upper boundary.

**Figure 9.**Average temperature in the highlighted area of Figure 8 with fluid flow modelling (solid) compared with no fluid modelling (dashed).

**Figure 10.**Average temperature in the highlighted slab portion, (a) floor (dashed) vs. (b) floor + soil (solid). T [°C] values for the last point in bold.

**Table 1.**Temperature sensors location for the reference energy pile [53].

Temperature Sensor | Depth, m |
---|---|

Ground surface | 0 |

Pile top | −0.5 |

T28 | −0.5 |

T29 | −2.5 |

T30 | −4.5 |

T31 | −6.5 |

T32 | −8.5 |

T33 | −10.5 |

T34 | −12.5 |

T35 | −14.5 |

T36 | −16.5 |

**Table 2.**Soil layer properties for the single pile simulation [53].

Layer nr | Depth, m | $\mathit{\rho}$, t/m${}^{3}$ | ${\mathit{c}}_{\mathit{p}}$, kJ/kgK | $\mathit{\lambda}$, W/mK |
---|---|---|---|---|

1 | 3.73 | 1.4 | 1.8 | 0.87 |

2 | 5.67 | 1.72 | 1.82 | 1.24 |

3 | 5.84 | 1.66 | 1.78 | 1.08 |

4 | 6.5 | 1.80 | 1.71 | 1.25 |

5 | 6.67 | 1.83 | 1.72 | 1.39 |

6 | 6.84 | 1.91 | 1.57 | 1.42 |

7 | 12.9 | 2.03 | 1.40 | 1.89 |

8 | 12.91 | 2.01 | 1.39 | 1.81 |

9 | 15.90 | 2.06 | 2.32 | 1.92 |

10 | 15.91 | 2.05 | 2.33 | 1.91 |

11 | 19 | 1.99 | 2.39 | 1.53 |

12 | 19.01 | 1.95 | 2.41 | 1.5 |

13 | 23.3 | 2.28 | 2.10 | 2.52 |

14 | 26.7 | 2.21 | 2.16 | 2.44 |

17 | 18 | 19 | 20 |

13 | 14 | 15 | 16 |

9 | 10 | 11 | 12 |

5 | 6 | 7 | 8 |

1 | 2 | 3 | 4 |

Case | Floor Slab Heat Flux, kWh/a | Heating Need, kWh/a | Heat Flux, % Difference | Heating Need, % Difference |
---|---|---|---|---|

COMSOL | 24066 | 142900 | - | - |

IDA-ICE slab | 24073 | 142580 | 0.03% | 0.2% |

IDA-ICE outlet | 37127 | 150196 | 54% | 5% |

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## Share and Cite

**MDPI and ACS Style**

Ferrantelli, A.; Fadejev, J.; Kurnitski, J.
Energy Pile Field Simulation in Large Buildings: Validation of Surface Boundary Assumptions. *Energies* **2019**, *12*, 770.
https://doi.org/10.3390/en12050770

**AMA Style**

Ferrantelli A, Fadejev J, Kurnitski J.
Energy Pile Field Simulation in Large Buildings: Validation of Surface Boundary Assumptions. *Energies*. 2019; 12(5):770.
https://doi.org/10.3390/en12050770

**Chicago/Turabian Style**

Ferrantelli, Andrea, Jevgeni Fadejev, and Jarek Kurnitski.
2019. "Energy Pile Field Simulation in Large Buildings: Validation of Surface Boundary Assumptions" *Energies* 12, no. 5: 770.
https://doi.org/10.3390/en12050770