# Comparison of Single- and Multipipe Earth-to-Air Heat Exchangers in Terms of Energy Gains and Electricity Consumption: A Case Study for the Temperate Climate of Central Europe

^{*}

## Abstract

**:**

## 1. Introduction

- the paper presents the results of experimental studies on pressure losses in multipipe heat exchangers made of 3, 5 and 7 parallel branches;
- these results were then used to compare pressure losses in these exchangers and analogous single-pipe exchangers (with the same total length of pipes used in their construction) for different airflows;
- then, analyses of the annual heat and cool gains and the annual electricity consumption by the EAHE supporting fan were conducted;
- finally, an analysis was carried out involving the search for the equivalent length of a single-pipe heat exchanger that would replace a given multipipe heat exchanger in terms of heat gains (the same heating capacity instead of the same length of the pipes)—analyses were performed for two boundary branch lengths and two selected airflows.

## 2. Materials and Methods

#### 2.1. Experimental Setup for Pressure Loss Measurements

- w—velocity of the flowing air (m/s);
- d—internal diameter of the pipe (m);
- ν—kinematic viscosity of fluid (in this case: air) (m
^{2}/s).

- 3 branch-pipes, L = 76d, d = PP DN50, d
_{main}= PP DN50; - 5 branch-pipes, L = 76d, d = PP DN50, d
_{main}= PP DN50; - 7 branch-pipes, L = 76d, d = PP DN50, d
_{main}= PP DN50.

#### 2.2. Calculations of Annual Energy Gains

#### 2.2.1. General Assumptions and Equations

- j−hour number of the year = 1 to 8760;
- $\Delta t-$time step, 1 h.

- n—number of branches in multipipe EAHE (3, 5 or 7), or 1 in the case of a single-pipe structure.

- ${\dot{m}}_{i,j}$—mass flowrate of air in the i branch of the multipipe exchanger, or total mass flowrate in the case of a single-pipe structure (kg/s);
- ${c}_{j}$—specific heat of air in j hour of the year (J/(kgK));
- ${t}_{i,j}$—temperature at the outlet of i branch of the exchanger (°C);
- ${t}_{e,j}$—temperature at the inlet to the exchanger (external air temperature) in the j hour of the year (°C).

- ${t}_{g,k}$—temperature of the ground at a given depth on day k of the year (°C);
- ${t}_{e,j}$—external air temperature in j hour of the year (°C);
- ${U}_{i,j}$—total heat transfer coefficient (W/(mK));

- D—external diameter of a pipe (m);
- d—internal diameter of the pipe (m);
- ${\lambda}_{w}$—thermal conductivity of the material constituting the pipe’s wall (W/(mK)).

- ${\lambda}_{a,j}$—thermal conductivity of air in j hour of the year, calculated as the average of the ground temperature at given depth and external air temperature (W/(mK)).

- $R{e}_{i,j}^{}$—Reynolds number for i branch and at j hour of the year,
- $P{r}_{j}^{}$—Prandtl number of air at j hour of the year.

- ${X}_{\mathrm{e},\text{}j}$—humidity content in the external air at j hour of the year, taken from climatic data (g/kg);
- ${X}_{\mathrm{N},i,j}$—humidity content at the i branch outlet and in j hour of the year (g/kg);
- $r-$heat of condensation of water vapor (J/kg).

- ${p}_{\mathrm{s},i,j}$—water vapor saturation pressure calculated at t
_{i,j}with Equation (14) from [54] (Pa); - $p$—actual pressure of air (Pa).

- a
_{0}= 31.6885; - a
_{1}= 0.130986; - a
_{2}= 2.52493·10^{−5}.

#### 2.2.2. Soil Temperature at a Given Depth throughout the Year

- k—number of the day in the year, range: 1–365;
- H—depth of the exchanger placement, assumed as 2 m;
- a
_{g}—thermal diffusivity of the ground (m^{2}/s); - k
_{v}—vegetation coefficient, assumed 0.85; - A
_{s}—annual amplitude of the average monthly temperature of the dry thermometer, assumed for Poznan as 10.1 K; - T
_{m}—average annual temperature of the outside air, assumed for Poznan as 8.26 °C; - ΔT
_{m}—difference between the temperature, T_{m}, and the average temperature of the ground at depth H = 10 m, assumed for Poznan as 2.24 K; - T
_{o}—phase shift, assumed for Poznan as 21 days.

_{g}= 4.40 · 10

^{−7}m

^{2}/s (for dry sand, [44]), which resulted from the following thermal parameters:

- density: ρ
_{g}= 1600 kg/m^{3}; - specific heat: c
_{g}= 753 J/(kgK); - thermal conductivity: λ
_{g}= 0.53 W/(mK).

#### 2.2.3. Electric Energy and Primary Energy for Driving the Fan

- ${V}_{j}$—total airflow through the EAHE in j hour during the year (m
^{3}/s); - $\Delta {p}_{j}$—pressure drop at EAHE in j hour during the year (Pa);
- ${\eta}_{\mathrm{fan}}$—total efficiency of the fan (−).

## 3. Results

#### 3.1. Experimental Flow Characteristics of Multipipe EAHEs

#### 3.2. Total Pressure Losses in Single-Pipe and Multipipe EAHEs

- pipe diameters in single and multipipe EAHE were assumed to be the same and equal to PP DN200 (internal diameter d = 0.1844 m);
- the length of a one-pipe heat exchanger used for calculations resulted from the assumption of the same heat exchange surface between the compared exchangers; i.e., if, for example, a single-pipe exchanger was compared with a five-pipe exchanger with a length for each branch L = 150d, the length of the one-pipe heat exchanger used for calculations was 5 × 150d;
- in a single-pipe heat exchanger, additional pressure losses were assumed when changing the direction of the pipe every 50 m in order to take into account the limited ground surface for the heat exchanger’s construction.

- λ—friction factor calculated from the Blasius formula = 0.3164/Re
^{0.25}, (−); - n—number of branches of equivalent multipipe EAHE (3, 5 or 7);
- L—length of single branch-pipe of the equivalent multipipe EAHE (m);
- d—internal diameter of pipe (m);
- $\zeta $—local pressure loss coefficient, assumed as 1 for a single elbow, taken from the handbook for engineering application [57], (−);
- $\rho $—air density (kg/m
^{3}); - w—air velocity in pipe (m/s).

- k
_{m}—average coefficient of total pressure losses for exchangers constructed of 3, 5 and 7 pipes (−); - w—air velocity in the manifold (in the main pipe, before division of air streams between branches of the exchanger) (m/s).

- w—air velocity in the manifold (in the main pipe, before separation of air streams between branches of the exchanger) (m/s);
- w
_{m}—average air velocity in a single branch-pipe, assuming the ideal distribution of air among all pipes: ${w}_{m}=w/n$, where n is a number of parallel branch-pipes (m/s); - λ—friction factor in a single branch-pipe calculated for w
_{m}; for laminar airflow, λ = 64/Re; for turbulent air flow, λ was calculated as 0.3164/Re^{0.25}.

#### 3.3. Energy Consuption for Fan Operation during a Year

- time of operation: one year;
- nominal (maximum) airflow: 600 m
^{3}/h; - air flowrate changes during the single day in two variants: 100% of the time at maximum airflow or scheduled system usage. Schedule is presented in Table 4 (the schedule is representative of a building wherein users are fully staffed from 8 a.m. to 4 p.m. and performance is reduced outside of these hours);
- days of operation during the year: 250 (assuming periods in which the EAHE is not used);
- energy consumption for fan operation calculated for a single day and added day by day, taking into consideration the number of days on which the EAHE is used;
- total efficiency of the fan: 39%.

#### 3.4. Full-Year Heating and Cooling Gains and Energy Cost of Harvesting Geothermal Energy

^{3}/h. This is a relatively small value, which, assuming the hygienic standard of the amount of air per one person at the level of approximately 30 m

^{3}/h, is sufficient for the ventilation of rooms used by 20 people. The results of the above analysis showed that in terms of thermal efficiency, single-pipe exchangers could replace multipipe exchangers, but they caused higher pressure losses and thus higher energy and primary energy consumption for the fan drive. However, by using larger pipe diameters, correspondingly lower pressure losses can be obtained. To check whether the same conclusions were valid for larger air flows, analogous calculations of energy consumption were carried out for exchangers that could provide fresh air for a building used by 50 people, i.e., for a nominal air stream of 1500 m

^{3}/h. The results are presented in Figure 13 and Figure 14, in which energy demand for fan operation during a year is presented. The equivalent lengths of the single-pipe heat exchangers that replace multipipe heat exchangers with given numbers of branches in the context of thermal performance (heat gained during the year) are also shown in Figure 13 and Figure 14.

## 4. Discussion

^{3}/h, a seven-pipe EAHE with a single branch length of 14 m DN200 (a total of 7 × 14 = 98 m of DN200 pipe) could be replaced in terms of heat exchange with a single-pipe heat exchanger with a diameter of DN250 and a length of 35.5 m (35.5 m of DN250 pipe), with the annual electricity consumption lower by approximately 35%. In the case of a ventilation airflow of 1500 m

^{3}/h, a seven-pipe EAHE with a single branch length of 54.4 m DN200 (total 7 × 55.4 = 388 m of DN200 pipe) could be replaced in terms of heat exchanged with a single-pipe heat exchanger with a diameter of DN315 and a length of 139 m (139 m of DN315 pipe), with almost the same annual electricity consumption. Of course, the results would be different if larger diameters of branches and/or collectors were also used in the multipipe exchanger. For this reason, the results of this work represent a case study for a limited number of variants and may inspire a more complex earth-to-air heat exchanger design methodology taking into account thermal, energy, environmental, economic and technical aspects as well as user preferences and their importance in the hierarchy.

## 5. Conclusions

- multipipe EAHEs could be replaced by single-pipe structures of with greater diameter with similar energy performance and electricity consumption during the year;
- for airflow of 600 m
^{3}/h, a seven-pipe EAHE of L = 14 m DN200 (a total of 7 × 14 = 98 m of DN200 pipe) could be replaced with a single-pipe DN250 of L = 35.5 m (35.5 m of DN250 pipe), with the annual electricity consumption lower by approximately 35%; - for airflow of 1500 m
^{3}/h, a seven-pipe EAHE of L = 54.4 m DN200 (total 7 × 55.4 = 388 m of DN200 pipe) could be replaced with a single-pipe DN315 of L = 139 m (139 m of DN315 pipe), with almost the same annual electricity consumption; - taking into account other designs of multipipe EAHEs (larger diameters of branches and/or manifolds) would change the heat yield and electricity consumption in favor of multipipe structures compared to single-pipe structures. However, such heat exchangers were not tested in this study and therefore were not analyzed in the calculations, which is an inspiration for future work born on the basis of the results of this article.

## Author Contributions

## Funding

## Conflicts of Interest

## Appendix A. Details of the Experimental Investigations

**Figure A2.**Comparison of the airflow measurement using noninvasive method and orifice plate flowmeter.

## Appendix B. Uncertainty Analysis of the Experimental Results

_{k}

_{,j}, k = 1, 2,…, K; j = 1, 2, …, J; where, K = number of measured results; J = number of independent variables. The set of, xj, contained 9 quantities (J = 9): L

_{i}, L

_{C-D}, L

_{B-D}, di, p, ∆p

_{i}, ∆p

_{C-D}, ∆p

_{A-D}and T. The minimum value of K was 6. There were 3 dependent variables, i.e., quantities that were calculated, y = f (x

_{j}): V

_{i}, V

_{tot}and ∆p

_{tot}. It was assumed that the systematic uncertainty of all directly measured quantities has a uniform distribution and that their random uncertainty had a Gaussian distribution. The following equations were used to calculate the uncertainty. Average value of the independent variable:

_{j}= nominal precision (accuracy) of the measuring equipment.

**Table A1.**Measured quantities and accuracy of the measuring devices [43].

Measured Quantity (Independent Variable) | Value and Unit | Nominal Precision (Accuracy) |
---|---|---|

L_{i} | 1850 mm | ±1 mm |

L_{C−D} | 1350 mm | ±1 mm |

L_{B−D} | 2850 mm | ±1 mm |

d_{i} | 46.1 mm | ±0.1 mm |

p_{min} − p_{max} | 99,800–102,000 Pa | ±100 Pa |

∆p_{i}_{,min} − ∆p_{i}_{,max} | 5–150 Pa | ±(0.05–0.5) Pa |

∆p_{C−D} − ∆p_{C−D,max} | 15–60 Pa | ±(0.05–0.5) Pa |

∆p_{A}_{−}_{D,min} − ∆p_{A}_{−}_{D,max} | 450–1900 | ±3 Pa |

T_{min} − T_{max} | 294–298 K | ±0.5 K |

**Table A2.**Results of the uncertainty analysis (percentage uncertainties with 95% confidence) [43].

Error | δL_{i} | δL_{C−D} | δL_{B−D} | δd_{i} | Δp | δ∆p_{i} | δ∆p_{C−D} | δ∆p_{A−D} | δT | δ∆p_{tot} | δV_{i} | δV_{tot} |
---|---|---|---|---|---|---|---|---|---|---|---|---|

Systematic | 0.03 | 0.04 | 0.02 | 0.13 | 0.06 | 0.30 | 0.30 | 0.30 | 0.10 | 0.32 | 0.91 | 0.91 |

Random | 0.15 | 0.17 | 0.11 | 1.20 | 0.10 | 0.63 | 0.72 | 0.58 | 0.10 | 0.63 | 2.10 | 2.12 |

General | 0.15 | 0.17 | 0.11 | 1.21 | 0.12 | 0.70 | 0.78 | 0.65 | 0.14 | 0.70 | 2.29 | 2.31 |

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**Figure 2.**Schema of the experimental setup: d

_{main}—internal diameter of a manifold (PP DN50 = 0.0461 m), L

_{in}—flow developing sector of a length at least >30d, d—internal diameter of each branch-pipe (PP DN50), Δp

_{i}—pressure drop at the measuring sector of i branch, ΔL—distance between parallel pipes = 6d, previously presented in the authors’ work [48].

**Figure 4.**Condensation of water vapor during the cooling process that occurs in the exchanger pipes in the summer, previously presented in the authors’ earlier work [50].

**Figure 5.**Ground temperature and external air temperature during the year taken into consideration in calculations, adopted from the authors’ previous work [43].

**Figure 6.**Flow characteristic: total pressure losses Δp as a function of total airflow V; the result of the experimental investigation for exchanger model: 3, 5 or 7 pipes, L = 76d, d = PP DN50, d

_{main}= PP DN50.

**Figure 8.**Total pressure loss coefficient vs. Reynolds number—results of experimental investigations.

**Figure 9.**Full-year energy usage for the fan flowing air through the earth-to-air heat exchanger; system usage: 100% of the time at maximum airflow.

**Figure 10.**Full-year energy usage for a fan flowing air through an earth-to-air heat exchanger; system usage: scheduled (performance changes outside peak usage hours).

**Figure 11.**Full-year energy usage for driving the fans for multipipe structures of length L = 14 m and single-pipe structures of equivalent length in the context of heating capacity with different pipe diameters: d = DN200, DN250 or DN315, V = 600 m

^{3}/h.

**Figure 12.**Full-year energy usage for driving the fans for multipipe structures of length L = 55.4 m and single-pipe structures of equivalent length in the context of heating capacity with different pipe diameters: d = DN200, DN250 or DN315, V = 600 m

^{3}/h.

**Figure 13.**Full-year energy usage for driving the fans for multipipe structures of length L = 14 m and single-pipe structures of equivalent length in the context of heating capacity with different pipe diameters: d = DN200, DN250 or DN315, V = 1500 m

^{3}/h.

**Figure 14.**Full-year energy usage for driving the fans for multipipe structures of length L = 55.4 m and single-pipe structures of equivalent length in the context of heating capacity with different pipe diameters: d = DN200, DN250 or DN315, V = 1500 m

^{3}/h.

**Table 1.**Experimental apparatus and its precision [49].

Measured Value | Apparatus | Precision |
---|---|---|

T (°C) | Laboratory thermometer | ±0.5 °C |

p (Pa) | Laboratory barometer | ±100 Pa |

Δp_{i}, Δp_{C–D}, Δp_{A–D} (Pa) | Micromanometer with range 0–50 Pa | ±0.05 Pa |

Micromanometer with range 50–500 Pa | ±0.5 Pa | |

Micromanometer with range 500–1990 Pa | ±3.0 Pa | |

L (m), L_{i} (m), ΔL (m) | Measuring tape | ±1.0 mm |

3 Pipes | 5 Pipes | 7 Pipes |
---|---|---|

1.77 | 1.83 | 1.87 |

Average for 3, 5 and 7 pipes: k_{m} = 1.82 |

**Table 3.**Comparison of total pressure losses given in Pa in different structures of single-pipe and multipipe EAHEs.

Type of EAHE: | Single-Pipe (Pipes in Series) | Multipipe (Parallel Pipes) | |||||
---|---|---|---|---|---|---|---|

V = 200 m^{3}/h, Re = 26,597 | |||||||

Number of pipes: | 3 | 5 | 7 | 3 | 5 | 7 | |

Length of a single pipe: | 76d | 15.0 | 30.4 | 40.4 | 4.8 | 4.8 | 4.8 |

150d | 35.0 | 60.1 | 85.2 | 5.6 | 5.1 | 5.0 | |

300d | 75.3 | 125.5 | 175.7 | 7.0 | 5.7 | 5.3 | |

V = 600 m^{3}/h, Re = 79,790 | |||||||

Number of pipes: | 3 | 5 | 7 | 3 | 5 | 7 | |

Length of a single pipe: | 76d | 102.8 | 219.3 | 287.8 | 43.6 | 43.6 | 43.6 |

150d | 250.8 | 434.0 | 617.2 | 48.5 | 45.6 | 44.7 | |

300d | 549.5 | 915.9 | 1282.3 | 58.4 | 49.6 | 46.9 |

Hour | Airflow | Hour | Airflow |
---|---|---|---|

0 | 40% | 12 | 100% |

1 | 40% | 13 | 100% |

2 | 40% | 14 | 100% |

3 | 40% | 15 | 100% |

4 | 40% | 16 | 100% |

5 | 40% | 17 | 70% |

6 | 70% | 18 | 70% |

7 | 70% | 19 | 40% |

8 | 100% | 20 | 40% |

9 | 100% | 21 | 40% |

10 | 100% | 22 | 40% |

11 | 100% | 23 | 40% |

**Table 5.**Assumed percentage reduction in the thermal efficiency of a multipipe heat exchanger due to uneven air distribution among the branches.

Number of Pipes: | 3 | 5 | 7 | |
---|---|---|---|---|

Length of a single pipe: | 76d | 10% | 15% | 25% |

300d | 5% | 10% | 20% |

**Table 6.**Results of full-year energy calculation: benefits (heating and cooling) and costs (electric energy and primary energy usage PE) related to usage of single- and multipipe EAHEs, V = 600 m

^{3}/h.

Type of EAHE: | Single-Pipe (Pipes in Series) | Multipipe (Parallel Pipes) | |||||
---|---|---|---|---|---|---|---|

Number of Pipes: | 3 | 5 | 7 | 3 | 5 | 7 | |

EAHE length: | 3 × 76d | 5 × 76d | 7 × 76d | 3 × 76d | 5 × 76d | 7 × 76d | |

Benefits | Heat (kWh/year) | 2179 | 3059 | 3668 | 1654 | 2027 | 2066 |

Cool (kWh/year) | 569 | 851 | 1085 | 436 | 557 | 584 | |

Cost | Electric energy (kWh/year) | 112 | 238 | 313 | 47 | 47 | 47 |

PE for driving fan (kWh/year) | 336 | 714 | 939 | 141 | 141 | 141 | |

EAHE length: | 3 × 300d | 5 × 300d | 7 × 300d | 3 × 300d | 5 × 300d | 7 × 300d | |

Benefits | Heat (kWh/year) | 4511 | 5037 | 5207 | 3972 | 4221 | 3937 |

Cool (kWh/year) | 1504 | 1858 | 1991 | 1272 | 1469 | 1430 | |

Cost | Electric energy (kWh/year) | 597 | 994 | 1391 | 63 | 53 | 50 |

PE for driving fan (kWh/year) | 1791 | 2982 | 4173 | 189 | 159 | 150 |

**Table 7.**Equivalent length of DN200 single-pipe EAHE replacing a given multipipe exchanger in terms of heat; the results of calculations of annual electricity consumption and primary energy consumption for fan drive, V = 600 m

^{3}/h.

Type of EAHE: | Single-Pipe (Pipes in Series) | Multipipe (Parallel Pipes) | |||||
---|---|---|---|---|---|---|---|

EAHE length: | 1 × 29 mDN200 | 1 × 38 mDN200 | 1 × 39 mDN200 | 3 × 14 mDN200 | 5 × 14 mDN200 | 7 × 14 mDN200 | |

Equivalent multipipe EAHE | 3 × 14 mDN200 | 5 × 14 mDN200 | 7 × 14 mDN200 | ||||

Benefits | Heat (kWh/year) | 1643 | 2064 | 2064 | 1654 | 2027 | 2066 |

Cool (kWh/year) | 416 | 535 | 535 | 436 | 557 | 584 | |

Cost | Electric energy (kWh/year) | 78 | 104 | 104 | 47 | 47 | 47 |

PE for driving fan (kWh/year) | 234 | 312 | 312 | 141 | 141 | 141 | |

EAHE length: | 1 × 117 mDN200 | 1 × 136 mDN200 | 1 × 114.5 mDN200 | 3 × 55.4 mDN200 | 5 × 55.4 mDN200 | 7 × 55.4 mDN200 | |

Equivalent multipipe EAHE: | 3 × 55.4 mDN200 | 5 × 55.4 mDN200 | 7 × 55.4 mDN200 | ||||

Benefits | Heat (kWh/year) | 3973 | 4218 | 3937 | 3972 | 4221 | 3937 |

Cool (kWh/year) | 1221 | 1342 | 1204 | 1272 | 1469 | 1430 | |

Cost | Electric energy (kWh/year) | 414 | 465 | 408 | 63 | 53 | 50 |

PE for driving fan (kWh/year) | 1242 | 1395 | 1224 | 189 | 159 | 150 |

**Table 8.**Equivalent length of DN250 single-pipe EAHE replacing a given multipipe exchanger in terms of heat; the results of calculations of annual electricity consumption and primary energy consumption for fan drive, V = 600 m

^{3}/h.

Type of EAHE: | Single-Pipe (Pipes in Series) | Multipipe (Parallel Pipes) | |||||
---|---|---|---|---|---|---|---|

EAHE length: | 1 × 26.5 m DN250 | 1 × 35 m DN250 | 1 × 35.5 m DN250 | 3 × 14 m DN200 | 5 × 14 m DN200 | 7 × 14 m DN200 | |

Equivalent multipipe EAHE: | 3 × 14 m DN200 | 5 × 14 m DN200 | 7 × 14 m DN200 | ||||

Benefits | Heat (kWh/year) | 1641 | 2032 | 2054 | 1654 | 2027 | 2066 |

Cool (kWh/year) | 420 | 531 | 538 | 436 | 557 | 584 | |

Cost | Electric energy (kWh/year) | 24 | 31 | 32 | 47 | 47 | 47 |

PE for driving fan (kWh/year) | 72 | 93 | 96 | 141 | 141 | 141 | |

EAHE length: | 1 × 107 m DN250 | 1 × 125 m DN250 | 1 × 105 m DN250 | 3 × 54.4 m DN200 | 5 × 54.4 m DN200 | 7 × 54.4 m DN200 | |

Equivalent multipipe EAHE: | 3 × 54.4 m DN200 | 5 × 54.4 m DN200 | 7 × 54.4 m DN200 | ||||

Benefits | Heat (kWh/year) | 3975 | 4229 | 3942 | 3972 | 4221 | 3937 |

Cool (kWh/year) | 1228 | 1353 | 1213 | 1272 | 1469 | 1430 | |

Cost | Electric energy (kWh/year) | 136 | 152 | 134 | 63 | 53 | 50 |

PE for driving fan (kWh/year) | 408 | 456 | 402 | 189 | 159 | 150 |

**Table 9.**Equivalent length of DN315 single-pipe EAHE replacing a given multipipe exchanger in terms of heat; the results of calculations of annual electricity consumption and primary energy consumption for fan drive, V = 600 m

^{3}/h.

Type of EAHE: | Single-Pipe (Pipes in Series) | Multipipe (Parallel Pipes) | |||||
---|---|---|---|---|---|---|---|

EAHE Length: | 1 × 24.5 m DN315 | 1 × 32 m DN315 | 1 × 33 m DN315 | 3 × 14 m DN200 | 5 × 14 m DN200 | 7 × 14 m DN200 | |

Equivalent multipipe EAHE: | 3 × 14 m DN200 | 5 × 14 m DN200 | 7 × 14 m DN200 | ||||

Benefits | Heat (kWh/year) | 1645 | 2019 | 2065 | 1654 | 2027 | 2066 |

Cool (kWh/year) | 426 | 534 | 547 | 436 | 557 | 584 | |

Cost | Electric energy (kWh/year) | 7 | 10 | 10 | 47 | 47 | 47 |

PE for driving fan (kWh/year) | 21 | 30 | 30 | 141 | 141 | 141 | |

EAHE length: | 1 × 98.5 m DN315 | 1 × 115 m DN315 | 1 × 96.5 m DN315 | 3 × 54.4 m DN200 | 5 × 54.4 m DN200 | 7 × 54.4 m DN200 | |

Equivalent multipipe EAHE: | 3 × 54.4 m DN200 | 5 × 54.4 m DN200 | 7 × 54.4 m DN200 | ||||

Benefits | Heat (kWh/year) | 3973 | 4228 | 3938 | 3972 | 4221 | 3937 |

Cool (kWh/year) | 1235 | 1360 | 1218 | 1272 | 1469 | 1430 | |

Cost | Electric energy (kWh/year) | 37 | 50 | 37 | 63 | 53 | 50 |

PE for driving fan (kWh/year) | 111 | 150 | 111 | 189 | 159 | 150 |

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**MDPI and ACS Style**

Amanowicz, Ł.; Wojtkowiak, J.
Comparison of Single- and Multipipe Earth-to-Air Heat Exchangers in Terms of Energy Gains and Electricity Consumption: A Case Study for the Temperate Climate of Central Europe. *Energies* **2021**, *14*, 8217.
https://doi.org/10.3390/en14248217

**AMA Style**

Amanowicz Ł, Wojtkowiak J.
Comparison of Single- and Multipipe Earth-to-Air Heat Exchangers in Terms of Energy Gains and Electricity Consumption: A Case Study for the Temperate Climate of Central Europe. *Energies*. 2021; 14(24):8217.
https://doi.org/10.3390/en14248217

**Chicago/Turabian Style**

Amanowicz, Łukasz, and Janusz Wojtkowiak.
2021. "Comparison of Single- and Multipipe Earth-to-Air Heat Exchangers in Terms of Energy Gains and Electricity Consumption: A Case Study for the Temperate Climate of Central Europe" *Energies* 14, no. 24: 8217.
https://doi.org/10.3390/en14248217