# Experimental and Theoretical Investigations of a Ground Source Heat Pump System for Water and Space Heating Applications in Kazakhstan

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## Abstract

**:**

## 1. Introduction

## 2. Apparatus

## 3. Energy, Exergy and Environment Impact Analysis

#### 3.1. Evaporator

#### 3.2. Compressor

^{−5}, ${c}_{7}$ = 7.89 × 10

^{−4}, ${c}_{8}$ = −7.51 × 10

^{−4}, ${c}_{9}$ = 1.85 × 10

^{−6}, ${c}_{10}$ = 33.6476.

#### 3.3. Condenser

#### 3.4. Expansion Device

#### 3.5. System Parameters

#### 3.6. Exergy Destruction

#### 3.7. Exergy Efficiency

#### 3.8. Total Equivalent Warming Impact

_{2}eq.), $m$ is the charge of the refrigerant (in kg), $L$ is the leakage rate per year (in %/year), $n$ is system operating life (in years); $\alpha $ is the recovery/recycling factor (in %), $E$ is the energy consumption per year (in kWh/year),$\beta $ is the indirect emission factor (in kg/kWh).

## 4. Results and Discussions

#### 4.1. Experimental Results

#### 4.2. Thermodynamic Model Validation

#### 4.3. Thermodynamic and Environmental Calculations

^{3}. The mass flow rates required for R450A and R1234ze(E) are close to that of R134a, with the values of 31.4 g/s and 32.0 g/s, respectively. However, refrigerant R450A and R1234ze(E) have lower values of $VRC$ than that of R134a, which requires a large volume compressor. In addition, R513A and R1234yf have closer values of $VRC$ to that of R134a at higher mass flow rates.

_{2}equivalent, respectively. The lowest value of direct emissions is observed for HFO refrigerants like R1234yf and R1234ze(E) with a value of 0.01. The lowest value of indirect emissions is observed for R152a with 31.64-ton eq. CO

_{2}while the highest value of 34.32-ton eq. CO

_{2}is associated with R1234yf due to its high compressor power consumption. The carbon-dioxide emission factor ($\beta $) is assumed to be 0.8 kg of CO

_{2}per kWh for coal-based electric power generation system [41].

## 5. Conclusions

- The experimental values of $CO{P}_{\mathrm{cycle}}$ vary in the range of 2.24–2.97, while $CO{P}_{\mathrm{system}}$ vary in the range of 2.11–2.76.
- The predicted and experimental results are found to be in good agreement within 6.2%.
- The thermodynamic model describes the energy and exergy efficiencies of the system with sufficient accuracy.
- As input data for model calculations, we have used measurements from the borehole heat exchanger, that takes into account the local ground conditions.
- The maximal exergy destruction is attributed to the compressor, followed by the expansion valve, evaporator, and condenser.
- The exergy efficiency of the condenser depends on the compressor discharge temperature for different refrigerants, and it is maximal in the case of R1234yf.
- The R152a is found to be a good alternative to R134a in terms of $CO{P}_{\mathrm{cycle}}$, $CO{P}_{\mathrm{system}}$, and $TEWI$ with estimated values of 3.09, 2.91, and 31.76-ton eq. CO
_{2}, respectively. - Refrigerant R450A and R513A are found to be safer alternatives to R134a with slightly (of order 3%) lower $CO{P}_{\mathrm{cycle}}$, $CO{P}_{\mathrm{system}}$, and $TEWI$.
- Refrigerant R1234yf and R1234ze are identified as interim replacements to R134a due to the formation of trifluoroacetic acid.

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Nomenclature

$\mathit{COP}$ | Coefficient of Performance |

$\dot{E}$ | Exergy rate, W |

$\mathit{e}$ | Specific exergy, J/kg |

$\mathit{E}$ | Energy consumption per annum, kWh |

$\mathit{GWP}$ | Global Warming Potential |

$\mathit{h}$ | Specific enthalpy, kJ/kg |

$\mathit{L}$ | Leakage rate per year, %/year |

$\dot{m}$ | Mass flow rate, kg/s |

$\mathit{m}$ | Refrigerant charge, kg |

$\mathit{n}$ | System operating life, year |

$\mathit{P}$ | Pressure, Pa |

$\dot{Q}$ | Heat capacity, W |

$\mathit{RE}$ | Relative Exergy |

$\mathit{T}$ | Temperature, °C |

$\mathit{TEWI}$ | Total Equivalent Warming Impact, kg eq. CO_{2} |

$\dot{V}$ | Volume flow rate, m^{3}/h |

$\mathit{VRC}$ | Volumetric Refrigeration Capacity, kJ/m^{3} |

$\dot{W}$ | Energy consumption, W |

Greek symbols | |

$\mathit{\alpha}$ | Recovery/recycling factor, % |

$\mathit{\beta}$ | Indirect CO_{2} emission factor, kg/kWh |

$\mathit{\eta}$ | Efficiency |

$\mathit{\rho}$ | Density, kg/m^{3} |

Subscripts | |

EAP | Evaporator Approach |

elec | Electrical |

evap | Evaporator, Evaporation |

CAP | Condenser Approach |

carnot | Reverse Carnot cycle |

comp | Compressor |

cond | Condenser, Condensation |

cycle | Vapor Compression cycle |

isen | Isentropic |

m | Motor |

pump | Hydraulic loop pump |

ref | Refrigerant |

source | Heat source |

sink | Heat sink |

SC | Subcooling |

SH | Superheating |

system | Overall system |

t | Transmission |

TEV | Thermostatic expansion valve |

total | Total |

2nd | The 2nd Law of Thermodynamics |

Superscripts | |

alt | Alternative |

dest | Destruction |

ex | Exergetic |

in | Inlet |

out | Outlet |

Abbreviation | |

ATES | Aquifer Thermal Energy Storage |

BHE | Borehole Heat Exchanger |

BTES | Borehole Thermal Energy Storage |

EES | Engineering Equation Solver |

GEP | Geothermal Energy Pile |

GHE | Ground Heat Exchanger |

GSHP | Ground Source Heat Pump |

HDPE | High-Density Polyethylene |

HFC | Hydrofluorocarbons |

HFO | Hydrofluoroolefin |

HTF | Heat Transfer Fluid |

TFA | Trifluoroacetate |

TRT | Thermal Response Test |

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**Figure 1.**Photographs of the experimental facility in Koksai Mosque, in the Almaty region of Kazakhstan: (

**a**) BHE installation; (

**b**) Buried BHE; (

**c**) Ground structure; (

**d**) Heat delivery unit; (

**e**) Water-to-water heat pump.

**Figure 3.**Schematic representation of the thermodynamic model: (

**a**) Water-to-water heat pump; (

**b**) Pressure-enthalpy diagram.

**Figure 7.**Variation of compressor electricity consumption measured with the temperature of the heat sink.

**Figure 8.**Variations of estimated delta temperatures based on measured temperature with the temperature of the heat sink.

**Figure 10.**Comparisons of predicted and measured heat capacities with the temperature of the heat sink for the condenser and evaporator.

**Figure 11.**Comparisons of predicted and measured $COPs$ of the cycle and system with the temperature of the heat sink.

**Figure 12.**Refrigerant mass flow rate required for a given heat capacity vs latent heat of vaporization of refrigerants.

**Figure 13.**Refrigerant mass flow rate and volumetric refrigeration capacity required for a given heat capacity for different refrigerants.

**Figure 19.**Normalized cycle parameter dependences for different refrigerants: (

**a**) Coefficient of performance vs. total equivalent warming impact; (

**b**) Cycle efficiency vs. exergy destruction.

Parameter | Unit | Compressor |
---|---|---|

Model | - | Copeland ZR28K3E-PFJ |

Displacement @ 50 Hz | m³/h | 6.83 |

Max. Internal Free Volume | L | 2.90 |

Dimensions (L × W × H) | mm | 246 × 246 × 377 |

Oil type | - | POE RL32-3MAF |

Oil quantity | L | 1.12 |

Heating capacity * | kW | 4.83 |

Input power * | kW | 1.38 |

$COP$ * | - | 2.57 |

Mass flow rate * | g/s | 24.7 |

Parameter | Unit | TEV |
---|---|---|

Model | - | Danfoss T2–4 |

Maximum evaporating temperature | °C | 15 |

Minimum evaporating temperature | °C | −45 |

Max. working pressure | kPa | 3400 |

Pressure drop * | kPa | 1024 |

Nominal capacity * | kW | 6.4 |

Min. capacity * | kW | 1.6 |

Parameter | Unit | Evaporator | Condenser | ||
---|---|---|---|---|---|

Model | - | B3-027-20-H | B3-027-30-H | ||

Heat transfer area | m^{2} | 0.468 | 0.728 | ||

Dimensions (L × W × H) | mm | 111 × 54 × 311 | 111 × 81 × 311 | ||

Weight | kg | 3.8 | 5.1 | ||

Material | - | AISI 316L | AISI 316L | ||

Flow arrangement | - | Counterflow | Counterflow | ||

Fluid side | - | R134a | Water | R134a | Water |

Number of plates | - | 10 | 9 | 15 | 14 |

Heat transfer coefficient * | W/(m^{2}·K) | 2177.1 | 5224.0 | 1347.1 | 7778.2 |

Total pressure drop * | kPa | 10.47 | 1.89 | 0.21 | 2.35 |

Parameter | Designation | Unit | Value * |
---|---|---|---|

Heat sink temperature | ${T}_{\mathrm{sink}}$ | ℃ | 40–50 {50} |

Heat source temperature | ${T}_{\mathrm{source}}$ | °C | ${T}_{\mathrm{source}}=0.01048\times {T}_{\mathrm{sink}}^{2}-1.081\times {T}_{\mathrm{sink}}+40.3$ {13} |

Compressor electricity consumption | ${\dot{W}}_{\mathrm{elec},\mathrm{comp}}$ | kW | ${\dot{W}}_{\mathrm{elec},\mathrm{comp}}=0.000195\times {T}_{\mathrm{sink}}^{2}+0.0098\times {T}_{\mathrm{sink}}+0.626$ |

Compressor efficiency | ${\eta}_{\mathrm{comp}}$ | % | Equation (9) |

Superheating temperature | ${T}_{\mathrm{SH}}$ | °C | ${T}_{\mathrm{SH}}=13.5-0.046\times {T}_{\mathrm{sink}}$ {8} |

Sub-cooling temperature | ${T}_{\mathrm{SC}}$ | °C | ${T}_{\mathrm{SC}}=5.1-0.071\times {T}_{\mathrm{sink}}$ {2} |

Evaporator approach temperature | ${T}_{\mathrm{EAP}}$ | °C | ${T}_{\mathrm{EAP}}=0.7+0.029\times {T}_{\mathrm{sink}}$ {2} |

Condenser approach temperature | ${T}_{\mathrm{CAP}}$ | °C | ${T}_{\mathrm{CAP}}=9.1-0.088\times {T}_{\mathrm{sink}}$ {2} |

Dead state temperature | ${T}_{0}$ | °C | 20 |

Dead state pressure | ${P}_{0}$ | kPa | 101.325 |

Pump1/pump2 volume flow rate | ${\dot{V}}_{\mathrm{pump}-1}$ | m^{3}/h | 0.595 |

${\dot{V}}_{\mathrm{pump}-2}$ | 0.543 | ||

Pump1/pump2 power consumption | ${\dot{W}}_{\mathrm{elec},\mathrm{pump}-1}$ | W | 60 |

${\dot{W}}_{\mathrm{elec},\mathrm{pump}-2}$ | 40 |

Property | Unit | R134a | R152a | R450A | R513A | R1234yf | R1234ze(E) |
---|---|---|---|---|---|---|---|

$GWP$ for 100 years | CO_{2} eq. | 1430 | 124 | 547 | 573 | 4 | 7 |

Molar mass | g/mol | 102.03 | 66.05 | 108.6 | 108.4 | 114.0 | 114.0 |

Normal boiling point | °C | −26.1 | −24.7 | −23.1 | −29.2 | −29.4 | −19.0 |

Critical pressure | MPa | 4.06 | 4.50 | 4.01 | 3.77 | 3.38 | 3.64 |

Critical temperature | °C | 101.1 | 113.15 | 75.1 | 96.5 | 94.7 | 109.4 |

UFL | vol. % | - | 16.9 | - | - | 12.3 | 11.3 |

LFL | vol. % | - | 3.9 | - | - | 6.2 | 5.7 |

Auto-ignition temperature | °C | - | 455 | - | - | 405 | 368 |

Refrigerant | ${\mathit{C}\mathit{O}\mathit{P}}_{\mathbf{cycle}}$ | ${\mathit{C}\mathit{O}\mathit{P}}_{\mathbf{system}}$ | ${\mathit{\eta}}_{2\mathrm{nd}},\%$ | ${\mathit{\eta}}_{\mathbf{cycle}}^{\mathbf{ex}},\%$ | ${\mathit{\eta}}_{\mathbf{system}}^{\mathbf{ex}},\%$ | ${\mathit{\eta}}_{\mathbf{evap}}^{\mathbf{ex}},\%$ | ${\mathit{\eta}}_{\mathbf{comp}}^{\mathbf{ex}},\%$ | ${\mathit{\eta}}_{\mathbf{cond}}^{\mathbf{ex}},\%$ | ${\mathit{\eta}}_{\mathbf{TEV}}^{\mathbf{ex}},\%$ |
---|---|---|---|---|---|---|---|---|---|

R152a | 3.09 | 2.91 | 35.3 | 32.1 | 30.2 | 53.6 | 58.8 | 94.9 | 85.7 |

R134a | 2.97 | 2.80 | 34.0 | 30.9 | 29.1 | 53.6 | 58.5 | 97.3 | 83.5 |

R1234ze(E) | 2.96 | 2.79 | 33.8 | 30.7 | 29.0 | 52.5 | 58.3 | 99.1 | 79.7 |

R450A | 2.89 | 2.73 | 33.1 | 30.0 | 28.4 | 50.4 | 58.4 | 97.6 | 81.3 |

R513A | 2.88 | 2.72 | 32.9 | 29.9 | 28.3 | 53.6 | 58.4 | 98.3 | 83.1 |

R1234yf | 2.83 | 2.67 | 32.3 | 29.4 | 27.8 | 53.2 | 58.3 | 99.3 | 82.1 |

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**MDPI and ACS Style**

Yerdesh, Y.; Amanzholov, T.; Aliuly, A.; Seitov, A.; Toleukhanov, A.; Murugesan, M.; Botella, O.; Feidt, M.; Wang, H.S.; Tsoy, A.;
et al. Experimental and Theoretical Investigations of a Ground Source Heat Pump System for Water and Space Heating Applications in Kazakhstan. *Energies* **2022**, *15*, 8336.
https://doi.org/10.3390/en15228336

**AMA Style**

Yerdesh Y, Amanzholov T, Aliuly A, Seitov A, Toleukhanov A, Murugesan M, Botella O, Feidt M, Wang HS, Tsoy A,
et al. Experimental and Theoretical Investigations of a Ground Source Heat Pump System for Water and Space Heating Applications in Kazakhstan. *Energies*. 2022; 15(22):8336.
https://doi.org/10.3390/en15228336

**Chicago/Turabian Style**

Yerdesh, Yelnar, Tangnur Amanzholov, Abdurashid Aliuly, Abzal Seitov, Amankeldy Toleukhanov, Mohanraj Murugesan, Olivier Botella, Michel Feidt, Hua Sheng Wang, Alexandr Tsoy,
and et al. 2022. "Experimental and Theoretical Investigations of a Ground Source Heat Pump System for Water and Space Heating Applications in Kazakhstan" *Energies* 15, no. 22: 8336.
https://doi.org/10.3390/en15228336