# Investigation of the Environmentally-Friendly Refrigerant R152a for Air Conditioning Purposes

^{*}

## Abstract

**:**

## 1. Introduction

_{3}) is a promising refrigerant but it is toxic (B1 ASHRAE group). The R290 (propane) and the R600a (iso-butane) are also natural refrigerants but they have high flammability (A3 ASHRAE group). The last choice is CO

_{2}which has GWP = 1 and it is not flammable and toxic, but it has a low critical temperature (~31 °C) which leads to transcritical cycle with relatively low efficiency and high-pressure levels. Table 1 summarizes the previous refrigerants and their characteristics [7,8,9].

_{2}seems to be a promising choice for the future, especially with the modified system with parallel compression, subcooling, and ejector devices [10,11] but there is a need for efficiency enhancement and creating certified personnel [1]. Among the HFC, the use of R152a seems to be a promising choice because of the low GWP which is lower than 150. Only the flammability problems have to be faced in order to establish it. However, it is important to state that R152a belongs to the A2 category and it is less flammable than the R290 and R600a which are also promising and used refrigerants. Therefore, the use of R152a has to be performed with experienced personnel and with the proper safety rules.

_{2}in the low stage is a promising choice which has also been examined. Cabello et al. [17] proved that the substitution of R134a refrigerant with R152a is possible in a cascade cycle with CO

_{2}. They performed experimental work and they found similar performance with both configurations and also they stated that the system had worked about two months without problems after the use of R152a. In another work, Yang et al. [18] found that the use of R152a in a cascade system with CO

_{2}is more efficient than the use of R134a/CO

_{2}and R124/CO

_{2}cascade systems.

## 2. Material and Methods

#### 2.1. Examined System

_{amb}), indoor space temperatures (T

_{ind}), and different rotational speeds. In the nominal conditions, it has cooling capacity 5 kW at 2000 rpm for T

_{amb}= 35 °C and T

_{ind}= 25 °C. It is useful to state that air is used in the condenser and evaporator as the external heat transfer fluid. Figure 1b shows the thermodynamic cycle in the pressure-specific enthalpy (p-h) diagram.

#### 2.2. Mathematical Formulation

_{e}) can be written in the following ways. Firstly, the energy balance in the refrigerant is given by the equation

_{e}), as it is given by the formula

_{e}) can be written as [21]

_{c}) can be written in the following ways. Firstly, the energy balance in the refrigerant is given as

_{c}), as it is

_{c}) can be written as [21]

_{el}) is equal to the work consumption (W) to the motor efficiency (η

_{m}), which is [22]

_{is}) which is defined as [23]

_{is}) is given using the formula [24]

_{r}) in the compressor is connected with the rotational speed (n) with the equation [27]

_{v}) can be assumed to be given with a correlation as the isentropic efficiency, as Llopis et al. [28] suggested, according to the formula

#### 2.3. Methodology of the Present Study

_{amb}) is ranged from 30 °C to 50 °C, the rotational speed (n) from 1000 rpm to 4000 rpm and the indoor temperature (T

_{ind}) from 20 °C to 30 °C. The nominal case is the one with T

_{amb}= 35 °C, T

_{ind}= 25 °C and n = 2000 rpm where the cooling capacity is around 5 kW and the COP is 6.46. In every case, the pressure levels in the condenser and in the evaporator, as well as the mass flow rate of the refrigerant (m

_{r}) are unknown parameters which are calculated by the developed program. Table 2 includes the main information about the examined system in this work.

#### 2.4. Model Validation

## 3. Results and Discussion

#### 3.1. Impact of the Rotational Speed on the Performance

_{amb}= 35 °C. More specifically, Figure 5 indicates that the increase of the rotational speed leads to higher condenser pressure level, lower evaporator pressure level, higher outlet air temperature from the condenser, and lower outlet air temperature from the evaporator.

#### 3.2. Impact of the Ambient Temperature on the Performance

_{ind}= 25 °C. Figure 6 shows results about the COP and it can be said that the COP is lower for higher ambient temperatures and higher rotational speeds. Figure 7 shows that the cooling capacity presents a small decrease with the ambient temperature increase while it has an important increase with the increase of the rotational speeds. The conclusions from Figure 6 and Figure 7 are similar to the respective of Figure 2 and Figure 3, respectively.

#### 3.3. Impact of the Indoor Temperature on the Performance

_{am}=35 °C − n = 2000 rpm, T

_{am}= 45 °C – n = 2000 rpm, T

_{am}= 35 °C – n = 3000 rpm and T

_{am}= 45 °C – n = 3000 rpm). Figure 10 shows the COP for the investigated cases. It is obvious that higher indoor temperature leads to higher COP for all the operating scenario. Practically, higher indoor temperature makes the cooling production easier because the evaporator temperature can be relatively high for adequate cooling production. Moreover, Figure 11 illustrates that the increase in the indoor temperature leads to higher cooling capacity. Therefore, it can be said that in a case where the indoor temperature is 27 °C for example, then the heat pump is more efficient than the default case for operation at 25 °C. Figure 12 displays the pressure ratio in the compressor which has a decreasing rate with the indoor temperature increase. Practically, the higher indoor temperature increases the evaporator temperature and so the pressure ratio is lower. This fact can be verified by the results of Figure 13.

_{am}= 35 °C – n = 2000 rpm) and it indicates that the low pressure has an important increase with the indoor temperature increase. This result verifies the evaporator temperature increase. The air outlet temperature in the indoor space is also increased with the indoor temperature increase which is a reasonable result. The high pressure in the condenser and the air outlet temperature from the condenser present a small increase with the indoor temperature increase.

#### 3.4. Deeper Analysis of the Examined Heat Pump

_{e}= 7 kW in Figure 14 and Figure 15 are shorter than the other curves due to restriction in the rotational speed (up to 4000 rpm).

^{2}equal to 99.19% for Equation (18) and 96.47% for Equation (19).

- Cooling capacity correlation (R
^{2}= 99.19%)$$\frac{{Q}_{e}}{{Q}_{e,0}}=1+0.637445\cdot \left(\frac{n-{n}_{0}}{{n}_{0}}\right)-0.3647\cdot \left(\frac{{T}_{am}-{T}_{am,0}}{{T}_{am,0}}\right)$$ - COP correlation (R
^{2}= 96.47%)$$\frac{COP}{CO{P}_{0}}=1-0.40875\cdot \left(\frac{n-{n}_{0}}{{n}_{0}}\right)-1.04965\cdot \left(\frac{{T}_{am}-{T}_{am,0}}{{T}_{am,0}}\right)$$

- (a)
- $-0.5<\frac{n-{n}_{0}}{{n}_{0}}<1.0$
- (b)
- $-0.1429<\frac{{T}_{am}-{T}_{am,0}}{{T}_{am,0}}<0.4286$

#### 3.5. Comparative Study with Other Refrigerants

## 4. Conclusions

- -
- In the nominal operating conditions, the examined heat pump has 5 kW cooling capacity and a COP equal to 6.46.
- -
- The increase of the rotational speed leads to higher cooling capacity and to lower COP.
- -
- The increase of the ambient temperature leads to lower cooling capacity and to lower COP.
- -
- The increase of the indoor temperature leads to higher cooling capacity and to higher COP.
- -
- It is found that the rotational speed is the most important parameter for the cooling capacity value, while the ambient temperature is the most important parameter for the COP value.
- -
- The R152a is found to be the most efficient refrigerant compared to six other refrigerants. The mean enhancement with the R600a is found to be 1.14%, while with R134a 4.36%, while with the R404a 20.20%.
- -
- The final results of this work can be utilized for the proper modeling of a cooling system with a heat pump with R152a. The developed models can be utilized for the simulation of this system in different operating conditions. Moreover, the advantages of the R152a are discussed and explained in this work and finally, this refrigerant is suggested as a reliable choice.

## Author Contributions

## Funding

## Conflicts of Interest

## Nomenclature

COP | Coefficient of performance, - | |

c_{p} | Specific heat capacity, J/kgK | |

h | Specific enthalpy, J/kg | |

m | Mass flow rate, kg/s | |

n | Rotational speed, rpm | |

p | Pressure, bar | |

P_{el} | Electricity consumption, W | |

Q | Heat rate, W | |

r | Compressor pressure ratio, - | |

(UA) | Total transmittance, W/K | |

V_{dis} | Compressor displacement volume, m^{3}/r | |

W | Work consumption, W | |

Greek symbols | ||

η_{c} | Condenser heat exchanger effectiveness, - | |

η_{e} | Evaporator heat exchanger effectiveness, - | |

η_{is} | Compressor isentropic efficiency, - | |

η_{m} | Motor efficiency, - | |

η_{v} | Compressor volumetric efficiency, - | |

Subscripts and superscripts | ||

amb | Ambient | |

c | Condenser | |

c,in | Inlet condenser | |

c,out | Outlet condenser | |

e | Evaporator | |

e,in | Inlet evaporator | |

e,out | Outlet evaporator | |

ind | Indoor | |

is | Isentropic | |

high | High | |

Low | Low | |

r | Refrigerant | |

Abbreviations | ||

EES | Engineering Equation Solver | |

GWP | Global Warming Potential | |

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**Figure 2.**Coefficient of performance for different rotational speeds and ambient temperatures (T

_{ind}= 25 °C).

**Figure 3.**Cooling capacity for different rotational speeds and ambient temperatures (T

_{ind}= 25 °C).

**Figure 4.**Compressor pressure ratio for different rotational speeds and ambient temperatures (T

_{ind}= 25 °C).

**Figure 5.**Pressure levels and outlet temperatures of the streams for different rotational speeds and ambient temperatures (T

_{ind}= 25 °C).

**Figure 6.**Coefficient of performance for different ambient temperatures and rotational speeds (T

_{ind}= 25 °C).

**Figure 7.**Cooling capacity for different ambient temperatures and rotational speeds (T

_{ind}= 25 °C).

**Figure 8.**Compressor pressure ratio for different ambient temperatures and rotational speeds (T

_{ind}= 25 °C).

**Figure 9.**Pressure levels and outlet temperatures of the streams for different ambient temperatures and rotational speeds (T

_{ind}= 25 °C).

**Figure 13.**Pressure levels and outlet temperatures of the streams for different indoor temperatures (T

_{am}= 35 °C and n = 2000 rpm).

**Figure 14.**Coefficient of performance for different ambient temperatures and cooling capacities (T

_{ind}= 25 °C and 1000 rpm < n < 4000 rpm).

**Figure 15.**Rotational speed for different ambient temperatures and cooling capacities (T

_{ind}= 25 °C and 1000 rpm < n < 4000 rpm).

**Figure 16.**Cooling capacity for different ambient temperatures and COP (T

_{ind}= 25 °C and 1000 rpm < n < 4000 rpm).

**Figure 17.**Rotational speed for different ambient temperatures and COP (T

_{ind}= 25 °C and 1000 rpm < n < 4000 rpm).

Working Fluids | Classification | GWP | ASHRAE GROUP | Cost ($/kg) | Limitations |
---|---|---|---|---|---|

R134a | HFC | 1120 | A1 | 5.3 | High GWP |

R404a | HFC | 3922 | A1 | 3.5 | High GWP |

R152a | HFC | 138 | A2 | 1.5 | Medium flammability, Low GWP |

R32 | HFC | 677 | A2L | 3.0 | Low flammability, Medium GWP |

R1234yf | HFO | <1 | A2L | 88 | Low flammability, Stability issues |

R1234ze | HFO | <1 | A2L | 90 | Low flammability, Stability issues |

R717 (NH_{3}) | Natural refrigerant | <1 | B1 | 1.5 | Toxicity |

R744 (CO_{2}) | Natural refrigerant | 1 | A1 | 0.7 | Low COP |

R290 (Propane) | HC (Natural refrigerant) | 3 | A3 | 1.3 | High flammability |

R600a (Iso-butane) | HC (Natural refrigerant) | 4 | A3 | 2.0 | High flammability |

Parameter | Symbol | Value |
---|---|---|

Air mass flow rate in the condenser | m_{c} | 1 kg/s |

Air mass flow rate in the evaporator | m_{e} | 1 kg/s |

Total transmittance in the condenser | (UA)_{c} | 1000 W/K |

Total transmittance in the evaporator | (UA)_{e} | 1000 W/K |

Motor mechanical efficiency | η_{m} | 80% |

Compressor displacement volume | V_{dis} | 5∙10^{−5} m^{3}/r |

Nominal compressor rotational speed | n_{0} | 2000 rpm |

Nominal ambient temperature | T_{amb,0} | 35 °C |

Nominal indoor temperature | T_{ind,0} | 25 °C |

Nominal cooling capacity | Q_{e,0} | 5 kW |

Nominal COP | COP_{0} | 6.46 |

**Table 3.**Comparison of the developed model with the literature results [20].

Parameter Investigation | Heating Production Temperature (T_{c,out}) | |||
---|---|---|---|---|

45 °C | 50 °C | 55 °C | ||

Q_{e} (kW) | This work | 7.11 | 6.76 | 6.39 |

Literature | 7.40 | 7.00 | 6.40 | |

Deviation | 3.91% | 3.42% | 0.16% | |

COP_{heating} | This work | 3.46 | 3.09 | 2.77 |

Literature | 3.64 | 3.12 | 2.67 | |

Deviation | 4.95% | 0.96% | 3.75% | |

T_{e,out} (°C) | This work | 4.57 | 4.74 | 4.92 |

Literature | 4.44 | 4.67 | 4.93 | |

Deviation | 2.93% | 1.50% | 0.20% | |

T_{e} (°C) | This work | 2.49 | 2.69 | 3.27 |

Literature | 2.41 | 2.64 | 3.21 | |

Deviation | 4.98% | 1.89% | 1.87 | |

T_{c} (°C) | This work | 47.58 | 52.58 | 57.58 |

Literature | 47.60 | 52.60 | 57.60 | |

Deviation | 0.04% | 0.04% | 0.03% |

**Table 4.**Comparison of the different working fluids with R152a for Q

_{e}= 5 kW and T

_{ind}= 25 °C.

T_{amb} (°C) | COP | ||||||
---|---|---|---|---|---|---|---|

R152a | R600a | R134a | R290 | R1234yf | R32 | R404a | |

30 | 8.227 | 8.186 | 8.014 | 7.916 | 7.776 | 7.752 | 7.322 |

31 | 7.786 | 7.742 | 7.573 | 7.481 | 7.336 | 7.32 | 6.89 |

32 | 7.383 | 7.337 | 7.169 | 7.083 | 6.933 | 6.925 | 6.495 |

33 | 7.012 | 6.964 | 6.798 | 6.718 | 6.563 | 6.562 | 6.13 |

34 | 6.671 | 6.621 | 6.456 | 6.381 | 6.221 | 6.228 | 5.794 |

35 | 6.356 | 6.303 | 6.140 | 6.07 | 5.905 | 5.918 | 5.482 |

36 | 6.064 | 6.009 | 5.847 | 5.781 | 5.612 | 5.631 | 5.192 |

37 | 5.791 | 5.735 | 5.574 | 5.511 | 5.338 | 5.364 | 4.92 |

38 | 5.538 | 5.479 | 5.319 | 5.26 | 5.083 | 5.114 | 4.666 |

39 | 5.300 | 5.240 | 5.080 | 5.025 | 4.843 | 4.881 | 4.427 |

40 | 5.078 | 5.016 | 4.856 | 4.804 | 4.619 | 4.662 | 4.202 |

41 | 4.868 | 4.805 | 4.646 | 4.597 | 4.407 | 4.455 | 3.989 |

42 | 4.671 | 4.607 | 4.447 | 4.401 | 4.208 | 4.261 | 3.787 |

43 | 4.486 | 4.419 | 4.26 | 4.216 | 4.019 | 4.077 | 3.596 |

44 | 4.310 | 4.242 | 4.082 | 4.041 | 3.84 | 3.902 | 3.413 |

45 | 4.143 | 4.074 | 3.914 | 3.875 | 3.67 | 3.737 | 3.238 |

46 | 3.985 | 3.915 | 3.754 | 3.718 | 3.509 | 3.579 | 3.07 |

47 | 3.835 | 3.764 | 3.602 | 3.568 | 3.355 | 3.429 | 2.908 |

48 | 3.692 | 3.62 | 3.457 | 3.425 | 3.208 | 3.286 | 2.752 |

49 | 3.556 | 3.482 | 3.319 | 3.288 | 3.068 | 3.149 | 2.601 |

50 | 3.426 | 3.351 | 3.187 | 3.157 | 2.933 | 3.017 | 2.454 |

Mean COP | 5.342 | 5.2815 | 5.119 | 5.063 | 4.8784 | 4.917 | 4.444 |

Enhancement | 1.14% | 4.36% | 5.51% | 9.50% | 8.65% | 20.20% |

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**MDPI and ACS Style**

Bellos, E.; Tzivanidis, C. Investigation of the Environmentally-Friendly Refrigerant R152a for Air Conditioning Purposes. *Appl. Sci.* **2019**, *9*, 119.
https://doi.org/10.3390/app9010119

**AMA Style**

Bellos E, Tzivanidis C. Investigation of the Environmentally-Friendly Refrigerant R152a for Air Conditioning Purposes. *Applied Sciences*. 2019; 9(1):119.
https://doi.org/10.3390/app9010119

**Chicago/Turabian Style**

Bellos, Evangelos, and Christos Tzivanidis. 2019. "Investigation of the Environmentally-Friendly Refrigerant R152a for Air Conditioning Purposes" *Applied Sciences* 9, no. 1: 119.
https://doi.org/10.3390/app9010119