# Design and Parametric Investigation of an Efficient Heating System, an Effort to Obtain a Higher Seasonal Performance Factor

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

_{2}is emitted into the atmosphere than the traditional system based on fossil fuels, indicating heat pumps’ significance. Villarino et al. [18] performed a comparative energy, economic, and environmental assessment of a heat pump-based system against the same technologies to provide the energy demand of an office building. Their results demonstrated that the proposed system is an excellent choice from all viewpoints due to a higher coefficient of performance (COP), lower environmental pollution, and reduced energy costs. Blázquez et al. [19] evaluated and compared the most significant factors, including initial investment, environmental impact, and availability, of widely used systems for heating and cooling purposes in building applications. They reported that a ground source heat pump is the best alternative to the traditional systems based on biogas and natural gas.

## 2. Methodology

#### 2.1. The Studied System

^{2}. The simulation model was based on the design parameters for a newly-built hospital in Kirkenes, north of Norway. The measurements from this case study were used in Section 2.3 to validate the simulations. The building’s heated demand was supplied by radiators and a mechanical ventilation system with heat recovery (MVHR). The heat recovery efficiency of the air handling unit (AHU) varied between 50–82%. The heating system was primarily supplied by a ground source heat pump and a gas boiler as an auxiliary heating source. Figure 1 illustrates schematics of the heating system used in the hospital. A ground source heat pump and an auxiliary gas boiler feed the hydronic system.

#### 2.2. Mathematical Modeling

_{Lorenz}is the Lorenz efficiency defined as the ratio between the actual and Lorenz coefficients of performance, and T

_{lm}is the logarithmic mean temperature evaluated by Equations (10) and (11).

_{hp}) and the entire system, including peak load during the year (SPF

_{tot}), as described in Equations (12) and (13). The studied operational parameters are the heat pump capacity, evaporator and condenser temperatures, ventilation coil supply/return temperatures, and the ventilation heat recovery percentage.

#### 2.3. Validation of Simulation Tool

## 3. Results and Discussion

_{hp}reduction than SPF

_{tot}. The figure further shows that when the evaporator temperature increases from −10 °C up to 5 °C, the rise of SPF

_{hp}is higher than the SPF

_{tot}increment. According to Figure 4, as the ventilation ratio varies from 70/50 °C/°C to 70/30 °C/°C—that is, the reduction of return temperature—the values of SPF

_{hp}and SPF

_{tot}will increase, which are favorable.

_{hp}is independent of the ventilation temperature ratio for the heat pump capacity of 600 kW. However, the variation of ventilation ratio from 70/50 °C/°C to 70/30 °C/°C results in a higher total SPF. The comparison of Figure 4a,b vividly reveals that for the same value of evaporator temperature and ventilation temperature ratio, using a heat pump with the capacity of 400 kW leads to a higher SPF

_{hp}than 600 kW heat pump. This is because the 400 kW heat pump operates at a lower temperature level and has a longer running time with full capacity leading to more effectiveness.

_{hp}at the minimum heat recovery percentage of 50%.

_{tot}. In contrast, Figure 5b shows that the highest SPF

_{hp}alludes to the heat recovery of 82%. The comparison of obtained SPF values demonstrates that the heat recovery of 75% could be an optimal option due to the highest SPF

_{tot}for 400 kW capacity and second-highest SPF

_{tot}for the capacity of 600 kW. Moreover, the figure reveals that the heat recovery percentage of 50% is another good alternative because of the highest SPF

_{hp}and SPF

_{tot}for the capacity of 400 kW and 600 kW, respectively.

_{tot}corresponds to the ventilation heat recovery of 50%. According to the table, for a 400 kW heat pump, by increasing the recovery percentage from 50% to 75%, SPF

_{tot}value increases since the mitigation of heating demand is lower than the decrement of total delivered energy. However, the increase of recovery percentage from 75% to 82% leads to a lower SPF

_{tot}because of the higher reduction of heating demand than the decrement of delivered energy. According to the table, for the heat pump capacity of 600 kW, the value of SPF

_{tot}is reduced by increasing the ventilation heat recovery percentage. This is rational because the decrease of heat demand is higher than reducing the total delivered energy. The table further presents that the increase in heat pump capacity from 400 kW to 600 kW improves SPF

_{tot}. In contrast, SPF

_{hp}alone remains relatively constant despite increasing its capacity.

_{hp}and SPF

_{tot}values. Besides, the figure depicts that while the rise in condenser temperature from 40 °C to 60 °C leads to a higher SPF

_{tot}, SPF

_{hp}reduces dramatically. The comparison of Figure 6a,b demonstrates that for condenser temperatures of 50 °C and 60 °C, the increase in heat pump capacity from 400 kW to 600 kW improves SPF

_{tot}while reducing SPF

_{hp}. According to Figure 6a,b, at the condensation temperature of 40 °C, there is no difference between 400 kW and 600 kW heat pumps because SPF values remain relatively constant.

_{tot}and lower SPF

_{hp}is attained by increasing the condenser temperature. Moreover, the figure indicates that SPF values will increase by increasing the evaporator temperature. Finally, from Figure 7, it can be observed that by choosing the heat recovery of 75% (or higher), the increase of heat pump capacity from 400 kW to 600 kW does not change the values of SPFs. Therefore, at 75% (or higher) heat recovery, a more favorable economic condition is achieved by selecting a heat pump with a lower capacity.

## 4. Conclusions

- According to the parametric study outcomes, the evaporator and condenser temperatures are key parameters that highly affect the heat pump and the total system performance;
- Because of a longer running time with full capacity, 400 kW is the best option from the heat pump performance viewpoint. However, the highest total seasonal performance factor is achieved by using a heat pump of 600 kW due to delivering more heat for charging the system;
- The results further show that by varying ventilation ratio from 70/50 °C/°C to 70/30 °C/°C—that is, the reduction of return temperature—the values of heat pump and total seasonal performance factors will increase, indicating the importance of the proposed configuration;
- What stands out from the results is that for the condensation temperature of 40 °C and the heat recovery of 50%, the increment of heat pump capacity does not change the heat pump and total system performance;
- At heat recovery of 75% (or greater), choosing a heat pump with a smaller capacity is economically beneficial because the seasonal performance values are independent of heat pump capacity.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Conflicts of Interest

## Nomenclature

Abbreviations | |

AHU | Air handling unit |

COP | Coefficient of performance |

GSHP | Ground source heat pump |

MVHR | Mechanical ventilation with heat recovery |

SPF | Seasonal performance factor |

TES | Thermal energy storage |

Latin letters | |

$\dot{m}$ | Mass flowrate, [kg s^{−1}] |

$\dot{Q}$ | Thermal energy, [kW] |

$\dot{W}$ | Power, [kW] |

$h$ | Enthalpy, [kJ kg^{−1}] |

${C}_{p}$ | Specific heat capacity, [kJ kg^{−1} K^{−1}] |

$T$ | Temperature, [°C] (or [K]) |

Greek letters | |

$\mathsf{\rho}$ | Density, [kgm^{−3}] |

$\eta $ | Efficiency, [-] |

Subscripts | |

amb | Infiltration gains (${\dot{Q}}_{amb})$ |

cap | Capacity |

cond | Condensor |

equipments | Internal convective gains (${\dot{Q}}_{equipments})$ |

eva | Evaporator |

hp | Heat pump |

in | Input |

lm | Logarithmic mean temperature |

out | Output |

rad | Radiator |

surfaces | Transmission heat gains (${\dot{Q}}_{surfaces})$ |

T | Temperature |

tot | Total (system) |

vent | Ventilation |

z | Zone |

zones | Heat transfer among zones (${\dot{Q}}_{zones})$ |

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**Figure 1.**Schematic view of the hydronic heating system installed in the studied hospital including a ground-source heat pump, auxiliary heater, radiators, and ventilation coils.

**Figure 2.**Schematic view of the Norwegian, Swedish, and variable flow hydronic connections used in the studied hydronic system, including measurement and regulator valves and a circulation pump.

**Figure 4.**The influence of the evaporator temperature, ventilation temperature ratio, and the heat pump capacity: (

**a**) 400 kW; (

**b**) 600 kW on the heat pump and total SPF values.

**Figure 5.**The influence of the evaporator temperature, ventilation heat recovery percentage, and the heat pump capacity: (

**a**) 400 kW; (

**b**) 600 kW on the heat pump and total SPF values for the ventilation temperature ratio of 70/30 °C/°C.

**Figure 6.**The influence of the evaporator temperature, condenser temperature, and the heat pump capacity: (

**a**) 400 kW; (

**b**) 600 kW on the heat pump and total SPF values for the ventilation temperature ratio of 70/30 °C/°C, and the heat recovery of 50%.

**Figure 7.**The influence of the evaporator temperature, condenser temperature, and the heat pump capacity: (

**a**) 400 kW; (

**b**) 600 kW on the heat pump and total SPF values for the ventilation temperature ratio of 70/30 °C/°C and the heat recovery of 75%.

Description | Value | Unit |
---|---|---|

Maximum delivered heat by radiators | 614 | kW |

Heat pump maximum delivery | 400–600 | kW |

Heat pump condensing temperature | 50 (40–60) | °C |

Heat pump evaporating temperature | −10–+5 | °C |

Auxiliary heater maximum delivery | 800 | kW |

Maximum design supply/return temperature | 70/50–70/30 | °C |

Design outdoor temperature | −20 | °C |

Maximum ventilation rate | 194,000 | m³h^{−1} |

Ventilation heat recovery | 50–82 | % |

**Table 2.**Variation of performance indicators with ventilation heat recovery percentage and heat pump capacity.

System Configuration | SPF_{hp} | SPF_{tot} | Total Delivered Energy (MWh) | Building Heating Demand (MWh) | |
---|---|---|---|---|---|

Heat Pump Capacity (kW) | Ventilation Heat Recovery % | ||||

400 | 50% | 4236 | 2190 | 1182 | 2589 |

75% | 4020 | 2315 | 539 | 1248 | |

82% | 4058 | 2194 | 436 | 957 | |

600 | 50% | 4008 | 2568 | 1009 | 2590 |

75% | 4021 | 2316 | 539 | 1248 | |

82% | 4059 | 2196 | 436 | 957 |

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**MDPI and ACS Style**

Harsem, T.T.; Nourozi, B.; Behzadi, A.; Sadrizadeh, S.
Design and Parametric Investigation of an Efficient Heating System, an Effort to Obtain a Higher Seasonal Performance Factor. *Energies* **2021**, *14*, 8475.
https://doi.org/10.3390/en14248475

**AMA Style**

Harsem TT, Nourozi B, Behzadi A, Sadrizadeh S.
Design and Parametric Investigation of an Efficient Heating System, an Effort to Obtain a Higher Seasonal Performance Factor. *Energies*. 2021; 14(24):8475.
https://doi.org/10.3390/en14248475

**Chicago/Turabian Style**

Harsem, Trond Thorgeir, Behrouz Nourozi, Amirmohammad Behzadi, and Sasan Sadrizadeh.
2021. "Design and Parametric Investigation of an Efficient Heating System, an Effort to Obtain a Higher Seasonal Performance Factor" *Energies* 14, no. 24: 8475.
https://doi.org/10.3390/en14248475