Conventional Ground Source Heat Pump Research Articles

Assessment of Environmental Impacts of Thermal Caisson Geothermal Systems

This paper investigates the total environmental impacts of a thermal caisson (TC) system by implementing a life cycle assessment methodology. The total environmental impacts consider the comprehensive effect on the environment across two life cycle stages: manufacturing and operation. A comparison between the TC results and two different HVAC systems, including air-conditioning/furnace and conventional ground-source heat pump (GSHP) systems, was made by adopting the ReCiPe 2016 methodology. This study reveals that the operation phase is the predominant contributor to environmental impacts across systems, mainly due to its extended duration. Specifically, the operational impacts of GSHPs are substantial, accounting for approximately 87% of total environmental impacts. A TC GSHP system demonstrates a notable environmental advantage, achieving a 79% reduction in total environmental impact when compared to traditional AC/furnace systems. This represents a 21% improvement over conventional GSHP systems. Despite this substantial reduction in total environmental impact, the TC GSHP system shows an almost 5% increase in the resource availability damage category relative to the conventional GSHP, which is attributed to its higher material consumption. These results highlight the TC GSHP system’s superior efficiency in reducing environmental impacts and its potential as a more sustainable alternative in residential heating and cooling applications.

Effectiveness of phase change materials and their properties on the performance of geothermal and foundation-based energy systems: A review

As buildings contribute notably to emissions of greenhouse gases, it is important to move towards building heating and cooling systems with good sustainability attributes and efficiencies, such as ground-source heat pumps (GSHPs). In this review, an integrated picture of the effect of utilizing phase change material (PCMs) having various physical properties on the performance of GSHPs and foundation-based geothermal systems is presented. Two major questions are addressed in this paper: how effective is a PCM for enhancing the performance of both conventional GSHP systems and foundation-based geothermal energy systems? The results show that PCMs can be effective at enhancing performance for conventional GSHP and foundation-based geothermal energy systems by, on average, 17% and 36%, respectively. However, the degree of PCM effectiveness depends on some parameters such as its physical characteristics (thermal conductivity, latent heat, phase change temperature) and design considerations (ground loop configuration, depth, etc.) among other factors. The results also show that, in general, the greater the PCM thermal conductivity, the higher the effectiveness of the PCM. Furthermore, by adding composites such as expanded graphite to the PCM, the thermal conductivity of a PCM increases more than 250% which can potentially improve the performance of geothermal systems. More research is warranted to maximize the system performance improvements by enhancing the PCM.

Long-term energy performance of thermal caisson geothermal systems

In Canada, buildings account for a considerable portion of energy use and contribute heavily to Canada’s greenhouse gas (GHG) emissions. As such, a transition towards energy-efficient heating and cooling systems is important. Sustainable ground-source heat pumps (GSHPs) are one type of energy-efficient heating and cooling systems. But, they have high capital costs and often decline in efficiency over time. In this study, we further develop a phase change material (PCM)-based thermal caisson (TC) system, and extend a numerical algorithm previously developed in the same research group to assess the long-term energy performance of these systems. Dual-purpose and low-cost TCs not only provide structural support to a building, but also provide high efficiency geothermal heating and cooling, through ground heat exchanger U-tubes and embedded PCMs. Linear regression analyses are also performed to formulate how values of the coefficient of performance (COP) of TC systems change over time based on results from the literature and the current model. The results show that the long-term energy performance of TCs is significantly influenced by the use of a PCM, which can improve the long-term COP of GSHP systems, by 22% on average. For the small residential building investigated in this study, the capital cost and the net present value (NPV) of a TC system can be up to 50% and 32% lower, respectively, than the corresponding values for a conventional GSHP system. In addition, the TC system has a return on investment (ROI) of 65% which is significantly higher compared to the conventional GSHP system. Furthermore, over the heat pump system lifetime (assumed 20 years in this work), the CO2 emissions of the TC-based system are approximately 19% lower than conventional GSHP systems. Overall, the techniques used in this study can be extended and applied to larger buildings and potentially lead to greater energy savings for these buildings, if TCs are widely adopted in the building sector

Multi-objective optimization of solar-assisted ground-source heat pumps for minimizing life-cycle cost and climate performance in heating-dominated regions

The use of solar-assisted ground-source heat pumps (SGSHPs) with serial and parallel configurations can reduce the energy consumption compared with conventional ground-source heat pumps (GSHPs). However, the environmental and economic issues associated with SGSHPs, which involve high initial costs and CO2 emissions, remain major barriers to their application. Therefore, SGSHPs should be carefully designed considering both the economic and environmental circumstances to guarantee their competitiveness over GSHPs. In this study, multi-objective optimization of SGSHPs with serial and parallel configurations was conducted to minimize the life-cycle cost (LCC) and climate performance (LCCP). Based on the estimated energy consumption using Transient System Simulation Tool (TRNSYS), the design parameters and refrigerants of the SGSHPs were optimized using an artificial neural network and multi-objective genetic algorithm in the four heating-dominated regions. The optimized SGSHP with a parallel configuration exhibited lower LCC and LCCP by up to 7% and 10%, respectively, compared to that with a serial configuration. Furthermore, as building insulation technology improves, the optimal system size decreases. In addition, R134a is the best option for minimizing LCC owing to its high performance, whereas R1234yf is the best option for minimizing LCCP in Helsinki and Stockholm, showing up to a 37% reduction in LCCP.

Numerical investigation of geothermal pavements: Design optimisation & boundary conditions

Geothermal pavements comprise a newfound type of thermal geo-structures, an innovation in pavement construction contributing to ground source heat pump (GSHP) systems, resulting in a better cost-efficiency compared to conventional GSHP systems. Ground heat exchangers are formed by embedding pipe into the pavement structure (e.g., base, sub-base or subgrades). Developing accurate models with appropriate boundary conditions is crucial to obtaining a deep understanding of the performance and function of geothermal pavement systems. This paper introduces an experimentally validated 3D finite element model (FEM) and compares the effect of surface boundary condition choices on the results of the simulation. The model uses two different approaches for boundary conditions: i) using ambient temperature and ii) implementing energy balance equations on the surface, as surface boundary conditions. The model is further utilised to perform a parametric study and the results are employed by a statistical tool (Minitab) to determine the optimum heat exchanger design for a geothermal pavement project in Adelaide, an Australian city subjected to temperate climate conditions and good solar irradiation throughout the year. Results show that the choice of both boundary conditions leads to similar fluid temperature trends, but with differences in values, particularly during the heating season, resulting in a reduced embedded pipe length of up to 30 % and up to a 10 % better annual average coefficient of performance (COP(when using the energy balance equations on the surface. The parametric study shows that the system annual COP increases with the length of the pipe and spacing between the pipes, whilst the pipe depth placement is inversely proportional to the annual average COP given the advantages obtained during the heating season over the cooling season. Finally, considering the interaction effect between various parameters, a pipe heat exchanger with 400 m length, 0.76 m pipe spacing and 0.45 burial depth is evaluated as the best design to maximise COP for the case study at hand.

상업용 건물을 대상으로 한 태양광열-지열 이용 Tri-generation 시스템의 성능분석

It is necessary to introduce renewable energy systems for zero energy building realization. Recently, many individual renewable energy systems are introducing the commercial buildings. However, the individual renewable energy systems have many disadvantages such as imbalance between energy generation and use, and intermittent energy production dependent on weather conditions. To resolve these disadvantages, a Tri-generation system combined with a photovoltaic-thermal (PVT) and ground source heat pump (GSHP) is proposed. The Tri-generation system can overcome the disadvantages of the individual system and stably provide thermal and electrical energy to buildings. Many researchers are conducting a feasibility assessment of the introduction of the Tri-generation system for energy independence in residential buildings, but there are few studies on performance analysis of the Tri-generation system for commercial buildings. In this study, to promote the supply of the Tri-generation system for commercial buildings, performance analysis of the system was conducted through an energy simulation model. The annual thermal and electrical production of the Tri-generation system was analyzed and the coefficient of performance (COP) was compared between the Tri-generation system and the conventional GSHP system. As for the performance analysis results, the COP of the Tri-generation system was up by 50% compared to the conventional GSHP system.

The Ontology-Based Approach Supporting Holistic Energy-Tunnel Design considering Cost, Heat Flux, and System Feasibility

As an emerging geothermal structure, the energy tunnel has been an important part of geothermal engineering. However, the conventional methods for designing energy tunnels mostly rely on complex numerical models. Furthermore, a macrolevel multidomain collaborative design method to consider multiple areas and design indicators is unavailable. This study combined ontology and semantic Web rule language to establish the domain knowledge of energy tunnels which is an enrichment of the conventional ground source heat pump domain knowledge and develop a comprehensive decision-making tool named OntoETS for the design of energy-tunnel systems. The tool can promote the optimal design scheme with an optimal combination of multiple indexes through an analysis of the economy, heat flux, and system feasibility of the energy-tunnel system from a macroperspective by combining multiple domains. Furthermore, a case study was conducted to demonstrate the effectiveness and practicability of the developed holistic decision-making system.

Performance analysis of a hybrid subway source heat pump system using capillary heat exchanger

A large amount of free heat generated by the running of subway is released to the tunnel. Due to arc structure of subway tunnels, conventional ground source heat pumps and large-diameter heat exchangers are difficult to efficiently extract the heat and maintain surrounding-rock thermal balance. To sustainably take advantage of these free heat, in this paper, a hybrid subway source heat pump system is proposed, which is integrated by subway source heat pump system, 4.3 mm diameter capillary heat exchanger and auxiliary cooling system. A dynamic simulation model of the hybrid heat pump system, which includes the heat transfer process between capillary heat exchanger and surrounding-rock was developed on TRNSYS. Field tests were conducted at a subway station of Qingdao (China) to validate this model. Under different strategies, the coefficient of performance of the hybrid heat pump system and characteristics of surrounding-rock temperature field are compared. The results indicated that the hybrid heat pump system can ensure appropriate surrounding-rock temperature without overheating (from 33.9 ℃ to 31.3 ℃). Additionally, the coefficient of performance of the subway source heat pump units was 4.432, increased by 2.52%, the energy consumption of the subway source heat pump system can be decreased by 5.55%.

Organic Rankine Cycle-Ground Source Heat Pump with Seasonal Energy Storage Based Micro-Cogeneration System in Cold Climates: The Case for Canada

In cold climatic regions such as those located across Canada, it is necessary to implement heating system technology that is ultra-efficient and that has near-zero rates of emissions. Such systems would satisfy consumers’ energy needs and also comply with environmental standards, especially because the systems would account for more than 80% of residential energy use. This paper investigates two complementary efficient systems that can support these heating systems; ground-source heat pumps (GSHPs) and organic Rankine cycle systems (ORCs). The study proposes to couple these two systems in a parallel configuration. A dynamic simulation model created in TRNSYS platform has been deployed to assess the performance of the combined ORC-GSHP based micro-cogeneration system. This former provides heating to a residential house during the heating mode as needed. It has the capacity to switch to a charging mode, during which the ORC system is directly coupled to the ground heat exchanger (GHE), which works as a thermal energy storage and supplies energy to the GSHP. The feasibility of this combined system arrangement, and its comparison with a conventional GSHP system are examined for use in residential buildings in three cities across the varied climatic regions within Canada, namely Edmonton (AB), Halifax (NS), and Vancouver (BC). Results showed that the proposed micro-cogeneration system recorded less energy use of over 80%. The addition of the ORC system had a definite effect on the performance of the GSHP in that it decreased the operating hours from 11–58% compared to the conventional GSHP case and maintained consistently higher COP values. These results may help to specify viable ORC-GSHP based micro-co/trigeneration systems in cold climatic applications and should be useful for prototype design and development.

Environmental performance analysis of a dual-source heat pump system

Using all phases of a life cycle assessment (LCA), this paper analyses the environmental impact of a dual-source heat pump (DSHP) system that uses either the air or the ground as external heat sources. Data on the production were provided by the manufacturer of the heat pump prototype. The use phase was considered by evaluating the seasonal and annual energy performance of the system, using dynamic simulations. The system maintenance and end-of-life were modelled in accordance with the current regulations and statistical data in this sector. The Ecoinvent database was used as a reference for background data. The ReCiPe, CED and IPCC 100a impact methods were used to assess the environmental impact categories. The results were compared with those of conventional air and ground source heat pump systems. A sensitivity study on the influence of the energy in the use phase was carried out in terms of a variation in energy use and for different energy mixes, including photovoltaic energy. The results demonstrated the environmental validity of the technology in comparison with the two conventional heat pumps used for residential applications in different conditions. The results could be used by heat pump manufacturers to improve the design and performance of their products, by designers in the selection of thermal technologies, and by researchers involved in the study of similar emerging renewable energy technologies.

Environmental impact assessment of office building heating and cooling sources: A life cycle approach

Heating and cooling sources occupy a large proportion of the total energy consumption of office buildings and hence the related environmental impacts cannot be underestimated. In this paper, a localized life cycle impact assessment (LCIA) method was established based on local environmental policies and energy regulations according to the framework of life cycle assessment (LCA). It is used to analyze the heating and cooling sources for office buildings in northern China. The environmental impact inventory was classified, characterized, standardized and weighted based on local energy resources. The exergy exhaustion (EE) factor was adopted to analyze the importance of local primary energy. Cost analysis was conducted to increase the practical value and significance of the research results. Questionnaires were used to determine the weight of environmental impact, EE, and cost analysis (CA) for combination scheme selection. Different heating and cooling sources and 7 combination schemes for office buildings in the cold regions of northern China were comprehensively evaluated. Results showed that gas-fired cogeneration + conventional electric refrigeration air conditioners and ground source heat pump (GSHP) for both heating and cooling were two recommended schemes which had the least comprehensive environmental impact index. These investigations can guide decision-makers and designers to choose environment-friendly and economical heating and cooling sources, and help government departments to formulate appropriate incentive policies to encourage the use of suitable, sustainable, and economical energy sources.

Designing and Optimizing Heat Storage of a Solar-Assisted Ground Source Heat Pump System in China

The cold accumulation problem can lead to performance degradation of heat pumps. This paper presents the design and optimization of a solar-assisted storage system to solve this issue. A ground source heat pump (GSHP) project was established using the transient system simulation program (TRNSYS) based on a ground heat exchange theoretical model, which was validated by a previously established experiment in Beijing. The Beijing, Harbin, and Zhengzhou regions were used in numerical simulations to represent three typical cities where buildings require space heating (a cold region, a severe cold region, and a hot summer and cold winter region, respectively). System performance was simulated over periods of ten years. The simulation results showed that the imbalance efficiencies in the Beijing, Harbin, and Zhengzhou regions are 55%, 79%, and 38%, respectively. The annual average soil temperature decreases 7.3°C, 11.0°C, and 5.3°C during ten years of conventional GSHP operation in the Beijing, Harbin, and Zhengzhou regions, respectively. Because of the soil temperature decrease, the minimum heating coefficient of performance (COP) values decrease by 23%, 46%, and 11% over the ten years for GSHP operation in these three regions, respectively. Moreover, the simulation data show that the soil temperature would still be decreasing if based on the previous solar energy area calculation method. Design parameters such as the solar collector size are optimized for the building load and average soil temperature in various cold regions. Long-term operation will test the matching rate of the compensation system with the conventional GSHP system. After the system is optimized, the solar collector area increases of 20% in the Beijing region, 25% in the Harbin region, and 15% in the Zhengzhou region could help to maintain the annual average soil temperature balance. The optimized system could maintain a higher annual average COP because of the steady soil temperature. It provides a method for the design of a solar collector area which needs to be determined in the seasonal heat storage solar ground source heat pump system.

Combination principle of hybrid sources and three typical types of hybrid source heat pumps for year-round efficient operation

Traditional single source heat pump systems, e.g., air source heat pump (ASHP) and ground source heat pump (GSHP), cannot work efficiently in the whole year. To develop an energy-efficient heat pump system for year-round operation, temperature grades of common natural energies are compared with each other. Based on the comparison, the combination principle of hybrid sources with complementary characteristics is discussed firstly. Then three typical types of heat pumps with hybrid sources are selected as representatives to show how to take full advantages of different heat sources or sinks for energy-efficient operation and how to extend functions of hybrid source heat pumps for new solutions to the disadvantages of conventional heat pumps. Finally, the annual performances of these three selected types of hybrid source heat pump systems for three corresponding specific cases are simulated by TRNSYS. The results show that hybrid source heat pump systems can maintain nearly the same heating capacity as they do without frost during the defrosting period; maintain energy-efficient year-round cooling with no risk of freezing during winter; keep the thermal balance of soil and maintain reliable cooling and heating over long periods of operation; fully utilize solar radiation of different intensities; and achieve year-round energy-efficient performance. In contrast to a conventional ASHP and GSHP system, the energy saving rate of a typical hybrid source heat pump system is approximately 15%, and the payback period is approximately five years. Hybrid source heat pumps provide a way to match multiple heat sinks/sources for different levels of building demand in different climates.

Evaluation of utilizing horizontal directional drilling technology for ground source heat pumps

The drilling cost of Ground Heat Exchangers (GHEs), which increases the capital cost, is one of the main obstacles to their widespread development. Horizontal Directional Drilling (HDD) is a lower cost no-dig drilling technology commonly used for drilling tunnels or for the installation of urban infrastructure such as pipes, cables, etc., using the prescribed underground path. Thus, using HDD technology for horizontal GHE (HGHE) is expected to improve the competitiveness of ground source heat pump (GSHP) systems, since its drilling cost and the requirement of surface land area are significantly smaller than those of conventional excavation.In this research, a horizontal U-shaped hole was drilled as an experimental GHE in Saga City, western Japan. This hole with diameter of 230 mm, length 63 m, and a maximum depth of 8 m was used to place a polyethylene pipe with a 52 mm ID as GHE, inside. The thermal response test (TRT) with a heat load of 35−45 W/m effectively demonstrated the good heat exchange ability of the HGHE due to the larger heat exchange surface and the lack of thermal interference between pipes. The developed numerical model in FEFLOW and based on GHE design as well as the field’s geological condition were validated through the history matching of the heat medium temperatures measured during the TRT. This model was then used to carry out a sensitivity analysis under different design conditions. The results showed that the heat exchange rates were significantly enhanced in larger diameter of GHEs, while the unit heat exchange rates declined in longer lengths of GHE. The deeper installation of GHE was found to be insignificant due to the delayed seasonal change of the ground temperature, not to mention the consequent higher drilling cost. In addition, the effect of groundwater flow indicated that faster groundwater velocities, and in perpendicular direction, show the maximum system improvement.Finally, an economic and comparative study was performed to calculate and compare the merits of HDD with equivalent conventional GSHPs including single and double U-tube, coaxial and slinky GHE. The results of economic analysis showed that HDD technology can reduce GHSP cost up to a maximum of 78 %.

A predictive TRNSYS model for long-term operation of a hybrid ground source heat pump system with innovative horizontal buried pipe type

This study presents an integrated hybrid ground source heat pump (HGSHP) predictive model assisted by liquid dry cooler (LDC). Combining with a new computational component imported to Transient System Simulation Tool (TRNSYS), the long-term simulation results proves that the HGSHP has better performance comparing to conventional ground source heat pump. In Birmingham, USA area, surrounding soil thermal storage is decreasing over time for both hybrid and conventional systems. After 10 years of simulation, the minimum temperature in the target zone is 12.53 °C for the HGHSP, which is 0.63 °C higher than the value of the conventional GSHP. The coefficient of performance (COP) for the hybrid system could stay at 3.33, which is also better than 3.23 for the conventional system. All the collected data shows that HGSHP integrated with liquid dry cooler plays an important role to maintain the soil thermal storage as well as promoting the overall system performance.

Utilizing shallow geothermal energy to develop an energy efficient HVAC system

Traditionally, shallow geothermal energy is utilized by a ground source heat pump. In fact, the temperature of shallow geothermal energy is typically quite suitable for the cooling/heating of building envelopes and fresh air. To utilize shallow geothermal energy more efficiently, an integrated system is proposed that combines pipe-embedded walls, pipe-embedded windows, and fresh air pre-handling system with the conventional ground source heat pump system. This proposal is based on the temperature comparison among indoor air, envelopes, fresh air and undisturbed soil. A simulation model of the integrated system is developed on the platform of TRNSYS. The free-running temperature and energy consumption of the integrated system applied in an office building in Beijing are investigated. The results show that the free-running temperature of the integrated system is always below 28 °C throughout the year, and the non-air conditioning period is extended by 34% compared with the conventional GSHP system. Moreover, the integrated system can greatly reduce the peak load, and the heat pump system capacity can be reduced by as much as 30%. The annual cumulated load for the building is reduced by approximately 43%. Consequently, the energy saving rate is approximately 29% compared with that of the conventional GSHP system. The emission reduction of CO2 is more than 7 kg per square meter. Therefore, the integrated system can fully utilize shallow geothermal energy to build an energy efficient HVAC system.

Experimental study of a domestic solar-assisted ground source heat pump with seasonal underground thermal energy storage through shallow boreholes

With the current need to reduce carbon emissions, new technologies have been developed in recent years to satisfy building thermal demands. Among others, ground-source heat pumps (GSHP) have been implemented, in both commercial and residential applications, to meet heating and cooling needs in a cleaner and more energy efficient way. Likewise, solar thermal systems have been integrated into conventional GSHP systems to reduce the size of the ground heat exchanger and provide seasonal heat storage. So far, this technology has been used in large commercial or residential buildings, mainly due to its high installation costs. This paper describes a study of an experimental Solar Assisted Ground Source Heat Pump (SAGSHP) system for domestic heating applications. The system uses an array of shallow (1.5-m deep) vertical boreholes to store heat seasonally in an underground ‘earth energy bank’. The results show that after 19 months of operation the system was able to show a good performance in order to cover the space heating requirements of the building in winter. Likewise, it was evidenced that the solar energy injected in the ground is useful not only to recover the soil from the thermal imbalance but also to store heat. Results also highlighted the need to improve the control strategy, mainly to avoid excessive inlet fluid temperatures at the evaporator.

Multicriteria performance investigations of a hybrid ground source heat pump system integrated with concentrated photovoltaic thermal solar collectors

The objective of this work is to propose a hybrid ground source heat pump system integrated with solar energy and investigate its multicriteria performances. A compound parabolic concentrated-photovoltaic thermal solar collector to output electricity and heat is comprehensively integrated with a basic ground source heat pump system. The thermodynamic models of subsystems were established and validated by comparing the simulation results to those from existing studies. The renewable resources were levelized to fossil fuels based on their contributions. The multicriteria performance of the hybrid system was analyzed by using the annual operation conditions of a hotel building. The results indicated that the primary energy ratio and exergy efficiency of the hybrid system are always higher than those of the conventional ground source heat pump system. Various inlet temperatures of solar and thermal tank subsystems in the proposed system was compared and analyzed in terms of the sustainability index, primary energy saving ratio, carbon dioxide emission reduction ratio, and annual cost saving ratio and the results indicated that their appropriate temperatures are 25 °C and 60 °C, respectively. A sensitivity analysis showed that except for the interest rate, the unit cost of electricity, service life, and maintenance coefficient have positive influences on the economic performance.

Development of a New-Type Multiple-Source Heat Pump with Two-Stage Compression

A new-type multiple-source heat pump cycle with two-stage compression was established on the basis of the problems of similarly existing heat pumps. The equivalent temperature levels of typical evaporators are applied to the different heat sources of the proposed cycle, and the high-temperature heat sources are shown to enhance vapor injection. Then, the mathematical model and prototype are developed, and the results from experimental simulation and validation showed that the solar collector can improve the heating performance of the proposed heat pump system. In the middle-temperature heating period, the outdoor temperature is less than −25°C, and the average coefficient of performance (COP) value of the proposed heat pump was 4.2, which was greater than the COPs of conventional ground source heat pumps.

Simulation of a novel deep ground source heat pump system using abandoned oil wells with coaxial BHE

As one of the most important geothermal applications, ground source heat pump (GSHP) systems have been applied for spacing heating and cooling of buildings, and the abandoned oil wells (AOW) with deep depth contain abundant geothermal energy. Therefore, this study proposed a new GSHP system using single AOW, and the deep coaxial borehole heat exchanger (BHE) with insulation is introduced to retrofit the wellbore of AOW for heat extraction. At first, a comprehensive heat transfer model for the deep coaxial BHE combing fluid, borehole and ground was built to evaluate the performance of the proposed GSHP systems during annual run. Then, Monte Carlo method was used for parameters sensitivity analysis to obtain the PRCC determining the intensity of parameters effect on total system COP. Lastly, the optimization of injection parameters was performed. The results indicated that flow rate showed the strongest influence on the total system COP. During the annual operation, it was found that the mean heat supply by the AOW-GSHP system was about 384 kW, and reached to 192 kW/m for unit depth which was obviously higher than that in conventional GSHP. And the mean heat extraction from AOW by the AOW-GSHP system reached to 294 kW, more than that by directing heating using AOW. By the optimization, it was found there was optimal inlet temperature getting maximum system COP and it existed a minimum injection pressure supporting system operation.