Gas Engine Heat Pump Research Articles

Analysis of the technical and economic aspects of gas engine heat pumps in various climates in Iran

Due to the scarcity of fossil fuels and the potential for energy shortages, the use of energy-efficient devices is of utmost importance. There is an increasing trend in the utilization of heat pumps in air conditioning systems (heating/cooling) for both residential and commercial buildings. This article focuses on the analysis of the technical and economic aspects of gas engine heat pumps (GEHP) in various climates throughout Iran. The evaluation of this article revolves around two perspectives: that of the consumers and the government. The implementation of GEHP has been carefully considered from the consumers' perspective to ensure it does not have any negative effects on them. Additionally, from the government's point of view, the available resources are considered, and the supply of electricity and gas, along with their cost and energy consumption, are thoroughly investigated by the Ministries of Energy and Petroleum. The findings indicate that, from the consumers' perspective, the economic efficiency of GEHP can be up to 11 times higher than that of electric heat pumps (EHP). Moreover, from the government's viewpoint, GEHP leads to a reduction of over 92 % in electricity consumption, 5 % in gas consumption, and 92 % in annual expenses for the Ministry of Energy. Furthermore, the implementation of GEHP increases the income of the Ministry of Petroleum by 9.8 times.

A case study of multi-energy complementary systems for the building based on Modelica simulations

The utilization of renewable energy sources and the development of energy storage technologies have enhanced the interconversion of various energy sources to slow down global warming. The building sector, as the main bearer of energy consumption, is essential for its energy saving and emission reduction. Integrating natural gas-based combined cooling, heating, and power systems with renewable energy generation facilities is an effective solution. For that, different scenarios are designed to provide energy for a specific office building and compared with the current scenario of depending only on the municipal grid. Equipment models for photovoltaic, battery, gas engine, absorption chiller-heater, and electric heat pump are created. The results show that the multi-energy complementary system has better economic and environmental characteristics, with a primary energy ratio of over 80 % and emission reduction of over 17 %; the advantages of configuring the unit capacity to meet the cooling and heating loads for 80 % of the year are obvious, and in this scenario abandoning battery storage has higher economics for users, with a static payback period from 7.3 years to 4.4 years, but the primary energy ratio decreased by 3 % and carbon emissions increased by 7.2 tCO2. It is recommended to consider the principle of gas-electricity complementarity, relying on the combined cooling, heating, and power system to meet part of the loads, with the remaining loads being supplemented by the municipal grid. The installation of batteries should be considered comprehensively based on the price of the batteries and the requirement for energy-saving and emission-reduction.

Establishing the energy content of natural gas residential consumption : example with Belgian field-test applications

In the context of the much-needed energy transition, monitoring of residential energy appliances is more and more common in order to evaluate (and improve) their field-test performance in real applications. Many residential heating appliances use natural gas as energy source : residential gas boilers, gas engine heat pumps, gas absorption heat pumps; fuel cell-based cogeneration units, internal combustion engine cogeneration units, etc. Unfortunately, for simplicity and costs reasons, only the volume of the consumed natural is measured at the inlet of the monitored residential heating appliance. This volume, and the equivalent energy level that it contains and that is required for efficiency calculations, is affected by the atmospheric pressure and the temperature at the field-test site, as well as by the always varying natural gas composition. This paper demonstrates the method that has been used in Belgian field-test studies conducted on residential heating appliances to establish the energy content of the consumed natural gas.

Review of Gas Engine Heat Pumps

In this paper the most promising developments of technology for gas engine-driven heat pumps for the last 15 years are presented. The purpose is to present the latest research studies and changes in this type of device, as well as to help readers to search for publications containing relevant aspects of gas engine heat pumps. Gas engine-driven heat pumps are devices for parallel heating and cooling production based on compressor heat pump technology. However, unlike heat pumps with compressors powered by electric motors, gas engine-driven heat pumps are driven by gas internal combustion engines. The reviewed solutions are an interesting alternative to traditional heating systems, characterized by the higher than 1.0 Performance Energy Ratio which expresses the degree of conversion of the energy contained in the fuel supplied to the device into energy transported to the utility needs. Presented in this review, papers show different solutions for conversion of the energy contained in the fuel into mechanical and thermal energy, and mechanical energy through the shaft system is used to drive the compressor of the heat pump. The presented study shows that, due to the complexity of the system and the wide range of applications, the technology has been subjected to detailed analyses and optimizations during the last 30 years in order to increase the efficiency of devices.

Coupling control of superheat and nitrogen oxides for gas engine heat pump

Gas engine heat pump (GEHP) is gradually developing due to the high energy efficiency. However, the gas engine is easily disturbed by load fluctuation, which affects the stability of GEHP operation and causes higher nitrogen oxides (NOx) emission concentrations. Therefore, an efficient control method is necessary to ensure system stability, improve energy efficiency and reduce NOx emissions. In this paper, a coupling control strategy of superheat and NOx is proposed. The results show that the superheat can maintain stability with the small overshoot and adjustment time of less than 400 s when the engine speed changes. When the superheat setting value changed continuously, the superheat overshoot and error are less than 0.5 °C and the adjustment time is about 100 s. Meanwhile, the system outlet temperature is stable, the overshoot is less than 1 °C. The amplitude variation of the refrigerating capacity is similar to the amplitude variation of the superheat. The variation range of total heat capacity is greater than that of refrigerating capacity. In addition, the performance and emission of the GEHP are respectively studied when the superheat is 4 °C and 7 °C, at the optimum excess air coefficient. The NOx emissions are always below 100 ppm, but the primary energy ratio (PER) is higher under the superheat of 4 °C. Therefore, the proposed coupling control strategy can achieve good stability, excellent performance and emission characteristics.

A case study of a pilot system with gas-engine heat pumps and a desiccant air handling system using higher chilled water temperature in Japan

• The exhaust hot water from gas-engine heat pumps can be effectively used. • Water at 12 °C from gas-engine heat pumps achieved a 20% higher performance. • Higher chilled water temperature had no influence on the indoor environment. • Coefficient of system was 0.76 when chilled water temperature was raised. A desiccant air handling unit (DAHU) is a major dehumidification system in which adsorbents adsorb moist air. The system requires hot water to regenerate these adsorbents. In this study, a gas-engine heat pump (GHP) with a simultaneous supply of chilled and recovered hot water from the engine was installed as a heat source for a DAHU. Because a DAHU does not require low-temperature chilled water for condensation dehumidification, the impacts of higher-temperature chilled water on a DAHU and the whole system were investigated. Preliminary to the measurement, the influence of the rise of the chilled water temperature on air state after pre-cooling coil and after-cooling coil was investigated. According to this preliminary reviews, the raise of the chilled water temperature does not affect on the air state, which means there is no influence of the dehumidification amount at desiccant wheel. Furthermore, the upper limit of the chilled water temperature is at 13˚C. Field measurements with two chilled water temperatures (7 °C and 12 °C) were conducted in summer 2019. The results from these two cases showed that the rise in the chilled water temperature of the GHP improves the coefficient of performance (COP) of the GHP from 0.8 to 1.0, without any influence on the air state in the DAHU or the indoor thermal environment (temperature and relative humidity). Overall, the distribution ratio of chilled and hot water from the GHP was very small compared to that of the whole system, where the system COP was almost the same, at approximately 0.73 between the two cases. However, there is a possibility to achieve 4% of better energy performance of the system by the increase of the chilled water temperature set point from 8 °C to 12 °C.

Gas Engine-Driven Heat Pumps for Small-Scale Applications: State-of-the-Art and Future Perspectives

Gas engine-driven heat pumps are an interesting option to satisfy space heating and cooling demands aiming at energy saving, environmental impact and operating costs’ reduction. This work presents (i) a comprehensive review updated on gas engine-driven heat pumps research activities, (ii) the investigation of the central role of this technology in the air conditioning sector and (iii) the future perspectives regarding gas engine heat pumps’ diffusion in the context of the energy sector decarbonisation. The outcomes highlight that gas engine heat pumps could have better environmental performance compared to electric heat pumps both in heating and cooling operations. Moreover, they could play a pivotal role in the fight against climate change and energy security since they can guarantee an energy mix differentiation moving from electricity to natural gas and renewable gases’ usage. Indeed, by 2030, a lower-carbon gas grid could be supported by renewable gases. A further investigation has concerned diffusion of gas heat pumps activated from biofuels produced by local biomass in an energy community scenario based on a low-temperature energy district network. A novel biomass-based GEHP interacting with a low-temperature district heating network is proposed here. This system could save more than 30% of primary energy compared to biomass-fuelled boilers.

Case study: gas engine heat pump (GEHP) as a water heater applied in bathroom

This paper investigates the suitability of sewage source gas engine heat pump (SSGEHP) as a retrofit application for a public shower facility. The system performance is evaluated by primary energy ratio (PER) based on a practical example. The performance analysis indicates that the PER of SSGEHP varied in the range of 1.4 to 1.9, showing good potential in primary energy saving (as high as 69%) and emissions reduction compared to gas boiler system. It only needs 1.6 years to recover the initial investment by using the SSGEHP water heating system to reform existing the gas boiler. Therefore, the SSGEHP may be a promising retrofit scheme for the existing gas boilers.

Multi-parametric evaluation of electrical, biogas and natural gas geothermal source heat pumps

The use of low-impact energy sources is gradually growing with the aim of reducing greenhouse gases emission and air pollution. The alternatives offered by geothermal systems are one of the key solutions for a future renewable development, enabling the electrification of heating systems and the use of biofuels. This research addresses an overview of geothermal heating systems using ground source heat pumps in different European countries. Besides the traditional electrical heat pumps, gas engine heat pumps aided by natural gas or biogas are analysed in three areas. From a previous research, the technical parameters defining the geothermal system are used here to evaluate the most appropriate system in each scenario. The evaluation of different influential factors (operational costs, initial investment, environmental impact, and availability) allows defining the most recommendable systems for each area. Results of this multi-parametric study show that gas engine heat pumps aided by biogas could mean an excellent solution in all countries, also contributing to the management of waste and polluting substances. If biogas systems were not available, the electrical heat pump would be the first option for areas 1 and 3 (Italy and Sweden) but not for area 2 (United Kingdom), where natural gas is preferred.

An Empirical Investigation of a Modified Gas Engine Heat Pump in Heating and Cooling Mode for the Residential Application

Gas Engine Heat Pump (GEHP) is found as an effective machine among energy conversion systems. However, further improvement of GEHP performance is still indispensable. In the current study, to recycle efficiently the flue gases waste heat of GEHP unit, it is suggested to utilize a condensing heat exchanger. To assess the performance of the proposed GEHP, an equipped test room was designed. The nominal capacity of the current GEHP is about 80 kW for heating and 71 kW for cooling. The experimental investigation was implemented for two common strategies, i.e. heating and cooling modes. The effect of outlet dry bulb temperature of 0 °C, 5 °C, 10 °C and 15 °C for heating, and 25 °C, 30 °C, 35 °C and 40 °C for cooling as well as water outlet temperature of 40 °C, 45 °C and 50 °C for heating and 8.5 °C, 11 °C, 14 °C for cooling on the performance of the GEHP is investigated. The 95% confidence interval has been considered in statistical analysis. In heating mode, results show that the efficiency of the condensing heat exchanger increases during the reduction of water out temperature and it leads to a Coefficient of Performance (COP) enhancement. Additionally, observation indicates that the decrement of the ambient air temperature from 5 to 0 ° C leads to the severe enhancement of fuel consumption of the gas engine. The performance indicators are re-evaluated using the non-condensing heat exchanger. It is concluded that the COP of GEHP with the condensing heat exchanger decreases by the steeper slope versus the reduction of the ambient dry bulb temperature compared to the non-condensing heat exchanger.

Experimental research and energy consumption analysis on the economic performance of a hybrid-power gas engine heat pump with LiFePO4 battery

Hybrid power gas engine heat pump (HPGHP) is a novel air conditioning system that uses a power battery as an auxiliary power source to achieve efficient engine operation. Considering that frequent changes in external load can cause frequent charge/discharge of the battery and adversely affect energy conversion efficiency, lithium iron phosphate (LiFePO4) battery was used as the auxiliary power source to analyze its economic performance. A dynamic energy control strategy based on engine economic zone and battery status was proposed to realize power distribution between gas engine and electric motor. By analyzing the fuel consumption rate, energy conversion efficiency and energy consumption, the superior performance of the LiFePO4 battery HPGHP was confirmed. Test results show that the minimum gas consumption rate of LiFePO4 battery HPGHP under low-load, medium-load and high-load conditions was 12.2%, 1.07%, and 6.54% lower than that of lead-acid battery HPGHP. Equivalent energy conversion efficiency was about 7.03%, 0.98%, and 10.42% higher than lead-acid battery HPGHP, 18.56%, 1.98%, and 27.2% higher than conventional GEHP. In addition, energy consumption analysis indicates that the annual primary energy rate (PER) of LiFePO4 battery HPGHP was about 39.85%, 28.35%, and 8.4% higher than electrical heat pump (EHP), GEHP and lead-acid battery HPGHP.

Study on Geospatial Distribution of the Efficiency and Sustainability of Different Energy-Driven Heat Pumps Included in Low Enthalpy Geothermal Systems in Europe

This research work aims at a multinational study in Europe of the emissions and energy costs generated by the operation of low enthalpy geothermal systems, with heat pumps fed by different energy sources. From an economic point of view, natural gas and biogas prices are, usually, lower than electricity ones. So it may be advantageous to use these energy sources to feed the heat pumps instead of electricity. From the environmental point of view, it is intended to highlight the fact that under certain conditions of electricity production (electricity mix), more CO2 emissions are produced by electricity consumption than using other a priori less “clean” energy sources such as natural gas. To establish the countries where each of the different heat pumps may be more cost-efficient and environmentally friendly, data from multi-source geospatial databases have been collected and analyzed. The results show that in the majority of cases, the electric heat pump is the most recommendable solution. However, there are some geographic locations (such as Poland and Estonia), where the gas engine heat pump may be a better alternative.

Experimental comparisons on a gas engine heat pump using R134a and low-GWP refrigerant R152a

Abstract Gas engine heat pump (GEHP) is attracting increasing interests owing to the high heating efficiency. However, the refrigerants used in existing GEHPs present high global warming potential (GWP) values, facing the challenge to be phased out. In this work, the heating performances of a water-source GEHP using R134a and low-GWP refrigerant R152a were investigated and compared. The influences of engine speed and evaporator inlet temperature on the refrigerant operating parameters, heating performances, and compressor efficiencies were evaluated. The results indicated that the GEHP using R152a showed higher heating efficiencies, higher compressor efficiencies, lower discharge pressures, and lower natural gas consumption as compared to R134a. As the gas engine speed increases from 1200 rpm to 1600 rpm, the primary energy ratio, isentropic efficiency and volumetric efficiency using R152a have an improvement of 2.6–10.4%, 3.5–10.7% and 5.8–7.3%, respectively, compared to R134a. The comparisons of experimental results indicate that the GEHP can achieve higher heating performance by using low-GWP refrigerant R152a as the drop-in alternative for R134a.

Gas engine heat pump system: Experimental facility and thermal evaluation for 5 different units

Gas Engine Heat Pump requires simplified characterization models that allow evaluating its economic and energy impacts. These simplified solutions can be implemented in complex simulation algorithms for different commercial solutions with a low computational cost.The study aims to develop a simplified characterization model highly accurate, easy to reproduce and apply. The methodology carried out uses an experimental installation to analyze different units tested under different operating conditions. With the results of the carried out experimentation, it will be possible to know the real thermal response of these HVAC systems and to develop the simplified characterization model based on operating curves. The thermal behaviour of the systems could be evaluated using the defined curves under any operating condition of the GEHP system. Moreover, they are based on parameters available in the manufacturer datasheets.The results of the validation show that this model is highly accurate. It has a maximum error of 25% and an average error of less than 7%. Also, the formulation shows that it is easy to reproduce and to apply. Last, uncertainty analysis shows reasonable confidence in the identified performance curves.

Technical optimization of the energy supply in geothermal heat pumps

Very low enthalpy geothermal systems have been traditionally associated to the use of electricity as primary energy heat pumps supply. Gas engine heat pumps (GEHP) have been recently introduced in the current market. In this research, the electric heat pumps (EHP) as well as the GEHPs (considering natural gas and biogas as combustibles) have been analysed. The calculation of the ground source heat pump (GSHP) system has been made for a building placed in three different areas. Results reveal the influence of the heat pump configuration on the whole geothermal design. This research finally considers the European policies whose aim is a sustainable low-carbon economy by 2020. According to the existing Energy Efficiency Directive, energy requirements are defined for new and existing residential and non-residential buildings in the Member States. Based on these standards, the research compares the geothermal heat pump scenarios and a traditional one to determine if they would meet the regulation. Final results show that the Directive is a highly-demanding regulation that can only be respected by using EHP in one of the areas. The rest of geothermal heat pumps scenarios are much closer to meeting the energy standards than the traditional fossil heating sources.

A study on the design and analysis of a gas engine heat pump water heater using shower wastewater as heat source

Abstract Shower wastewater contains large amounts of heat, and recovering and utilizing shower wastewater heat energy to heat shower water is of great significance for energy saving. This paper proposed a gas engine heat pump water heater (GEHPWH) using shower wastewater as the heat source. Thermodynamic models were built to evaluate the performance of the GEHPWH and compare it with an electrical heat pump water heater (EHPWH). The results show that the GEHPWH has higher hot water outlet temperature and coefficient of performance (COP) than the EHPWH under the same conditions. Furthermore, the GEHPWH can maintain stable hot water outlet temperature and higher primary energy ratio (PER) in variable water flow mode, which resolves the issue that the conventional EHPWH needs an auxiliary heat source. Finally, based on a case, the GEHPWH reveals smaller energy consumption and lower operating costs compared with three other conventional hot-water schemes.

A comparative study on electric and gas engine heat pump

The paper compares heat pumps driven by electric motors (EHP) with heat pumps driven by gas engines (GEHP). GEHPs are still a novelty on the Polish HVACR market - therefore, the subject of the study is to indicate whether in Polish climatic conditions their use is profitable. A thorough analysis of the energy consumption of selected devices was carried out due to the consumption of utilities needed for their propulsion and the related costs. This has been done by calculating seasonal efficiency coefficients and using an innovative method of comparative modifiers allowing for unification of the performance of EHP and GEHP pumps. The results obtained include average energy efficiency coefficients, operating costs and payback times. Discussion of the calculation results proved that under certain assumptions GEHP pumps may be competitive with EHP heat pumps due to the possibility of managing waste heat at high temperatures.

Modeling and matching performance of a hybrid-power gas engine heat pump system with continuously variable transmission

Based on the steady-state efficiency of the engine and the motor and characteristic curve of Lithium iron phosphate (LiFePO4) battery, an energy management strategy is proposed for a coaxial parallel hybrid-power gas engine heat pump (HPGHP) with V-belt continuously variable transmission (CVT) by using logic threshold approach to control the dynamical transitions between the various operation modes. The torque distribution between engine and motor, and CVT ratio are regulated through predetermined optimal operation lines of hybrid powertrain system in different operations. The results demonstrate that the energy management strategy can satisfy heat pump demand performance and reduce gas consumption effectively, as well as keep battery state of charge (SOC) in reasonable range. The average thermal efficiency of driving system in three main operating modes is 3.8%, 1.9% and 2.5% higher than that of multi-stage transmission system respectively, indicating that the system has better energy saving performance.

The influence of building using function on the operating characteristics of the gas engine driven heat pump with energy storage system (ESGEHPs)

The objective of this study is to improve the applicability and efficiency of the gas engine driven heat pump with energy storage system when supplying heating and cooling to the different types of buildings. The physical models of four types of buildings, including residential, hotel, office and university building, were sampled and simulated by the DesignBuilder software using the weather data of typical weather year in Tianjin. The building cooling and heating load characteristics of the typical air-conditioning day (17/07/2016) and the typical heating day (07/01/2017) was chosen as the research data. It was found that the four types of buildings had different load demand due to the different function and characteristics of the buildings. The control strategy of the gas engine driven heat pump with energy storage system with four modes, such as Mode L, Mode P, Mode F and Mode O, was developed to meet the various building heating and cooling load demand. The simulation results showed that the annual primary energy ratio of the gas engine driven heat pump with energy storage system is about 21.4% (residential), 35.2% (hotel), 23% (office)and 26.6% (university) higher than traditional gas engine heat pump system. And a compared experiment was given, which demonstrated that the simulation relative errors of the university building cooling load, the cooling/heating capacity of the gas engine driven heat pump with energy storage system, fuel-consumption and primary energy ratio were lower than 12%, except the heating load with the relative error of 35.6%. From these results, the gas engine driven heat pump with energy storage system could be used in different types of buildings with a more stable operation characteristic, higher primary energy ratio and more suitable performance. The results presented in this paper is of some reference basis for optimizing the gas engine driven heat pump with energy storage system and developing a new route for raising cooling/heating quality, energy saving and consumption reducing.

Study on the heating performance and optimal intermediate temperature of a series gas engine compression-absorption heat pump system

To upgrade the heating performance of gas engine heat pump (GEHP) system at low air temperature and achieve cascade utilization of waste heat of gas engine, a series gas engine compression-absorption heat pump (GECAHP) system combining a GEHP and an absorption heat pump is proposed and modeled. The GEHP is driven by the gas engine motive power and the absorption subsystem is activated by gas engine waste heat. Based on a mathematical model, the heating performance of the series GECAHP system at low air temperature and the optimal intermediate temperature are investigated. The simulation results show that the heating capacity of the series GECAHP system has an evident tendency to augment with the increase of gas engine speed and water inlet temperature, while the primary energy ratio just have a little degradation. Compared with the GEHP system, the series GECAHP system can effectively improve the heating capacity at the low air temperature, but the primary energy ratio is relatively low, only between 1.0 and 1.1. In addition, the optimal intermediate temperature increases with the growth of gas engine speed, ambient air temperature and water inlet temperature as well as with the decrease of recovery water temperature.