Combined Heat Pump Research Articles

The effect of temperature and light on strawberry production in a solar greenhouse

Strawberry production is greatly affected by environmental factors, especially temperature and light. A solar greenhouse with opaque photovoltaic (OPV) modules and a solar combined air source heat pump system was built for strawberry production. The aim of this study was to assess the impact of differences in both temperature and light factors caused by OPV modules and solar heating on strawberry growth and quality in a constructed greenhouse. The ‘Jingzangxiang’ strawberry was selected and planted in the greenhouse. The indoor temperature with the heating system was 5.3–7.3 °C higher than the ambient temperature at the coldest period in the city of Kunming. At noon, the chlorophyll content of the shaded strawberry plants was 1.3 times higher than that of the unshaded plants in sunny weather, and the average shaded photosynthetically active radiation (PAR) was 230 μmol·m−2·s−1 in the greenhouse, where 25.9% of the roof was covered with OPV modules. Under this shading treatment, the optimum light range of PAR for the ‘Jingzangxiang’ strawberry was 387–437 μmol·m−2·s−1, and the optimum temperature range during the daytime was 20.5–27.4 °C. The largest single strawberry fruit weighed 33.9 g, and the soluble solids content of the shaded strawberry fruit was 16.4%, which was higher than that of the unshaded strawberry samples. Furthermore, the yield of the shaded samples was 1.2 times that of the unshaded samples. In summary, strawberry plants shaded by OPV modules were superior to unshaded strawberry plants in terms of growth, quality and yield. This research provides experimental support and information on the optimal temperature and light ranges for the growth of the ‘Jingzangxiang’ strawberry in solar greenhouse.

Theoretical and experimental study of a novel solar indirect-expansion heat pump system employing mini channel PV/T and thermal panels

This paper presents the investigation of a novel mini channel PV/T and thermal collectors combined heat pump system, using both experimental and theoretical methods. Data were produced under conditions typical for winter days in Lvliang, China. A simulation model is developed to conduct theoretical evaluation based on real-world conditions. The experimental and simulated electrical and thermal efficiency of PV/T panels, thermal efficiency of thermal collectors and COP of heat pump are compared. It is shown that the experimental and simulated results are in close agreement. The errors range from 4.0% to 9.1%, giving us confidence that this model is reasonable to predict the seasonal performance of the system. The experimental and simulated results of the system provide fundamental data for performance analysis in winter conditions and inform further improvements of similar systems in the future.

Parallel vs series configurations in combined solar and heat pump systems: A control system analysis

This paper presents the modelling of two Solar Heat Pump systems, one for Domestic Hot Water and other one for Space Heating in two different configurations. Both system’s configurations can commute between parallel and series operation. The Configuration “A” uses a heat pump with two evaporators, allowing to work as an air source Heat Pump or as a water source Heat Pump. The Configuration “B” uses a heat exchanger to preheat the air entering to an air-to-water Heat Pump. These configurations are simulated in TRNSYS 17 for evaluating their performance in three Chilean cities: Santiago, Concepción and Puerto Montt. The control system applies a switching criterion between operation modes based primarily on the available solar irradiation. According to the results, the individual performance figures of the Heat Pump and of the Solar Collectors increase. Nonetheless, the results show that the Seasonal Performance Factor of the overall system decreases when it is switched from parallel to series. In the case of space heating, the Configuration A using evacuated tubes collectors shows a decrease of the Seasonal Performance Factor from 5.85 to 4.78 in Santiago, 5.35 to 4.30 for Concepción and 4.70 to 3.87 for Puerto Montt. In all case studies, unglazed collectors applications show a maximum SPF decrease of 0.04 and a maximum increase of 0.01. The results obtained can be influenced by the applied switching criterion used in this study, which does not force the Solar Collectors to increase their operational time by cooling them with the Heat Pump. Then, for the case studies, the non-inclusion of additional solar collector’s operational time leads to decrease the system performance.

Geothermal heat pump systems in cold regions: efficiency improvement by use of ambient air

We examine the problem of efficiency in both air-source and geothermal heat pumps in regions with low ambient air temperature, and the advantage of using a combination of both systems in one equipment. Both geothermal and air heat pumps have their advantages and disadvantages. Geothermal heat pumps are more expensive to install and, in colder climates, experience a progressive decrease in efficiency with constant use during the winter season because of chilling of the ground adjacent to geothermal heat exchangers during heat extraction. Air-source heat pumps are less expensive to install and experience a decrease in efficiency as ambient temperature is getting lower. A numerical model simulation was conducted using the program “INSOLAR.GSHP.12” for a 200 sq.m. house in Moscow. The model tested the efficiency of combined use of a ground heat pump at ambient temperatures below -10°C, and air heat pump for ambient temperatures above -10°C. The results were compared to simulation of using only a geothermal heat pump. The results show a 13.3% reduction in energy consumption using the combined ground and air heat pumps over the energy requirement of using only the geothermal heat pump.

Повышение экономичности процессов генерации теплоты в коммунальной теплоэнергетике и теплотехнологиях на основе комбинированных когенерационно-теплонасосных технологий

Наиболее эффективной технологией генерации электрической и тепловой энергии для нужд коммунальной теплоэнергетики и теплотехнологий является комбинированная выработка энергии с использованием современных когенерационных установок на основе газопоршневых двигателей и газотурбинных установок, работающих на природном газе или биогазе. Комбинированная выработка энергии на такой базе существенно снижает затраты топлива в сравнении с традиционной раздельной выработкой электроэнергии на тепловых конденсационных электростанциях или на теплоэлектроцентралях и тепловой на котельных установках. Дальнейшее заметное повышение энергоэффективности процессов генерации теплоты для рассматриваемых нужд может быть достигнуто путем включения в процесс теплонасосных установок, т.е. создание комбинированных когенерационно-теплонасосных установок. Они будут иметь наивысшую топливную экономичность в сравнении со всеми существующими в традиционной теплоэнергетике. Это обусловлено целым рядом факторов. Современные когенерационные установки (КГУ) на базе газопоршневых двигателей (ГПД) и газотурбинных установок (ГТУ) имеют электрический к.п.д. выше, чем тепловая электростанция (ТЭС) или теплоэлектроцентраль (ТЭЦ) – 30…45 % и 28…35 %, соответственно. В котлах-утилизаторах более эффективно используется высокотемпературная сбросная теплота двигателей, в результате чего суммарный к.п.д. установок достигает 85…88 %. Такие установки обеспечивают децентрализацию производства электрической и тепловой энергии, поэтому на автономных КГУ существенно ниже, а иногда практически отсутствуют потери в электрических и тепловых сетях, достигающие в централизованных системах 8…12 % и 15…30%, соответственно. Немаловажным является и то, что они повышают надежность работы всего объекта, делая его независимым от внешних сетей. Включение в процесс генерации теплоты теплонасосной установки (ТНУ) вызывает заметное повышение энергоэффективности, увеличивая топливную экономичность, благодаря использованию практически даровой низкопотенциальной теплоты природного, промышленного или бытового происхождения, а также высокой эффективности преобразования в ТНУ этой теплоты в теплоту более высокого потенциала с использованием электрической энергии КГУ.
 Целью работы является оценка перспектив применения комбинированных когенерационно-теплонасосных установок на базе ГПД и ГТУ для повышения энергоэффективности и энергосбережения при генерации теплоты в коммунальной теплоэнергетике и теплотехнологиях, в частности, в процессах сушки.

Performance Analysis of a Combined Solar-Assisted Heat Pump Heating System in Xi’an, China

This study proposed a combined solar-assisted heat pump (SAHP) system that could operate in the serial mode or parallel mode. For this proposed system, a stable year-round operation could be achieved without the assistance of electric heating or low-temperature heat pump. By analyzing the heat balance equations, a correlation of the combined SAHP system for the two modes switched was obtained, which provided a theoretical basis for the optimal operation of this system. In addition, the performance of the proposed system applied in a university bathroom in Xi’an district was investigated using TRNSYS. The results illustrated that compared to the serial and parallel systems, the proposed system exhibited a good performance on energy efficiency. The annual average coefficient of performance (COP) of the proposed system was 5.7, obviously higher than those of the serial system and the parallel system, which were 3.3 and 4.3, respectively. Therefore, the results in this study could provide the theoretical guidance and reference for practical engineering design.

Analysis of the application of combined solar-assisted accumulation ground source heat pump system for heat supply of the building

Analysis of the application of combined solar-assisted accumulation ground source heat pump system for heat supply of the building

Can fuel cell micro-CHP justify the hydrogen gas grid? Operating experience from a UK domestic retrofit

Fuel cell based micro combined heat and power (micro CHP) has been the subject of numerous simulation studies. We report on actual practical performance of a proton exchange membrane fuel cell (PEMFC) micro CHP in a UK dwelling over the 2017–18 heating season and compare its performance with a Stirling engine micro CHP which it replaced. Results show that the PEMFC micro CHP achieves a much higher annual electricity output over a year, with household self-consumption and operating economics dependent on electric vehicle charging. Empirical models derived from this operating experience show that the value of this technology is less sensitive to building parameters, occupancy, and climate change when compared to engine-based micro CHP. We consider the potential role of this technology in the decarbonisation of heat, and highlight the benefit of reliable electricity generation injected into low voltage distribution to mitigate winter demand peaks from heat pumps. A comparative analysis of the primary energy efficiency of different methods of meeting domestic energy demand using natural gas with carbon capture shows that a mixed solution to decarbonisation of heat, combining heat pumps, PEMFC micro CHP, and hydrogen boilers, should not degrade energy efficiency substantially by comparison with an all-electric solution and could be more acceptable to consumers.

Performance simulation of combined heat pump with unglazed transpired solar collector

Ambient air temperature reduction in winter season reduces Coefficient of Performance (COP) of heat pumps. By using of solar thermal energy to increase the evaporator fluid temperature, compressor work decreases and thus the COP of heat pump increases. In this study, the concept of solar assisted heat pump was presented by combination of an unglazed transpired solar collector and an air-to-air heat pump. In this configuration, inlet air of evaporator was preheated by unglazed transpired solar collector. A mathematical model based on first principle method was developed and performance of this system was investigated over a cold season of Kerman city (located in Kerman province in the south of Iran). Results showed that for a 2.5 kW heat pump a 2.5 m2 collector was required and this collector could decrease the electricity consumption and Co2 generation of the conventional air-to-air heat pump up to 10%. It was also concluded that, if the collector heats the ambient air less than 0.3 °C then the COP of solar assisted heat pump would be less than COP of heat pump.

Investigation of a hybrid system with ground source heat pump and solar collectors: Charging of thermal storages and space heating

A hybrid installation that includes solar collectors and a ground source heat pump was developed and tested. There are many studies in the field of combined heat pump systems describing relatively large installations, designed for climatic conditions and soil thermal properties different from those in Bulgaria, where the experimental data are limited. The paper presents the construction of a small size hybrid installation containing diurnal and seasonal storages and supporting five different modes of operation with emphasis on the charging of borehole heat exchanger (BHE), heating mode with ground source heat pump (GSHP) and the followed natural relaxation. The paper also proposes a methodology for determination of different system energy efficiencies. High quality data for the different system operation modes in terms of soil and weather conditions typical of the Plovdiv region were obtained.The study proves the necessity of BHE charging with thermal energy from the sun during the summer mainly to avoid the ground thermal depletion. The comparison of the three heating modes investigated shows evident advantage of the ground source heat pump heating (GSHPH). The installation must be tested in the future for a longer time period.

Environmental impact assessments of heat pump–gas fired water heater hybrid system for space heating application

Hybrid systems combining heat pump and gas heater can demonstrate the economic benefits, while their environmental performance is rarely investigated. In this paper, a comprehensive environmental performance investigation has been conducted to reveal the potential for emission reductions. A new environmental impact methodology has been built, and various influencing factors are evaluated. In respect of the climates, the hourly energy consumption emission first increases and then declines, which is the result of multiple effects from the weighting factors of fuel source emissions and each heating sector’s performance. Under the operation condition map for the current study, the effects of the target (final) water temperatures, electricity generation emission factor reduction, and price ratios are revealed to be the top 3 heaviest fluctuations for emissions for hourly system operation energy consumption, followed by each heating sector’s efficiency enhancements. The environmental impacts due to hourly system operation do not closely follow the hourly energy consumption profile for the effect of climate conditions and can be quite opposite when considering the effect of fuel source price ratios. In addition, the lifetime environmental performance has been examined for typical cities in China. In the cold region, such as Shenyang, the emission due to the natural gas contributor shares more than 46% of the total emissions. For warm cities (Shanghai, Wuhan, and Chengdu), the emission of the natural gas is only responsible for ~ 9% or even less of the total emissions. A switch from R410A (GWP100:1924) to R452B (GWP100:675) can also lead to ~ 11% emission total reductions for city of Shanghai, Wuhan, and Chengdu. It is anticipated that the viewpoints and insights from this study can be beneficial for the engineers, policymakers, scholars, public, and manufactures to maintaining the maximum sustainability and economic benefits.

Proposal and thermodynamic analysis of a combined open-cycle absorption heat pump and thermal desalination system driven by high-humidity exhaust gas

A combined system based on an open-cycle absorption heat pump (OAHP) and a low-temperature multi-effect evaporation (LT-MEE) water desalination process is configured, modeled, and analyzed. The system is applicable to be run by high-humidity gases, and the flue gas from the combustion of natural gas is used here. Compared with conventional absorption heat pumps, the OAHP is characterized by a gas-solution direct-contact absorber, where not only the sensible heat but also the latent heat and water vapor in flue gas are partially recovered. The OAHP-MEE system has good internal synergy, as demonstrated by a 36%–74% water production gain over the simple system when driven by flue gas with temperature of 120 °C–250 °C. With the increase of the feed-gas temperature, the combined system becomes increasingly favorable over the simple system in energy utilization and water production. For a specified feed gas condition, an optimal water recovery rate of OAHP and a maximum number of effects of MEE exist, mutually leading to a maximum water output. Using a cooler to cool the strong solution entering the absorber not only has a favorable effect on water production, but also widens the parameters' ranges, thus offering good flexibility for design and operation.

Optimisation for interconnected energy hub system with combined ground source heat pump and borehole thermal storage

Ground source heat pumps (GSHP) give zero-carbon emission heating at a residential level. However, as the heat is discharged, the temperature of the ground drops, leading to a poorer efficiency. Borehole inter-seasonal thermal storage coupled with GSHP maintains the efficiency at a high level. To adequately utilize the high performance of combined GSHP and the borehole system to further increase system efficiency and reduce cost, such a combined heating system is incorporated into the interconnected multi-carrier system to support the heat load of a community. The borehole finite element (FE) model and an equivalent borehole transfer function are proposed and respectively applied to the optimisation to analyze the variation of GSHP performance over the entire optimisation time horizon of 24 h. The results validate the borehole transfer function, and the optimisation computation time is reduced by 17 times compared with the optimisation using the FE model.

Renewable and Highly Efficient Energy Systems Through Innovative Combination of Solar Thermal and Heat Pump Systems

Solar thermal heat and heat pumps are key technologies to increase the share of renewable energy in industry and to facilitate an independent energy supply. Within the Austrian research project “Renewable process heat – integration of solar thermal energy and heat pumps in industrial processes” (short EnPro) 12 industrial case studies were performed and have shown the high potential for combined solar heat and heat pump systems in industry on supply as well process level integration. Based on the assessment of different combination concepts from a technical and economic point of view, standardised integration concepts for the combination of the two renewable technologies were developed. Thereby, a high multiplication potential can be realised for industrial applications. For a maximum impact, an easy-to-use tool was developed to identify and evaluate the potential for increasing energy efficiency and the integration of solar thermal heat and/or heat pump systems in industry.

Simulation study of a combined solar and heat pump system for heating and domestic hot water in a medium rise residential building at Concepción in Chile

Combined solar and heat pump (SHP) systems have not yet been introduced massively in Chile. On the other hand, large-scale residential buildings offer an interesting emplacement for applying these kinds of systems, but the methodologies for predicting accurately its performance are not so obvious. Thus, this paper presents the modelling of a SHP system designed for a five floor residential building, developed in TRNSYS 17. First, a detailed model of a residential building is done to understand their thermal behaviour. In this analysis, it is determined that the heat load of each building apartment depends strongly on its location. Notably, the first floor is the most demanding one, reaching the highest load for an apartment: 7.52 (kW). The total heat load of the buildings is 348.35 (kW) and the total space heating energy demand in winter season is 932,295 (kWh). On the other hand, two parallel SHP systems with air-to-water heat pumps are simulated: one for the domestic hot water demand; the other one for the heating demand. For evaluating the latter, a reduced simulation model is considered by coupling the system to 18 different air nodes, selected in function of their location in the building. The results show that the SPF for a same system in different apartments depends primarily on its heating demand. Thus, the individual components performance remains practically invariant. This allows to estimate the overall performance of a centralized heating system for the whole building, whose predicted SPFheat is 4.64 using Flat Plate Collectors (FPC) and 4.88 using Evacuated Tube Collectors (ETC). On the other hand, the performance figure of the DHW system is lower, reaching SPFDHW of 3.93 and 4.27 using FPC and ETC respectively ETC in a system that provides around 378,353 (kWh) useful energy a year.

Thermodynamic Efficiency of Heat Pump Heating Scheme Using Ground and Sewage Heat

Background. Currently, the development and research of thermodynamic or energy efficiency of combined heat pump heat supply systems with the use of several low-temperature sources of energy becomes relevant. Objective. The aim of the paper is to determine the dependence of the relative productivity of the vertical ground heat exchanger on the hot water heat consumption by the building and the ambient temperature. Methods. A thermodynamic analysis of scheme was carried out, on the basis of which conclusions were made on improving the working conditions of combined heat pump heat supply system and reducing the specific energy consumption for heat generation in the heating system. Results. The correlation for determining the total specific energy expenditure for the heat pump system with the use of ground and sewage heat is obtained. It is shown that the heat pump heating system scheme with the use of additional sewage heat is more effective than the initial heating scheme. The effectiveness depends on the consumption of hot water in the building, and the ambient temperature. Conclusions. It is determined that using this scheme in designing the heat pump heating system can significantly reduce capital and operating costs. The use of obtained dependencies in the development of heat pump systems will ensure the maximum energy efficiency of their operation.

Investigation of a gas-fuelled water heater based on combined power and heat pump cycles

In this paper, we propose a novel gas-fuelled hot water system based on combined power and heat pump cycles. The proposed system essentially integrates a premixed gas burner, an organic Rankine cycle (ORC) power plant, and an air source heat pump for supplying hot water. An ORC power plant generates mechanical power from the thermal energy produced from the combustion of natural gas in the burner. Subsequently, the generated power directly drives a vapour compression cycle heat pump. Cold tap water is heated by three heat exchangers in series to gradually increase its temperature. It is preheated in the condenser of the heat pump, then heated in the condenser of the ORC power plant, and finally further heated by the flue gas exiting from the burner in a post heater. The flue gas exiting the post heater will be mixed with ambient air to further extract its residual heat in the evaporator of the heat pump. A comprehensive numerical analysis has been presented in this paper, and the results show that the proposed system can achieve an overall fuel-to-heat efficiency up to 147% when the cold water is heated from 10 to 65 °C and the ambient air temperature is in the range of −5 to 5 °C. The research results demonstrated that the proposed technology has a great potential for domestic hot water applications.

Discussion of a combined solar thermal and ground source heat pump system operation strategy for office heating

Combined operation of solar thermal and ground source heat pump (GSHP) is widely applied in regions with unbalanced cooling and heating demands. The combined system could achieve a better performance if it is well performed. Optimal operation of the combined system is an interesting topic since different systems have their own characteristics in design, site, local resource etc.The effect of different operation strategies of the combined system to the system performance, soil temperature variation are discussed in this paper. A results discussion of a combined solar thermal and GSHP system for office heating under different operation strategies by simulation is presented firstly, and the real operation of the combined system for a building heating in Beijing, north of China, utilize solar thermal as an assistant system of HP unit is addressed then. Water temperature variation in water tank and the HP unit is plotted and discussed as well, finally, solar thermal energy directly storage into the ground, soil temperature variation in the autumn season is introduced at the end.A system simulation tool, TRNSYS, is used to model three different operation strategies of the combined system in winter season: solar thermal preheats return water in the condenser side, evaporator side of the HP unit and the combination of the two. The simulation results manifest the system would be more economically efficient if solar thermal preheats return water of condenser side of the HP unit, but the utilization of solar thermal would be maximized if it preheats the return water of the evaporator side of the HP unit.A real operation of a combined system in winter season in an office building is presented then, in which the operation data in typical days 2014/12/25 to 2014/12/26 are analysed. The data discovers that with the assistant of solar thermal, heat pump could work temporarily, with a COP of 5.2 is found in the day.

ヒートポンプ・ボイラ併用による高効率熱利用温水供給システム : パイロットプラントの実験結果

ヒートポンプ・ボイラ併用による高効率熱利用温水供給システム : パイロットプラントの実験結果

Study of hybrid dryer prototype and its application in pregerminated rough rice drying

ABSTRACTIn this study, a hybrid dyer, combining heat pump drying (HPD) with fluidized bed drying (FBD) concepts were designed and fabricated. The pregerminated rough rice (pre-GRR) was dried in multistage using this hybrid dryer to compare with the single-stage drying by hot air dryer. The objectives were to test the application of this hybrid dryer and determine the suitable drying condition for pre-GRR. The result indicated that the punched plate distributor was the most suitable distributor. The pre-GRR should be dried by the three-stage drying method using either FBD or HPD at 45°C in the last stage to obtain higher head rice yield, lower fissure grain, and better color values than their counterparts. The scanning electron micrographs proved that starch gelatinization occurred when applying FBD at temperatures between 100 and 140°C causing the adhesive connections inside the kernels and subsequent decrease in fissures.