909 低温ヒートシンクを利用するCO_2サイクルの冷房性能予測(OS12-(1) 流体工学・熱流体,オーガナイズドセッション)

Machine learning and in silico discovery of metal-organic frameworks: Methanol as a working fluid in adsorption-driven heat pumps and chillers

An experimental study has been carried out on a continuously operated pilot fractional distillation column equipped with an external heat pump. The distillation column was a 15 cm diameter glass unit containing eleven single bubble cap plates. A methanol-water mixture was fed to the column and the heat pump working fluid was R114. The actual coefficient of performance (COP)A of the heat pump increased with an increase in the mass flow rate of the working fluid. A maximum (COP)A value of 4–3 was obtained with a gross temperature lift of 41–3°C. The performance of two reciprocating compressors was compared. The experiments have shown that continuous heat pump assisted distillation using an external working fluid can greatly reduce the energy used in a distillation process. No control problems were encountered in the experiments.

At Olkaria II power plant located in Kenya, the brine from the separator is re-injected back into the ground. This study analyzes a flash geothermal-solar hybrid cycle using the working fluids n-butane, n-pentane, cyclopentane, hexamethyldisiloxane and toluene in order to utilize the brine. The studied working fluids have no potential to deplete the ozone or cause global warming. The working fluids were analyzed in terms of net power output and pump power required. This was done by heating Therminol VP-1 fluid to a maximum temperature of 400 °C using the parabolic trough solar collector and varying the working fluids mass flow rate, Therminol VP-1 flow rate and pressure, and the brine pressure and flow rate. They were varied to investigate their effect on the power output of the Organic Rankine Cycle. The working fluid with higher net power output was selected as a suitable working fluid for the hybrid cycle. The selected working fluid was used to determine the average hourly power output in each month of the hybrid system using the irradiance of Olkaria II power station. N-butane showed the best results in net power output hence it was selected as a suitable working fluid as compared to the other working fluids. When the hybrid system was analyzed using n-butane to obtain the hourly average power output in each month, the results revealed that the month of February has the highest hourly average power output where the Steam Turbine has an average hourly power output of 10.48 MW and Binary Turbine net power output of 18.56 MW. The minimum average hourly power output was obtained in the month of June where the Steam Turbine has an average hourly power output of 9.08 MW and Binary Turbine net power output of 16.88 MW.

Cold climate heat pumps (CCHPs) expand the heat pump market to climates where heating demand is dominant. They can achieve more than 70% energy savings compared with electric resistance heating and operate at lower cost than using tank-stored propane to fuel a furnace. A high-efficiency heat pump with a heating seasonal performance factor (HSPF)—as defined by the Air-Conditioning, Heating, and Refrigeration Institute (AHRI 2008)—greater than 10.0 would be more efficient than gas heating in terms of source energy. However, developing a cost-effective CCHP involves some challenges. A typical single-speed, air-source heat pump (ASHP) with an HSPF of 7.7 Btu/Wh does not work well under cold outdoor temperature conditions typical of cold climate locations for four major reasons: Discharge temperature is too high—The low suction pressure and high compression pressure ratio at low ambient temperatures causes high compressor discharge temperatures in excess of the maximum limit for many of the compressors on the market. Furthermore, system charge of a heat pump is usually optimized in the cooling mode, which leads to overcharge conditions in the heating mode, further increasing the discharge temperature.; Heating capacity is insufficient if sized to meet the building design cooling load— Heating capacity of a single-speed heat pump decreases with ambient temperature. The heating capacity at -13°F (-25°C) typically decreases to 20%–40% of the rated heating capacity at 47°F (8.3°C) (~equivalent to the rated cooling capacity at 95°F [35°C]). Therefore, a single-speed heat pump, typically sized to match the building design cooling load, cannot provide adequate heating capacity to match the building heating load at low ambient temperatures. The capacity deficit is filled by inefficient resistance heat, thus lowering the system efficiency and significantly increasing power demand.; Cyclic loss is significant if sized to meet the building design heating load—If a single-speed heat pump is sized to meet the heating load, it will be significantly oversized relative to the cooling load in many cold climates. This will cause excessive on/off cyclic loss during the cooling and heating operations at moderately low ambient temperatures. Thus, capacity modulation capability (e.g., using a variable-speed or multi-stage compressor) is necessary for a CCHP, which uses its full capacity to meet the peak heating load and partial capacity to meet the cooling and part-load heating loads.; Coefficient of performance (COP) is low—Heating COP degrades significantly at low ambient temperatures owing to the large temperature difference between the heat source and sink. A target CCHP should be sized to meet the building design heating load while minimizing the cyclic loss for the cooling and heating operations at moderate ambient temperatures.

Optimal design of heat pump integrated low-grade heat utilization systems

Chapter 2.3 - Ground source heat pumps

Long-term energy and exergy analysis of heat pumps with different types of ground and air heat exchangers

Ground source heat pumps (GSHPs) attract attention as one of the future energy saving system. In the conventional GSHP system, which uses an indirect heat exchange method, vertical systems use two long pipes connected by a U-shaped fitting at the bottom of a hole bored in the ground. These pipes form part of a closed loop, called the ground loop, through which a mixture of water and antifreeze circulate. In contrast, a GSHP that uses a direct expansion method circulates a mixed refrigerant through the ground loop. The purpose of this study is to investigate the heat exchanging performance of the GSHP using direct expansion method. The coefficients of performance (COP) were obtained for the direct expansion type of GSHP running in the cooling and the heating mode. The amount of heat transferred was evaluated by obtaining an enthalpy difference at the indoor unit. It was found that the COP in the cooling mode was over 12 and in the heating mode was around 7.

In recent years, the adoption of heat pumps for building heating has steadily increased. However, the hot water heating market, particularly in buildings with existing hot water systems, has lagged behind. One of the primary challenges in retrofitting these buildings is the decline in heat pump efficiency as the compression ratio increases. Heat pumps that generate boiler-temperature water often suffer from low efficiency, with the coefficient of performance (COP) values below 2. A new technology known as the “Double Hybrid” heat pump has emerged, claiming to surpass theoretical efficiency limits by utilizing multi-stage condensers. This study investigates the performance and optimization of a Double Hybrid heat pump system in both heating and cooling modes. A gradient-based optimization approach has been applied to enhance and maximize the (COP). Theoretical results indicate that integrating an air coil for refrigerant subcooling and incorporating a second internal heat exchanger (IHX) significantly enhance system efficiency in both heating and cooling modes. In heating mode, the maximum COP reaches 4.52, exceeding the theoretical limit of 3.43 COP for a comparable water-to-water heat pump with ideal heat exchangers and an ideal compressor, Reflecting a notable 31.77% improvement in COP. Similarly, in cooling mode, the COP improves from 3.46 to 3.79, representing an 9.53 % increase under the same conditions.

Approximately one quarter of energy-related emissions in Germany are caused by the domestic sector. At 81%, the largest share of these emissions is due to heat supply. Many measures are available to reduce these emissions. One of these measures, which is considered to play an important role in many studies, is the replacement of fossil-fired boilers with electric heat pumps. In order to be able to analyse the impact of high penetrations of heat pumps on the energy system, the coefficient of performance (COP) must be modelled with high temporal resolution. In this study, a methodology is presented on how to calculate high-resolution COPs and the electrical load of heat pumps based on thermal load curves and temperature time series. The COP is determined by the reciprocal Carnot factor. Since heat pumps are often designed bivalently due to the cost structure, the methodology described can also be used for evaluating the combination of immersion heater and heat pump (here for the air/water heat pump). As a result the theoretical hourly COPs determined are calibrated with annual performance factors from field tests. The modelled COPs show clear differences. Currently, mostly air source heat pumps are installed in Germany. If this trend continues, the maximum electrical load of the heat supply will increase more than would be the case with higher shares of ground source heat pumps.

Review of enhancement for ocean thermal energy conversion system

Heat pump (HP) dryers have been used as one of the useful and promising drying techniques in food industries owing to their low energy consumption and costs, high coefficient of performance (COP), high energy efficiency, high drying efficiency, low drying temperature, and time, and less quality loss of dried products. It can be operated over a wide range of temperatures and humidity, providing the optimum conditions for drying of heat-sensitive food materials (vitamins). Many studies were done on food products drying by various HP drying systems such as simple HP, solar-assisted HP, infrared- assisted HP, vacuum HP and ultrasound intensified HP dryers. This paper reviews the effect of different and recent HP drying methods on the drying performance and quality of dried apple, banana, grape, jujube, kiwifruit, and pineapple. Also, this study reported the suitable mathematical models for HP drying modeling of various fruit crops. The HP dryer provides high-quality dried fruits as their drying conditions can be controlled. In addition, combination of solar/infrared/vacuum/ultrasound techniques and HP dryer has been used as an efficient and rapid drying method compared to HP drying alone. The effective moisture diffusivity (Deff) values lie within in range of 10−7 to 10−11 m2/s for some fruit crops during drying by HP dryer. Abbreviations: COP: Coefficient of performance; Deff: Effective moisture diffusivity; HP: Heat pump.

Some basic introduction about the current background of heating in the UK and ground source heat pumps (GSHPs) and natural gas (NG) boilers was outlined in this report. Moreover, this report also provided a detailed literature-based review of previous studies of both GSHP and NG boiler, concentrating on environmental impact, costs and benefits. For the purpose, a 12kW peak heating load house which is located in London established by the IES VE have been considered as the case study. Finally, it is concluded that the coefficient of performance (COP) of GSHP should be higher than 2.2 to achieve lower carbon emissions compared with NG boilers in the current period. And under normal conditions, the efficiency of the GSHP is in the range of 2.2 to 4, so it is more environmentally friendly than the NG boiler. As for a GSHP with a COP of 4, it has been found that the carbon emissions will be reduced by about 25% in the current period, 40% in 2030 and even 90 percent in 2050 after replacing the NG boiler. Besides, the results show that using low operating temperatures will contribute to reduce carbon emissions. In the aspect of economic, it can be concluded that the installation of the GSHP is cost-effective in most cases and the higher the COP, the shorter the payback period. Under the subsidy of Renewable Heat Incentive (RHI), for a GSHP with a COP of 4, its payback period is about 20 years. However, if the COP is lower than 2.6, the capital costs cannot be fully recouped. In the end, the results and the limitations occurring in the research process have been analysed and advice on future improvements was given.

Selection of working fluid for low enthalpy heat source Organic Rankine Cycle in Dholera, Gujarat, India

This study illustrates the potential of high temperature heat pumps (HTHPs) integration into district heating network (DHN) through a twofold approach, using DHN as a heat sink and source. It is used as a heat sink of HTHP that uses waste heat from the supermarket’s refrigeration system as a heat source whereas it is used as a heat source to HTHP that provides heat to industrial applications. When the DHN acts as the heat sink, the integrated system provides a coefficient of performance (COP) of the waste heat recovery (WHR) system between 3.2 and 5.4, reducing the operating costs between 50% and 100% with an average price ratio of 2.25 compared with the standard CO2 refrigeration system. If the DHN is the heat source, the integrated system provides a COP from 2.8 to 5.7 for a heat sink of 110 °C. The alternative low-GWP refrigerants assessment illustrates that HC-290, HFO-1234ze(E) and HFO-1234yf were considered the ideal candidates to replace the HFC-134a, whereas HCFO-1233zd(E) and HCFO-1224yd(Z) were the most promising low-GWP refrigerants to replace HFC-245fa. Finally, the environmental results showed that the utilisation of the DHN as the heat sink in the integrated system solution produces about 60% lower equivalent CO2 emissions than the DHN generation mix. Moreover, using DHN as the heat source, the equivalent CO2 emissions can be reduced up to 98% in Sweden compared to conventional natural gas boilers. Hence, the combination of HTHPs and the DHN represents a step forward in the mitigation of climate change through the utilisation of sustainable energy conversion technologies.