An Approach to Capturing Residual Energy From the Subway System: Methodological Considerations

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

Heating performance of a vapor compression heat pump cascaded with a thermoelectric heat pump

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.

In South Africa, there is an ongoing constraint on the electricity supply at the national grid to meet the demand. Eskom is implementing various measures such as the Integrated Demand Management and the promotion and encouragement of the use of energy efficient devices like an Air Source Heat pump (ASHP) water heater to replace the high electrical energy consuming conventional geysers for sanitary hot water production. The ASHP water heater market is fast gaining maturity. A critical mathematical model can lead to performance optimization of the systems that will further result in the conservation of energy and significant reduction in global warming potential. The ASHP water heater comprises of an ASHP unit and a hot water storage tank. In this study, a data acquisition system (DAS) was designed and built which monitored the energy used by the geyser and the whole building, the temperature at the evaporator, condenser, tank outlet hot water, tank inlet cold water, the ambient temperature and relative humidity in the vicinity of the ASHP evaporator. It is also worthy to mention that the DAS also included to a flow meter and two additional temperature sensors that measured the volume of water heated and inlet and outlet water temperature of the ASHP. This work focused on using the mathematical equation for the Coefficient of Performance (COP) of an ideal Carnot’s heat pump (CHP) water heater to develop basic computation in M-file of MATLAB software in order to model the system based on two reservoir temperatures: evaporator temperatures (Tevp) of 0°C to 40°C (approximated to ambient temperature, Ta) and condenser temperatures (TCon) set at 50°C, 55°C and 60°C (approximated to the hot water set temperature of 50°C, 55°C and 60°C) respectively. Finally, an analytical comparison of a CHP water heater to the practical ASHP water heater was conducted on a hot water set point temperature of 55°C. From the modelling results, it can be deduced that at 0°C Tevp, the COP was 5.96 and 2.63 for CHP and ASHP water heater respectively, at a hot water set temperature of 55°C. Above 20°C Tevp, the rate of change of COP increased exponentially for the ideal CHP system, but was constant at 0.01/°C for the practically modelled ASHP water heater.

Aiming at the performance deterioration of air source heat pump at low temperature in cold area, an air source heat pump system with sodium chloride aqueous solution as low temperature phase change heat storage material was proposed to increase the air inlet temperature of the unit under low temperature conditions and improve the low temperature performance of the heat pump unit. The system form, unit energy consumption model, and economic model were given, and the operating economy of the traditional electric auxiliary heat air source heat pump system and the phase change heat storage air source heat pump system were compared through computational intelligence powered methods. On this basis, the operation economy of the heat pump system using different concentrations of sodium chloride solution as the heat storage material was simulated and optimized, and the operation efficiency and energy-saving performance of the system were analyzed by taking an actual residential building in a cold area as an example. The simulation results showed that the Heating Seasonal Performance Factor (HSPF) of the heat pump system using 8.5% sodium chloride aqueous solution as the heat storage material is 2.24, and the HSPF of the traditional electric auxiliary heat pump system is 1.83. Compared with the traditional electric auxiliary heat pump system, the phase change heat storage heat pump system saves heating energy consumption by 19.6% and defrosting energy consumption by 38.8%. The heat pump system using 10% sodium chloride aqueous solution as the heat storage material has the best operating economy, and the system HSPF is 2.33, which saves heating energy consumption by 23.2% and defrosting energy consumption by 34% compared with the traditional heat pump system. The operation condition of phase change heat storage air source heat pump system is stable, and the system performance is significantly improved.

Research and application of park multi-source synergistic and complementary heating system and its coordinated control method

Chapter 2.3 - Ground source heat pumps

A solar-air source heat pump with thermosiphon to efficiently utilize solar energy

An investigation on the environmental impact of various Ground Heat Exchangers configurations

Heat pump systems are promising technologies for current and future buildings and this research presents the performance of air source heat pump (ASHP) system. The system was monitored, analysed and simulated using TRNSYS software. The experimental data were used to calibrate the simulation model of ASHP. The specific climate conditions are evaluated in the model. It was noticed for the heating mode that the coefficient of performance (COP) varied from 1.98 to 3.05 as the outdoor temperature changed from –7.0 ºC to +5.0 ºC, respectively. TRNSYS simulations were also performed to predict seasonal performance factor of the ASHP for Vilnius city. It was identified that seasonal performance prediction could be approximately 15% lower if frost formation effects are not included to air-water heat pump simulation model.

The replacement of fossil-fuelled heating systems with systems using renewable energy sources is a central energy and climate policy concern and one of the prerequisites for reducing CO2 emissions to a climate-friendly level. The Swiss decarbonization strategy considers the use of electric air-to-water heat pumps (HP) operated with electricity generated from renewable sources or from a power mix with low CO2 content. However, the installation of HPs, which is essential for decarbonizing heat supply in buildings, is proceeding very slowly, and fossil fuel heating replacement is still the rule rather than the exception. This study investigates how a strong climate protection law (Energy Act of Basel-Stadt) has managed to overcome resistance to the installation of HPs, which is observed in many other Swiss cantons. The research question to be answered is whether the experience made with HP implementation in one location (with Basel-Stadt as forerunner canton) would be similarly viable in another location (Canton of Geneva). The results indicate that although the two cantons have different characteristics in terms of building stock, the potential of buildings where HP installation is considered ‘easy’ is high in both cases (50% in Basel-Stadt and 40% in Geneva). This is equivalent to 40% (in both cities) of the energy used for thermal use that is currently produced by fossil energy and that could be instead generated with HPs. Although there are many factors to take into account in order to design effective policies that are truly effective for the extensive installation of HP, it is worth remembering that there are many cases where it is already possible to easily install a HP today, and these should be the starting point.

Air source heat pump (ASHP) water heaters are efficient devices for sanitary hot water heating. The coefficient of performance (COP) of the air to water heat pump (AWHP) is constantly lower than that of the corresponding ASHP unit. The study focused on determining the COP of both the ASHP unit and the AWHP. This was achieved by the implementation of both experimental and simulation methods, with the help of a data acquisition system and the REFPROP software. The system comprised of a 1.2 kW split type ASHP unit and a 150 L high pressure geyser. A power meter, flow meters, temperature sensors, pressure sensors, ambient temperature and relative humidity sensor were installed at precise locations on the split type AWHP. Controlled volumes of 150, 50 and 100 L were drawn off from the AWHP during the morning, afternoon and evening for a year. The average COP for the summer and winter, in terms of the input electrical and output thermal energies of the AWHP were 3.02 and 2.30. The COPs of the ASHP unit, in terms of the change in the enthalpies of the refrigerant at the inlet and the outlet of the condenser and the evaporator, were 3.52 and 2.65 respectively. The study showed that the difference between the COP of the ASHP unit and that of the AWHP could be ascribed to the electrical energy consumed by the fan and the water circulation pump during the vapour compression refrigeration cycles. The work provides an energy optimisation opportunity to the manufacturers of this technology, helping to enhance the efficiency and COP of ASHP water heaters. Highlights The COPt of the ASHP unit was higher than the COPe of the AWHP. The COPe of the AWHP was the ratio of the input electrical energy consumed and the output thermal energy gained by the stored water. The COPt of the ASHP unit was enthalpies-dependent and a function of inlet and outlet enthalpies of the evaporator and condenser. The inlet and outlet refrigerant temperatures profiles of the condenser confirmed thermal energy dissipation.

Nowadays, due to the energy and environmental crisis, using renewable energy is considered to reduce environmental pollution. In this paper, a comprehensive review of geothermal source heat pumps (GSHPs) and air source heat pumps (ASHPs) are studied from various aspects including refrigerant change, single-stage heat pump and heat pump with an economizer. This study is conducted to meet the heating needs of the central laboratory of Hakim Sabzevari University. These cycles are analyzed using energy, exergy, and environmental and economic equations (4E analysis). The results show that the coefficient of performance (COP) and exergy efficiency values for the GSHP cycle are higher than the ASHP cycle, and the best refrigerant for both is R134A. The economic and environmental analysis also reveals that using the GSHP cycle can save the electricity to 239 MWh/year (by cycle equipment), which reduces CO2 emissions to 140 tons/year and saves costs 27,280 $/year, compared to ASHP.Moreover, by using an economizer in the heat pump cycle, the COP of the GSHP cycle improved by 9%. The exergy efficiency about 6.8% and the COP of the ASHP cycle grew about 7.5% and its exergy efficiency by 7.4%. It is concluded that the economizer has a more significant impact on the GSHP cycle.

A significant part of energy in Norway is utilized for space heating due to the cold climate and heat pump technology has gained popularity in the country for space heating. According to the European heat pump association, Norway has the most heat pumps per capita in Europe, providing 16 TWh of heat energy annually. This review paper discusses the most common types of heat pumps in Norway. A comparison between the performance and payback time of different types of heat pumps in Norway is presented. Ground source heat pumps are more suitable than air source heat pumps due to maintaining a higher coefficient of performance during cold periods. The amount of thermal energy extracted using ground source heat pump systems is estimated to be 3 TWh and expected to be 8 TWh by 2030. However, more than 90% of heat pump installations in Norway are air source heat pumps. Compared to air source heat pumps, ground source heat pumps face many challenges, such as high initial cost, lack of public awareness, and insufficient professional workforce. The sales of heat pumps dropped by 13% in 2020, mainly due to the Covid-19 impact on the market. However, the sales increased significantly in 2021 due to the ongoing energy crisis and increase in energy prices.

Feasibility Analysis of Building Heating System Based on Thermal-Economical Evaluation