Small Heat Pump Research Articles

Cost-benefit analysis and comparison of grid-stabilizing energy flexibility options and their applications in relation to the German energy system

With an increasing share of renewable energies, flexibility is becoming an important factor to ensure the German electricity grid stability. Therefore, decision-makers have to deal with the implementation of the necessary transformations and adaptions. To provide an indication, a cost–benefit analysis and comparison of grid-stabilizing energy flexibility options and their applications for a current and an outlook scenario is conducted. In the results, due to its low costs, the flexibilization of existing CHP (combined heat and power generation) plants stands out as a particularly attractive option. Similarly, the flexibilization of existing wind turbines and photovoltaic systems, as well as the flexibilization of small heat pumps, appear to be highly attractive in the outlook (integration is enabled by pooling). Furthermore, in the future, large-scale batteries and PEM (Polymer electrolyte membrane) electrolysis as well as controlled charging (pooling) will become increasingly beneficial for the energy system. The overall worst performing flexibility option is power-to-methane, which requires additional effort from the system in both scenarios. In general, the research showed that even for similar flexibility options, the resulting systemic benefit highly depends on the specific flexibility application. Nonetheless, the results give an indication towards important sources of flexibility and further research priorities.

A small ammonia heat pump using linear compressor

The electrification of space heating and hot water via heat pumps is a widely pursued policy aim but field trials demonstrate poorer seasonal performance than anticipated. Linear compressors without crank mechanism can be oil-free. The potential for capacity modulation by adjusting the compressor stroke offers significant advantages over traditional methods including on-off control and variable frequency given that heat pumps operate at part load most of time. R717 (ammonia) has superior latent heat which offers a higher heating capacity compared to R134a, making it a very promising refrigerant for small heat pumps but there is no compatible compressor due to corrosivity. This paper introduces a novel small ammonia heat pump using an oil-free linear compressor technology that is compatible with R717. A numerical model was established to predict the heat pump baseline performance. The outcomes show a linear relation for specific power input, heating capacity, and Coefficient of Performance (COP) against ambient temperature. The system can achieve COP of 2 when ambient temperature is 0 °C. With linear compressor, there will be no on-off cycling for heat pumps so that the seasonal COP will be significantly higher than on-off control and variable frequency drive systems.

Thermodynamic performance assessment and application feasibility analysis of small heat pump water heater using CO2/R41 azeotropy mixture as refrigerant for sustainable development

In order to improve the application possibility of CO2/R41 azeotropy mixture in the refrigeration industry, the optimum mass ratio of composition is defined and determined according to the thermodynamic properties and safety. On the basis of the first and second laws of thermodynamics, a model is proposed to evaluate the performance of CO2/R41 single-stage transcritical cycle (CO2/R41 cycle) in which a throttling valve is integrated and CO2/R41 azeotropy refrigerant is adopted. The performance of CO2/R41 cycle at the optimum mass ratio of CO2/R41 azeotropy mixture is then compared with that of a CO2 two-stage transcritical cycle with throttling valve (CO2 two-stage cycle) and that of a CO2 single-stage transcritical cycle with expander (CO2 expander cycle). The results show that the optimum mass ratio of CO2/R41 azeotropy mixture is 0.583/0.417. Compared with CO2 two-stage cycle and CO2 expander cycle, CO2/R41 cycle has the advantages of a simpler structure, lower optimum high pressure, appropriate discharge temperature of the compressor, and higher COP. Therefore, the CO2/R41 azeotropy mixture with the mass ratio of 0.583/0.417 is eco-friendly and can be considered as a good alternative refrigerant for application in the refrigeration industry. The simple CO2/R41 cycle shows great feasibility to replace the complex CO2 two-stage cycle and CO2 expander cycle.

Integration of Heat Pumps in Buildings and District Heating Systems—Evaluation on a Building and Energy System Level

The use of heat pumps in buildings is one of the best and often the only option for the decarbonization of the building stock. District heating seems a promising solution in urban areas and in existing buildings when the use of heat pumps is restricted and also technically and economically challenging (source exploitation, space restrictions, sound emissions, etc.). Heat pumps can be integrated in various ways in buildings and district heating systems: large central high-temperature heat pumps in district heating, medium-size heat pumps block- or building-wise or small heat pumps decentral apartment-wise. The best option depends on the individual district heating CO2 emissions and the electricity mix as well as on the perspective of the building owner versus that one of the district heating system and its future development. Austrian examples of district heating systems and different variants of integrating heat pumps are investigated in a comprehensive way by means of an energetic and environmental simulation-based analysis. This assessment includes a detailed investigation of the capabilities of the booster heat pump to increase the PV own-consumption and is also expanded to include various scenarios for the development of the electricity mix and the decarbonisation of district heating.

Modelling the two-phase flow of propane in a capillary tube: Determination of the two-phase viscosity based on detailed experiments

Abstract Capillary tubes are widely used as throttle device in small heat pumps. A reliable and predictive capillary model within an overall heat pump model can reveal the design potential of the capillary towards an optimized heat pump operation. A flow model is presented that predicts the single and two-phase flow of propane through a straight copper capillary tube of 1.1799 mm inner diameter and 1 m length that evokes a pressure drop. An extensive and precise experimental database is generated by thorough experiments also providing refined specifications of the inner diameter and roughness of the capillary tube. Experiments are carried out for inlet pressures of 16-25 bar, mass flows of 13.5-18 kgh − 1 (3430-4573 kgm − 2 s − 1 ) and subcoolings of 5-9 K. Based on the generated experimental database, multiple common two-phase viscosity correlations are evaluated within the flow model. A proposed modified two-phase viscosity correlation results in the best fit of experimental and predicted the flow of propane through the capillary with a mean relative error of only 4 %.

Integration of Heat Pump Storage Systems in Manufacturing Systems via Data Farming and Monte Carlo Simulation

The electrification of industrial energy demand is essential for effective climate protection and a successful energy transition. In production systems with fluctuating heating and cooling demands, heat pumps can make a significant contribution to electrification and increased efficiency in a demand-oriented production with automated standby operation. In order to dimension a suitable heat pump storage system, well-founded statistical information about the production system is required. For the creation of stochastic heating and cooling demand profiles, numerous material flow simulations were therefore carried out as part of a case study, whereby the simulated time is always a production week in seconds resolution with shutdown at the weekend. Input data for the simulation are real energy measurement data from an energy monitoring system. The results of the Monte Carlo simulation show that relatively small heat pumps and storages can ensure the reliable heat and cold supply of the manufacturing system thanks to the superposition and mutual compensation of numerous sources of uncertainty in the manufacturing system. In the case study presented in this paper, covering a constantly running HP in only 95 % of all possible cases instead of the entire 100 % leads to a drastic reduction in storage volume by a factor of about 25.

Experimental study on P-V diagram and valve displacement of a HC290 rotary compressor

HC290 is a substitute for R22 and R410A for small heat pumps, room air conditioners, and light commercial refrigeration equipment since it has a negligible environmental impact and high efficiency. The performance, P-V diagram and valve dynamic displacement of a rotary compressor using R22 and R290 as the refrigerant, under five different operating conditions, were measured and analyzed in this paper to help understand the characteristics of internal thermodynamic process and the distribution of indicated power losses. Further, a new method for analyzing the P-V diagram of a rotary compressor was proposed. Compared with the R22 compressor, some conclusions about the discharge process starting angle, dynamic variation of pressure in the cylinder, volumetric efficiency, indicated efficiency, and loss distribution of the R290 rotary compressor under high efficiency conditions were given. The performance variation of the R290 compressor under other conditions was explained. Several measures to increase the energy efficiency of the R290 rotary compressor were proposed.

Theoretical study of a thermoelectric-assisted vapor compression cycle for air-source heat pump applications

This paper proposes a thermoelectric-assisted vapor compression cycle (TVCC) for applications in air-source heat pump systems which could enhance the heating capacity of the system. Performances of TVCC are calculated and then compared with that of basic vapor compression cycle (BVCC). The simulation results show that when coefficients of performance (COPs) of the two cycles are almost equal, the TVCC under maximum COP condition of the thermoelectric modules still performs better than BVCC by 13.0% in heating capacity through selecting the appropriate intermediate temperature. In addition, the TVCC can also achieve an improvement of 16.4%–21.7% in both the heating COP and capacity when compared with the BVCC with an assistant electric heater that is provided with the equivalent power input of thermoelectric heat exchanger. Thus, the TVCC could be beneficial to the applications in small heat pumps if there is always need for auxiliary electric heat.

The Experimental Study of Water Storage Performance on Small Heat-Pump Energy Storage Air-Conditioner

Based on the performance of energy storage air conditioning system, a small heat pump water heat storage air conditioner was designed with some experiments in winter running. The experiments show that the heat storage system can improve inlet temperature of the refrigerating compressor effectively when proceeding heating mode, and the outlet temperature is also higher relatively; In the low-temperature heating condition, the maximum heating capacity can up to more than the rated heating capacity and the defrosting performance is better too; But the heat storage capacity of the system is quite limited for the thermal storage material is water.

Introduction and analysis of a concept for decentralized heat pumping in hydronic networks

This work describes a system that utilizes small distributed circulation and heat pumps in order to locally adjust the heating and cooling capacity of a hydronic heat pump system. Thereby, flexibility of the whole system is increased, which allows for better control of heating capacity, increases comfort and at the same time reduces the temperature lift of the main heat pump.Those pumps are integrated in a conventional distribution network. The small heat pumps transfer energy between the unit's supply and return thereby influencing the overall system temperature lift.A mathematical model of a hydronic heating system was used in order to determine required efficiencies of decentralized heat pumps for different evaporation temperatures of the central heat pump and different geometries. A setup with conventional centralized temperature setting served as reference.As a result, the efficiency of the decentralized heat pump should be at least 0.2 for a system with low evaporation temperatures of 0°C, whereas for a system with high source temperatures this value increased to 0.32. A small reduction in electric power was observed even when compared to a highly efficient setup. The system is feasible with available technology, but the sizing of the unit is depending on the whole system and the desired operating regime.

Experimental study on a hybrid photovoltaic/heat pump system

Several studies have found that the decrease of photovoltaic (PV) cell temperature would increase the solar-to-electricity conversion efficiency. Different working fluids such as air and water have been used for the cooling of PV modules, but the improvement in energy performance has been found to be small. In this paper, R134a refrigerant was employed to cool the PV modules. With its low evaporating temperature, it was expected to achieve better cooling effect and electrical performance of the PV modules than using air and water working fluids. An experimental rig of a hybrid micro PV panel-based heat pump system was constructed for the performance testing in a laboratory at the University of Nottingham. A small PV panel was made of 6 glass vacuum tube – PV module – aluminium sheet – cooper tube (GPAC) sandwiches connected in series, acting as the evaporator. This was coupled with a small heat pump system. The glass vacuum tubes reduced the heat loss from the PV panel to the ambient, resulting in the improvement of thermal performance. Three testing modes were proposed to investigate the effect of solar radiation, condenser water flow rate and condenser water supply temperature on energy performance. The testing results showed that an averaged COP reached 3.8, 4.3 and 4.0 under the three testing modes with variable radiation, condenser water supply water temperature and water flow rate, respectively, but this could be much higher for a large capacity heat pump system using large PV panels on building roofs. The COP increased with the increasing solar radiation, but decreased with the increasing condenser water supply temperature and water flow rate. The electrical efficiency of PV panel was improved by up to 1.9% based on a reference PV efficiency of 3.9%, compared with that without cooling. The condenser water supply temperature and water flow rate had little effect on the electrical performance.

A thermodynamic analysis of a transcritical cycle with refrigerant mixture R32/R290 for a small heat pump water heater

In this study, a thermodynamic analysis on the performance of a transcritical cycle using azeotropic refrigerant mixtures of R32/R290 with mass fraction of 70/30 has been performed. The main purpose of this study is to theoretically verify the possibility of applying the chosen refrigerant mixture in small heat pumps for high temperature water heating applications. Performance evaluation has been carried out for a simple azeotropic mixture R32/R290 transcritical cycle by varying evaporator temperature, outlet temperature of gas cooler and compressor discharge pressure. Furthermore, the effects of an internal heat exchanger on the transcritical R32/R290 cycle have been presented at different operating conditions. The results show that high heating coefficient of performance (COP h) and volumetric heating capacity can be achieved by using this transcritical cycle. It is desirable to apply the chosen refrigerant mixture R32/R290 in small heat pump water heater for high temperature water heating applications, which may produce hot water with temperature up to 90 °C.

Cool Argument: Engineering Students’ Written Arguments about Thermodynamics in the Context of the Peltier Effect in Refrigeration

In this paper, we investigate university engineering students’ written arguments in the context of the thermodynamics principles involved in refrigeration. The students were given writing frames to complete reports following investigations on thermoelectric coolers, sometimes called “thermoelectric module” or “Peltier cooler”. The device is a semiconductor-based electronic component that functions as a small heat pump. By applying a low voltage DC power source to a cooler, heat moves through the module from one side to the other. One module face, therefore, will be cooled while the opposite face is simultaneously heated. The task immerses students in the context of providing evidence and justifications for temperature change using general principles of thermodynamics. The context of the study provides examples on the nature of arguments in the applied field of engineering where appeals to scientific principles are made to justify the design of an industrial product. The writing frame engaged the students in the recording, analysis and interpretation of experimental data including data from a simulation program. Several lines of analyses have been conducted including the epistemic levels of students’ arguments. This paper will report on one aspect of analysis focusing on the quality of students’ written arguments. A simplified version of Toulmin's Argument Pattern (1958) has been used as a guiding model to investigate the written arguments. Results indicate that very few students were able to accurately interpret the experimental data and only 35% of the arguments from 31 reports were valid. Most texts used conclusions that were not derived from the evidence used. We propose some rubrics to further support the writing and evaluation of arguments.

TRT system for Heat Pumps Design

The paper deals with problematic of Thermal Response Test (TRT) system. The correct design of borehole heat exchangers for ground source heat pumps and the knowledge of rock massive thermal properties is paramount. For small heat pumps systems these parameters are estimated. However, for larger objects the thermal conductivity should be measured on site. Thermal Response Test is an useful tool for thermal conductivity estimation. This test is instrumental to find out a response of rock massive in which a heat pump might be installed. The paper describes basic principles of TRT and its utilization for heat pump boreholes design.

Domestic ventilation unit with heat exchanger and heat pump

A ventilation heat recovery unit was installed in an Electricity Council Research Centre test house. The unit consists of a cross flow heat exchanger augmented by a small heat pump. It supplies warm air to all inhabited rooms, while extracting air from kitchen and bathroom. Trials were run during the winter of 1986/87. The unit provided a ventilation air flow of 180 m 3 h-1, and a gross heat input to the house of 1.7 kW; this figure is averaged over time, and includes the effect of defrost periods. An overall coefficent of performance of 3 was achieved. Such a system can provide the greater part of the heating requirement of a low-energy house, and has its own advantages over other heating systems.

Noise from Small Heat Pumps

Noise from Small Heat Pumps

Economic possibilities and limitations of heat pumps with electric drive

The principles of the heat pump are analysed with special reference to the heating of homes and buildings, use being made of the concepts ‘Exergy’ and ‘Anergy’. Economic criteria are introduced to take account of capital and installation costs and the rates of amortization and interest to be applied to both heat pumps and conventional fuel systems. Also, the relative costs of fossil fuels and electricity are used, together with a mean coefficient of performance of the heat pump. A comparison is made not only between the two systems but also for composite systems in which the output of the heat pump is supplemented or replaced by direct heating (electrical resistance or fossil fuel) during winter peaks. The effect of the electricity tariff on the attractiveness of a heat pump system is examined, together with the potential advantage of heat storage systems. It is concluded that the most attractive application of heat pumps arises with district heating schemes due to the lower capital charges associated with large installations. In certain cases, however, the combination of a small heat pump designed to meet say 70% of winter demand, supplemented by burning stored fuel at times of peak demand, could be economic for individual installations, especially if the capital cost of the supplemental system could be reduced. The scope for improving the coefficient of performance of heat pumps is outlined.