Per Lundqvist

A method to estimate the circulated composition in refrigeration and heat pump systems using zeotropic refrigerant mixtures

Abstract In recent years a number of refrigerant mixtures have appeared on the market. Some of these refrigerant mixtures are zeotropic, e.g. R407C and R417A. When zeotropic refrigerant mixtures are used in a system, the circulated composition may change from the nominal to a different composition. The changes in composition may be due to leakage or hold-ups of liquid or vapour phase, different solubility in the oil by the different components, or the fact that the system has been charged in an incorrect way. For the understanding of performance measurements made on systems, it is important to know the composition of the circulated refrigerant mixture. A promising method to estimate the circulated composition has been developed. The method has been applied and evaluated on a well equipped lab rig at the Department of Energy Technology at the Royal Institute of Technology. The tests show that it is possible to estimate the composition of the circulated refrigerant mixture to within 2%, by measuring only two temperatures and pressures.

Performance of a Single-Family Heat Pump at Different Working Conditions Using Small Quantity of Propane as Refrigerant

The performance of a domestic heat pump that uses a low quantity of propane as refrigerant has been experimentally investigated. The heat pump consists of two minichannel aluminium heat exchangers, a scroll compressor, and an electronic expansion valve. It was charged with the minimum amount of refrigerant propane required for the stable operation of the heat pump without permitting refrigerant vapor into the expansion valve at incoming heat source fluid temperature to the evaporator of +10°C. The inlet temperature of the heat source fluid passing through the evaporator was varied from +10°C to −10°C while holding the condensing temperature constant at 35°C, 40°C, 50°C, and 60°C, respectively. The minimum refrigerant charges required at above-tested condensing temperatures were found to decrease when the condensing temperature increased and were recorded as 230 g, 224 g, 215 g, and 205 g, respectively. The results confirm that a heat pump with 5 kW capacity can be designed with less than 200 g charge of refrigerant propane in the system. Due to the high solubility of propane in compressor lubrication oil, the amount of refrigerant which may escape rapidly in case of accident or leakage is less than 150 g.

The Ground Source Heat Pump : A System Analysis With a Particular Focus on The U-Pipe Borehole Heat Exchanger

The mass flow rate of the secondary refrigerant flowing in the borehole heat exchanger of a ground source heat pump is an influential system parameter whose variation can influence the pumping powe ...

Low-grade heat source utilization by carbon dioxide transcritical power cycle

One way to reduce the fossil fuel consumption and mitigate environmental impact is to utilize low-grade heat sources for power production. In this paper, a transcritical carbon dioxide power cycle ...

Modelling and experimental validation of advanced refrigeration systems in supermarkets

Abstract The effective use of energy and the replacement of CFC and HCFC refrigerants are two factors that have influenced the design and operation of refrigeration systems in supermarkets during recent years. The potential for increasing energy efficiency in refrigeration systems, indoor climate and refrigerated cabinets is large. Since the energy systems of a supermarket are relatively complex, improvements in one subsystem affect other systems, thus making analysis of potential improvements non-additive. A computer model, CyberMart, that predicts building heating and cooling loads, HVAC (heating, ventilation, and air conditioning), and refrigeration system performances of a supermarket, has been developed. The focus of the model is on energy use, environmental impact (TEWI), and life cycle cost (LCC) of the refngeration system. The refrigeration system solutions included in the model are: direct system, completely indirect system, partially indirect system, cascade system, parallel system with mechanical sub-cooling (where the refrigerant in the low-temperature system is sub-cooled with the brine of the intermediate temperature level), and district cooling (that cools the condenser of the refrigeration machines). Measurements of different parameters such as outdoor and indoor temperatures, relative humidity, and compressor power have been carried out in several stores to validate the model. A theoretical description of the model and results from the model and measurements are presented in this paper.

Thermodynamic pre-determination of power generation potential in geothermal low-temperature applications

BackgroundSmall capacity, low temperature, geothermal heat sources provide significant opportunities for distributed, small scale power generation. Project definitions and pre-dimensioning however require advanced thermodynamic engineering at a cost independent of project size. In order to reduce this cost, a new method has been developed to allow basic level engineers to perform pre-optimisation of thermodynamic potential as well as expected performance using available power plant technology at such pre-optimized conditions.ResultsBy reducing the complexity of second-law computations, a simple two-dimensional diagram is shown representing the dimensioning criteria required for maximum power generation using the particular heat source and sink while considering expected power plant performance, using systems and components on the market.MethodsBy sensitivity analysis the combination of thermodynamic analysis and real world data correlations was simplified and arranged for pre-dimensioning of business cases.ConclusionsOptimal pre-dimensioning of power generation system for any geothermal heat source, with a defined heat sink, can be determined without advanced thermodynamic expertise. This reduces the cost for business case proposals, pre-dimensioning and tender specifications of small-scale power generation systems for low temperature heat sources. The intended implication of this work is to increase the use of low-temperature geothermal wells for distributed power generation.

CFC and HCFC refrigerants retrofit — experiences and results

Abstract This paper discusses levels of acid, moisture and residual mineral oil in converted refrigerant and heat pump plants. The work has been concentrated in three main areas: current retrofit practice, database of results from laboratory analysis of oil samples from converted plants and lab tests of combinations of R134a, ester oil, residual R12, residual mineral oil and moisture. The current retrofit practice study shows that most commonly used methods are satisfying as far as the moisture level is kept low. A comparison with the database study shows that measured values are at a level with the target values, given by the refrigeration companies. As a complement, sealed tube tests have been initiated in order to further clarify the effect of different combinations of contaminants.

Who is Governing the Commons : Studying Swedish Housing Cooperatives

Abstract This study examines current governance structures related to multifamily buildings designed by single actors (developers) and operated in cooperative forms. The study analyses the long-term sustainability of the resource regime of study (multifamily buildings) and inked governance structures by applying Ostrom’s eight design principles for long-term survival of self-organized resource regimes (Common-pool resources or CPR’s). The study also searches for signs of movement towards social innovation and collective action in current governance structures. We argue that the structures governing planning, production and operation of housing cooperatives in Sweden do not fulfil the eight design principles for the long-term survival of the resource regime of study, nor do they encourage movement towards social innovation or collective action. In order to ensure the long-term survival of the resource regime of study and to increase innovation in governance structures, five adjustments are proposed; changes in the structures governing risk/profit distribution, communication, collaboration and information between actors in the Swedish cooperative housing sector.

Global Efficiency of Heat Engines and Heat Pumps with Non-Linear Boundary Conditions

Analysis of global energy efficiency of thermal systems is of practical importance for a number of reasons. Cycles and processes used in thermal systems exist in very different configurations, making comparison difficult if specific models are required to analyze specific thermal systems. Thermal systems with small temperature differences between a hot side and a cold side also suffer from difficulties due to heat transfer pinch point effects. Such pinch points are consequences of thermal systems design and must therefore be integrated in the global evaluation. In optimizing thermal systems, detailed entropy generation analysis is suitable to identify performance losses caused by cycle components. In plant analysis, a similar logic applies with the difference that the thermal system is then only a component, often industrially standardized. This article presents how a thermodynamic “black box” method for defining and comparing thermal efficiency of different size and types of heat engines can be extended to also compare heat pumps of different apparent magnitude and type. Impact of a non-linear boundary condition on reversible thermal efficiency is exemplified and a correlation of average real heat engine efficiencies is discussed in the light of linear and non-linear boundary conditions.

A bottom-up approach for energy systems – a case study on energy and service efficiency explored by human activity system modelling

This article presents the procedure for a bottom-up modelling effort where the concept of human activity system (HAS) is used to model the lifestyle and the behaviour of residents of a housing area in the Stockholm City district of Rinkeby with great need for refurbishment. The aim of this paper is to present and advocate a bottom-up approach for modelling energy system based on the concept of HAS and EUS and to highlight the user side of the energy system (energy efficiency and service conservation); and to present the methodological findings for the project entitled ‘Situations of opportunity in the growth and change of three Stockholm City districts’, called SitCit for short. The modelling process comprises of several steps, i.e., building of conceptual, qualitative and quantitative models. The software Stella has been used as the main tool for qualitative and quantitative parts of the modelling of the HAS and EUS.