Fault Detection Algorithm for Multiple-Simultaneous Refrigerant Charge and Secondary Fluid Flow Rate Faults in Heat Pumps

In this research, an experimental study is performed to investigate the effects of system operating variables on the cooling and heating characteristics of heat pump system using geothermal heat source and carbon dioxide as a refrigerant. System variables analyzed include compressor frequency, electronic expansion valve opening, refrigerant charge, secondary fluid temperature and flow rate. Results show that optimum refrigerant charge and electronic expansion valve opening position exist at the maximum point of COP curve, and both cooling and heating capacity increase but COPs decrease with the increase of compressor frequency. The change of a secondary fluid temperature leads to variation of overheat area and enthalpy difference in the evaporator and gas cooler. which again results in considerable variations of cooling and heating capacity and COP. In the case of effects of secondary water fluid flow rate, both cooling capacity and COP increase with the increase of secondary flow in evaporator or gas cooler, whereas heating capacity and COP decrease with the increase of flow rate in gas cooler.

Design and performance study of the ground-coupled heat pump system with an operating parameter

A simple analytical model is developed for optimum ejector steady-state performance under the assumption that the driver gas mass flow rate exceeds the suction side mass flow rate. This requires the mixing to be at constant pressure and the suction side inlet Mach number to be small. Since the model is formulated in terms of enthalpy, it is applicable to arbitrary motive and suction gases. For purposes of verification, the model is compared with exact numerical results, and with the experimentally determined entrainment ratio used to correct the suction side mass flow rate for changes in temperature or molecular weight. The effect on ejector performance of the pertinent dimensionless parameters is considered. For example, it is shown that the use of a motive fluid with a ratio of specific heats near unity is detrimental to performance. I. Introduction O VER the past few decades there have been many fluid mechanic studies of ejector pumps. Currently, there is renewed interest in ejectors for pumping the subatmospheric effluent of cw chemical lasers,1-4 with primary emphasis on optimized ejector performance. Since an ejector is a pump, performance is in terms of a compression ratio, in particular, the ratio of the exhaust gas stagnation pressure divided by the stagnature pressure of the inlet suction gas. (The suction gas is referred to as the secondary flow; the motive gas is referred to as the primary flow.) Optimum performance is defined here as the largest compression ratio for given primary and secondary flow rates and for a given secondary stagnation pressure. An objective of this work is to derive simple, approximate formulas for the optimum compression ratio in terms of a minimum number of key dimensionless parameters. This approach provides a simple estimate of the maximum possible compression ratio, given the primary and secondary fluids, their stagnation conditions, and their flow rates. Conversely, it does not determine such fundamental characteristics as the transition1 between the mixed and super sonic regimes. Some generality is retained in the choice of parameters for the thermodynamic properties of both primary and secondary gases. This is important for laser application where the-composition of both gases often differs considerably from steam or air. Because of its analytical simplicity, the derivation provides useful insight into the dominant process in an ejector, e.g., a natural consequence of the analysis is an ejector figure of merit. The assumptions underlying the derivation, the derivation itself, and its method of application are presented in Sec. II. The effect on ejector performance of changes in primary gas stagnation enthalpy, ejector nozzle Mach number, etc., are discussed in Sec. III. Of particular interest are the sections which show that a value near unity for the ratio of specific heats of the primary gas leads to a small compression ratio, and that a low subsonic Mach number is required for the secondary inlet flow for optimum compression. To establish the validity of the analysis, a comparison is provided in Sec. Ill with exact computer solutions for a steam and air ejector pumping a chemical laser flow. A simple derivation is also given for the entrainment ratio used by the Heat Exchange In

The vapor compression cooling devices operate on the same principle as heat pumps. In these types of machines thermal energy is transferred from the cold environment to the warmer side using provided power by the compressor. In this study, the effect of air flow rate on the cooling performance of vapor compression cooling devices has been investigated by simulating a designed system in AVL CRUISE™ M program. The simulated model is air-to-air cooling machine and refrigerant R134a was used as circulated gas inside the system. COP value of the system has been calculated in different working conditions and obtained results have been fully discussed. Accordingly, enthalpy variation in every element of the heat pump has been calculated in different working conditions and discussed on P-h diagram. This study presents a simulation method that is a practical solution method in the field of heat pumps, cooling machines and refrigerators which can be considered before installing device in order to have a proper prediction of the system performance.

Evolutionary design of dynamic neural networks for evaporator control

One of the main directions for improving heat supply systems is the tendency to switch to low-temperature heating systems by using heat pump units is the tendency of implementation the low-temperature heating systems based on the use of heat pump units. In the work, the main attention is focused on the improvement of thermal parameters and circuit design features of elements of the heat pump system of heat supply using soil energy. For this purpose, the toolkit of mathematical modelling of processes in ground heat pumps is applied, taking into account the climatic conditions of Ukraine. The paper proves the technical possibility of creating an autonomous system of alternative heat supply for energy-saving technologies with the possibility of using ground energy, taking into account environmental requirements. It is substantiated that the use of the proposed systems is a promising direction for Ukraine, which is experiencing a shortage of its own energy resources, because it provides an opportunity to increase the share of organic fuel substitution and reduce the volume of heat emissions into the environment. A mathematical model of heat processes in the elements of the heat exchange equipment of the heat pump system based on renewable energy (soil energy) and secondary energy (wastewater) was developed, taking into account environmental requirements (preventing hypothermia of the soil during the operation of soil pipes and damage to vegetation, respectively), which allows choosing a rational mode of operation of the system under seasonal climatic changes and technological conditions. Numerical modelling of heat processes in elements of the heat exchange equipment of the heat pump system using groundwater and waste water was performed, and the energy and environmental efficiency of the system under variable climatic and technological factors was determined. Analysis and generalization of the calculation results of the heat pump heat supply systems using alternative energy based on the proposed mathematical model, taking into account environmental requirements (preventing thermal relaxation of the soil) allows to take into account the change in the temperature gradient around the soil heat exchanger and more accurately determine the heat flow from each section of the heat exchanger. It has been established that for heat pumps with soil heat exchangers, the maximum substitution ratio of the traditional fuel is 75 %, and the economically feasible quantity of soil heat exchangers is 9 units. Heat pumps using waste water can completely replace traditional heat supply systems. For individual consumers, it is possible to recommend heat pump units with soil heat exchangers, at the same time, it is necessary to provide a backup source of energy to increase the reliability of heat supply.

Thermal-Hydraulic Performance Analysis and Tube Inlet Orifice Design of a Once-Through Steam Generator

Effect of secondary gas injection on the peanut shell combustion and its pollutant emissions in a vortexing fluidized bed combustor

Current status of the performance of GSHP (ground source heat pump) units in the Republic of Korea

Fluidization in granular materials occurs primarily as a result of a dynamic balance between gravitational forces and forces resulting from the flow of a fluid through a bed of discrete particles. For systems where the fluidizing medium and the particles have significantly different densities, density wave instabilities create local pockets of very high void fraction termed bubbles. The fluidization regime is termed the bubbling regime. Such a system is appropriately termed a self-excited nonlinear system. The present study examines chaos suppression resulting from an opposing oscillatory flow in gas-solid fluidization. Time series data representing local, instantaneous pressure were acquired at the surface of a horizontal cylinder submerged in a bubbling fluidized bed. The particles had a weight mean diameter of 345 &mgr;m and a narrow size distribution. The state of fluidization corresponded to the bubbling regime and total air flow rates employed in the present study ranged from 10% to 40% greater than that required for minimum fluidization. The behavior of time-varying local pressure in fluidized beds in the absence of a secondary flow is consistent with deterministic chaos. Kolmogorov entropy estimates from local, instantaneous pressure suggest that the degree of chaotic behavior can be substantially suppressed by the presence of an opposing, oscillatory secondary flow. Pressure signals clearly show a "phase-locking" phenomenon coincident with the imposed frequency. In the present study, the greatest degree of suppression occurred for operating conditions with low primary and secondary flow rates, and a secondary flow oscillation frequency of 15 Hz. (c) 1998 American Institute of Physics.

A fault detection technique for air-source heat pump water chiller/heaters

Organic Rankine Cycle-assisted ground source heat pump combisystem for space heating in cold regions

Frequency response and bandwidth of an electrostatic flow probe

Prospect of modeling industrial scale flow batteries – From experimental data to accurate overpotential identification

A simplified method to evaluate the energy performance of CO 2 heat pump units