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

An Evaluation of the Energetic Performance of a Residential Hybrid Solar Assisted Air Source Heat Pump Water Heater

In data-based method for fault detection, principal component analysis (PCA) has been used successfully for fault detection in system with highly correlated variables. The aim of this paper is to combine the exponentially weighted moving average (EWMA) control scheme with PCA model in order to improve fault detection performance. In fact, PCA is used to provide a modeling framework for the develop fault detection algorithm. Because of the ability of EWMA control scheme for detecting small changes, this technique is appropriate to improve the detection of a small fault in PCA model. The performance of the PCA-based EWMA fault detection algorithm is illustrated and compared to conventional fault detection methods using simulated continuously stirred tank reactor (CSTR) data. The results show the effectiveness of the developed algorithm.

A critical mathematical model can lead to reliable prediction of the dynamic behaviour of a system. In this study, a robust and accurate data acquisition system (DAS) was employed to monitor the electrical energy consumption of a 150-L geyser and 150-L split and integrated types air source heat pump (ASHP) water heaters. This study equally focused on using the multiple linear regression models to correlate the coefficient of performance (COP) of the split and the integrated types ASHP water heaters to the difference between the hot water set-point temperature and the ambient temperature (Ts − Ta) and the relative humidity (RH). The models derived for both the split and integrated types ASHP water heaters had good determination coefficients of 0.900 and 0.901, respectively. The ReliefF algorithm tests showed that in either of the systems, the RH was a secondary factor while the (Ts − Ta) was a primary factor. The cost of DAS used in obtaining the data required for the model derivation was relatively low but of high measurement accuracy.

Air source heat pump (ASHP) water heater is an energy efficient device implemented for sanitary hot water production. Mathematical models were developed and built in respect to SIRAC and Kwikot split type ASHP water heaters that correlate the predictors (difference between hot water set point temperature and ambient temperature (Ts-Ta) and relative humidity (RH)) to the COP. The models depicted that the rate of change of the COP of the SIRAC and Kwikot systems with respect to the RH was −0.0006/% and 0.0189/%, respectively. Also, the rate of change in the COP of the SIRAC and Kwikot systems in relation to (Ts-Ta) was −0.0897/°C and −0.1231/°C. The models were simple and could be used to predict the COP of both systems with over 95% confidence level. Furthermore, based on the predicted COP from the mathematical models, on both systems, a significant difference was observed among the COP means of the two ASHP water heaters with respect to all the hot water drawn off scenarios. The result revealed that the SIRAC performed better relative to the Kwikot type based on the one-way ANOVA test. The p-value obtained from ANOVA was 0.0180 which indicates that there is a significant difference between the COPs of both systems.

Experimental study of a control strategy for a cascade air source heat pump water heater

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.

The performance of the instantaneous air-source heat pump water heaters which is made of the different double pipe heat exchangers respectively was studied, the influence of double-pipe inner wall thickness on the heat transfer area, the water flow velocity, the heat transfer coefficient, and the water system resistance of the double pipe heat exchanger was analyzed, and the influence of double-pipe inner wall thickness on heat pump water heater performance was studied in this paper. The experimental results show that: the energy efficiency of heat pump water heater is improved by the appropriate design of double pipe length, in addition, the heat capacity can be increased, and power consumption can be reduced.

A robust Principal Component Analysis (PCA) model-based approach to Fault Detection and Isolation (FDI) was developed for the Helical Coil Steam Generator (HCSG) systems of the International Reactor Innovative and Secure (IRIS) nuclear reactor. The PCA model was developed using the data generated from a simulation of the system dynamics. Because all the operation modes can be excited through well-designed simulations, a PCA model developed from simulation data is more robust to changes in operation conditions than a PCA model developed from historical data collected during routine operation conditions. In order to deal with model uncertainty that exists in a simulation model, the mismatch between PCA model predictions and online plant measurements was analyzed to characterize the model uncertainty. Based on the assumption that model uncertainty has a structured property, a complete algorithm for the PCA-based FDI was derived such that the FDI results are robust to model uncertainty. When this new method was applied to the IRIS HCSG systems, the results showed that this approach could avoid false alarms and fault misdiagnosis due to changes in operation conditions and model certainty. The approach would overcome the limitations of traditional data-driven model based FDI when routine operational data do not contain sufficient information, and the limitations of physical model based FDI when these models are too complicated for a direct use in FDI design and contain model uncertainty.

In this paper an approach to design controllers based on principal components analysis (PCA) models is presented. Closed-loop control can be formulated and implemented within the reduced space defined by a PCA model. This PCA controller, results in an integral controller, which can be used as an inferential controller when a measurement of a primary variable is not available. The main contributions of the paper are: a) the incorporation of an adjustable gain on the classical PCA controller; b) the proposal of a set of tuning rules; c) the performance evaluation of this new controller, in nominal operation conditions and in faulty situations. Some experimental results, obtained with the three tank benchmark (European COSY project), are presented.

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.

Fault detection, identification and reconstruction of sensors in nuclear power plant with optimized PCA method

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

To generate boiling water beyond 100 °C via heat pump technology, the prototype of an ultra-high temperature air source heat pump water heater (ASHPWH) based on a single-stage compression cycle of R134a was established, and an experimental investigation on it was conducted under an environment temperature of 25 °C. Then, thermodynamic analyses were carried out on the basis of the experimental results, especially when the prototype produced 95.9 and 100.3 °C water. The experimental and analytical results indicate that water beyond 100 °C was achieved through the prototype. When producing 100.3 °C water, the discharge temperature and compression ratio of the compressor of the prototype are only 108.4 °C and 4.07, respectively, which are in moderate levels. Correspondingly, the work input of the compressor is 0.622 kW, the heating capacity is 2.786 kW, and the heating coefficient of performance is 4.48. In addition, when producing 95.9 and 100.3 °C water, the system exergy efficiencies of the prototype are 50.76% and 49.73%, which are larger than those of the existing ASHPWHs, demonstrating that dividing the condensing process into two parts of high-grade exergy and low-grade exergy and utilizing them separately is effective. That is the essential reason of generating boiling water beyond 100 °C as expected only through the single-stage compression cycle.

The detection and diagnosis of faults is becoming necessary in ensuring energy savings in heat pump units. Faults can exist independently or simultaneously in heat pumps at the refrigerant side and secondary fluid flow loops. In this work, we discuss the effects that simultaneous refrigerant charge faults and faults associated with the flow rate of secondary fluids have on the performance of a heat pump operating in summer season and we developed a correlation to detect and diagnose these faults using multiple linear regression. The faults considered include simultaneous refrigerant charge and indoor heat exchanger secondary fluid flow rate faults (IFRFs), simultaneous refrigerant charge and outdoor heat exchanger secondary fluid flow rate faults (OFRFs) and simultaneous refrigerant charge, IFRF and OFRF. The occurrence of simultaneous refrigerant charge fault, IFRF and OFRF caused up to a 5.7% and 8% decrease in cooling capacity compared to simultaneous refrigerant charge and indoor heat exchanger secondary fluid flow rate faults, and simultaneous refrigerant charge and outdoor heat exchanger secondary fluid flow rate faults, respectively. Simultaneous refrigerant charge fault, IFRF and OFRF resulted in up to an 11.6% and 5.9% decrease in COP of the heat pump unit compared to simultaneous refrigerant charge fault and IFRF, and simultaneous refrigerant charge fault and OFRF, respectively. The developed FDD correlations accurately predicted the simultaneous refrigerant charge and faults in the flow rate of the secondary fluid within an error margin of 7.7%.

Principal Component Analysis (PCA) is a commonly employed technique in industrial systems for process monitoring and fault diagnosis, owing to its capability to efficiently process large datasets. Traditionally, it is applied to single-valued variables, where critical information can be lost in real scenarios with data uncertainties. Interval-valued PCA methods like Symbolic Covariance PCA (SCPCA) and Complete Information PCA (CIPCA) have been developed to enhance fault detection by incorporating data uncertainties in the PCA model. This paper presents a novel adaptation of SCPCA for detecting incertain sensor faults, marking the first correct implementation of SCPCA for fault detection and isolation (FDI). It aims to compare the performance of the new SCPCA with that of CIPCA, evaluating its reliability and accuracy in detecting sensor faults in a greenhouse prototype system.