1.1 Background and Motivation
Nowadays, since the growing environmental concern about global warming caused by greenhouse gas emission, the development of renewable energy to reduce carbon emission has become an important issue. Meanwhile, to overcome this issue, renewable energy devices have been developed, such as wind turbine, solar cell, photovoltaic cell, and heat pump.
According to European Heat Pump Association (EHPA), by passing Renewable Energy Sources (RES) directive where aero-, hydro, and geothermal energies captured by heat pumps, has made them recognized as a unique renewable technology for heating and cooling. The reduction energy demand of heat pumps leads to much lower amounts of green house gases per se. Depending on the national power production, heat pumps can provide heating, cooling and hot water nearly emission free. However, they can make a major contribution towards climate achievements and energy challenges [1].
The first heat pump emerged in the 1940s when Robert C. Webber,an American inventor discovered the idea of pumping heat via his freezer in his home. The idea was later furthered by another individual known as Lord Kelvin, and theoretically became a scientific concept. The main objective is to move heat from one location (the 'source') at a lower temperature to another location (the 'sink' or 'heat sink') at a higher temperature using mechanical work or a high-temperature heat source [2]. The basic concept of heat pump is still using the basic refrigeration cycle. Thus, heat pump can change which coil acts as the condenser and which is the evaporator by utilizing a reversing valve. In cooler climates, it is common to have heat pumps that are designed only to provide heating.
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Most of the researches concentrate on modifying components of heat pump to increase the energy performance. On contrary, decent operating strategy also plays an important role in energy saving and cost reduction. However, sponsored by National Science Council, we are complying research about “Energy saving technology research and development project for livelihood system” [3]. The main objective is to develop a device that can provide heating and cooling energy for household appliances simultaneously. Inspired from the heat pump technology, the Smart Energy Management Device (SEMD) has been introduced to overcome this problem. With this novice technology, it is hoped that the SEMD can improve traditional heat pump’s performance, reliability, efficiency, and long cycle life.
Moreover, in conjunction with Taiwan government policy about saving energy and reducing carbon emission, the main objective of this research is to establish control strategies to save energy consumption and minimize electricity usage of household appliances. Hence, green environment can be achieved. Furthermore, we implement Swarm Intelligence Technology to develop optimal control strategy. Then, by applying numerical analysis, we analyze either energy or electricity consumption of each SEMD component. This highly efficient control strategy is expected can achieve minimum energy consumption and cost.
1.2 Literature Review
In thermodynamic system, the SEMD performance is not only affected by its components but also by operating strategies. In the previous studies, most researchers focus on improving the energy performance of heat pumps and solar assisted heat pumps instead of energy management. Besides, decent operating strategy also becomes an imperative factor in saving energy.
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Zhang et al. proposed numerical and experimental method to optimize the air source heat pump water heater. Air energy was absorbed at the evaporator and pumped to storage tank via a Rankine cycle. The coil pipe/condenser released condensing heat of the refrigerant to the water side. The result shows that the energy performance can be improved by choosing proper capillary tube length, filling quantity of refrigerant, condenser coil tube length and water tank capacity [4].
Lee et al. proposed a study of heat pump system which is applied for indoor swimming pool. Since water is evaporated from the pool surface, the exhausted air contains more water and specific enthalpy. In response to this indoor air, heat pump is generally used in heat recovery for indoor swimming pools. This paper utilizes particle swarm optimization to optimize the life cycle energy cost of heat pump system. The former consists of outdoor air mass flow and heat conductance of heat exchangers; the latter comprises compressor type and boiler type. In this regard, the optimized outdoor air flow and the optimized design for heating system can be deduced by using particle swarm algorithm [5].
Wang et al. investigated the performance of heat pump for high temperature water and found that the heat pump using parallel cycles with serial heating has the best energy performance when the condensing water temperature exceeds 75℃. The experimental results indicate that the average heating capacity and coefficient of performance of the High Temperature Heat Pump (HTHP) could be improved significantly in high-temperature conditions due to the parallel cycles with serial heating on the water side and the modified compressor. All the results indicate that the HTHP using parallel cycles and modified compressor with serial heating on the water side is very competitive in industrial heating applications [6].
Brenn et al. presents annual efficiencies of these systems and compares internal
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combustion engine and electrically driven heat pumps in terms of primary energy consumption and CO2 emissions. Because heat pump performance depends strongly on the heating circuit's flow temperature level, the comparison is performed for air-to-water and geothermal heat pump systems. In addition, this research compared the energy performance of natural gas driven heat pumps and electrically driven heat pumps, the results showed that these two kinds of heat pumps have equal energy performance [7].
Fardoun et al. proposed a study about heat pump design and optimization tool. The operational data provided by different manufacturers for each component is used by system’s designers to specify installation and operational procedures of the system. The optimum of an individual piece of equipment results in sub-optimal system performance due to unforeseen interactions between the different system components. However, in order to optimize the performance, it is essential to identify and monitor key parameters of the system, such as power consumption and refrigeration effect [8].
Kim et al. designed a dynamic model of a water heater system driven by a heat pump to investigate transient thermal behavior of the system which was composed of a heat pump and a hot water circulation loop. From the simulation, the smaller size of the water reservoir was found to have larger transient performance degradation, and the larger size can caused additional heat loss during the hot water storage period. Therefore, the reservoir size should be optimized in a design process to minimize both the heat loss and the performance degradation [9].
Hsiao et al. used an ice storage subcooler to improve the heat pump performance.
The system supplies heating and cooling demands to two greenhouses with temperature ranging 308~323 K and 273~291 K respectively and utilizes an ice storage tank to subcool the condensed refrigerant which can enhance
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the system coefficient of performance (COP). The ice storage tank will charge storing ice when the cooling load is less than the nominal cooling capacity. The experimental presented that the COP of a heat pump with subcooler is higher than the one without subcooler, which are 12% and 15% in charge and discharge mode, respectively [10].
Chen investigated and compared the performance of four different operating strategies which consist of simple temperature control, temperature and water amount control, optimization temperature control and optimization temperature and water amount control. In this research, Particle Swarm Optimization has been utilized to optimize the heat pump system. The results showed that the optimization temperature and water amount control has the best performance in both energy consumption and energy cost [11].
Rankin et al. presented a study about demand side management for commercial building using an inline heat pump water heater methodology. The results based on actual data from the monitored installations showed a significant peak demand reduction for each installation. The peak demand for whole hotel’s building with occupancy of 220 people has been taken into account for one installation. The savings incurred by the building owner also included significant energy consumption savings due to the superior energy efficiency of the heat pump water heater. In one case study, the peak demand contribution was reduced by 86% for hot water heating and 36% for the whole building [12].
Hepbasli et al. proposed study dealt with reviewing Heat Pump Water Heater (HPWH) systems in terms of energetic and exergetic aspects. The performance evaluation has been modeled by using energy and exergy analysis methods. Moreover, a comprehensive review of studies conducted on them were classified and presented.
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It is expected that this comprehensive review will be very beneficial to everyone involved or interested in the energetic and exergetic design, simulation, analysis, performance assessment and applications of various types of heat pump water heater systems [13]. Moreover, due to solar energy is a clean energy, some studies [14~16]
investigated solar assisted heat pumps.
1.3 Research Structure
Following is the structure of the thesis which can be shown in figure 1.1:
Chapter 1: Introduction
The research background, literature review, and the objective of this study are introduced