A heat pump water heater (HPWH) operates on an electrically driven vapor-compression cycle and pumps energy from the air in its surroundings to water in a storage tank, thus raising the temperature ...of the water. HPWHs are a promising technology in both residential and commercial applications due to both improved efficiency and air conditioning benefits.
Residential HPWH units have been available for more than 20 years, but have experienced limited success in the marketplace. Commercial-scale HPWHs are also a very promising technology, while their present market share is extremely low.
This study dealt with reviewing HPWH systems in terms of energetic and exergetic aspects. In this context, HPWH technology along with its historical development was briefly given first. Next, a comprehensive review of studies conducted on them were classified and presented in tables. HPWHs were then modeled for performance evaluation purposes by using energy and exergy analysis methods. Finally, the results obtained were discussed. 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 HPWH systems.
During the last decade, a number of studies have been conducted by various investigators in the design, modeling and testing of solar assisted heat pump systems (SAHPSs). This paper reviews the ...studies conducted on the energy and exergy analysis of SAHPS systems in Turkey and around the world as of the end of December 2004. The studies undertaken on the SAHPS systems are categorized into four groups as follows: (i) SAHPSs for water heating, (ii) SAHPSs with storage (conventional type) for space heating, (iii) SAHPSs with direct expansion for space heating, and (iv) Solar-assisted ground source heat pump greenhouse heating system (SAGSHPGHS). This paper investigates the studies on SAGSHPs, especially ground-source heat pumps, also known geothermal heat pumps, at the Turkish universities in more detail, by giving Turkey's solar energy potential.
•A dual-source (air and ground) inverter driven heat pump (DSHP) is presented.•The dynamic model of the DSHP has been made with TRNSYS.•DSHP reduces the ground temperature drift due to unbalanced ...building loads.•DSHP can work with shorter borehole (BHE) fields (up to 50%).•The optimal switching (air-ground) temperature depends on the size of BHEs.
In this paper the energy performance of a Dual-Source Heat Pump (DSHP) system able to use both air and ground as external heat source is analysed by using TRNSYS and the experimental data obtained by testing a DSHP prototype. The DSHP seasonal and annual performance factors are compared with those offered by the same DSHP in which only ground (ground-source mode) or only external air (air-source mode) is used as external heat source in order to evaluate the benefits achievable with the exploitation of a double external heat source (ground and air) with the same unit. Yearly dynamic simulations have been carried out by coupling the DSHP to a detached residential building located in Bologna, characterized by unbalanced heating and cooling loads, and coupled to a geothermal loop based on borehole heat exchangers (BHEs). With the help of the dynamic simulations it has been demonstrated that DSHPs can be very useful in order to solve the problems linked to the ground temperature drift which can be originated by the presence of an undersized borehole heat exchanger field and/or by unbalanced heating and cooling loads. In fact, the use of external air as auxiliary heat source with respect to ground during the most severe season enables to obtain more stable energy performance even in presence of undersized BHEs. In this paper it is shown how an optimal trade-off in terms of annual energy performance and investment costs can be obtained by reducing the size of the DSHP borehole field of 15–55% with respect to the borehole field needed by a conventional ground-coupled heat pump having the same size. In this way the DSHP can be used during the retrofitting of thermal plants based on ground-coupled heat pumps in which an undersized BHEs field is present.
Ultra-low district heating (ULTDH) networks are operated at temperatures below 30 °C. However, the temperatures supplied are still too low for direct heating of the consumers. Heat pumps use the ...heating network as a source and can supply the consumers with space heating and domestic hot water as needed. Although individual manufacturers provide performance figures for the source temperature of 20 °C, these are usually derived from extrapolation from standard conditions with source temperatures of 0 °C and 10 °C. Up to now practical measurements are missing how efficiently heat pumps work in an ULTDH network environment and how the network temperature spread affects the performance. In this paper test rigs are used to investigate heat pumps under the conditions in ULTDH networks at a network supply temperature of 20 °C. It is shown that heat pumps can operate up to twice as efficient as with a geothermal probe. Furthermore, the network temperature spread has a significant influence on the performance of the heat pump. Heat pumps operate significantly better with a low source temperature spread.
•Test rig measurements for heat pump efficiency in an ULTDH network environment.•Network supply temperature of 20 °C.•Impact of the network temperature spread on the heat pump performance.•COP maximum COP of 10 at a source outlet temperature of 17 °C in the ULTDH network.•Heat pumps compressor limitations must be considered in ULTDH networks.
This study reviews gas engine-driven heat pump (GEHP) systems for residential and industrial applications in terms of energetic and exergetic aspects for the first time to the best of the authors’ ...knowledge. These systems are novel heat pump systems (one of today's promising new technologies). Although the first investigations had been performed at late 1970s, the first merchandized GEHP was produced and introduced in the market in 1985. Gradually, it has become widespread all over the world for various purposes. Main application of GEHPs are for space and water heating/cooling purposes. However, they can be integrated to industrial applications, especially to drying processes.
In this study, historical development of GEHP systems was briefly given first. Next, the operation of these systems was described, while studies conducted on them were reviewed and presented in tabulated forms. GEHPs were then modeled for performance evaluation purposes by using energy and exergy analysis methods. Finally, an illustrative example was given, while the results obtained were discussed. In addition, a new project on integration of GEHP systems to food drying processes in Turkey initiated by the authors was introduced. It is expected that this comprehensive study will be very beneficial to everyone involved or interested in the energetic and exergetic design, simulation, analysis and performance of assessment of GEHP systems.
•The review of recent studies on heat delivery above 80 °C using vapour compression heat pumps•Discussion on advances in natural fluids for its use as high temperature working fluids•Discussion on ...the component development for high temperature heat pump operation•The review of fluid mixture proposals, cycle variations and system design in high temperature domain
The use of high temperature heat pumps (HTHPs) operating with natural fluids has been shown to be a potential environmentally friendly solution to increase energy efficiency in industrial processes. Industrial processes release a significant amount of energy as low quality waste heat to the environment. This paper reviews the research and development of efficient and cost effective HTHP technology that can utilize this waste heat. Natural fluids are of focus with consideration given to the comparable technologies using synthetic fluids. This review reveals the different challenges from fluid selection, component development to system optimization. The various innovative solutions to these challenges and promising technologies for further studies are discussed. The purpose of this paper is to serve as a start point for research by bringing together ideas, simulations and experimental results as a resource or reference tool for future development in HTHP using natural working fluids.
A large fraction of the energy demand is due to space heating. Direct solar heating might reduce the need of fossil fuels. However the poor solar collector efficiency when outside temperature and ...solar radiation are low, as in the heating season, limit most of solar collectors application to domestic hot water heating. Similarly air source heat pumps are penalized just when the heating demand is higher. Then a possible solar contribution to the outside air as a heat pump cold source was first analyzed, evaluating different integration modes of the two sources. Subsequently the coupling of a ground source and a solar section appeared a more favourable application, also because solar heat could recharge the ground in periods of low or no heating demand. At the same time the solar section might reduce the length of the expensive boreholes. Solar assisted absorption heat pumps were successfully experimented. Recently studies were devoted to a solar assistance of heat pumps by PV/T collectors, that offer both a fraction of the electricity to drive the heat pump and a solar assistance to the heat pump cold source, be it the ground or the outside air.
•Solar and Heat Pump systems with Parallel/Series switching based on solar radiation.•A strategy is proposed to find an optimal irradiation value to execute the switching.•Series mode leads to an ...increase on individual components’ performance.•However, series mode decreases systems’ seasonal performance in most climate case studies.•A control logic solution is discussed to better seize the series mode potential.
This paper presents the modelling of two Solar Heat Pump systems, one for Domestic Hot Water and other one for Space Heating in two different configurations. Both system’s configurations can commute between parallel and series operation. The Configuration “A” uses a heat pump with two evaporators, allowing to work as an air source Heat Pump or as a water source Heat Pump. The Configuration “B” uses a heat exchanger to preheat the air entering to an air-to-water Heat Pump. These configurations are simulated in TRNSYS 17 for evaluating their performance in three Chilean cities: Santiago, Concepción and Puerto Montt. The control system applies a switching criterion between operation modes based primarily on the available solar irradiation. According to the results, the individual performance figures of the Heat Pump and of the Solar Collectors increase. Nonetheless, the results show that the Seasonal Performance Factor of the overall system decreases when it is switched from parallel to series. In the case of space heating, the Configuration A using evacuated tubes collectors shows a decrease of the Seasonal Performance Factor from 5.85 to 4.78 in Santiago, 5.35 to 4.30 for Concepción and 4.70 to 3.87 for Puerto Montt. In all case studies, unglazed collectors applications show a maximum SPF decrease of 0.04 and a maximum increase of 0.01. The results obtained can be influenced by the applied switching criterion used in this study, which does not force the Solar Collectors to increase their operational time by cooling them with the Heat Pump. Then, for the case studies, the non-inclusion of additional solar collector’s operational time leads to decrease the system performance.
Shallow geothermal systems such as open and closed geothermal heat pump (GHP) systems are considered to be an efficient and renewable energy technology for cooling and heating of buildings and other ...facilities. The numbers of installed ground source heat pump (GSHP) systems, for example, is continuously increasing worldwide. The objective of the current study is not only to discuss the net energy consumption and greenhouse gas (GHG) emissions or savings by GHP operation, but also to fully examine environmental burdens and benefits related to applications of such shallow geothermal systems by employing a state-of the-art life cycle assessment (LCA). The latter enables us to assess the entire energy flows and resources use for any product or service that is involved in the life cycle of such a technology. The applied life cycle impact assessment methodology (ReCiPe 2008) shows the relative contributions of resources depletion (34%), human health (43%) and ecosystem quality (23%) of such GSHP systems to the overall environmental damage. Climate change, as one impact category among 18 others, contributes 55.4% to the total environmental impacts. The life cycle impact assessment also demonstrates that the supplied electricity for the operation of the heat pump is the primary contributor to the environmental impact of GSHP systems, followed by the heat pump refrigerant, production of the heat pump, transport, heat carrier liquid, borehole and borehole heat exchanger (BHE). GHG emissions related to the use of such GSHP systems are carefully reviewed; an average of 63t CO2 equivalent emissions is calculated for a life cycle of 20 years using the Continental European electricity mix with 0.599kg CO2 eq/kWh. However, resulting CO2 eq savings for Europe, which are between −31% and 88% in comparison to conventional heating systems such as oil fired boilers and gas furnaces, largely depend on the primary resource of the supplied electricity for the heat pump, the climatic conditions and the inclusion of passive cooling capabilities. Factors such as degradation of coefficient of performance, as well as total leakage of the heat carrier fluid into the soil and aquifer are also carefully assessed, but show only minor environmental impacts.
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