Hot Water Production System Research Articles

Corrigendum to “Effects of latent heat storage and controls on stability and performance of a solar assisted heat pump system for domestic hot water production” [Solar Energy 150 (2017) 394–407

Corrigendum to “Effects of latent heat storage and controls on stability and performance of a solar assisted heat pump system for domestic hot water production” [Solar Energy 150 (2017) 394–407

Thermodynamic analysis and assessment of a novel integrated geothermal energy-based system for hydrogen production and storage

In this paper, thermodynamic analysis and assessment of a novel geothermal energy based integrated system for power, hydrogen, oxygen, cooling, heat and hot water production are performed. This integrated process consists of (a) geothermal subsystem, (b) Kalina cycle, (c) single effect absorption cooling subsystem and (d) hydrogen generation and storage subsystems. The impacts of some design parameters, such as absorption chiller evaporator temperature, geothermal source temperature, turbine input pressure and pinch point temperature on the integrated system performance are investigated to achieve more efficient and more effective. Also, the impacts of reference temperature and geothermal water temperature on the integrated system performance are studied in detail. The energetic and exergetic efficiencies of the integrated system are then calculated as 42.59% and 48.24%, respectively.

Indirect expansion solar assisted heat pump system for hot water production with latent heat storage and applicable control strategy

Integration of renewable energy with energy conversion application for hot water production is a significant technology to be studied for industrial, commercial and residential proposes. It has been further enhanced since the international energy agency (IEA) puts effort to standardize such kind of technology. In this paper, a novel study has been carried out experimentally to control an indirect solar assisted heat pump (IDX-SAHP) system integrated with a latent heat storage (PCM) tank. The PCM heat exchanger tank was designed specially and controlled automatically which allowed storing excess energy during the day and releasing it when needed. In addition, a system control strategy has been purposely designed and implemented in a Building Management System (BMS) to ensure the stable and reliable system operations. The experimental results show that the PCM heat exchanger tank installation has a significant effect on the system operation stability and can improve the COP of the IDX-SAHP system at different weather conditions and a specified hot water load profile.

Effects of latent heat storage and controls on stability and performance of a solar assisted heat pump system for domestic hot water production

Solar assisted heat pump systems have been widely applied in domestic hot water productions due to their sustainability and stability in operations. However, their performance efficiency requires further improvement using advanced technologies such as energy storage with phase change materials (PCM) and optimal system controls. Accordingly, a test rig of a new indirect solar assisted heat pump (IDX-SAHP) system has been designed, built and instrumented. The IDX-SAHP system consists of three operational loops: solar thermal, solar assisted heat pump and load profile. A PCM heat exchanger tank was purposely designed and installed in the system solar thermal loop to store solar energy, when applicable, and release heat when required by the heat pump. In addition, an air cooling heat exchanger was also installed in the solar thermal loop to absorb heat from the ambient air for the heat pump. A detailed control strategy has been designed and implemented for the system for efficient operation in different modes and maintain constant load supply water temperature during an operational day. In different weather conditions of sunny and overcast, comprehensive measurements were carried out on the test rig and system structures with and without the PCM tank. Test results showed that the system could efficiently meet the daily domestic hot water demand and the PCM heat exchanger integration exerted a significant effect on system stability and performance efficiency. Quantitatively, the average COP of the IDX-SHAP system with a PCM tank could increase 6.1% and 14.0% on sunny and cloudy days respectively compared to systems without PCM tank integration.

Evaluation of different heat pump systems for sanitary hot water production using natural refrigerants

Heat pumps that work with a high degree of subcooling in subcritical systems have shown a significant margin of improvement when working with sanitary hot water applications. Recently, two different approaches to overcome the high degree of subcooling have been presented in the literature: with a subcooler (separate from the condenser) and by making all the subcooling in the condenser. In this paper, a comparative evaluation between both alternatives is presented, and the obtained results are compared with a representative solution already available on the market using natural refrigerants for this application. The results of this analysis have shown that in a system with subcooling in the condenser, it is possible to obtain a COP comparable to that of transcritical CO2 heat pump water heaters. Furthermore, the system with subcooling has been demonstrated experimentally as being capable of producing water up to 90°C and has shown a COP up to 20% higher than some CO2 commercial products (catalogue data reference).

Thermodynamic comparison of a steam, hot water and hot air production system consuming Soma and Afsin lignites under stoichiometric conditions

This study presents thermodynamic comparison of a steam, hot water and hot air production system consuming Soma and Afsin lignites under stoichiometric combustion conditions. For this purpose, using the results from stoichiometric combustion reaction and proximate-ultimate analyses of the lignite samples, energy and exergy analyses are performed. Moreover, the concept and capacity of steam (424 K, 5 bar), hot water (363 K) and hot air (573 K) production system are chosen in accordance with a tea factory. Consequently, in case of stoichiometric combustion of the same amount of Afsin and Soma lignites, it is observed that the amount of steam from Soma lignite combustion is approximately three times more than that of Afsin lignite combustion. Additionally, energy and exergy efficiencies of the system using Afsin lignite are calculated to be 66% and 19%, respectively while those of system using Soma lignite are estimated to be 73% and 24%, respectively.

Thermodynamic comparison of a steam, hot water and hot air production system consuming Soma and Afsin lignites under stoichiometric conditions

This study presents thermodynamic comparison of a steam, hot water and hot air production system consuming Soma and Afsin lignites under stoichiometric combustion conditions. For this purpose, using the results from stoichiometric combustion reaction and proximate-ultimate analyses of the lignite samples, energy and exergy analyses are performed. Moreover, the concept and capacity of steam (424 K, 5 bar), hot water (363 K) and hot air (573 K) production system are chosen in accordance with a tea factory. Consequently, in case of stoichiometric combustion of the same amount of Afsin and Soma lignites, it is observed that the amount of steam from Soma lignite combustion is approximately three times more than that of Afsin lignite combustion. Additionally, energy and exergy efficiencies of the system using Afsin lignite are calculated to be 66% and 19%, respectively while those of system using Soma lignite are estimated to be 73% and 24%, respectively.

The efficiency of the heat pump water heater, during DHW tapping cycle

This paper discusses one of the most effective systems for domestic hot water (DHW) production based on air-source heat pump with an integrated tank. The operating principle of the heat pump is described in detail. Moreover, there is an account of experimental set-up and results of the measurements. In the experimental part, measurements were conducted with the aim of determining the energy parameters and measures of the economic efficiency related to the presented solution. The measurements that were conducted are based on the tapping cycle that is similar to the recommended one in EN-16147 standard. The efficiency of the air source heat pump during the duration of the experiment was 2.43. In the end of paper, authors conducted a simplified ecological analysis in order to determine the influence of operation of air-source heat pump with integrated tank on the environment. Moreover the compression with the different source of energy (gas boiler with closed combustion chamber and boiler fired by the coal) was conducted. The heat pump is the ecological friendly source of the energy.

Seasonal performance assessment of sanitary hot water production systems using propane and CO2 heat pumps

Heat pump water heaters can increase the energy efficiency in sanitary hot water production, which is a relevant share of the final energy consumption in multiresidential and tertiary buildings. Refrigerants for these heat pumps are changing due to the F-Gas Regulation which bans high-GWP fluids. While CO2 is an established solution, propane is a promising low-GWP alternative for heat pump water heaters serving large users in the tertiary sector, where refrigerant charge limits (due to propane's flammability) can be bypassed by installing the heat pump outdoors. Here, the components of a CO2 and a propane air-water heat pump systems of 40 kW are sized and their COPs are compared in different climates; then, the two heat pumps are coupled to a storage tank and a user demand profile (hospital and school). For three different locations, tank size necessary to maintain users' comfort and seasonal performance factor are evaluated through simulation.

Design, Fabrication, and Efficiency Study of a Novel Solar Thermal Water Heating System: Towards Sustainable Development

This paper investigated a novel loop-heat-pipe based solar thermal heat-pump system for small scale hot water production for household purposes. The effective use of solar energy is hindered by the intermittent nature of its availability, limiting its use and effectiveness in domestic and industrial applications especially in water heating. The easiest and the most used method is the conversion of solar energy into thermal energy. We developed a prototype solar water heating system for experimental test. We reported the investigation of solar thermal conversion efficiency in different seasons which is 29.24% in summer, 14.75% in winter, and 15.53% in rainy season. This paper also discusses the DC heater for backup system and the current by using thermoelectric generator which are 3.20 V in summer, 2.120 V in winter, and 1.843 V in rainy season. This solar water heating system is mostly suited for its ease of operation and simple maintenance. It is expected that such novel solar thermal technology would further contribute to the development of the renewable energy (solar) driven heating/hot water service and therefore lead to significant environmental benefits.

A Study of the Influence of Solar Panels Coupled with Thermal Systems for a Residential Building, by Applying Methods of Evaluation as EN 15316-4-3:2014 and TRANSOL

The present study performs calculations for a series of parameters involved in the definition of energy performance of a real residential building, by applying EN15316-4-3:2014 methodology; results are compared with simulations made with TRANSOL, analysing the influence of coupling solar panels with domestic hot water production (DHW) and heating systems. In a first stage, the influence of using solar panels for DHW production is evaluated, and calculations for thermal and electric needed energy are performed. Variation of solar fraction is analised. Secondly, a combi-system (DHW+heating) was considered, and the calculations were performed accordingly, as EN 15316-4-3:2014 describes. The data provided with TRANSOL were compared with the results obtained by applying EN 15316-4-3:2014, and conclusions are extracted. At the end, a parametric study of solar fraction is followed, taking into account different numbers of solar panels, in both situation, for DHW and DHW & heating coupling systems cases. The critical approximation introduced by EN 15316-4-3 is identified. Values of determined fraction are compared.

Dynamic Simulation of Solar Thermal Collectors for Domestic Hot Water Production

In this paper a system for the Domestic Hot Water (DHW) production based on solar collectors is analyzed by means of a dynamic approach based on a Simulink model and by using the F-chart method, able to evaluate system performances on a monthly basis. Following the dynamic approach, it is possible to evaluate hour by hour the energy collected by the solar panels and the temperature of the hot water produced by the system, by taking into account the impact of different daily DHW consumption profiles on the percentage of thermal energy produced by the solar collector (Solar Coverage Factor, SCF). The comparison between the prediction made both by using the Simulink model and the F-Chart method in terms of SCF is shown by taking into account the effect on SCF of the typology of solar collector (unglazed, glazed and evacuated collectors), of the storage tank volume connected to the solar panels and of the hourly DHW consumption profile. The results point out that SCF is strongly dependent on the daily DHW consumption profile, which cannot be taken into account in a quasi-static approach like the F-chart method.

Performance Assessment of a Multi-energy System for a Food Industry

The energy saving is becoming an important topic also in the food industry. For this reason, it is important to use multi-energy systems to produce hot water for processes and space heating. The application considered in this paper, which concerns a chocolate factory, focuses on the hot water production through a multi-source storage tank. The water inside the tank is heated by four solar panels when there is enough solar radiation and by a gas back-up boiler. The cold aqueduct water, which it is going to be heated in the accumulator, is first preheated recovering waste heat from the condenser of the chiller. The system was equipped with an energy monitoring and recording device. The thermal model was used to analyse the hot water production system during the summer season considering the options of the heat recovery and of the solar thermal exploitation. The performance analysis was developed in order to establish energy savings that may be achieved.

Sizing of a Domestic Hot Water Heating and Storage System for Short Operating Cycles - A Theoretical Approach

A methodology for the sizing of domestic hot water heating and storage systems is defined, by assuming an extreme operating condition cycle composed of only two parts, a water consumption period and a system repositioning period. In both parts to respond to the extreme hot water demanding conditions, the heating is always on. The subsequent exergy analysis of this domestic hot water production system compares the irreversibility and the exergy efficiency of the water storage and the tankless situation. To carry out such analysis, some basic assumptions were made: a constant temperature heat source, a short duration operating cycle and a constant thermal energy supply. Under these circumstances it is shown that the hot water storage system leads to lower exergy losses while the tankless system is more exergy efficient, but requiring a higher instantaneous thermal power input. The use of the joule effect electricity, as the system heat source, be it a water storage one or a tankless one, maximizes the system irreversibility losses and minimizes the system exergy efficiency. The tankless system, with the joule effect electricity heat source is the worst situation.

Research progress of high-efficiency, low-temperature hot water systems

The energy used to heat urban buildings accounts for 27% of total building energy consumption in China. Current hot water production systems are mainly based on direct use of fossil fuels or electricity, which is of low primary energy efficiency and produces severe air pollution. Based on the principles of “high-grade energy as driving source, low-grade heat for low-temperature demand, and natural energy fully used”, we have developed various high-efficiency, low-temperature hot water systems, including: (1) a fuel-driven, air-source heat pump system that uses existing energy as the driving power of the air-source heat pump to extract additional heat from the ambient air, achieving energy saving rates of 20%-40% and payback times of 3-7 years; (2) a fuel-driven, water-source heat pump system that can use an absorption heat pump to relieve underground thermal imbalance and reduce the required number of boreholes and consumption of the conventional electric heat pump; (3) a hybrid ground-source heat pump system with heat compensation that can store ambient heat in the ground efficiently via heat thermosyphon and heat pump modes, maintaining excellent system performance in long-term operation; (4) a hybrid solar air-source heat pump system that can make full use of solar energy of varying intensities and ambient heat with different temperatures, so as to improve system efficiency and reduce the initial investment of a conventional solar heat pump or air-source heat pump; (5) a hybrid air-source heat pump system aided by seasonal energy storage that combines advantages of solar energy and ambient heat, with enhanced heating reliability and economic feasibility relative to the normal air-source heat pump; (6) a hot water system based on heat recovery from data centers, which uses an integrated air conditioner with heat thermosyphon and heat pump modes to collect waste heat in a water loop, from which a water-source heat pump extracts heat to produce low-temperature hot water with an energy saving rate of 60%. All the above proposed hot water systems are assessed to have high energy efficiency, heating reliability and economy feasibility, which should be important in energy savings and emission reduction within the building sector.

A Boiler Room in a 600-Bed Hospital Complex: Study, Analysis, and Implementation of Energy Efficiency Improvements

The aim of energy efficiency is to use less energy to provide the same service. In hospitals, energy efficiency offers a powerful and cost-effective tool to reduce greenhouse gas emissions, fuel consumption, and also running costs. Over a six-month period, the six gas-fired boilers that provide both a hospital’s heat and hot water were monitored. Analysis of the data obtained led to several actions being implemented in the hospital boiler room control system to improve the efficiency of the heat production system. Comparative studies were conducted, during similar weather periods, of the performance of the hospital’s hot water production system before and after the controls were implemented. Results indicate that the control actions applied proved to be effective. Finally; the paper offers a financial; primary energy saving and CO2 reduction analysis that points to a 3,434.00 €/week savings in natural gas consumption; and a cut in CO2 emissions of 20.3 tons/week; as compared to the reference facility.

Performance and economic evaluation of a hybrid photovoltaic/thermal solar system for residential applications

Photovoltaic/thermal (PV/T) systems are capable of converting solar irradiation to thermal energy and electricity simultaneously. As PV/T solar systems become more popular and commercial solutions find their way into the market, it is necessary to evaluate both the energetic and economic benefits of such systems at different climatic conditions. The vast majority of the commercial solutions for residential applications are mainly intended to be used as solar water heaters with the bonus of electricity generation over the same collector area, replacing traditional solar heater solutions. In this paper, the energetic and economic performance of commercially available PV/T systems for electricity and domestic hot water production is being evaluated for use in three European countries, each under entirely different climatic and economic conditions. Economic spider diagrams are being presented to indicate how legislation and fuel prices would affect the value of such systems and useful observations are being made regarding the evaluation of their energetic performance.

Experimental analysis of an on demand external domestic hot water production system using four control strategies

In the paper, an experimental investigation on the performance of a space/water heating system using an on demand external domestic hot water production system (DHWPS) with different control strategies is reported. The tested DHWPSs consisted of a plate heat exchanger, a circulating pump, a flow switch and a thermostatic regulation valve. Four different control valves were considered in the analysis, comprising a 3-way mixing valve on the DHW-side, two different 2-way valves on the tank-side and a 3-way valve on the tank-side. Experiments have been performed heating the water in the tank up to 80°C and considering DHW draw-off flow rates of 5, 10, 15 and 20 l/min at a set temperature of 45°C. In the study the thermal behaviour of the four DHWPSs is analysed and compared, as well as its effects on the thermal performance of the tank during consumption operation. Results show that the control strategy of the DHWPS significantly influences the quality of the DHW supply and the thermal performance of the storage tank.

Exergy analysis and life cycle assessment of solar heating and cooling systems in the building environment

The serious environmental degradation of our planet in the past century and the limitation of supplies of conventional fuels have led humanity to search for new energy forms. The housing sector has a big environmental impact and it makes a good candidate for changes to be implemented in order to make steps towards a sustainable society. This study deals with the exergy analysis and the Life Cycle Assessment (LCA) of solar systems for space heating, cooling and hot domestic water production. These systems will be applied to a residence in the wide Thessaloniki area, in Northern Greece. The analysis is based on the given energy needs of an average house. Furthermore, a photovoltaic system (PV) will be used for electricity production. Besides Solar energy, the existing geothermal field will be utilized via heat pumps. The system is designed to exploit solar and geothermal energy and an exergy analysis of the different elements of the system is performed so that improvements can be achieved in its efficiency and its cost be reduced. It has been shown that the exergy efficiency of the solar systems and the geothermal system are relatively low. Since almost all of the environmental impacts of the renewable energies are connected to the manufacturing of the devises for their utilization, the environmental impacts will be analyzed only at the manufacturing stage. The use of Life Cycle Assessment (LCA) will be used. It has been shown that the use of solar cooling has the highest environmental impact. This analysis applies for all regions since the energy needs could be adjusted and the solar radiation of that region taken into consideration.

Field Surveys of Non-Residential Solar Water Heating Systems in Taiwan

To develop indigenous alternative and renewable energy resources, long-term subsidy programs (1986–1991 and 2000–present) for solar water heaters have been enforced in Taiwan. By the end of 2010, the total installed area of solar collectors had exceeded 2 million square meters. However, over 98% of solar water heaters were used in residential systems for hot water production, with the areas of installed solar collector being less than 10 square meters. There were only 98 systems with area of solar collectors installed exceeding 100 square meters put into operation from 2001 to 2010. These systems were mainly installed for water heating in dormitories, swimming pools, restaurants, and manufacturing plants. In the present study, a comprehensive survey of these large-scale solar water heaters was conducted. The objectives of the survey were to assess the system performance and to collect feedback from individual users. It is found that lack of experience in system design and maintenance are the key factors affecting reliable operation of a system. Hourly, daily and long-term field measurements of a dormitory system were also examined to evaluate its thermal efficiencies. Results indicated that thermal efficiency of the system is associated with the daily solar radiation. Hot water use pattern and operation of auxiliary heater should be taken into account in system design.