Heat Pump Hot Water Research Articles

Experimental study on the performance of a gas engine heat pump for heating and domestic hot water

The present work is aimed at exploring the performance characteristics of a gas engine heat pump (GEHP) system in the aspect of the heating and domestic hot water. A test prototype was established using R134a as working fluid. The performance characteristics of the gas engine and the GEHP system working were studied by experiments in heating mode. The results showed that the output efficiency of the gas engine increased when the gas engine speed is constant. The coefficient of performance (COP) and primary energy ratio (PER) of the GEHP system decreased with the growing of the gas engine speed, but increased with increasing condenser water inlet temperature and ambient air temperature. And the PER of the GEHP system was between 1.23 and 1.48 under experimental condition. In addition, the energy of heat recovery accounted for about 30%–45% of the total heating capacity of the GEHP system, and the temperature of the domestic hot water which was heated by the waste heat could reach 40°C–60°C, thus ordinary families' demands for domestic hot water could be satisfied.

Performance analysis and economic assessment of solar thermal and heat pump combisystems for subtropical and tropical region

In the present research, combinations of solar collectors and air-source heat pumps for domestic hot water (DHW) are addressed in terms of hydraulic layout and climate conditions. TRaNsient SYstems Simulation (TRNSYS) software was implemented to simulate and examine the heating capacities of various DHW systems. For validating the numerical results, a demonstration site featuring a solar collector and heat pump combisystem with real-time monitoring sensors was established in Tainan, Taiwan. The corresponding parameters of TRNSYS modules were also tested and validated using experimental data. For comparison with the electrical heating water system, three common DHW systems—a conventional solar DHW system, a single-tank solar combisystem, and a dual-tank solar combisystem—were selected, and their technical and economical aspects were assessed. To determine the effect of climate conditions, two metropolitan cities in Taiwan were simulated: Taipei represented subtropical cities and Kaohsiung represented tropical cities. Results for both Taipei and Kaohsiung showed that the dual-tank solar combisystems had the lowest electrical consumption levels and operating costs. The incremental capital costs of the solar combisystems were considered, and realistic payback periods were calculated to determine economic feasibility.

Experiments of a Heat Pump Water Heating System Using Stored Solar Energy to Defrost

Abstract A new solar-assisted hot water heat pump system is proposed that uses stored solar energy to defrost the outdoor unit. The system is mainly featured by two water tanks, one of which can be used to collect part of the solar heat during daytime and is used in the defrosting processes during night. Experiments were conducted in lab conditions to test the performance of this novel design, in which the solar heating systems was represented by electrical heating. Results show that the new system had a system COP almost 82% higher than the traditional system where the reverse-cycle defrosting uses the water thank as the evaporator. The advantage of this system is that it can make use of the low grade solar heat, which is difficult to collect or use in normal solar water heating system. This system is particularly suitable for regions with cold and humid winters like the hot summer and colder winter zone in China.

A semi-analytical refrigeration cycle modelling approach for a heat pump hot water heater

ABSTRACTThe use of heat pump systems in applications like the production of hot water or space heating makes important the modelling of the processes for the evaluation of the performance of existing systems, as well as for design purposes. The proposed semi-analytical model offers the opportunity to estimate the performance of a heat pump system producing hot water, without using detailed geometrical or any performance data. This is important, as for many commercial systems the type and characteristics of the involved subcomponents can hardly be detected, thus not allowing the implementation of more analytical approaches or the exploitation of the manufacturers’ catalogue performance data. The analysis copes with the issues related with the development of the models of the subcomponents involved in the studied system. Issues not discussed thoroughly in the existing literature, as the refrigerant mass inventory in the case an accumulator is present, are examined effectively.

Multi-Objective Optimization for Equipment Capacity in Off-Grid Smart House

Recently, the off-grid smart house has been attracting attention in Japan for considering global warming. Moreover, the selling price of surplus power from the renewable energy system by Feed-In Tariff (FIT) has declined. Therefore, this paper proposes an off-grid smart house with the introduced Photovoltaic (PV) system, Solar Collector (SC) system, Hot Water Heat Pump (HWHP), fixed battery and Electric Vehicle (EV). In this research, a multi-objective optimization problem is considered to minimize the introduced capacity and shortage of the power supply in the smart house. It can perform the electric power procurement from the EV charging station for the compensation of a shortage of power supply. From the simulation results, it is shown that the shortage of the power supply can be reduced by the compensation of the EV power. Furthermore, considering the uncertainty for PV output power, reliable simulation results can be obtained.

Life cycle assessment of domestic heat pump hot water systems in Australia

Water heating accounts for 23% of residential energy consumption in Australia, and, as over half is provided by electric water heaters, is a significant source of greenhouse gas emissions. Due to inclusion in rebate schemes heat pump water heating systems are becoming increasingly popular, but do they result in lower greenhouse gas emissions? This study follows on from a previous life cycle assessment study of domestic hot water systems to include heat pump systems. The streamlined life cycle assessment approach used focused on the use phase of the life cycle, which was found in the previous study to be where the majority of global warming potential (GWP) impacts occurred. Data was collected from an Australian heat pump manufacturer and was modelled assuming installation within Australian climate zone 3 (AS/NZS 4234:2011). Several scenarios were investigated for the heat pumps including different sources of electricity (grid, photovoltaic solar modules, and batteries) and the use of solar thermal panels. It was found that due to their higher efficiency heat pump hot water systems can result in significantly lower GWP than electric storage hot water systems. Further, solar thermal heat pump systems can have lower GWP than solar electric hot water systems that use conventional electric boosting. Additionally, the contributions of HFC refrigerants to GWP can be significant so the use of alternative refrigerants is recommended. Heat pumps combined with PV and battery technology can achieve the lowest GWP of all domestic hot water systems.

Experimental Research of the Dual-source Evaporator Under Spraying Condition

In this paper, a heat pump hot water unit with the dual-source evaporator using air or water as the heat source is proposed. The idea is firstly to use the heat from the bath wastewater to heat the domestic hot water. If the stored wastewater is insufficient, the ambient air will be applied for assisting the heat pump. The structure of the dual-source evaporator is simpler and compacter compared with the traditional form of two evaporators arranged in parallel. For testing it, the heat pump hot water unit with the evaporator is established. The performance of the unit and the dual-source evaporator are investigated experimentally when the bath wastewater is used as the heat source. Experimental results show that the coefficient of performance (COP) of the heat pump can reach 5.02 when the wastewater temperature is 32℃, and the heat transfer coefficient of the evaporator can reach to 1003.56 W/m2 K. And the temperature of wastewater can be decreased to 8℃ by cyclical utilization. So the effect of heat recovery is remarkable for the heat pump hot water unit with the dual-source evaporator. When air is used as the only heat source, the performance of the heat pump is about the same as that of a conventional air-source heat pump, and this paper does not research on it.

R744 ejector technology future perspectives

Carbon Dioxide, CO2 (R744) was one of the first commonly applied working fluids in the infancy of refrigeration more than 100 years ago. In contrast to ammonia it mainly disappeared after the first generation of synthetic refrigerants have been introduced to the market after 1930. One reason was that the transition from low-rpm belt driven compressors towards the direct electrical motor driven compressors (50-60 Hz) was not performed for CO2 compressors before the revival introduced by Gustav Lorentzen in the 90is of last century. Since 1988 an enormous R & D effort has been made to further develop CO2 refrigeration technology in spite of the opposition from the chemical industry.Today CO2 refrigeration and heat pumping technologies are accepted as viable and sustainable alternatives for several applications like commercial refrigeration, transport refrigeration, vehicle air conditioning & heat pumping, domestic hot water heat pumps and industrial applications. For some applications, the current threshold to introduce R744 technology can be overcome when the system design takes into account the advantage of the thermo dynamical- and fluid properties of CO2. I.e. the system is designed for transcritical operation with all it pros and cons and takes into consideration how to minimize the losses, and to apply the normally lost expansion work. Shortcut-designs, i.e. drop in solutions, just replacing the H(C)FC refrigeration unit with an CO2 systems adapted for higher system pressures will not result in energy efficient products. CO2 systems do offer the advantage of enabling flooded evaporators supported with adapted ejector technology. These units offer high system performances at low temperature differences and show low temperature air mal-distributions across evaporators.This work gives an overview for the development possibilities for several applications during the next years. Resulting in a further market share increase of CO2 refrigeration and heat pump systems, as energy efficient alternatives to current systems not applying natural working fluids.

Artificial neural networks for the performance prediction of heat pump hot water heaters

ABSTRACTThe rapid progression in the use of heat pumps, due to the decrease in the equipment cost, together with the favourable economics of the consumed electrical energy, has been combined with the wide dissemination of air-to-water heat pumps (AWHPs) in the residential sector. The entrance of the respective systems in the commercial sector has made important the modelling of the processes. In this work, the suitability of artificial neural networks (ANN) in the modelling of AWHPs is investigated. The ambient air temperature in the evaporator inlet and the water temperature in the condenser inlet have been selected as the input variables; energy performance indices and quantities characterising the operation of the system have been selected as output variables. The results verify that the, easy-to-implement, trained ANN can represent an effective tool for the prediction of the AWHP performance in various operation conditions and the parametrical investigation of their behaviour.

Performance of Low GWP Fluids in Heat Pump Systems

Heat pumps are increasingly gaining popularity as the world is moving towards low-carbon energy systems. Use of heat pumps for domestic heating and hot water is widely seen as a sustainable option, and a step further from conventional fuel dependence. In spite of being ‘green’ in terms of carbon-pollution, there is a need to move towards low GWP working fluids in heat pump systems to ensure minimal impact to the environment. Low GWP fluids and mixtures have been emerging in the light of sterner legislations being introduced to limit, if not to totally prevent, further use of high GWP fluids. Replacement fluid has to satisfy a number of criteria, primarily to perform similarly to the original fluid. We have compared high and low GWP fluids, as well as several mixtures, as working fluids in the same operational scenario. Low GWP fluids are fundamentally different from conventionally used one, but their performance has some promising features.

Experimental study on a novel PV/T air dual-heat-source composite heat pump hot water system

In this study, the performance of a novel photovoltaic/thermal (PV/T) air dual-heat-source composite heat pump hot water system was investigated experimentally and analyzed theoretically. First, a system that simulates a solar PV/T collector by electric heating was built and tested to validate the superiority of the hot water system. The system was divided into dual-heat-source operating mode and single-heat-source operating mode. Results showed that the average COP and COPsys for dual-heat-source operating mode were 2.49 and 2.24, respectively, and for single-heat-source operating mode were 1.40 and 1.31, respectively, which indicate that the former had better system performance. Then, the actual PV/T collector was used in the system. The results showed that the average electrical gain and heat gain were 278W and 664W, respectively. The average electrical efficiency and heat efficiency were 14.5% and 36.02%, respectively. Meanwhile, the comprehensive efficiency was more than 50%. The average COP and COPsys of the heat pump were 4.08 and 3.07, respectively, along with the system exergy efficiency of 0.33. Therefore, the PV/T air dual-heat-source composite heat pump hot water system has excellent performance and is worth promoting and applying.

Role of distributed storage in a 100% renewable UK network

This study considers generation and demand challenges of a 100% renewable UK electricity grid and poses the question whether this can be addressed through the use of distributed energy storage. To explore this issue, hourly demand and electricity generation profiles for a year have been constructed for a variety of renewable sources and demand scenarios. Alongside baseline projections, further scenarios have been produced that include extensive uptake of electric heat pumps for domestic heating and hot water, as well as moderate uptake of electric vehicles. It is proposed that these technologies are used on a local scale to help integrate the additional renewable electricity generated within a predetermined zone of the electricity network. Analysis has been carried out to determine the pinch points in the UK network where renewable electricity generation is greater than local electricity demand. From this, consideration has been given to understanding the real impact distributed energy storage in the form of heat pumps and electric vehicles can have in helping balance a 100% renewable UK electricity grid. Initial results have found that, depending on the demand scenario and location on the network, there is the potential to accommodate up to 50% of the excess electricity generated.

Performance Comparison of Direct Expansion Solar-assisted Heat Pump and Conventional Air Source Heat Pump for Domestic Hot Water

Abstract In this work, performances of conventional air source heat pump water heater (ASHPWH) and direct expansion solar-assisted heat pump water heater (DX-SAHPWH) under various operating conditions are analyzed to make comparison between the two systems. The DX-SAHPWH system in this study uses a plate type roll-bond solar collector with optimized flow channel as the evaporator, which can take both solar energy and ambient air as the heat source. Performances of both systems are investigated experimentally and numerically. The influences of operating conditions (air temperature, water temperature, solar radiation intensity, et al) are analyzed, and performance comparison under various operating conditions is made between the two systems. Results show that, in clear day conditions, the COP of DX-SAHPWH is obviously higher that of ASHPWH because the solar energy can improve the evaporating temperature of the heat pump obviously; in overcast day conditions (without frost formation), COP of both systems are almost the same; and in night conditions, especially in clear night conditions, the DX-SAHPWH shows poor performance because of the poor convectional heat exchanging performance of the solar collector/evaporator and the radiative heat loss to the night sky. And annual performance analysis shows that the average COP of the DX-SAHPWH system is remarkably higher than the conventional ASHPWH system, especially in winter season.

Development of Glazed and Unglazed PVT Collectors and First Results of their Application in Different Projects

Abstract After a short introduction on glazed and unglazed PVT collectors, we report on two projects with different applications of uncovered PVT collectors: (1) regeneration of ground bore-hole storages coupled to heatpumps for space heating and domestic hot water and (2) pre-heating of domestic hot water in multi family houses.

Experimental Study of a Novel PV/T- Air Composite Heat Pump Hot Water System

Solar energy utilization and heat pump are common technologies of renewable energy utilization for solving the problem of energy crisis and environmental pollution in present. This paper proposed a novel PV/T-air composite heat pump hot water system. The system was comprised of independently developed flat plate solar PV/T collector based on micro-channel heat pipe array and air source heat pump, which were combined by a new composite evaporator. The performance of the system were experimentally studied, COP of heat pump reduced from 5.61 to 1.69 and the average was 3.03. Comprehensive COPsys of PV/T-air composite heat pump system ranged from 6.07 to 1.33, the average was 2.99. The result showed the system was worthy of promotion and application.

Research on Application of Air Source Heat Pump Hot Water System in Energy Saving Building

Air source heat pump hot water system is a kind of high efficient energy saving technology model, and it has no pollution to the environment. In this paper, a bathroom of one college in Panzhihua area is researched as a project example, and the working principle of air source heat pump hot water system is introduced, furthermore, the system benefit is analyzed. The result proves the air source heat pump hot water system has good economic benefits, energy saving and environmental protection benefits, and it has a broad development space and application prospect in building energy saving.

Modeling the impact of integrating solar thermal systems and heat pumps for domestic hot water in electric systems – The case study of Corvo Island

The use of solar thermal systems with electricity backup and heat pumps as hot water suppliers in residential buildings seems to be a very promising way to increase energy efficiency. Nevertheless, the massive adoption of such solutions in small networks (neighborhood, village) may induce problems in the electric grid management. This study explores the impact of such systems in small electric grids, using an hourly electricity backup load model. To test and validate the model, we used the island of Corvo (Azores), a small isolated community where it is being implemented a project of electrification of domestic hot water systems (DHW). We consider different load scenarios to manage the backup of DHW systems and analyze its consequences on the peak load and overall energy demand. For Corvo, for the best case where the backup is limited and distributed along off-peak hours, we observed an increase of 24% in the peak load and 7.5% in the annual energy demand. Critical values of peak load are found in winter, when daily solar irradiation is lower than 2000 Wh/m2/day. We conclude that the solar thermal systems are responsible for most of the peak load increase, but since they have the flexibility to adjust the electric backup hours due to the thermal storage capacity, the use of these systems can minimize the impact on the grid. Heat pumps on the other hand, albeit being more efficient in terms electric backup, are less flexible to contribute to the grid management as they operate continuously.

The Heating Coefficient Experimental Analysis of Solar Water-Assisted Low Temperature Air Source Heat Pump System

In winter,Many families use air source heat pump because of the low evaporation temperature of the system, resulting in lower heating efficiency of system. To solve this problem, the low temperature solar assisted hot water was added to the project which is on the basis of air source heat pump, and the system has been tested. After analysis of the collection efficiency of solar collectors at low temperatures and comparative analysis of the temperature cycle, pressure, energy consumption of the low-temperature solar-assisted systems and air source heat pump system, the optimal collector temperature and law of heat pump refrigerant cycle changes of the system were obtained. Theoretically, comparative analysis of low temperature air source heat pumps and solar hot water secondary air source heat pump compression ratio and COP. It gives the key parameters affecting the compression ratio and COP, pointing out ways to improve the heat pump COP. Finally, a key measure to improve the thermal performance of the unit system is proposed, to provide a reference for future practical applications and research. Foreword Air source heat pump in ambient air contains rich low grade solar potential as a source of heat, it has inexhaustible characteristics [1] . The main reason for restricting the use of air source heat pump in northern area of our country is when the outdoor air temperature is low in winter, the outdoor coil frost severe heating efficiency air source heat pump is greatly reduced. Martinez suggested experimental study on the application of solar radiant floor heating systems , solar water temperature is 50-60°C, low efficiency, especially when overcast snow lower system efficiency [2] .In view of the outdoor coil frosting problem, direct expansion solar assisted heat pump water heater system using the proposed by Li Yuwu, from a certain extent alleviated the problem of heat in winter for coil winter fros, improving the heating coefficient and improved the operating characteristics of the unit. However, this system requires the direct absorption of heat in air tube, and the specific heat of air is small, difficult to heat storage, illumination by solar radiation impact, unstable system operation [3]. Based on the above issues, for the low-level office building , the new rural residential , this study presents low temperature solar auxiliary air source heat pump system , the device uses low-temperature solar hot water heat pump system as low , both full use of solar energy , but also eliminates the original system frost problems and improve the efficiency of solar collectors and heat set to improve the evaporation temperature of the evaporator , thereby increasing the compression ratio of the heat pump unit .

C111 ヒートポンプ給湯用プレート式凝縮器の熱交換特性(OS4 省エネルギー・コジェネ・ヒートポンプ(1))

This study deals with heat transfer characteristics in a blazing plate heat exchanger used as a condenser in heat pump hot water heater. In this report, experiments of single channel heat exchanger were carried out by using a pump driven two-phase flow loop. The test section has one path for each fluid, refrigerant and water. The effects of mass flow rate of refrigerant and water, wave height of plate, and setting arrangement, vertical with downward refrigerant flow or horizontal, were examined. HFC134a was used as the refrigerant. Superheated vapor was supplied to the condenser, and heated water. Water was flowing in the counter flow direction. The wall temperature distribution of the refrigerant path was measured by an infrared camera. As a result, it was shown that the lateral temperature distribution for the horizontal arrangement was affected by the wave pattern while that for the vertical arrangement was uniform.

New test methodologies to analyse direct expansion solar assisted heat pumps for domestic hot water

Since there are not specific standards for testing direct expansion solar assisted heat pumps for domestic hot water, new testing methodologies are proposed supported by laboratory experiments. Two methodologies were developed for performance measurement: modified BIN method and long term performance prediction with a TRNSYS model validated with specific experimental conditions. The long term performance prediction is a methodology similar to the already obtained for solar thermal systems. A system was tested in Lisbon during one year, covering almost all possible local weather conditions. The hot water tapping test cycle used was in agreement with recent standards EN16147:2011 or EN15316-3-1:2007. The influence of average daily air temperature, dew point temperature and solar irradiation was analysed. The seasonal performance factor was calculated for two cities in Portugal (Lisbon and Porto) and for additional four cities in Europe (Davos, Athens, Helsinki and Strasburg). The establishment of a procedure to calculate the seasonal performance of this kind of systems is very important according to the directive 2009/28/EC of the European Parliament and of the Council.