Multi-functional Heat Pump System Research Articles

Performance simulation and analysis of a solar-assisted multifunctional heat pump system for residential buildings

ABSTRACT As building electrification is recognised as an important opportunity to reduce greenhouse gas emissions, the integration of solar energy and heat pump represents a promising solution towards net-zero carbon buildings. This paper presents a hybrid multifunctional solar-assisted heat pump (SAHP) system that can provide space heating, space cooling, domestic hot water, and onsite electricity generation. Photovoltaic-thermal collectors are used for electricity generation, heat collection, and radiative cooling. The system design and controls support fourteen operational modes involving different components. TRNSYS software is used to model and simulate the multifunctional SAHP system. With a 2-m3 storage tank and 30-m2 PVT collectors, the multifunctional SAHP system has a seasonal performance factor of 2.7 in Baltimore and 3.7 in Las Vegas. The onsite electricity generation can cover 53% of the building’s electricity needs in Baltimore and 83% in Las Vegas.

Energy efficiency analysis of novel combined open absorption multifunctional heat pump and FlashME desalination system with a compressed air dryer

Energy intensive thermal desalination and compressed air-drying processes coupled with low grade heat recovery units can significantly contribute to carbon and energy footprint reduction. In this paper, a novel combined system based on an open absorption multifunctional heat pump and FlashME desalination system with a compressed air dryer is proposed to recover the latent heat from flue gas and efficiently utilize it to drive the desalination process for seawater treatment and supply the compressed dry air. The energy performance of the combined system is analyzed under the effect of various key operational parameters by simulating the validated process model. The results of energy analysis indicate that the novel system can recover the latent waste heat from flue gas with an efficiency of 83.02 % and supply the compressed dry air at low humidity of 1.41 g/kg by operating at a thermal COP of 1.95. Furthermore, the system can efficiently utilize the recovered low-grade heat to produce freshwater at a recovery rate of 23.14 %. The findings of the critical performance analysis show that the drying, and latent heat recovery performance of the coupled system is dependent mainly on the inlet parameters of the spray solution and the flue gas humidity. However, the water recovery of FlashME is totally dependent on heat capacity and the regeneration pressure such that the performance ratio increases from 1.51 to 4.03 by operating with hot seawater of 60–80 °C, when the regeneration pressure is raised up to 53.48 kPa. Moreover, the coupled system configured in parallel double stage can lower 11.43–37.78 % regeneration load along with 54.24 % improvement in distillate productivity when the operating pressure is raised up to 800 kPa and the rise in airflow rate in dryer can decrease the 10.41–52.45 % regeneration load on external heat source.

Experimental and numerical investigation on the heating performance of a novel multi-functional heat pump system with solar-air composite heat source

Multi-functional heat pump system with the functions of air conditioning and producing domestic water can operate throughout the year, so its working condition is more complicated than ordinary heat pump. The integration of composite heat source with multi-functional heat pump can be an effective approach to improve the operational stability. Based on the concept of multi-energy complementarity, a solar-air composite source multi-functional heat pump (SA-CMHP) system is proposed to fulfill the energy demand in buildings. The experimental prototype is built to study the performance of SA-CMHP in space heating mode. The experimental results show that SA-CMHP achieves the optimal performance at the EXV opening degrees of (20, 20). Mathematical model of SA-CMHP is developed, and the impact of ambient temperature, solar irradiation and wind speed on heating performance is identified. It is revealed that the rise of outdoor ambient temperature is beneficial for the improvement of heat transfer performance of both evaporators. The evaporation capacity of solar collector increases as solar irradiation rises, while the variation of the evaporation capacity in outdoor air heat exchanger shows the opposite trend. With the wind speed rising from 1 m/s to 6 m/s, the COP rises from 2.11 to 2.40.

Water Heating and Operational Mode Switching Effects on the Performance of a Multifunctional Heat Pump

In this study, a multifunctional air and water source heat pump system was developed with a parallel refrigerant piping arrangement, which possessed six operational functions: space cooling (SC), space heating (SH), water heating (WH), water cooling (WC) and two composite operational modes. The two composite operational modes were the SC/WH mode and the SH/WH mode. The performance of the multifuctional heat pump system under different ambient conditions was investigated based on the testing standards of CNS 14464 and CNS 15466. In this study, the effect of the direct water heating (DWH) and circulating water heating (CWH) methods on the performance was investigated. It was found that the water heating performance of the system by the DWH method is better than that of the system by the CWH method. The water heating capacity and COPw,h of the DWH method can be improvement by 2.6% to 22.1% and 2.9% to 50.8%, respectively. Moreover, this study developed a refrigerant pressure balance method to achieve an effective steady state of the refrigerant pressure after operational mode switching. By the refrigerant pressure balance method, the required time to attain the steady state could be greatly reduced—by 50%. However, the deviation of the refrigerant mass flow rate between the refrigerant pressure balance method and the refrigerant pump down method after operational mode switching ranged from 0.15% to 7.6%.

Economic and environmental benefits of a novel multi-functional heat pump system for dishwasher

In present study, a novel heat pump named multi-functional heat pump systems for dishwashers is introduced. 45 oC hot water cycle and hot air cycle are provided by the single-stage heat pump cycle to complete the cleaning and drying process. Moreover, the high temperature water at 85 °C is provided by the two-stage heat pump cycle system to achieve the disinfection function, and the 26°C cold air is realized by the single-stage refrigeration cycle for rapid cooling. Thermodynamic analysis of multi-functional heat pump systems for dishwashers under four different operating conditions with R22 / R134a as working fluid was carried out. The results show that COP (coefficient of performance) of the system is above 3.2 under all four conditions, which meets the energy efficiency rating index. Comparing energy efficiency and environmental benefits and operating costs of multi-functional heat pump systems for dishwashers with the traditional electric heating dishwashers, these can be known that primary energy consumption, carbon dioxide emissions and operating cost of multifunctional heat pump dishwasher are 1.24 * 105kJ, 10.55kg and 21.70 Yuan respectively under the condition of per running energy consumption for 40kW·h, above three all lower than the traditional electric heating dishwasher.

Optimization and analysis of a multi-functional heat pump system with air source and gray water source in cooling mode

A multi-functional heat pump system has been proposed to effectively utilize waste heat and heat capacity in gray water for heating and cooling of residential buildings. Condenser heat recovery is integrated into the system. This system was tested in two environmental chambers that mimic the outdoor and indoor environments, respectively. In this paper, the investigation of the optimized system is focused on the system optimization and performance in cooling mode. The drawbacks of the initial prototype are analyzed and fixed. The system performance in the initial and optimized prototypes are compared and analyzed. At outdoor temperature 35°C, compared to initial type, the COP of optimized prototype increases up to 20.07% for space cooling mode and up to 21.51% for space cooling with hot water supply mode. This system is tested and analyzed at space cooling mode, space cooling with hot water supply mode and hot water supply only mode.

Operation characteristics of a novel dual source multi-functional heat pump system under various working modes

The dual source multi-functional heat pump (DMHP) system, which can adopt air source and solar energy to provide air conditioning and domestic water for building all the year round, is the integration of solar thermal collecting system and multi-functional heat pump system. This paper presents an investigation into the operation characteristics of the novel DMHP system under various working modes by theoretical and experimental methods. For each working mode, a dynamic model has been proposed and validated with the experimental data. With the verified model, the switch point between air source and solar energy can be identified by comparing the operation performance of different working modes under a range of boundary conditions. The results indicate that the performance of air source space heating mode is superior to that of solar space heating mode with the ambient temperature above 4°C, and solar water heating mode is more efficient than air source water heating mode when the ambient temperature is below 3°C. On this basis, annual performance of the system under different climate conditions reveals that the DMHP system can obtain relatively high COP with the optimal working strategy in the whole year especially for the district with cold winter. Furthermore, the exergy loss ratio in each component of the DMHP system has been discussed to provide the reference for further optimization. In general, the DMHP could be a promising building energy supply system with the advantage of high equipment utilization, compact structure, and full-featured, and this research would promote the development of such an innovative technology leading to significant energy saving and carbon emission reduction in building sector.

Numerical simulation and experimental validation of indirect expansion solar-assisted multi-functional heat pump

A novel indirect expansion solar-assisted multi-functional heat pump (IX-SAMHP) system which composes of the multi-functional heat pump system and solar thermal collecting system is proposed and studied in this paper. This system can fulfill space heating, space cooling and water heating with high energy efficiency by utilizing solar energy. For solar water heating mode and solar space heating mode, a dynamic model is presented and validated with the experimental results. The simulation results show good consistency with the experimental data, and the established model is able to predict the system performance at a reasonable accuracy (with the root mean square deviations less than 5%). On this basis, the performances of the IX-SAMHP system are investigated under different parametric conditions. For solar water heating mode, simultaneously operating the solar thermal collecting system and multi-functional heat pump system can be an energy efficiency method. With the solar irradiation rising from 0W/m2 to 800W/m2, the COP increases from 2.35 to 2.57. In solar space heating mode, the effect of the mass flow rate of water in evaporator is investigated. To balance the heating capacity and COP, the mass flow rate of water should be adjusted according to different temperature demands and heat load.

Optimization and analysis of a multi-functional heat pump system with air source and gray water source in heating mode

A multi-functional heat-pump system utilizing the ambient air and gray water as heat source and sink has been optimized for heating and cooling of residential buildings, respectively. This optimization is made based on an existing prototype of the multi-functional heat pump system in the authors’ previous study [1,2]. The optimized prototype consists of a heat pump system and a hot water supply system. The prototype is set in two environmental chambers that they simulate the outdoor and indoor environments, respectively, for performance testing. The system was designed to allow four combinations of a water-source evaporator and an air-source evaporator acted as heat sources in space and/or hot water heating modes. The four combinations consist of (a) air-source-only, (b) water-source-only, (c) air-and-water-sources-in-parallel, and (d) air-and-water-sources-in-series, in the refrigerant cycle. In this paper, the drawbacks of the initial prototype in heating mode are discussed and the modifications are proposed. The results show that the performance of optimized prototype superior to that of initial one. The optimized multi-functional heat pump system, compared with initial prototype, can be more practical and provide significant energy savings in space heating and hot water supply.

An experimental exergetic comparison of four different heat pump systems working at same conditions: As air to air, air to water, water to water and water to air

In this study, we designed a multifunctional heat pump system using just one scroll compressor and which can be run in four different modes, namely air to air, air to water, water to water and water to air, in order to make an experimental energetic and exergetic performance comparison. Experimental system consists of two condensers and two evaporators and uses R22 as working fluid. One of the evaporators and condensers uses water and the others use air as heat source/sink. Heating capacities of four heat pump types are equal to each other. It is realized by adjusting the mass flow rate and temperature level of external fluid of condenser. Results show that the heat pump unit which has the maximum COP (coefficient of performance) value is water to air type with 3.94 and followed by water to water type with 3.73, air to air type with 3.54 and air to water type with 3.40. Ranking of four heat pump types with respect to their mean exergy efficiency is as follows; water to air type with 30.23%, air to air type with 30.22%, air to water type with 24.77% and water to water type with 24.01%. Exergy destruction rates of the systems were investigated in this study and the results revealed that the heat pump type which has the maximum exergy destruction is air to air type with 2.93 kW. The second highest one is air to water type with 2.84 kW. The third highest one is water to air type with 2.64 kW and last one is water to water type with 2.55 kW. It is understood that the temperature of the evaporator external fluid affects the exergetic efficiency of the system more than the mass flow rate. In contrast to the previous, the dominant parameter which has more important effect on the exergy destruction of the heat pump unit is the mass flow rate of evaporator external fluid.

Performance analysis of a multi-functional heat pump system in cooling mode

A multi-functional heat pump system is proposed to effectively utilize waste heat and heat capacity in gray water for heating or cooling of residential buildings. Heat is also reclaimed from a plate heat exchanger installed at the discharge outlet of the compressor to provide sufficient hot water for residential use. To study the performance of this innovative system, laboratory testing has been performed with a prototype consisting of an outdoor heat pump, an indoor air handler, a gray water tank and a hot-water tank. This system is set in two environmental chambers that they mimic the outdoor and indoor environments, respectively. In this paper, the investigation of the proposed system is focused on the performance in cooling mode. The multi-functional heat pump system has been run under (i) space cooling mode and (ii) space cooling plus hot-water supply mode, with the same temperature conditions. The system performances in these two modes are compared and analyzed. The system is designed to allow four combinations of heat sinks with a water sink condenser and an air sink condenser. The four combinations are (1) air sink only, (2) water sink only, (3) air sink and water sink in parallel and (4) air sink and water sink in series, at the refrigerant cycle. Performance of the four combinations of heat sinks is experimentally investigated at a typical indoor air temperature of 26.7 °C and various outdoor air temperatures at 29.4 °C, 35 °C, and 40.5 °C. The results show that the heat sink combinations influence the cooling capacity and coefficient of performance (COP) of the system. The system performance and the optimal heat sink combination depend on the outdoor temperature. The impacts of outdoor temperature and gray water temperature on the performance of the system are discussed. The dynamic performance of the system for heating hot water from 30 °C to 48.9 °C is also studied. The proposed system has been shown providing significant energy savings in space cooling and hot-water supply. Moreover, the optimal source combination is critical in pursuing the maximum energy savings.

Exergy analysis and comparison of multi-functional heat pump and conventional heat pump systems

In this paper, the thermal dynamic analysis of a multi-functional heat pump system (MHPS) is made in comparison with a conventional heat pump air conditioning system. Energy and exergy efficiencies of the different systems are calculated to study influences of the components parameters, operation conditions and operation modes on the system performance. Variation of the MHPS performance with increasing hot water temperature is investigated, and performances of the major components are also studied in order to optimize the structure and operation of MHPS.

Experimental performance analysis of an improved multifunctional heat pump system

An improved multifunctional heat pump (MFHP) system that integrates an air-source evaporator and a water–water heat exchanger was developed. An experimental set-up and a mathematical model were constructed to evaluate the performance of the MFHP system. Some characteristics of the system, such as the effects of water–water heat exchanger, hot water outlet temperature, and cooling capacities of the air-source and water-source evaporators, were discussed based on experimental data. Experimental results show that the MFHP system could simultaneously supply hot water for bathing and cold air for air conditioning. In addition, the coefficient of heating performance (COPh) varied from 3.69 to 5.70. Analysis results show that the COPh and the hot water volumetric flow rate of the MFHP system were closely related to the inlet and outlet temperature of hot water and wastewater. Empirical models of COPh and hot-water flow rate were proposed to predict the heating performance of the MFHP system. The improved MFHP system is shown to have satisfactory energy saving performance.

Performance analysis of a multi-functional Heat pump system in heating mode

A multi-functional heat-pump system is proposed to efficiently utilize the gray water as heat source and sink for heating and cooling of residential buildings, respectively. Heat is reclaimed from the plate heat exchanger installed at the outlet of the compressor to provide sufficient hot water for residential use. To study the performance of this innovative system, laboratory testing is performed with a prototype consisting of an outdoor heat pump, an indoor air handler, a gray water tank and a hot water tank. This system is set in two environmental chambers that they represent: the outdoor and indoor environments, respectively. In this paper, the investigation of the system is mainly focused on the heating performance. The system is designed to allow four combinations of two heat sources that they are a water-source evaporator and an air-source evaporator. The four combinations consist of air source only, water source only, air source and water source in parallel and air source and water source in series, in the refrigerant cycle. Performance of the four combinations of heat sources is experimentally investigated at a typical indoor air temperature of 21.1 °C and various outdoor air temperatures at 1.1, 8.3, and 15.6 °C. The results show that the heat source combinations influence the heating capacity and coefficient of performance (COP) of the system. Also, the system performance and the optimal heat source combination depend on the outdoor temperature. As outdoor temperature decreases, the variation of system performance among different combinations becomes small. The system performance in modes of space heating and space heating plus hot water supply are compared and analyzed. The COP of the system in the space heating plus hot water supply mode increases in all heat source combinations, compared with that in space heating only mode. The performance of the system for heating hot water from 30 °C to 48.9 °C is also studied. This proposed system can provide significant energy savings in space heating and hot water supply. The optimal source combination is critical in pursuing the maximum energy savings.

Research on refrigerant flow characteristics and performance of a multi-functional heat pump system

Multi-functional domestic heat pump systems (MDHPS) can reduce operating costs, lessen thermal pollution to the environment, and improve equipment utilization rate. Compared with the traditional heat pump system, the MDHPS has a wider range and more dramatic changes in operating conditions. This paper incorporates the refrigerant flow characteristic and performance analysis of an electronic expansion valve (EEV)-controlled MDHPS which operating in four typical modes (sanitary water heating mode, space cooling mode, space cooling combined with condensing heat recovery mode, radiant floor heating mode). The calculating results demonstrate that there are considerable differences in the refrigerant mass flow range when the MDHPS operates in the different modes. Moreover, sudden changes in working conditions due to mode switching easily result in large-scale fluctuations of system parameters. Therefore, to ensure the MDHPS to work more reliably and efficiently, a control scheme of the EEV specialized for the MDHPS is proposed and applied in the presented experimental system. The experimental results indicate that the system is able to perform efficiently and stably under various conditions by this control method. In the sanitary water heating mode, the average heating coefficient of performance (COP) reaches 2.2, 3.2 and 4.1 when the ambient temperature is 5 °C, 20 °C and 35 °C, respectively. In the condensing heat recovery mode, besides yielding free sanitary hot water, the average cooling COP can be improved 9% when the water temperature ranges from 30 °C to 55 °C. In the radiant floor heating mode, the COP is 3.3 at 6 °C ambient temperature.

Energy and exergy analysis of multi-functional solar-assisted heat pump system

This paper reports the exergetic modeling and performance evaluation of a novel multi-functional solar-assisted heat pump (SAHP) system based on an experimental study. Comparisons between the multi-functional SAHP system and conventional hot water heating systems, i.e. electric water heater, gas-fired water heater and air source heat pump, are made with respect to energy and exergy efficiencies. The results show that the multi-functional SAHP system has the highest energy performance, average 2.98. In addition, the multi-functional SAHP system offers the highest exergy efficiency among the four kinds of hot water heating systems. Copyright The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org, Oxford University Press.

05/02305 Performance of multi-functional domestic heat-pump system

05/02305 Performance of multi-functional domestic heat-pump system