Source Heat Pump Unit Research Articles

A novel index model for defrosting initiating time point of air source heat pump based on the cusp catastrophe theory

In winter, the operating performance of air source heat pump (ASHP) units deteriorates due to the accumulation of frost on the outdoor coil surface. In order to reduce the impact of this disaster phenomenon, ensure stable operation and save energy, it is necessary to accurately determine the initiation of defrosting after a period of unit operation. Although some existing defrosting initiation control strategies are effective, too much data volume and accuracy are required. To address these issues, a different perspective on mutation from previous studies is taken. This study combines the cusp catastrophe theory with frost accumulation, and presents a defrosting initiation index model for ASHP. After a brief description of the cusp catastrophe theory, the discriminant index model based on the cusp catastrophe theory (DICC) is proposed, state variable and control variables of the index model are determined. Then, the unit was tested for 10-days. To solve and verify the DICC, 10-days experimental data was used and it was found that DICC can efficiently predict the heating capacity decreases. Consequently, the DICC-based defrosting initiation control strategy was compared with the existing strategies, and the unit’s performance improvement compared to the original strategy was evaluated, as the results show, a 3.9% improvement in coefficient of performance (COP) and a 4.9% increase in heating capacity. Therefore, the strategy proposed in this paper is suitable for ASHP units with limited data capacity and low data accuracy, also can ensure the accurate initiation of defrosting and efficient operation.

Unsteady characteristics of sleeping thermal comfort during defrosting of a T-ASHP system

Defrosting is necessary for the normal operation of air source heat pump (ASHP) units to solve the frosting in the winter, which deteriorates the performance of ASHP. During this defrosting period, the ASHP cannot provide heat to the indoor space, leading to adverse thermal comfort, which may reduce the sleep quality. Hence, a task/ambient ASHP (T-ASHP) system was designed in this study, and the transient thermal environment was investigated through a computational fluid dynamic (CFD) method. The duration of t oz (average air temperature in the occupied zone) increase period was 4.33 times as long as t oz decrease period, although the duration of the phase 1 heating period was 1.9 times as that of defrosting period. During the defrosting procedure, the PMV value decreased to the lowest value of −0.83, and the period of feeling cool and slightly cool lasted for 45.4 min. The hand, foot and leg parts were much cooler than the whole body, and the non-uniformity of the PMV value on body parts was obviously enlarged during the defrosting period. Higher draught risk around 22% near the head and trunk regions was found during the defrosting period and was significantly reduced in the follow-up heating period. Practical application: The results from this study emphasize the sleeping thermal comfort during defrosting of air source heat pumps. The present study gave a map of transient thermal comfortable levels influenced by the operating of defrosting and re-heating. These results should serve as a recommendation to air source heat pump designers to determine suitable defrosting technology to maintain normal indoor thermal comfort.

The Impact of an Air to Water Heat Pump in the Residence of a University Campus

The implementation of an energy efficiency intervention in the students’ residence of the university campus may lead to a reduction in the energy consumed and electricity cost. The study focused on retrofitting a 1000 L, 12 kW boiler, with a 4.0 kW Air Source Heat Pump (ASHP) unit. A data acquisition system was built and deployed, to monitor the baseline performance of the electric boiler and the actual performance of the installed ASHP water heater (which was used to retrofit the electric boiler during the assessment period). The results show an annual electrical energy saving of 34805.94 kWh and load factor reduction of 0.124 due to the replacement of the electric boiler with the ASHP unit. The payback period of the ASHP system was 1.7 years, using the method of net present value of money. Wilcoxon rank sum test was employed to compare both the daily volume of water and energy consumed by the electric boiler and the ASHP water heater to test if their difference was of any significance. We concluded that, there exists a significant difference in the average daily energy consumed by the boiler and the ASHP water heater in both summer and winter season with the utilization of the Wilcoxon rank sum test. We could conclude that, a rollout of the ASHP units to retrofit the existing electric boiler in the students’ residence in the University campus is economically viable and calls for such an intervention is imperative.

Transient Simulation and Optimization of Regional Integrated Energy System

A modeling method of regional integrated energy system based on bus method and transient simulation is proposed, and the system optimization is based on the dynamic balance of supply and demand in the whole year energy supply cycle. A CCHP system of gas turbine coupled with ground source heat pump and electric refrigeration unit is constructed. The energy relationship of the system is described by bus structure, and the transient calculation model is built on TRNSYS platform. The weighted sum of annual total cost saving rate, primary energy saving rate and environmental pollutant shadow cost saving rate is taken as the optimized objective function, and on the basis of annual dynamic balance, the Hooke-Jeeves algorithm is used for optimization of the system configuration. A complex commercial area in Beijing is taken as an example, and different weighting coefficients are set for optimization of the system configuration. The results show that, from the perspective of economy, environmental benefit and primary energy consumption, performance of the system increases and then decreases with rise of gas turbine power; under the simulated cooling/heating load, the maximum number of optimum configuration is seen in the combination of 35 kW gas turbine + 723 kW GSHP and 1178 kW electric chiller; in comparison with traditional distributed system, the annual cost saving rate, primary energy saving rate and environmental pollutant shadow cost saving rate of the system are 29.4%, 49.6% and 58.2%, respectively.

Performance analysis of a hybrid subway source heat pump system using capillary heat exchanger

A large amount of free heat generated by the running of subway is released to the tunnel. Due to arc structure of subway tunnels, conventional ground source heat pumps and large-diameter heat exchangers are difficult to efficiently extract the heat and maintain surrounding-rock thermal balance. To sustainably take advantage of these free heat, in this paper, a hybrid subway source heat pump system is proposed, which is integrated by subway source heat pump system, 4.3 mm diameter capillary heat exchanger and auxiliary cooling system. A dynamic simulation model of the hybrid heat pump system, which includes the heat transfer process between capillary heat exchanger and surrounding-rock was developed on TRNSYS. Field tests were conducted at a subway station of Qingdao (China) to validate this model. Under different strategies, the coefficient of performance of the hybrid heat pump system and characteristics of surrounding-rock temperature field are compared. The results indicated that the hybrid heat pump system can ensure appropriate surrounding-rock temperature without overheating (from 33.9 ℃ to 31.3 ℃). Additionally, the coefficient of performance of the subway source heat pump units was 4.432, increased by 2.52%, the energy consumption of the subway source heat pump system can be decreased by 5.55%.

Development of evaluation indexes for assessing the regional operating performances of air source heat pump (ASHP) units operated in different climate regions based on the equivalent temperature drop method

During the actual operation of an ASHP unit installed in different climate regions, ambient operating conditions can vary constantly over an entire heating season, thus the actual output heating capacity of ASHP units may vary significantly from region to region. To enable a convenient evaluation of output heating capacity of a space heating ASHP unit installed in different climate regions, regional performance evaluation indexes including Ta′¯, HERR(Ta’), βTa and βRH based on ETD method have been developed. These evaluation indexes are generalized and can be used to evaluate the regional performance of ASHP units operated in any regions. It can also be used to specify the key factors affecting the operating performances of ASHP units in different regions. With the developed evaluation indexes, the regional operating performances of ASHP units installed in 278 Chinese cities were evaluated. The results demonstrated that the total output heating energy for ASHP units operated in Southern Chinese provinces may be lower than those in Northern China. In Shanghai, Ta′¯ at −6.0 °C is lower than that at −3.0 °C in Beijing, suggesting the total output heating energy from an ASHP units operated in Shanghai over an entire heating season would be lower than that in Beijing. Furthermore, in southern Xinjiang and northern Fujian Provinces, the total output heating energy from ASHP units may be higher than those operated at the nominal condition. In addition, in Tibet, Beijing, Liaoning, etc., the total output heating energy from the ASHP units would be affected more by Ta, thus ASHPs’ manufacturers are recommended to develop ASHP units suitable for operation in low temperature ambient. In most regions in southern China, RH would affect more on the total output heating energy from the ASHP units, thus ASHPs’ manufacturers are recommended to develop ASHP units having frosting suppression provisions and accurate defrosting measures.

Linear Regression Analysis and Techno-Economic Viability of an Air Source Heat Pump Water Heater in a Residence at a University Campus

This study quantifies the potential of a 4.0 kW air source heat pump (ASHP) unit retrofitted to a 12.0 kW, 1000 L electric boiler coupled to a 1000 L storage tank. A data acquisition system was built to monitor the performance of the electric boiler and the ASHP water heater. The annual electrical energy saving and the load factor reduction from the electric boiler because of the ASHP unit retrofit was 34,805.94 kWh and 0.124. The net present value payback period of the ASHP system was 1.60 years. A Wilcoxon rank sum test was employed to compare both the volumes of hot water and electrical energy consumed by the two systems. Linear regression models of the daily volumes of hot water and electrical energy consumed by both systems were established. The results should be of great value to the management of universities that are considering energy-efficient interventions with a significant return on investment.

Evaluation of the coefficient of performance of an air source heat pump unit and an air to water heat pump

Air source heat pump (ASHP) water heaters are efficient devices for sanitary hot water heating. The coefficient of performance (COP) of the air to water heat pump (AWHP) is constantly lower than that of the corresponding ASHP unit. The study focused on determining the COP of both the ASHP unit and the AWHP. This was achieved by the implementation of both experimental and simulation methods, with the help of a data acquisition system and the REFPROP software. The system comprised of a 1.2 kW split type ASHP unit and a 150 L high pressure geyser. A power meter, flow meters, temperature sensors, pressure sensors, ambient temperature and relative humidity sensor were installed at precise locations on the split type AWHP. Controlled volumes of 150, 50 and 100 L were drawn off from the AWHP during the morning, afternoon and evening for a year. The average COP for the summer and winter, in terms of the input electrical and output thermal energies of the AWHP were 3.02 and 2.30. The COPs of the ASHP unit, in terms of the change in the enthalpies of the refrigerant at the inlet and the outlet of the condenser and the evaporator, were 3.52 and 2.65 respectively. The study showed that the difference between the COP of the ASHP unit and that of the AWHP could be ascribed to the electrical energy consumed by the fan and the water circulation pump during the vapour compression refrigeration cycles. The work provides an energy optimisation opportunity to the manufacturers of this technology, helping to enhance the efficiency and COP of ASHP water heaters.
 Highlights
 
 The COPt of the ASHP unit was higher than the COPe of the AWHP.
 The COPe of the AWHP was the ratio of the input electrical energy consumed and the output thermal energy gained by the stored water.
 The COPt of the ASHP unit was enthalpies-dependent and a function of inlet and outlet enthalpies of the evaporator and condenser.
 The inlet and outlet refrigerant temperatures profiles of the condenser confirmed thermal energy dissipation.

Measurement and analysis of cooling (heat) performance of renewable energy technology projects based on ground source heat pump systems

The design, configuration and operation of the soil-source heat pump system in four actual projects are monitored, collected and investigated. Combined with various test parameters of the project, the energy efficiency of the ground source heat pump system was compared and measured, and detailed data analysis was conducted from the aspects of heat exchange of ground source heat pump system, heat efficiency coefficient of ground source heat pump system, performance of ground source heat pump unit and performance of soil source heat pump system. It provides a basis for the formulation of operation strategy of soil-source heat pump system in the future, so as to serve the sustainable development of energy saving technology of shallow soil-source heat pump system.

Scheme design and economic analysis of an office building’s cold and heat source system in hot-summer and cold-winter zone

In the context of green development and sustainable development, in response to the national policy of “carbon neutrality and peak carbon dioxide emissions”, we will fully implement clean energy heating and reduce air pollution. Air energy is the representative, bringing the comfortable, efficient, safe and energy-saving environment to people. For an office building in Nanjing, which is located in hot-summer and cold-winter zone, an air source heat pump unit is designed as a cold and heat source system to meet the demand for heating in winter and cooling in summer. At the same time, compared with the traditional cold and heat source system which is designed central heating in winter and multi-line refrigeration in summer, the result of economic analysis shows that the use of air source heat pump as the cold and heat source system of office buildings is more economical and energy-saving. It is suitable to popularize and apply in China’s hot-summer and cold-winter zone.

Research on Individual Distributed Air Conditioning Systems using Water Source Heat Pump Units

Research on Individual Distributed Air Conditioning Systems using Water Source Heat Pump Units

A comparative study on system performances of multi-split air source heat pump with different energy accumulators and storage methods

Adding an energy accumulator to an air source heat pump (ASHP) unit can significantly improve its defrosting performances. However, the added energy accumulator may impact the system performances during heating period, which was rarely investigated in the published studies, especially for multi-split ASHP units (a kind of more and more widely used ASHP unit). In this paper, a comparative study on system performances of a multi-split ASHP unit under frosting condition with different energy accumulator structures and energy storage methods was experimentally carried out. The experimental results showed that the multi-ASHP unit employing fin-tube energy accumulator with serial energy storage method can achieve the longest heating period, which was 3.3%, 13.4%, and 9.4% longer than that employing spiral-tube energy accumulator with serial energy storage method, spiral-tube energy accumulator with parallel energy storage method, and fin-tube energy accumulator with parallel energy storage method, respectively. For spiral-tube energy accumulator using serial energy storage method, using parallel energy storage method, can shorten the energy storage period from 59 to 33 min. For fin-tube energy accumulator using serial energy storage method, using parallel energy storage method can shorten the energy storage period from 33 to 6 min. In addition, compared to serial energy storage method, using parallel energy storage method may significantly reduce the heating capacity, input power and heating COP of the multi-split ASHP unit during the energy storage period.

Research of Individual Distributed Air Conditioning Systems using Water Source Heat Pump Units

Research of Individual Distributed Air Conditioning Systems using Water Source Heat Pump Units

An experimental study on the frosting characteristic and performance of a micro-channel evaporator in an air source heat pump unit

Frosting and refrigerant distribution uneven easily are two key problems restricting the wide application of micro-channel heat exchanger in the field of air source heat pump (ASHP). In this paper, frosting experiments were carried out on two kinds of micro-channel heat exchanger in three cases that with different refrigerant distribution characteristics. Frost and temperature distribution characteristics and their influence on the heat pump’s COP and heating capacity was studied. The results show distribution of refrigerant in heat exchanger directly affects the frost and temperature distribution on the surface of micro-channel heat exchanger, and affects the heating capacity and COP of ASHP greatly. Vertical placement of flat tubes and horizontal placement of the headers can be beneficial to the refrigerant distribution compared with that with the headers vertically placed. Flow direction of refrigerant in the heat exchanger must be from bottom to top to avoid deteriorated heat transfer performance and instability of ASHP. Difference between the lowest temperature and largest temperature on heat exchanger surface can be used as an index to judge whether ASHP works in high performance state.

A modeling study on the revere cycle defrosting of an air source heat pump with the melted frost downwards flowing away and local drainage

Reverse cycle defrosting is widely used for air source heat pumps. When a multi-circuit heat exchanger is vertically installed in a heat pump as an outdoor coil, the melted frost could be kept downwards flowing or locally drained during defrosting by using water collecting trays. To analyze the performance differences of melted frost, two defrosting models were developed and previously reported by authors. In this study, the defrosting performance of an air source heat pump was numerically investigated based on the two models, with the melted frost downwards flowing away or local drainage considered. The following physical parameters are predicted and analyzed, including the thermal resistance of refrigerant, temperature of melted frost on tube and fin’s surface, mass of melted frost and energy consumption from refrigerant during defrosting. As calculated, after the melted frost locally drained, the predicted total energy consumption could be decreased from 898.1 kJ to 727.5 kJ, and defrosting efficiency increased from 47.5% to 57.6%. This work is helpful to optimizing the intelligent control strategy of an air source heat pump unit, as well as saving energy for buildings.

Investigation of ultrasonic array defrosting method based on synergism of standing wave intermittent phase-stagger and multi-frequency for finned-tube evaporator

Frost dramatically deteriorates the operating performance of an air source heat pump unit and leads to additional energy consumption. Results of our previous study show that intermittent ultrasonic vibration can greatly improve the coefficient of performance (COP) under frosting condition. To meet the ultrasonic defrosting demands of large-scale evaporators and to eliminate the standing wave effect of ultrasonic defrosting, an optimised ultrasonic array method for defrosting is proposed based on synergism of standing wave intermittent phase-stagger and multi-frequency excitation. Firstly, the surface vibration characteristics and defrosting effect difference of copper plate with standing wave intermittent phase-stagger in random mode and regular mode are investigated using a plate model. On this basis, the surface vibration characteristics and defrosting effect of a finned-tube evaporator are analysed in both phase-stagger modes. Finally, to optimise further the defrosting effect of the ultrasonic array, the standing wave intermittent phase-stagger and multi-frequency excitation are integrated to realise chaotic motion of the standing wave on the evaporator surface. Finite element analysis results and experimental results indicate that the standing wave effect of ultrasonic array defrosting can be eliminated using random intermittent phase-stagger, and the defrosting efficiency under random intermittent phase-stagger is superior to the regular method. Moreover, when arrayed ultrasonic transducers are controlled by synergistic random intermittent phase-stagger and multi-frequency excitation, there is no dead defrosting angle on the evaporator surface, the average frost layer thickness is approximately 0.282 mm, and it is 81.1% of mode I (intermittent and multi-frequency excitation).

Quantitative Assessment of the Impact of Retrofitting an Electric Boiler with an Air Source Heat Pump Unit on a University Campus

Quantitative Assessment of the Impact of Retrofitting an Electric Boiler with an Air Source Heat Pump Unit on a University Campus

Experimental study on the melted frost influence on the metal energy storage during an air source heat pump defrosting

When an air source heat pump works at reverse cycle defrosting mode, the metal temperature of its indoor coil decreases and that of outdoor coil increases. The energy storage of two coils’ metal at heating mode would influence the system defrosting efficiency. For a vertically installed outdoor coil having multiple circuits, meanwhile, the melted frost downwards flowing from upside circuit(s) also delay the defrosting process of downside circuit(s). To quantitatively evaluate the influence from two parameters, metal energy storage and melted frost, four experimental cases were designed and carried out in this study, based on a specially made three-circuit outdoor coil. Three circuits are working at the frosting mode, while two and three are used at the defrosting mode in four cases. As concluded, the melted frost influence on defrosting efficiency and metal energy storage effect would be increased from 4.87% to 10.45% and from 0.77% to 1.49%, respectively, after the outdoor coil changed from two- to three-working circuit. Outcomes of this study are meaningful for the structure optimization and energy saving of air source heat pump units at defrosting mode.

Application of Modelling and Statistical Inferences To Compare Performance of Hot Water Heating Devices in the Residence of University Campus

Implementation of an energy efficiency intervention in a university campus can resulted in both energy and electricity cost saving. The study focused on retrofitting a 12 kW electric boiler of 1000 L tank with a 4.0 kW air source heat pump (ASHP) unit. A data acquisition system was built to monitor the performance of the electric boiler before intervention and the ASHP water heater after implementation. The results depicted that the average daily electrical energy and hot water consumed during the summer season with the utilization of the electric boiler and the ASHP water heater were 132.53 kWh and 1836 L, and 37.52 kWh and 1818.2 L, respectively. Wilcoxon rank sum test was employed to compare both the daily volume of hot water and electrical energy consumed for both winter and summer seasons by the electric boiler and the ASHP water heater. Linear regression models of the electrical energy consumed as function of volume of hot water consumed, per day for both hot water heating devices was established. The models’ determination coefficients and the root mean square errors of the electric boiler and ASHP water heaters was 0.960 and 1.33, and 0.970 and 0.23 for summer and 0.970 and 0.21, and 0.980 and 0.08, for winter seasons. All four models gave very good predictions with the measured experimental values.

Study on Performance of Ground Source Heat Pump System Based on Active Chilled Beam

This paper takes the ground source heat pump unit of a research and development centre in Beijing as the research object. This collected the operation data in the cooling condition and the heating condition respectively. Based on the measured data, this paper calculated the coefficient of performances and the energy efficiency ratio of the unit. The results show that when the active chilled beam is used as the air-conditioning terminal device, the inlet temperature of the heat pump unit is greatly improved. The ground source heat pump unit meets the standard and has a higher energy efficiency ratio; The operation of a single unit is more efficient than that of multiple units at the same time.