Cycle Characteristics of a New High-Temperature Heat Pump Based on Absorption–Compression Revolution

Abstract

A large amount of the waste heat generated during industrial production is not used, which leads to a low energy utilization rate. The recovery of industrial waste heat using heat pumps has the advantages of low energy consumption, high efficiency, safety, and environmental protection. Industrial waste heat has a wide temperature distribution range. Traditional absorption and compression heat pumps can only work in a narrow temperature range due to the thermodynamic cycle, the thermal properties of the working medium, the temperature and pressure resistance of the compressor, and other factors; they cannot simultaneously meet the requirements of a “high heating temperature” and “wide temperature-range heat transfer”. To solve the above problems, this paper proposes a high-temperature heat pump unit based on a coupled cycle of absorption and compression, which can recover low-temperature steam and 50 °C waste heat and produce hot water at 110–130 °C. EES software is used for the mathematical modeling and simulation analysis of the heat pump unit. The results show that, when the driving steam temperature is 140 °C and the waste heat temperature is 50 °C, the heating temperature can reach 110~130 °C and the COP of the system can reach 4.22. Increasing the waste heat outlet temperature and the condensation temperature of the absorption cycle strengthens the COP of the coupled cycle; meanwhile, increasing the evaporation temperature and heating temperature of the absorption cycle reduces the COP of the coupled cycle. The results of this study significantly broaden the operating temperature range and heating temperature of electric heat pumps; our findings therefore have essential research significance for improving energy efficiency in industrial fields.

1. Background

Energy is a critical factor in human progress and in the development of modern society, and it has significantly contributed to humans’ survival, social development, and quality of life. According to the International Energy Agency’s Global Energy Review 2021 [1], global industrial energy consumption will reach 26.4 million tons of standard coal in 2022, an increase of about 4.4% over 2020. In 2021, the total global energy supply was 171,996.6 terawatt hours, of which industrial consumption accounted for about 37%. As the energy supply becomes increasingly stretched, the shortage of energy will significantly limit the development of industry. The industrial production process produces some industrial test waste heat, mainly high-temperature flue gas, water, oil, slag, and other resources. Failure to fully recycle these resources results in wasted energy and reduced energy efficiency. Recovering the waste heat effectively is problem that urgently needs to be solved. Currently, the main waste heat recovery methods are waste heat power generation, heating, steam regeneration, heat pump recovery, and so on. Waste heat generation and steam regeneration require high-pressure and high-grade waste heat sources, so their application scope is narrow. Hot water heating is also limited because it requires a long line. In the industrial waste heat recovery scenario, using heat pump technology for waste heat recovery has high efficiency, environmental protection, broad applicability, simple operation, and other technical advantages. It is an efficient technology with practical application prospects and is suitable for industrial waste heat recovery.

The premise of heat pump technology is to use the refrigerant first in a low-temperature environment to absorb heat through a phase change and then in a high-temperature environment, increasing the temperature through compression, to release heat energy. According to the usage environment and application fields, heat pumps are divided into compression and absorption types. Due to the limitations of the working medium and the temperature and pressure resistance of the compressor, compression heat pumps have difficulty recovering waste heat above 100 °C, and absorption heat pumps have low energy efficiency due to the limitations of the thermodynamic cycle. High-temperature heat pump systems that focus on the water discharge interval above 100 °C are the main subject of theoretical simulations and of some experimental research. There are few products suitable for civil and industrial promotion. Under considerable temperature rises and high levels of condensation, traditional single-stage compression heat pump cycles face problems such as an excessively high pressure ratio, excessively high exhaust temperatures, and substantial reductions in the cycle COP and heat production.

In order to solve the above problems, researchers have sought out new cyclic modes, such as the two-stage compression cycle, the two-stage overlapping cycle, the quasi-two-stage compression cycle, and the coupled cycle. Yan Chaojie [2] conducted modeling analysis and experiments on the quasi-two-stage compression heat pump cycle. The results show that the R245fa process performed best. The second-stage compression cycle has the highest efficiency, and the COP coefficient is above 2.85. Li Guanming [3] built a stacked high-temperature heat pump experimental platform with an evaporation temperature of 20–40 °C and a condensation temperature of 90–130 °C. The experimental results show that the COP of this system can reach 5.4. The energy use efficiency is only 41–47%. Exergy damages high-temperature compressors the most, followed by low-temperature compressors and evaporative condensers. Hassan, A.H. [4] et al. described the design and performance of a high-temperature heat pump with an innovative, sensitive, and latent integrated heat storage system. The heat pump operates with a heat source of 40 ~ 100 °C and a heat sink above 130 °C. The simulation results show that the heating performance coefficient COP is about 4 when the heat source temperature is 80 °C. Fan Chaochao [5] et al. proposed a new air-source high-temperature heat pump with a heating temperature of 80–100 °C. The calculation results show that, when the condensation temperature is 100 °C and the evaporation temperature drops from 25 °C to −10 °C, the COP of the EIHP cycle increases by 15–27% and the volume calorific value increases by 22–51%. Song Jian [6] proposed a green energy-saving high-temperature air-source heat pump unit, combining electromagnetically induced steam generation technology with air-source heat pump technology. The unit first uses an air-source heat pump to produce 80 °C hot water, which is then heated to more than 100 °C by an electromagnetic induction device. The COP of the system is 3.2 and reaches 2.9 when the cyclic temperature rises to 60 °C in summer. An Meiyan [7] et al. proposed a heat-coupled compression–absorption heat pump, which uses R245fa and a lithium bromide aqueous solution as the working medium; they conducted simulation calculations with a thermal temperature above 100 °C as the target. The results show that the maximum COP is more than 2.58 at 30–40 °C and the optimal COP is 2.83 at 60–70 °C. Verdnik, M. [8] et al. calculated and analyzed the cycle of a high-temperature steam compression heat pump using R600 to produce a 110–160℃ heat source based on recovering 40–60℃ waste heat. The results show that, in a sub-critical environment, the waste heat temperature is 60 °C, the temperature rise is 80–110 °C, the COP of the unit is 4.4, and the heating temperature is 30.7 kW. When the heat-source outlet temperature is 160 °C, the COP of the team is 3.1. Yang Zhe [9] proposed a high-temperature heat pump process to produce 120 °C water and then calculated this system’s simulation. The results show that, when the superheat is reduced from 10 °C to 2 °C, the system heat is increased by 14.7%, the compressor input power is increased by 7.2%, and the COP is increased by 11.5%. Feng Huimin [10] et al. proposed a second type of lithium bromide absorption–compression combined high-temperature heat pump system and carried out analysis and calculations. The results show that the performance coefficient of the unit is 0.42–0.43 when the driving heat source temperature is 56 °C, and the output heat source temperature is 105 °C.

In summary, the existing high-temperature electric heat pumps mainly improve the heating temperature through process improvements (such as using overlapping cycles and introducing injectors), improving the working medium (such as by using a mixed working medium or self-developed working medium), and improving the compressor performance. The above solutions to increasing the heat pump heating temperature focus on improving the heat pump cycle. To broaden the operating temperature range and heating temperature of heat pumps in the field of waste heat recovery, a high-temperature heat pump based on an absorption and compression coupling cycle is proposed in this paper. Combined with the advantages of the absorption cycle and the compression cycle, raising the heat pump heating temperature up to 120 °C and the temperature to 80 °C significantly broadens the application of heat pumps in the field of industrial waste heat recovery. The coupled-cycle high-temperature heat pump has the advantages of a wide operating temperature range and high heating temperatures. The simulation analysis data can guide the design and application of heat pumps in industrial waste-heat recovery systems.

1.1. Introduction to the Theoretical Cycle

Figure 1 shows the operation process of a high-temperature heat pump unit. The heat pump uses low-temperature waste heat and industrial waste steam as the driving heat source with waste-heat recovery abilities [11]. The low-temperature compression cycle in the right of the figure absorbs waste heat through the evaporator and releases it into the absorber cycle through the coupled heat exchanger. The two heat-release components of the absorption cycle are the condenser and absorber [12]. The condenser and absorber of the absorption cycle are used as the evaporator of the high-temperature compression cycle to further compress and promote the heat released by the absorption cycle. The condenser of the high-temperature compression cycle discharges a great deal of heat to produce hot water. Hot water can be used as factory water or for domestic heating, improving the economic benefits of the unit.

1.2. Modeling Analysis of the Thermodynamic Cycle

In this paper, energy balance equations and mass balance equations are established for each component in the proposed high-temperature heat pump unit model. The EES software [13] (an engineering equation solver used to solve a series of algebraic equations, V10.570) is used to solve these equations. REFPROP software [14] (a database of fluid thermodynamics and transport properties, V9.1) inputs the relevant refrigerant thermodynamic parameters into the equations. To simplify the calculation process and improve the accuracy of the solution process, the four basic methods of compression, condensation, throttling, and evaporation in the operation of the heat pump unit model are specified as follows:

(1)

The phase transition of the refrigerant in the heat exchanger is an isobaric process;

(2)

The enthalpy of the refrigerant remains unchanged before and after throttling and lowering the pressure;

(3)

The heat loss of the refrigerant and the carrier refrigerant is ignored during the processes of phase transition and pipeline flow;

(4)

The actual cycle coefficient of the unit is set as the product of the motor efficiency, mechanical efficiency, and isentropic efficiency. The motor efficiency was set to 0.85, the mechanical efficiency was set to 0.85, and the isentropic efficiency was set to 0.90 [15].

(5)

The difference between the heat exchange end of the evaporator and the condenser should be set to 10 °C, and the degree of superheat and subcooling should be set to 5 °C [16].

The thermodynamic modeling process of the heat pump system and the energy and mass conservation equation of each component are given below:

Absorption cycle generator:

$$Q_G=q_{x-2}{h}_{x-out}+q_{x-3}{h}_w-q_{x-1}{h}_{x-in}$$

(1)

$$Q_G=m_{D-H}{C}_p\left(T_{D1}-T_{D2}\right)$$

(2)

In the above formula: $Q_G$ is the heat load of the generator in the absorption cycle; $q_{x-1}$ and $q_{x-2}$ are the mass flow rates of diluted and concentrated lithium bromide solution, respectively; $h_{x-in}$ and $h_{x-out}$ are the enthalpy values of the diluted solution entering the generator and of the full solution exiting the generator, respectively; $q_{x-3}$ is the coolant steam flow rate at the generator outlet; $h_w$ is the coolant steam flow rate at the generator outlet; $m_{D-H}$ is the drive heat-source flow; $C_p$ is the specific heat capacity of the water; and $T_{D1}$ and $T_{D2}$ are the drive heat sources in and out of the generator temperature, respectively.

Absorption cycle condenser 1:

$$Q_{C-1}=q_{x-3}\left(h_w-h_1\right)$$

(3)

$$Q_{C-1}=q_{c1}\left(h_{c1}-h_{c5}\right)$$

(4)

In the above formula: $Q_{C-1}$ is the heat load of the condenser in the absorption cycle; $h_1$ is the condenser outlet saturated liquid; $q_{c1}$ is the R245fa refrigerant mass flow rate; $h_{c1}$ is the enthalpy of R245fa before entering the compressor; and $h_{c5}$ is the R245fa enthalpy value after discharge from the absorber.

Absorption cycle throttling device:

$$h_1=h_2$$

(5)

In the above formula, $h_2$ is the enthalpy value of the refrigerant water outlet throttling device.

Absorption cycle part of the coupled heat exchanger:

$$Q_{E-C}=q_{x-3}\left(h_3-h_2\right)$$

(6)

In the above formula, $Q_{E-C}$ is the heat load of the absorption circulation evaporator in the coupled heat exchanger, and $h_3$ is the enthalpy value of the refrigerant steam outlet evaporator.

Absorption cycle absorber:

$$Q_A=q_{x-3}{h}_3+q_{x-2}{h}_{out-2}-q_{x-1}{h}_{in-1}$$

(7)

In the above formula: $Q_A$ is the absorption cycle absorber heat load; $h_{out-2}$ is the enthalpy value of the lithium bromide concentrated solution outlet heat exchanger; and $h_{in-1}$ is the enthalpy value of the lithium bromide dilute solution exiting from the absorber port.

Absorption cycle heat exchanger:

$$q_{x-2}\left(h_{x-out}-h_{out-2}\right)=q_{x-1}(h_{in-1}-h_{x-in})$$

(8)

High-temperature side compression cycle:

Compressor:

$$W_1=q_{\begin{array}{l}fa\\ \end{array}}(h_{c2}-h_{c1})$$

(9)

In the above formula: $W_1$ is the compressor work quantity; $q_{\begin{array}{l}fa\\ \end{array}}$ is the refrigerant R245fa’s mass flow rate; and $h_{c2}$ is the enthalpy of the refrigerant after it exits the compressor.

Condenser:

$$Q_C=q_{fa}\left(h_{c3}-h_{c2}\right)$$

(10)

$$Q_C=m_{h-w}{C}_p\left(T_{hw2}-T_{hw1}\right)$$

(11)

In the above formula: $Q_C$ is the heat load of the condenser; $h_{c3}$ is the enthalpy value of the refrigerant outlet condenser; $m_{h-w}$ is the mass flow of hot water; and $T_{hw1}$ and $T_{hw2}$ are the hot water inlet and outlet condenser temperatures, respectively.

Throttle device:

$$h_{c3}=h_{c4}$$

(12)

Evaporator:

$$Q_E=q_{fa}\left(h_{c1}-h_{c4}\right)$$

(13)

In the above formula, $Q_E$ is the heat load of the evaporator and $h_{c4}$ is the enthalpy value of the refrigerant liquid outlet throttling device.

Low-temperature side compression cycle:

Compression part of the coupling heat exchanger:

$$Q_{E-C}=q_{Ra}(h_{c6}-h_{c7})$$

(14)

In the above formula: $q_{Ra}$ is the refrigerant R134a’s mass flow rate; $h_{c6}$ is the enthalpy value of the refrigerant steam at the compressor outlet; and $h_{c7}$ is the enthalpy value of the refrigerant liquid at the condenser outlet.

Throttle device:

$$h_{c7}=h_{c8}$$

(15)

Evaporator:

$$Q_{E2}=q_{Ra}(h_{c9}-h_{c8})$$

(16)

$$Q_{E2}=m_{y-w}{C}_p(T_{yw1}-T_{yw2})$$

(17)

In the above formula: $Q_{E2}$ is the evaporator’s absorbed heat; $h_{c8}$ and $h_{c9}$ are the enthalpy values of the refrigerant in and out of the evaporator, respectively; $m_{y-w}$ is the mass flow of the residual hot water; and $T_{yw1}$ and $T_{yw2}$ are the residual hot water’s inlet and outlet evaporator temperatures, respectively.

Compressor 1:

$$W_2={\mathrm{q}}_{Ra}(h_{c6}-h_{c9})$$

(18)

In the above formula, $W_2$ is the compressor’s work quantity.

2. Results

2.1. Influence of the Absorption Cycle Evaporation Temperature on Cycle Performance

2.1.1. Influence of the Absorption Cycle Evaporation Temperature on the Concentration of Lithium Bromide Solution

The absorption cycle uses the water in the lithium bromide solution as the refrigerant and lithium bromide as the absorber, requiring the solution to have a specific concentration difference to ensure the safe operation of the unit. The concentration of the lithium bromide solution should not exceed 66%; otherwise, it will precipitate crystals when the temperature decreases, endangering the safety of the crew. When the concentration of the solution is too low, the water absorption capacity and the heat load of the unit decrease, which affects the economic value of the unit. As shown in Figure 2, when the absorption evaporation temperature increased from 50 °C to 70 °C, the concentrations of both the concentrated and diluted lithium bromide solutions showed a downward trend. With the increase in the evaporation temperature, the temperature of the water vapor entering the absorber increases, and the absorption capacity of the lithium bromide solution rises due to the characteristics of the lithium bromide solution. The concentration of the diluted and concentrated lithium bromide solutions decreases. The concentration of the lithium bromide decreased from 65.8% to 56.3% in the concentrated solution and from 57.5% to 45.8% in the diluted solution.

2.1.2. Effect of the Absorption Cycle Evaporation Temperature on the Absorption Cycle’s COP

The solution’s concentration difference increases from the upper part when the absorption cyclic evaporation temperature increases. That is, the range of solution exhausts rises, and the heat load of the absorber and condenser in the unit increases. As shown in Figure 3, the COP of the absorption period showed an upward trend, rising from 1.75 to 1.84.

2.1.3. Effect of the Absorption Cycle Evaporation Temperature on the Power Consumption and COP of a Low-Temperature Compressor

The coupled heat exchanger comprised an absorption circulation evaporator and a low-temperature compression condenser. The evaporation temperature is correlated with the condensing temperature. Increasing the evaporation temperature of the absorption cycle also increases the condensing temperature of the low-temperature compression cycle. As shown in Figure 4, as the absorption evaporation temperature increases, the compressor power consumption of the low-temperature compression cycle exhibits an increasing trend, from 62.6 kW to 168.5 kW, and the COP decreases from 13.4 to 5.6. Increasing the condensing temperature increases the temperature and the pressure of the refrigerant steam entering the condenser, which requires an increase in the work of the compressor.

2.1.4. Effect of the Absorption Cycle Condensation Temperature on the COP of the Cycle Unit

Relative to the whole cycle of the heat pump unit, the increase in the absorption evaporation temperature affects both the absorption cycle and the low-temperature compression cycle. To more directly determine the effect of the absorption evaporation temperature on the whole unit cycle, COP was used to evaluate the whole unit’s performance. As shown in Figure 5, as the absorption evaporation temperature increased, the COP of the circulating unit showed a downward trend from 2.86 to 2.29; this was mainly caused by the sharp rise in the power consumption of the compressor on the low-temperature compression side.

2.2. Effect of Absorption Cycle Condensation Temperature on Cycle Performance

2.2.1. Effect of the Absorption Cycle Condensation Temperature on the Concentration of the Lithium Bromide Solution and the COP of Absorption

As the condensation temperature of the absorption cycle increases, the amount of condensate water precipitated by the refrigerant after the condensation process decreases, and the amount of water vapor entering the absorber is reduced, increasing the concentration of the lithium bromide dilute solution. As shown in Figure 6, when the absorption cycle condensation temperature rises from 80 °C to 100 °C, the concentration of the lithium bromide dilute solution rises from 52.6% to 61.9%. The influence of the increase in the absorption cycle condensation temperature on the COP showed that the COP exhibited a decreasing trend. However, the decreasing range was not extensive from a numerical perspective, spanning from 1.78 to 1.72.

2.2.2. Effect of the Absorption Cycle Condensation Temperature on the Power Consumption and COP of the High-Temperature Compressor

For the high-temperature-stage compression cycle, increasing the condensation temperature of the absorption cycle is the same as increasing the refrigerant temperature of the high-temperature stage compressor inlet. When the heat load of the high-pressure condenser remains unchanged, the inlet refrigerant parameter of the high-pressure compressor is increased, and its power consumption decreases, as shown in Figure 7. When the absorption cycle condensing temperature increases, the power consumption of the high-temperature compressor decreases from 354.6 kW to 131 kW. When the heat load of the condenser is unchanged, the compressor’s power consumption decreases, and the COP of the high-temperature compression type shows an increasing trend, rising from 6.4 to 15.5.

2.2.3. Effect of the Absorption Cycle Condensation Temperature on the COP of the Cycle Unit

The condensation temperature of the absorption cycle has little influence on the COP of the absorption cycle but has a significant effect on the power consumption of the high-temperature compressor. Compared with that of the whole heat pump unit, the compressor’s power consumption decreases under the condition of a constant heat load. As shown in Figure 8, the cyclic COP of the unit showed an upward trend, rising from 2.09 to 4.22.

2.3. Effect of the Heating Temperature on the Cycle Performance

2.3.1. Effect of the Heating Temperature on the Power Consumption and COP of the High-Temperature Compressor

With the increase in the heating temperature, the heat load of the condenser in the high-temperature-stage compression cycle increases, which requires the high-temperature-stage compressor to undertake extra work. As shown in Figure 9, with the rise in the heating temperature, the power consumption of the high-temperature compressor gradually increases from 231.1 kW to 522.1 kW. The COP showed a decreasing trend, decreasing from 9.28 to 4.56. Although the heat load of the high-temperature condenser rises, the increase in the power consumption of the high-temperature compressor is more prominent.

2.3.2. Effect of the Heating Temperature on the Cyclic COP of the Unit

The influence of the heating temperature on the cyclic COP of the unit mainly involves increases in the condenser’s heat load and in the power consumption of the high-pressure compressor. As shown in Figure 10, as the heating temperature increases, the COP of the unit exhibits a decreasing trend, decreasing from 2.86 to 1.43. Throughout the whole cycle of the heat pump unit, the rise of the heating temperature requires the heat load of the high-pressure condenser to be increased to a certain extent, which brings about a sharp increase in the power consumption of the high-pressure compressor. In contrast, the increase in the compressor’s power consumption is more pronounced.

2.4. Influence of the Waste Heat Outlet Temperature on the Cycle Performance

2.4.1. Influence of the Residual Hot Water Outlet Temperature on the Power Consumption and COP of the Low-Pressure Compressor

As the outlet temperature of the residual hot water decreases, the working condition of the low-temperature compression cycle deteriorates continuously, and the evaporation temperature of the low-temperature compression cycle drops constantly. As shown in Figure 11, when the residual hot water temperature decreases from 30 °C to 10 °C, the power consumption of the low-temperature compressor increases from 62.59 kW to 146.6 kW. When the heat load of the low-temperature condenser remains unchanged, the decrease in the evaporation temperature reduces the temperature of the refrigerant steam at the inlet of the low-temperature compressor. In contrast, the compressor must undertake extra work to compensate for this loss. The COP of the low-temperature compression cycle decreased from 13.4 to 5.72 due to the sharp increase in the compressor power consumption.

2.4.2. Influence of the Residual Hot Water Outlet Temperature on the Power Consumption and COP of the Low-Pressure Compressor

Because of the decrease in the outlet temperature of the residual hot water, the power consumption of the low-temperature compressor increases sharply, and the heat load remains unchanged when the heating temperature remains unchanged. For the overall cycle of the heat pump unit, the unit cycle COP must be reduced. As shown in Figure 12, as the outlet temperature of residual hot water decreases, the cyclic COP of the unit decreases from 2.86 to 2.22.

3. Summary and Prospects

In the era of energy savings and carbon reduction, heat pumps that are used to recover industrial waste heat can help us to achieve our energy goals [17]. A large amount of the waste heat generated by traditional industrial production is not effectively recycled, resulting in environmental pollution and resources being wasted. Heat pump technology can convert waste heat into usable heat energy. Multi-dimensional research on waste heat utilization, renewable energy consumption, flexible and efficient energy conversion, energy storage, and other related technologies in industrial fields is important to achieving clean, flexible, efficient, and safe energy utilization; these technologies are also pivotal to the achievement of carbon neutrality.

The proposed absorption–compression coupling cycle has the following advantages:

(1)

High efficiency and energy savings: compared with traditional absorption heat pumps, the absorption–compression heat pump has a higher energy efficiency ratio, making significant savings in energy consumption and improving energy efficiency [18].

(2)

Recycling waste heat: the absorption–compression heat pump uses waste heat to drive the absorption cycle to recover and utilize the waste heat generated in industrial processes, reducing energy waste [19].

(3)

Wide application range: absorption–compression heat pumps can work in a wide range of pressure and temperature HVACs, heating, cooling, and other fields, and have a wide range of application prospects [20].

(4)

Multi-energy utilization: the absorption–compression heat pump can use different energy sources, such as electric and waste heat, as its driving energy. This diversified energy utilization capacity increases its utilization rate in various fields.

Although the absorption–compression coupling cycle has many advantages, most of the existing studies are predominantly theoretical. Some of its shortcomings are as follows:

(1)

High cost: compared with traditional heat pumps, the process of using an absorption–compression coupled-cycle heat pump requires a lot of heat-exchange equipment, significantly increasing its manufacturing costs; this means that the unit requires a high initial investment, and this investment has a long payback period [21].

(2)

The process requirements are strict: the manufacturing of the absorption–compression coupling circulation heat pump requires a more advanced technical level and a more complex production process, and the heat exchanger needs to be specially designed for different scenarios.

Based on the advantages and disadvantages of the absorption–compression cycle, the future development directions are as follows:

(1)

New circulating medium: the development and application of a new circulating medium would improve the performance and efficiency of the absorption–compression coupled circulating heat pump. For example, a freon mixed working medium could significantly improve its energy efficiency ratio [22].

(2)

Optimizing cycle processes: optimizing cycle processes can improve the system’s energy efficiency and reduce costs [23].

(3)

Expansion of applications: the absorption–compression coupled-cycle heat pump can be used in multi-energy combined drives, including waste heat and electricity. It can be used to build air conditioning, in industrial production, and in other fields involving heating.

4. Conclusions

The absorption–compression-type high-temperature coupled heat pump unit proposed in this paper adopts a new absorption–compression coupled-cycle process to achieve the goal of recovering heat from excess 50 °C hot water to produce hot water with temperatures of 110–130 °C. This new heat pump cycle process overcomes technical problems such as the limited temperature of the hot water produced by compression cycles, the high power consumption of compressors, and the low performance coefficient of absorption cycles. Additionally, it significantly expands the application scenarios of heat pumps in the utilization of industrial waste heat. Based on the above calculation results and analysis, the following conclusions are drawn:

(1)

When the evaporation temperature of the absorption cycle increased from 50 °C to 70 °C, the heat load of the absorber and condenser increased and the COP of the absorption cycle rose from 1.75 to 1.84. The COP of the low-temperature compression cycle was reduced from 13.4 to 5.6. The COP of the circulating unit decreased from 2.55 to 2.05.

(2)

The COP decreased from 1.78 to 1.72 when the condensation temperature of the absorption cycle increased from 80 °C to 100 °C. The COP of the high-temperature compression cycle rose from 6.4 to 15.5. The unit cycle’s COP increased from 2.09 to 4.22.

(3)

When the heating temperature increased from 100 °C to 120 °C, the power consumption of the high-temperature compressor increased from 133.7 kW to 353.5 kW. The COP of the high-temperature compression cycle decreased from 15.47 to 6.35. The coupling cycle’s COP decreased from 3.54 to 1.84.

(4)

When the temperature of the waste heat outlet was reduced from 30 °C to 10 °C, the power consumption of the low-temperature compressor increased from 62.59 kW to 146.6kW. The COP of the low-temperature compression cycle decreased from 13.4 to 5.72. The COP of the coupling cycle was reduced from 2.86 to 2.22.

The absorption–compression coupled high-temperature heat pump unit proposed in this paper uses new absorption–compression connected-cycle technology to recover the waste heat at 50 °C to produce hot water with temperatures of 110 °C to 130 °C. To improve the COP of the coupling unit, the evaporation temperature should be increased and the condensation temperature should be reduced. At the same time, increasing the heating temperature and decreasing the waste heat outlet temperature weakens the operation performance of the coupling cycle, so an appropriate heating temperature and waste heat outlet temperature should be selected in practical applications. The new process of using a coupling cycle based on a heat pump cycle proposed in this paper overcomes the technical problems of the limited heating temperatures of the compression cycle, the high power consumption of the compressor, and the low performance coefficient of the absorption cycle. Additionally, it significantly expands the application contexts of heat pumps in the utilization of industrial waste heat.