Air Source Heat Pump System Research Articles

An investigation on the environmental impact of various Ground Heat Exchangers configurations

Ground Source Heat Pumps (GSHPs) are used for space heating and cooling, where the Ground Heat Exchangers (GHEs) are used to extract or reject heat from/to the ground. GHEs come in various configurations, vertical or horizontal. Compared to Air Source Heat Pumps (ASHPs), GSHPs, albeit having a higher installation cost, achieve a better coefficient of performance (COP) and, hence, electricity savings. This reduction in consumed energy is translated to a reduction in fossil fuels and environmental “harmful” gas emissions. As the environmental impact does not lie in a single aspect, it would be useful not to stop the discussion in terms of COP and cost, but to identify whether a GSHP system is indeed a sufficiently overall greener solution. Hence, a more comprehensive investigation on the environmental impact of different types of GHEs as part of a GSHP compared to an ASHP system is attempted in the current study. A case study of a residential building with a fixed heating and cooling load is considered for moderate climate conditions. Using GLD software, a GSHP system is studied for various GHE configurations. The system undergoes a Life Cycle Analysis (LCA), with the yearly heating and cooling load as functional unit, for a direct environmental impact comparison between the GHE configurations and an ASHP system. The openLCA software is used for the application of two different methods, namely CML2001 and Eco-Indicator99 for seven and three impact categories respectively. It is concluded that the ASHP system exhibits the highest impact for all the main categories, while among the GSHP systems the vertical coaxial GHE configuration exhibits the highest impact and the horizontal GHEs the lowest, at times significantly below the ASHP impact. The largest reduction among all categories for the vertical and horizontal GHEs respectively is about 22% and 24% for the CML2001, and 17% and 21% for the Eco-Indicator99.

Energy Performance Optimization of a House with Grid-Connected Rooftop PV Installation and Air Source Heat Pump

The use of air source heat pump systems for space heating and cooling is a convenient retrofitting strategy for reducing building energy costs. This can be combined with the rooftop installation of photovoltaic panels, which can cover, to a significant degree—or even significantly exceed the building’s electricity needs, moving towards the zero energy building concept. Alternatively, increased capacity for rooftop photovoltaic (PV) installation may support the ongoing process of transforming the Greek power system away from the reliance on fossil fuels to potentially become one of the leaders of the energy transition in Europe by 2030. Standard building energy simulation tools allow good assessment of the Heating, Ventilation and Air Conditioning (HVAC) and PV systems’ interactions in transient operation. Further, their use enables the rational sizing and selection of the type of panels type for the rooftop PV installation to maximize the return on investment. The annual performance of a three-zone residential building in Volos, Greece, with an air-to-water heat pump HVAC system and a rooftop PV installation, are simulated in a TRNSYS environment. The simulation results are employed to assess the expected building energy performance with a high performance, inverter driven heat pump with scroll compressor and high efficiency rooftop PV panels. Further, the objective functions are developed for the optimization of the installed PV panels’ area and tilt angle, based on alternative electricity pricing and subsidies. The methodology presented can be adapted to optimize system design parameters for variable electricity tariffs and improve net metering policies.

A numerical study on evaluating the thermal environment in a space served by a bed-based air source heat pump (B-ASHP) system

Both air source heat pumps (ASHPs) and traditional Chinese-Kangs heating systems are widely used. However, they have their pros and cons. By combining the merits from both an ASHP and a Chinese-Kang heating system, a prototype bed-based ASHP (B-ASHP) system has been proposed, and its operating characteristics experimentally obtained under a fix set of design/operating parameters for the bed-based heating terminal. Therefore, a follow-up numerical study was carried out to numerically evaluate the impacts of optimizing these design/operating parameters, including the location, dimension, surface temperature and surface emissivity of the bed-based heating terminal, on the indoor thermal environment and the operating efficiency of the B-ASHP system. The numerical study results suggested that the variation in these parameters did impact both indoor thermal environment and the operating efficiency of the B-ASHP system, in terms of the uniformity of indoor thermal environment, indoor air velocity distribution and the output heating capacity, as well as the installation space requirement and cost implication. Therefore, care must be exercised in properly balancing all influencing parameters. Also, to both maintain an acceptable indoor thermal environment that can meet the Chinese National Standard, and achieve the best possible operating efficiency of the B-ASHP system, the bed surface temperature of its bed-based heating terminal may be set at around 35 °C. Furthermore, although the changes in surface emissivity did not significantly impact on indoor thermal environment, a higher surface emissivity should be preferred when a lower bed surface temperature was used, so as to further improve potentially the operating efficiency of the B-ASHP system.

A novel dual-temperature ejector-compression heat pump cycle - exergetic and economic analyses

• Two dual-temperature air-source heat-pump systems are compared. • Different eco-friendly refrigerants are evaluated in the systems, and their effects are compared. • The DAHP-II outperforms the DAHP-I system significantly in terms of economic and exergy efficiency. • The refrigerant type shows slightly effect on system exergy efficiency, while affects the economic obvious. High-efficiency air source heat pumps are of great importance for energy saving and environmental protection, especially for the cold area in north China. In this study, the thermo-economic performance of the dual-temperature ejector-compression air-source heat-pump (DAHP) cycle, is conducted wherein R1234yf, R290, and R134a are used as refrigerants. Two configurations are examined: DAHP-I (without an ejector, conventional system for comparison) and DAHP-II (enhanced by an ejector). The effects of the principal operating parameters on the system performance, including the exergy destruction ( Ex d_tot ), exergy efficiency ( η ex _sys ) and economic, are investigated, and the two systems are compared. The results indicate that the DAHP-II significantly outperforms the DAHP-I in terms of Ex d_tot , η ex _sys and economic index, and the R290 is the most suitable refrigerant applied for the DAHP-II system. Compared with DAHP-I, the Ex d_tot for DAHP-II is reduced by 24.0%–54.8%. For DAHP-II, although the refrigerant type affects Ex d_tot and η ex _sys slightly, while the effect on economic is noticeable. Comparing with R1234yf, the system using the R134a and R290 as the working fluid, the total annual capital cost rate ( C ˙ t o t ) can be reduced by 6.2% and 11.0% respectively. Besides, the DAHP-II outperforms the DAHP-I system significantly with the R134a, R290 and R1234yf as refrigerant in terms of economic. The relative decrease ratio in total annual capital cost rate ( C ˙ t o t ) are 21.6%, 13.5% and 24.0% respectively. This study provides a basis for the application of DAHP system.

Investigation on the regulating methods of air source heat pump system used for district heating: Considering the energy loss caused by frosting and on–off

Air source heat pump (ASHP) has been used in Northern China for district heating. However, few investigations on its regulating methods have been conducted till now. To increase the energy-saving effect of AHSPs, a simulation model, which considered the energy loss caused by frosting and on–off, was developed in this paper. Based on this model, three combination regulating modes suitable for district heating using ASHPs as heating source were proposed. Then the heating performance of ASHPs used for district heating in seven cities was investigated using this model. Results showed that both the energy loss corrections of frosting and on–off have evident impacts on the power consumption and seasonal coefficient of performance (SCOP). Owing to the energy loss correction of frosting, the power consumption of ASHP unit is increased by 3.85%–17.41%, and meanwhile SCOP is decreased by 3.72%–14.83%. The influence of the energy loss of on–off decreases gradually with the increase of heating area. In the three regulating modes, the power consumption of ASHP unit changes slightly, while the energy saving rate of water pump can reach 80.97%–86.46%. When the pitch of buried pipe was 300 mm, ASHP can meet the heating demand in all the three regulating modes.

Hybridization of Heat Pump Systems With Natural Ventilation To Improve Energy Efficiency in Cooling Dominated Buildings

Building foundation piles can be used as heat exchangers in ground-source heat pump (GSHP) systems to provide highly efficient renewable heating and cooling (H&C). Unbalanced H&C loads lead to heat build-up in the ground, decreasing the system's overall performance. In this study, the introduction of natural ventilation (NV) has been examined to decrease cooling load imbalance in cooling-dominated buildings to improve system efficiency. Building energy simulations estimated the H&C loads for an office building in three Portuguese cities: Lisbon, Porto and Faro, yielding heating loads of 0.2–3.6 MWh/year and cooling loads of 260–450 MWh/year. Four renewable H&C technology scenarios were used to assess energy performance: (1) an air-source heat pump (ASHP) system; (2) a GSHP system utilizing energy piles; (3) hybrid ASHP-NV and (4) hybrid GSHP-NV. Over 50 years of operation, in Scenario (1) COP values of 2.45–2.55 (heating) and 3.62–4.15 (cooling) were obtained. In (2), COP values increased to 4.15–4.34 (heating) but fell to 3.36–3.79 (cooling), which increased annual final energy needs by 7–8%. Unbalanced cooling loads increased the ground temperature by 21–24 °C, which is unlikely to be acceptable. Compared to (1), introducing NV reduced cooling loads by 65–90% in Scenarios (3) and (4), with the final energy needs decreasing by 59–80% and 62–88%, respectively. A further benefit of the GSHP-NV hybrid is that the ground temperature increase was limited to 8‑12 °C. For cooling, the COP in (3) decreased compared to (1) (3.14–3.69), while in (4), COP improved to 3.45–6.10. This study concludes that hybrid GSHP-NV systems should be considered in some cooling-dominated scenarios.

Study of stand-alone building heating system operating with renewable energy sources under moderate continental climate conditions

The climatic conditions in Moscow limit to a certain extent the utilization of renewable energy sources for heat supply. Long heating period, relatively low average daily sunshine hours during heating period, and low outside temperatures act as barriers to realising the full potential of renewable energy sources. The paper presents an evaluation of feasibility and effectiveness of using various renewable energy sources in the heat supply system of Block 23 of the National research university «MPEI». The system arrangement for heat supply of the building with renewable energy sources is described. Experimental data have been obtained on the basis of this system. The calculated time dependences of building heat consumption and heat pump system (HPS) outputs are given. In addition, for the air-source heat pump system, the dependence on the outdoor temperature is given. Values of HPS efficiency indices are also presented. A comparative analysis of the efficiency of air-source HPS and liquid-to-liquid HPS with a geothermal circuit in winter conditions is carried out.

Simulation study on performance of an air source heat pump system combined with phase change thermal storage using alternative refrigerants

To solve the problems of conventional air source heat pump (ASHP) system in cold regions, a novel air source heat pump system combined with phase change thermal storage (ASHPPCTS) was proposed. A Mathematical model of the proposed system was established when charging refrigerants, such as R410A, R134a, R32 and R290, and the operating performance was simulated and analyzed. Besides, the influence of ambient temperature on operating performance of different refrigerants was also investigated. The simulation results showed that R32 is not recommended for the application in the ASHPPCTS system due to its extremely high supply water temperature in the initial discharging process; R134a is not high-efficient in the ASHPPCTS system because of its low total heat storage capacity and COP value; R410A shows excellent performance in almost every aspect, e.g., large total heat storage capacity, high COP value, and proper supply water temperature, which makes it suitable for the proposed system; R290 also shows great performance in the ASHPPCTS system, although its operating characteristics in the ASHPPCTS system is not as prominent as those of R410A. However, considering the low GWP value of R290, it can be regarded as the perfect alternative refrigerant used in the proposed system in cold regions to replace R410A. This research provided a reference on refrigerant replacements for the novel proposed system.

Performance improvement of vapor-injection heat pump system by employing PVT collector/evaporator for residential heating in cold climate region

The adoption of vapor injection (VI) cycle could overcome the defects of the conventional one-stage air source heat pump (ASHP) system under extremely low ambient temperature conditions. Nevertheless, the ASHP system with VI cycle still could not operate efficiently due to the low evaporating temperature in the fin-tube evaporator. For such a situation, the PVT (Photovoltaic/Thermal) collector/evaporator could reach higher evaporating temperature attributed to its physical structure, thereby improving the system COP. This study proposes the detailed mathematical model of the vapor-injection heat pump system by incorporating PVT collector/evaporator and verifies the effectiveness of the proposed system. Parametric studies have been then conducted. The proposed system can operate off-grid and its COP can reach 4.0 at the ambient temperature of −10 °C and the solar irradiation of 500 W/m2. The practical electrical efficiency of PV panels achieves at 15.1%, whereas the thermal efficiency of the system is 44.8%. A hybrid control method including three modes has been also proposed based on the results for improving the system performance. The levelized cost of heat (LCOH) of this system is 0.054 $/kWh, which is 51.5% lower than that of electric heating system (0.111 $/kWh).

Techno-economic analysis of air source heat pump combined with latent thermal energy storage applied for space heating in China

In order to improve the heating performance of conventional air source heat pump system operated in cold regions, an air source heat pump system combined with latent thermal energy storage (ASHPLTES) has been proposed in the previous work. In this paper, a techno-economic analysis of ASHPLTES was carried out in four typical cities of China and compared with quasi-two-stage ASHP (QTASHP) system, coal fired boiler, wall-hanging gas boiler, and direct electric heating. Mathematical models were developed to evaluate the energy, environmental, and economic performances of different heating systems. The results showed that heat pump systems such as QTASHP and ASHPLTES were suitable for space heating due to the advantages of energy saving and environmental protection, although the initial and running cost of heat pump systems was higher than that of conventional heating systems. However, the currently high cost of heat pump systems could be reduced by the increasing productivity and the governmental subsidy. In addition, the static payback period of ASHPLTES compared with QTASHP in Harbin will be cut down to around 6 years if the discount percentage of LTES unit is set as 40%, which indicated that ASHPLTES will be a better choice in severe cold region of China.

A determination method of defrosting start time with frost accumulation amount tracking in air source heat pump systems

In this paper, a novel determination method of defrosting start time based on frost accumulation amount tracking (FAAT) is proposed for air source heat pump systems. This method keeps tracking of the amount of newly deposited frost every time step using typical sensors adopted in the commercial heat pump systems. This is to predict the current volumetric blockage ratio in real-time and determine the defrosting start time. To develop the method, firstly, the reliability of the prediction results is validated with experimental data. Then, the feasibility of the suggested determination method is evaluated under various air ambient and system operating conditions. The result shows that the determination method has a root mean square error of 6.2% on a time basis and 5.1% on a capacity basis. Lastly, the influence of non-uniform frost distribution on the evaporator is investigated. It is shown that the determination method attains the robustness under varying frost non-uniformity.

Residential Buildings’ Foundations as a Ground Heat Exchanger and Comparison among Different Types in a Moderate Climate Country

Shallow Geothermal Energy Systems (SGESs) constitute Renewable Energy Systems (RES), which find application in the residential sector through the use of Ground Source Heat Pumps (GSHPs). GSHPs are associated with Ground Heat Exchangers (GHEs), whereby heat is gained/lost through a network of tubes into the ground. GSHPs have failed to flourish in the RES market due to their high initial costs and long payback periods. In this study, the use of Energy Geo-Structure (EGS) systems, namely, the foundation (or energy) piles and the foundation bed of a residential building in Cyprus, was computationally modeled in the COMSOL Multiphysics software. First, the single-houses’ trend in number of units and area in Cyprus was examined and a theoretically typical house with nearly Zero Energy Building (nZEB) characteristics was considered. The heating and cooling loads were estimated in the TRNSYS software environment and used as inputs to investigate the performance of the GSHP/GHE systems. Both systems were shown to exhibit steady performance and high Coefficient of Performance (COP) values, making them an alternative RES solution for residential building integration. Next, the systems were economically evaluated through a comparison with a convectional Air Source Heat Pump (ASHP) system. The economic analysis showed that the cost of the suggested conversions of the foundation elements into GHEs had short payback periods. Consequently, either using the foundation piles or bed as a GHE is a profitable investment and an alternative to conventional RES.

A semi-theoretical model for energy efficiency assessment of air source heat pump systems

Although significant progress has been made in relation to air source heat pump (ASHP) modeling, it is difficult to reflect the actual dynamic characteristics of the start-up process by a completely theoretical model, and a regression model cannot reflect the energy efficiency differences between systems intuitively. A semi-theoretical model for fixed speed ASHP which considers the modifications of no-load power consumption, cycling losses and defrost discount has been developed based on the statistical analysis of field monitoring data. Thermodynamic perfectibility was introduced to evaluate the steady-state performance at continuous operation. By taking the running and cycle time as input parameters, it is possible to relate the operation mode to system energy efficiency. In the verification of the seasonal coefficient of performance, the error is <10%. The identification of the cycling losses from field monitoring data illustrated that the impact of cycling losses drops off with the increase of the running time and the percentage of running time in an ON-OFF cycle. In energy efficiency diagnosis applications, the quantified losses concluded that the least energy efficient project is caused by no-load consumption and cycling losses. The application of the simulation integrated with building heating system illustrates that the proposed model cooperated with iterative algorithm can realize minute-by-minute dynamic simulation. This paper provides a foundation for operation strategy research and energy efficiency analysis of the fixed speed ASHP system.

Development of the Performance Prediction Equation for a Modular Ground Heat Exchanger

Although ground source heat pump (GSHP) systems are more efficient than conventional air source heat pump (ASHP) systems, their high initial investment cost makes it difficult to introduce them into small buildings. Therefore, the development of a method for reducing the installation costs of GSHPs for small buildings is essential. This study proposes a modular ground heat exchanger (GHX) for cost reduction and an improved workability of GSHPs. In addition, a numerical model was constructed for the analysis of the performance of the modular GHX. However, to easily introduce the new GHX at the building design stage, the development of a performance prediction method for the introduction of modular GHXs to small buildings is necessary. Therefore, the entering water temperature (EWT) equation was derived from the calculation methods in the heat transfer process, and the ground temperature model was developed in consideration of the operation condition. The numerical results showed that the average values of EWT and ground temperature were 8.11 °C and 8.00 °C, respectively under an average ambient temperature of 0.42 °C. In addition, the performance prediction model was compared with the numerical results. The results showed that the coefficient of variation of the root mean square error (RMSE) of the ground temperature and EWT model were 5.20% and 1.33%, respectively.

Comparative study of upgraded CO2 transcritical air source heat pump systems with different heat sinks

For improving the coefficient of performance of system for heating, CO2 transcritical heat pump system is upgraded by using two compressors. In this paper, three CO2 transcritical systems with two-compressors (the CO2 cascade system, the CO2 two-stage compression system and the CO2/CO2 mechanical subcooling system) are discussed and compared with CO2 single-stage compression transcritical heat pump system under three different heat sinks. The three heat sinks are the small temperature difference fan-coil unit, the floor-coil radiator and the traditional designed radiator. And the optimal operation states of three upgraded systems are analyzed. When the thermodynamic performance of CO2 transcritical heat pump system is optimized, the initial investment cost of its equipment often increases and the overall cost will be affected during the life cycle of the equipment. Thus, an objective function that comprehensively considers the initial investment cost and operating cost is defined, and the comparative analysis of four CO2 transcritical heat pump systems is combined meteorological parameters of five typical regions in China for home heating. The results show that under nominal working conditions of three heat sinks, COPs of CO2 cascade system, CO2 two-stage compression system and CO2/CO2 mechanical sub-cooling system are all increased by more than 10% compared with that of single-stage system and the growth extent of COP increases with the rise of return water temperature of heat sink, but based on the economic analysis, it is implied that CO2 cascade system, CO2 two-stage compression system and CO2/CO2 mechanical sub-cooling system are not conducive to their application in home heating compared with single-stage system, and more suitable for the situations with low evaporation temperatures and large capacities. The analysis results show that the economy of single-stage system and the three upgraded systems are related to the evaporation temperature and heating capacity. Under the analysis conditions in this paper, CO2 cascade system is the least economical. Single-stage system and the other two upgraded systems can become the most economical system in different application ranges under three heat sink conditions.

Assessment of potential groundwater contamination by ground source heat pump operation using solute transport models

Globally, over the past few decades, there has been a rapid increase in the use of ground source heat pump (GSHP) systems for heating and cooling purposes. Although these systems are more energy efficient than conventional air source heat pump systems, their association with potential groundwater contamination risks, e.g., the leakage of heat exchanger fluids like glycol, is a major concern. In this study, HYDRUS software was used to simulate the transportation of fluids from such systems into an aquifer. To better understand the transport environment, a geological survey was conducted and a > 50 m deep observation well was dug close to the GSHP installation site. To determine the physical properties of the soil, core samples were collected and analyzed; to determine the flow rate of the groundwater as well as the hydrological properties of the aquifer, measurements were conducted using a velocimeter that was installed in the borehole of the observation well. A laboratory column containing aquifer soil was used to determine drainage breakthrough curves. The hydrological parameters of the soil and the solute were used for the simulation under a virtual groundwater environment. The flow of groundwater resulted in the dispersion of the contaminant from its source, and its concentration was significantly reduced owing to degradation presumedly by biological activity. Additionally, two methods for the elimination of the contaminant from aquifers (enforced biodegradation and decontamination by pumping) were identified.

Study on the Performance of Multiple Sources and Multiple Uses Heat Pump System in Three Different Cities

Various efforts have been made worldwide to reduce energy use for heating, ventilation, and air-conditioning (HVAC) systems and lower carbon dioxide (CO2) emissions. Research and development are essential to ensuring the efficient use of renewable energy systems. This study proposes a multiple sources and multiple uses heat pump (MMHP) system that can efficiently respond to heating, cooling, and domestic hot water (DHW) loads using multiple natural heat sources. The MMHP system uses ground and air heat as its primary heat sources and solar heat for heat storage operations and ground temperature recovery. For the efficient use of each heat source, it also determines the heat source required for operation by comparing the heat source temperatures in the same time zone. A model for predicting the heat source temperatures, electricity use, and coefficient of performance (COP) was constructed through simulation. To analyze the efficiency of the proposed system by comparing the existing air source heat pump with ground source heat pump systems, a performance analysis was conducted by setting regional and system configurations as case conditions. The results demonstrate that the electricity use of the MMHP system was 13–19% and 1–3% lower than those of air source heat pump (ASHP) and ground source (GSHP) systems, respectively. In addition, the MMHP system was the most favorable in regions with a low heating load.

Performance analysis and optimization for a novel air-source gas-fired absorption heat pump

In district heating technologies, gas fired boilers and conventional heat pumps have poor performance at low ambient temperature. To tackle this issue, this study has proposed a novel air-source gas-fired absorption heat pump for district heating with flue gas recovery. Compared with conventional absorption heat pumps, the proposed solution in this study can absorb heat from both air and flue gas. Additionally, the working fluid works properly when air temperature is below 0 °C, safe and nonflammable. To analyze the economic and the thermodynamic performance of this air-source gas-fired absorption heat pump, a mathematical model, considering energy, exergy, economy and environment, has been developed. According to the simulation results of the model, the proposed air-source gas-fired absorption heat pump system here had good stability and feasibility under various operational conditions. However, as the payback period and the exergy destruction were found to be conflicting with each other, a multi-objective optimization method was established to minimize the system’s payback period and exergy destruction simultaneously. Additionally, the technique for order preference by similarity to an ideal solution decision-making method has been applied to look for the optimal solutions in the Pareto frontier, with optimal solutions of the system under different operational conditions recommended.

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%.

Experimental research on a solar air-source heat pump system with phase change energy storage

A solar air-source heat pump system with phase change energy storage is investigated in this paper. By employing phase change storage in this system, it overcomes the frosting problem in the evaporator and improves the COP of heat pump under the extreme weather condition. The system is constructed and the experiment is carried out in Shijiazhuang. The testing results reveal that the average COP of the heat pump is around 4.92 in the clear days, 1.79 in extreme weather conditions, and 2.12 in the rainy or snow days, which is much higher than the traditional heating mode. Through economic analysis, it is found that the operating cost of the whole heating season is around 22.5% of the oil-fired boiler, 55.4% of the gas boiler, 27.1% of the electric boiler, and 65.6% of the air source heat pump. With the help of phase change storage, solar energy and air source can be utilized to the maximum extent to achieve the purpose of energy-saving and emission reduction in the extremely cold area.