**Abstract:**
The composite low-temperature source heat pump water heater is an innovative system that utilizes ambient air, solar radiation, and other low-temperature heat sources to provide hot water efficiently. This paper presents the research content, methodology, and progress of the unit, along with a detailed analysis of its structure, characteristics, and performance testing. Preliminary results indicate that due to its high energy efficiency and environmental benefits, this technology has great potential to become a leading solution for small and medium-sized hot water supply systems.
**Keywords:** composite low temperature heat pump, water heater, market potential, application prospect
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**Research Background**
Traditional domestic hot water systems often rely on electric boilers, gas heaters, or solar water heaters. These systems typically suffer from low thermal efficiency, high energy consumption, and environmental impact. Solar water heaters, while eco-friendly, have high initial costs and are affected by weather conditions. Heat pumps, on the other hand, transfer heat from a low-temperature source to a high-temperature one, offering a higher coefficient of performance (COP). As a result, they are increasingly used in hot water generation.
A heat pump operates by using work to move heat from a low-temperature area to a high-temperature one. Its working principle is similar to that of a refrigerator, but instead of cooling, it focuses on heating. The challenge lies in applying this technology to produce hot water, especially when combining multiple low-temperature sources such as air and solar radiation. This has led to the development of composite low-temperature source heat pump units, which aim to maximize COP and expand their usability.
These units can generate hot water at 40–60°C with a COP of 4 or higher, meaning they consume only a quarter of the energy compared to traditional electric water heaters. By integrating renewable energy sources, they reduce reliance on fossil fuels, lower pollution, and increase overall efficiency. This makes them a sustainable and environmentally friendly option for hot water production.
The concept of heat pumps dates back to the 19th century, with significant advancements in the early 20th century. In the 1970s, due to the oil crisis, interest in heat pump technology surged. Countries like Japan, Sweden, and France began developing air-source heat pumps for residential use, while others focused on large-scale commercial applications. Today, China is rapidly advancing in heat pump technology, particularly in air-source systems. Research into solar-assisted, ground-source, and hybrid systems is ongoing, paving the way for broader adoption.
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**Research Content and Progress**
**1.1 R&D Main Content and Methods**
**1.1.1 R&D Focus**
This project involves collaboration between academia and industry, focusing on the design, optimization, and application of composite low-temperature source heat pump systems. Key areas include the development of heat exchangers, heat pump main units, and related technologies for both residential and commercial use. The goal is to create efficient, cost-effective, and scalable solutions for hot water generation.
Main research topics include:
1) Basic research on composite low-temperature heat pump systems, including heat exchanger design, refrigerant properties, and system simulation.
2) Technology development, such as miniaturization of heat exchangers and integration with air conditioning systems.
3) Industrialization, including mass production of heat pump water heaters and market expansion.
The overall objective is to develop a prototype, obtain necessary certifications, and establish demonstration projects that reduce operating costs by 30% compared to traditional systems.
**1.1.2 Research Methods**
The research follows three main approaches:
1) **Theoretical**: Developing design methods for different heat sources and simulating complex systems.
2) **Experimental**: Building and testing prototypes, optimizing components and system performance.
3) **Engineering Application**: Implementing real-world systems and promoting the technology through demonstration projects.
**1.2 Research Progress**
**1.2.1 Unit Configuration**
The first prototype of the air-source heat pump water heater has been completed. It consists of a refrigeration cycle with a compressor, evaporator, condenser, and expansion valve. The condenser is integrated into a water tank with internal coils. The system uses insulation materials like polyurethane foam to maintain efficiency.
**1.2.2 Unit Features**
- High efficiency: Consumes only 1/3–1/4 of the energy of electric heaters.
- Environmentally friendly: No emissions or combustion.
- Safe: No risk of fire, explosion, or electrical hazards.
- Long lifespan: Up to 15 years with minimal maintenance.
- Wide application: Suitable for residential, commercial, and public buildings regardless of climate.
**1.2.3 Test Results**
The unit was tested extensively. At temperatures above 6°C, the COP reaches 3. The system is fully automated, with smart controls and accurate metering for user billing. Performance curves show that COP increases with rising ambient temperature.
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**Application Prospects**
As an energy-efficient and green solution, the composite low-temperature source heat pump water heater is expected to play a key role in building heating and hot water systems in China. Its ability to operate effectively in both northern and southern regions, combined with low operating costs and no pollution, makes it highly competitive in various industries.
Although this technology is mature in developed countries, it is still in the early stages in China. Ongoing research aims to improve design, installation, and operation practices, ensuring safe and efficient performance. With growing demand for hot water in homes and commercial buildings, the market potential for this technology is vast. As energy efficiency improves and costs decrease, the composite low-temperature source heat pump will become a preferred choice for small and medium-sized hot water systems.
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