Traditional domestic hot water installations usually use electric boilers, oil-fired boilers, gas boilers or household electric water heaters, gas water heaters and solar water heaters. The thermal efficiency of these devices is low, a large amount of energy consumption, is not conducive to environmental protection. Solar water heater initial installation cost is higher, and affected by climate and installation conditions. Heat pump to achieve the transfer of heat from low temperature to high temperature, high coefficient of performance. Therefore, as a hot water preparation device, the heat pump system has been more and more widely used.

Heat pump is done by doing work to heat the medium from low temperature to high temperature medium flow device. Heat pump and refrigerator work principle and process are exactly the same, the only difference is that the purpose of the application is different: the purpose of the refrigerator is to remove heat from low-temperature heat source, or get cold, such as home refrigerators, air conditioners, etc .; usually The heat pump is to get a higher temperature for the purpose of heat. However, how to use this technology to make hot water, especially how to make use of air and solar radiation as a composite low temperature source to produce hot water, is still a technology to be developed and improved.

Composite low-temperature source heat pump hot water unit is the use of air, solar radiation, etc. as a low-temperature heat source, through the mechanical work of these low-temperature heat transfer to the hot water heat exchanger, making 40 ℃ ~ 60 ℃ hot water, the output power And the ratio of input power (referred to as COP value) can reach 4 or more, that is made of the same hot water, the power consumption is only 1/4 of the electric water heater. The composite low temperature source can maximize the COP value of the heat pump to expand its use range and range. The compound low-temperature source heat pump hot water unit can overcome the defects of low energy efficiency and heavy pollution, such as electric hot water boiler, fuel hot water boiler and electric water heater, and greatly increase the efficiency. Therefore, this technology is energy-saving and has significant environmental benefits. Utilizing renewable energy, it is an energy-saving technology and a low-grade heat utilization technology in energy conversion and transmission.

The theoretical basis of the heat pump originated in the nineteenth century Carnarvon paper. Until the 20th century 20-30 years, heat pump equipment development has made rapid development. At that time, the United Kingdom installed the first heat pump to use air as a source of heat for hot water supply and heating. In 1937, Japan built a large-scale building with a heat pump air-conditioning system using low-temperature spring water as its source. Before and after 1950, Britain and the United States started to use the underground coil to absorb geothermal heat as a household heat pump research. Due to the impact of the oil crisis, the heat pump in the 70's to get greater development. Japan, Sweden and France and other countries to produce outdoor air as a heat source of small home heat pump. Britain and Germany have developed large heat pump units that combine heat recovery with commercial and public buildings.

In recent years, our country has entered the stage of rapid development in the application of heat pump technology, especially the research and application of air source heat pump is progressing rapidly. Domestic researchers on the solar heat pump, water source heat pump and ground source heat pump applied research and engineering demonstration. These have played a very good role in promoting the application of heat pump in building heating and air conditioning. At present, the composite low-temperature heat pump heating technology and application research has just started.

1.1 R & D main content and methods

1.1.1 R & D main content

Our school-enterprise cooperation mainly focuses on the design and optimization methods of different low-temperature heat sources, heat pump mainframes and heat exchangers in complex low-temperature source heat pump water heaters, and the application technologies of compound low-temperature source heat pump systems, and the research and development and development of low-temperature source heat pump industry Closely related to commercial composite low-temperature source heat pump hot water unit, household composite low-temperature source heat pump water heaters and related equipment. The main research content:

1) Basic research on composite low-temperature source heat pump hot water system: design and calculation methods and optimization of different low-temperature source heat exchangers; research on characteristics of high-temperature source heat pump refrigerant; simulation and optimization of compound low-temperature source heat pump hot water system.

2) technology development of composite low-temperature source heat pump hot water system: solar heat collector, air heat exchanger and water - refrigerant heat exchanger heat exchanger technology and its miniaturization technology; heat pump hot water system for air-conditioning technology Development.

3) Industrialization of compound low-temperature source heat pump hot water system: development and production of applicable domestic composite low-temperature source heat pump water heaters and commercial low-temperature heat pump water heaters; development and production of various types of heat exchangers suitable for composite low- Heaters; market cultivation and development.

The overall objective: To establish and develop heat transfer design and calculation methods and computer aided design of heat exchangers; To design and develop a prototype of composite low-temperature source heat pump hot water unit and to identify and promote; Products through the relevant national industry license certification and access to the corresponding patent And intellectual property rights; construction of composite low-temperature source heat pump hot water supply demonstration project, and to reach than the traditional hot water supply system operating costs reduced by 30%.

1.1.2 research methods

1) Theoretical research: Based on the previous research work, a heat pump design method suitable for different low-temperature heat sources and hot water heat exchange systems is proposed. According to different conditions of use and application, to determine the design of the host selection. Through the theoretical improvement, in-depth analysis of physical phenomena and computer simulation methods to solve the complex low-temperature heat pump hot water system optimization design problems.

2) Experimental research: design, production, installation, commissioning of heat pump prototype. Mainly include the design of various heat exchangers, heat transfer enhancement and the miniaturization of the main body; the determination of various parameters of the prototype; the optimized design of the mainframe and its system.

3) Engineering application research and promotion: design and installation of composite low-temperature heat pump hot water system demonstration project, research and development of the corresponding parts, equipment and construction technology.

1.2 research progress

1.2.1 unit configuration

The first air source heat pump hot water unit prototype we have jointly developed has been completed. Heat pump water heater is composed of a refrigeration cycle, including the host and the condenser in two parts. The main part includes evaporator, fan, compressor and expansion valve; the condenser is a holding tank with condensing coil inside. See Figure 1. The refrigerant absorbs the heat of the outside air in the evaporator, releases heat within the condensing coil by the heat pump cycle, and heats the water in the tank. Water tank insulation with closed-cell rubber sponge or polyurethane foam, and has good insulation properties.

1.2.2 Unit Features

1) High efficiency and energy saving: The hot water unit takes hot air as the low-temperature heat source and consumes only 1/3 ~ 1/4 of the electric heater. Compared with coal, oil and gas hot water units, Save more than half of the operating costs.

2) Environmentally-friendly and pollution-free: This system runs without any combustions and emissions and is a sustainable and environment-friendly product.

3) safe and reliable operation: the operation of the system without the traditional flammable, explosive, poisoning, short circuit and other hazards that may exist in traditional water heaters (fuel or gas or electric water heaters), is a safe and reliable hot water system.

4) long service life, low maintenance costs: the unit's service life of up to 15 years or more; safe and reliable operation, and can achieve unmanned operation, automatic intelligent control. Comfortable and convenient, automated, high degree of intelligence, the system uses a self-controlled thermostat, 24h to provide constant temperature hot water.

5) A wide range of applications, free from the impact of climate: The hot water unit can be widely used in large and medium-sized hot water supply system in residential, hotel and public buildings and other places; the operation of the system is not affected by climate, can be run around the clock. See Table 1 for details.

1.2.3 unit test results

The developed unit conducted a more comprehensive test. Table 2 for the hot water supply capacity of the unit. The unit make full use of the heat of the environment, to provide users with hot water. The system is fully automatic control, household metering centralized display to ensure that the accurate measurement of the user charges. Such as the configuration of the water tank can be achieved during low-cost operation. Figure 2 shows the measured unit performance curve. As can be seen from the figure, as the outdoor temperature increases, the unit's COP value also increases. When the air temperature is above 6 ℃, the unit's COP value reaches 3 already.

As an effective energy-saving green product, the composite low-temperature source heat pump hot water unit will play more and more important role in the building heating system in our country. Composite low temperature source heat pump hot water unit can be used in the vast area of ​​our country south and north. Due to its advantages of low operating cost, high coefficient of performance and no pollution, the compound low-temperature source heat pump water heater unit is also highly competitive in many hot water preparation plants. Therefore, as a hot water heating system for the preparation of equipment, composite low-temperature source heat pump hot water unit will be more widely used. Compound low-temperature source heat pump hot water unit has great market potential and broad application prospects.

Composite low-temperature heat pump water heaters as a commodity in the United States and other developed countries have matured, but in our country has just started. One of the important reasons is that our research on the application of the composite low-temperature source heat pump water heater unit is still not perfect. In particular, the research and summary of the influence of various composite low temperature sources on the design, installation and operation of the heat exchanger heat exchangers are almost empty. We will summarize the practical experience in design, installation and operation adjustment in time and formulate appropriate technical measures to promote the application of the technology and technical services to make the heating system safe, reliable, economical and effective. One of the water supply. Through engineering applications, continuous improvement of product performance, improve energy efficiency.

However, it should also be noted that the materials, equipment and related technologies used in the composite low-temperature source heat pump heating technology are not significantly different from the traditional refrigeration and air-conditioning systems. The heat pump mainframe, heat exchangers and other equipment can also be processed by similar enterprises produce. Therefore, the application of composite low-temperature source heat pump heating technology will enable a number of enterprises to invest in this industry. Relevant materials, equipment, industrialization, will greatly reduce the composite low-temperature heat pump heating technology, the initial investment, and thus effectively promote the popularity of the technology. With the development of our economy and improvement of people's living standards, domestic hot water has become the basic demand of ordinary people. Hot water supply has become an indispensable system for public buildings, especially hotel and hotel. The market prospect is very broad. The compound low-temperature source heat pump hot water unit because of its technical advantages and energy-saving advantages, will become a small and medium-sized hot water supply system has a very competitive option.