The air source heat pump fan is attached to the air conditioner to assist in the cooling and heating function

The air source heat pump fan is attached to the air conditioner to assist in the cooling and heating function

In the process of accelerating the promotion and implementation of the "coal-to-electricity" project for heating in northern rural areas, as an upgraded form of ordinary heating and cooling air conditioners, low ambient temperature air source heat pump heaters have low product prices, simple system forms, convenient installation, and reliable operation. The characteristics of flexible control are becoming more and more recognized and accepted by people. The related technology is developing rapidly, and it is expected to become the main model of "coal-to-electricity" equipment. Aiming at the current low ambient temperature air source heat pump hot fan product standards have not been issued and the understanding is vague, this paper introduces the technical principles and characteristics of the products, and provides guidance and reference for the development of the "coal to electricity" project.

　　 1. Product definition and classification of low ambient temperature air source heat pump heaters

　　1.1 Heat pump belongs to the category of refrigeration equipment

　　To clarify the product classification range of low ambient temperature air source heat pump heat fans, we need to start with the concept of heat pumps. The standard "Refrigeration Equipment Terminology" (JB/T 7249-1994) formulated by the Ministry of Machinery Industry of China defines a heat pump as "a refrigeration system that transmits heat to a certain space or object. At this time, the evaporator is removed from outdoor air, water, etc. Absorbing heat, the condenser releases heat to heat a certain space or object. For example, if the flow of refrigerant is changed, the heat pump system can also be used to cool a certain space or object." Therefore, it can be seen from the definition that a heat pump is a refrigeration system , Belongs to refrigeration equipment. Some governments did not approve the business scope of refrigeration equipment in the heat pump equipment bidding process in the early stage.

　　1.2 Low ambient temperature air source heat pump heaters are air conditioners

At present, the corresponding standard specifications for low ambient temperature air source heat pump heaters are being drafted. According to the draft of the specifications, it is defined as "a vapor compression refrigeration cycle driven by an electric motor, a heat pump (fluorine) unit with air as a heat (cold) source, A refrigeration system that absorbs heat from outdoor low-temperature air and releases heat to the room to heat the indoor air, and a unit that can produce hot air at an ambient temperature of not less than -20°C."

　　 From the definition of the heat pump, it can be seen that the heating process and the cooling process of the heat pump are reversed, which is completely consistent with the principle of the heating and cooling air conditioner. When the purpose of heat pump operation is to directly regulate indoor air, this type of equipment can be called "air conditioner". Therefore, low ambient temperature air source heat pump heaters are in the air conditioning category.

　　 When the name of the low ambient temperature air source heat pump hot fan was not clear in 2017, experts used the names "ultra-low temperature heating air conditioner" and "ultra-low temperature air conditioner" in the technical demonstration documents of the government bidding. Therefore, there is no doubt that the low ambient temperature air source heat pump hot fan is an air conditioner.

　　2. The problems of ordinary heating and cooling air conditioners in cold areas

　　 Ordinary heating and cooling air conditioners have been widely used in the heating in the middle and lower reaches of the Yangtze River, which is hot in summer and cold in winter, but they are not effective in cold northern regions. The climate in cold regions of our country is dry in winter, even if the temperature is low, the frosting of air conditioners will not be too serious. The factors restricting the application of air conditioning in cold areas mainly include the following three aspects:

　　2.1 When the heat demand is large, the heating capacity is insufficient

　　 With the decrease of outdoor environment temperature, the heating load of building heating is gradually increasing, while the heating capacity of air conditioner is decreasing accordingly. For example, in the outdoor environment of ordinary 3HP (hp) air conditioners, the heating at -7°C and -20°C attenuates 21.7% and 47.0% respectively. When the condensing temperature of the air conditioning system does not change, the decrease in outdoor air temperature will reduce the evaporation temperature of the system, causing the specific volume of the circulating working fluid to increase, resulting in a decrease in the suction volume of the unit, a reduction in the circulating volume of the system working fluid, and the actual heating capacity of the unit Will drop sharply.

　　2.2 Poor operating reliability or failure to operate normally in a low temperature environment

　　 With the decrease of the ambient temperature, the suction pressure of the circulating working fluid decreases, resulting in the continuous increase of the compressor compression ratio and the rapid increase of the discharge temperature. When the outdoor temperature drops to a certain value, the compressor discharge temperature will exceed the allowable working range, the compressor will automatically shut down for protection, and the unit will stop working normally. At the same time, as the compressor discharge temperature increases, the viscosity of the lubricant drops sharply after being heated, and the lubrication performance becomes worse. The compressor frequently starts and stops.

　　2.3 Poor thermal comfort

　　 Ordinary air conditioner indoor unit adopts side air supply method, which leads to high temperature at the air supply outlet and upper area, low temperature in the personnel activity area, and temperature stratification in the vertical direction. In northern rural areas, most of the existing air conditioners in farmers’ homes are conventional fixed-frequency air conditioners, which have low heating capacity and insufficient heating capacity in low-temperature environments. Coupled with the unstable power grid in some rural areas, fixed-frequency air conditioners cannot operate normally under extremely low voltage conditions. In addition, the space and floor height of houses in rural areas are larger and higher than those of urban commercial houses. Conventional fixed-frequency air-conditioning is used for heating, and the indoor temperature rise is relatively slow. These are the reasons for the poor thermal comfort experience.

　　3. Introduction of low ambient temperature air source heat pump hot fan technology

　　3.1 System principle

　　 In order to solve the heating problems of ordinary heating and cooling air conditioners in the northern cold regions, low ambient temperature air source heat pump heaters came into being. Give an example to illustrate the solution of two-stage enthalpy-enhanced compression rotor type low ambient temperature air source heat pump hot fan technology. The specific system operation principle is shown in the figure below.

The system is mainly composed of two-stage compression rotor type inverter compressor, flasher, evaporator, condenser, throttle valve A, throttle valve B and other components. The two cylinders of the two-stage compression rotor type inverter compressor bear low pressure respectively. Stage compression and high-pressure stage compression.

The low-pressure refrigerant vapor s* from the evaporator first enters the low-pressure stage compressor and is compressed to an intermediate pressure (processes 1-2), and then is mixed with the refrigerant vapor at the outlet of the flash evaporator (point 6 is the mixture of points 2 and 3) status). The mixed vapor continues to enter the high-pressure stage compressor to be compressed to the condensing pressure (process 6-7), and then enter the condenser to release heat to the indoor air and then condense into a refrigerant liquid (process 7-9). The high-pressure refrigerant liquid s* from the condenser is first throttled by the throttle valve A to become a gas-liquid mixture (process 9-10), then enters the flash evaporator, and is separated into saturated steam (point 3) and saturated liquid (point 3). 4). The gaseous refrigerant from the throttling flash rises, mixes with the exhaust of the low-pressure stage compressor, and enters the high-pressure stage compressor; the liquid refrigerant in the flash evaporator passes through the second throttling of the throttle valve B into a low-temperature low-pressure liquid (process 4~5), it enters the evaporator and exchanges heat with the outdoor air, and becomes low-temperature and low-pressure steam (process 5~1), and then enters the low-pressure stage compressor to start a new cycle.

In summary, the system adopts a two-stage compression heat pump cycle with secondary throttling and incomplete cooling. Compared with single-stage compression under the same working conditions, the compressor discharge temperature is reduced, the pressure ratio is reduced, and it can be operated at a lower ambient temperature. Work down. Compared with single-stage compression, the dual-stage variable capacity technology adopted by the system improves the heating capacity and the coefficient of performance under heating conditions, especially at low ambient temperatures. It provides a reliable technical guarantee for the heating application of low ambient temperature air source heat pump hot air blower in cold areas.

　　3.2 Product features and advantages

　　 Compared with ordinary heating and cooling air conditioners, low ambient temperature air source heat pump hot fans have the following advantages in heating and heating:

　　(1) Expand the scope of use of air source heat pumps, and realize that the unit can operate stably in an outdoor low temperature environment of -30°C without using electric auxiliary heating;

(2) When the rated working condition is 7℃, the heating energy efficiency of the low ambient temperature air source heat pump hot fan can be increased by 5%-10% compared with ordinary heating and cooling air conditioners, and at low temperature working condition -20℃, it can increase by 20% about;

　　(3) Compared with the rated heating capacity, the heating capacity can be achieved without attenuation under the environment of -20℃ and -30℃;

　　(4) Users can set the air outlet temperature by themselves, so as to realize constant temperature air supply;

　　(5) Air convection is generated by the wind from the equipment, and the room temperature rises extremely quickly, and the indoor temperature can meet the heating requirements of users.

　　(6) The comfort of the product is improved, and the floor-to-ceiling fan is used to supply air from the bottom of the room to avoid the hot head and cold feet when the air conditioner is blown.

4 Conclusion

　　(1) The low ambient temperature air source heat pump hot fan belongs to the category of air conditioners, which can realize the heating and cooling functions of the room;

　　(2) Low ambient temperature air source heat pump hot air blower effectively overcomes and solves the heating problems of ordinary heating and cooling air conditioners in cold areas, so that the unit can continue to provide stable heating;

　　(3) Combining the subsidy policy and the feasibility of implementation, the low-ambient temperature air-source heat pump air heater has a huge prospect in the future "coal-to-electricity" market.