Basic knowledge of air source heat pump at a glance

Basic knowledge of air source heat pump at a glance

1. What is a heat pump?

　　 Heat pump is not a water pump, or even a pump, but a complete set of equipment. The English name of heat pump, heatpump, has 2 definitions:

　　 Definition 1: Circulating equipment that absorbs heat from a low-temperature heat source and sends it to a high-temperature heat source.

　　 Definition 2: A device that uses a part of high-grade energy (mechanical energy, electrical energy or high-temperature heat) as compensation to transfer heat from a low-temperature heat source to a high-temperature heat source.

　　 Let us recall the knowledge of physics:

　　 The first law of thermodynamics: the law of conservation of energy.

　　 The second law of thermodynamics: Heat can be transferred spontaneously from a high-temperature object to a low-temperature object, but it cannot be spontaneously transferred from a low-temperature object to a high-temperature object.

　　 Is the heat pump a monster that violates the laws of thermodynamics? Is the heat pump a perpetual motion machine?

　　 Let’s take a look at the working principle of the heat pump:

Pressure cooker: greater than 1 atmosphere, the boiling point of water will exceed 100 ℃,

　　 In other words, under high pressure, water vapor will condense into liquid when it exceeds 100°C!

　　 At 2 atmospheres, the boiling point of water is 121°C!

　　 low pressure cooker: when the pressure is less than 1 atmosphere, the boiling point of water will be lower than 100℃,

　　 In other words, under low pressure, water will evaporate into gas below 100°C!

　　 At 0.12 atmospheres, the boiling point of water is 50°C!

The compressor performs work to make the working fluid produce a physical phase change (gas-liquid-gas), and use this reciprocating cycle phase change process to continuously absorb heat through the low-pressure boiler (evaporator) and release heat from the high-pressure boiler (condenser). The heating device absorbs free heat, heats up the cold water through a heat exchanger, and delivers the hot water to the user through the water circulation system.

The steam engine started the first industrial revolution, and the world has entered a new era of energy utilization. Its principle is the Carnot cycle, which uses heat energy to convert into mechanical energy. The energy efficiency is always lower than 1.

The heat pump opens a new era of energy saving. The principle is the reverse Carnot cycle, which uses mechanical energy to convert low-temperature heat energy into high-temperature heat energy. The energy efficiency is always greater than 1, and the heat pump is the best way to save energy.

The highest density of various energy forms is electricity.

The best use of energy:

2. Advantages of air source heat pump

　　 Air source has many advantages. The most basic ones are safety, efficiency, pollution-free, and convenience. Some experts say that if heat pumps are called renewable energy, the annual average energy efficiency ratio of heat pumps must be greater than 2.7?

　　 Let’s argue that this sentence is correct. At present, 70% of China’s electricity comes from coal. From this point of view, experts are right, but the heat pump application for the following two reasons is highly recommended:

　　1, if the electricity comes from clean energy such as hydropower, wind power, solar wind power, etc., then the application of heat pumps is very environmentally friendly;

　　2, if the electricity used is the surplus electricity in the grid, this electricity is not used, which is equivalent to waste. At this time, the heat pump uses this part of the electricity, which can play a good role in peak and valley reduction. Except for the above-mentioned areas with long sunshine hours (such as Tibet and Yunnan), heat pumps are more advantageous than CSP in most areas of China. Heat pumps are the protagonist, and it is not economical to invest in heat pumps and solar energy.

　　 There are two sides to everything, and heat pumps are no exception. So what are the disadvantages of heat pumps?

　　 3. Disadvantages of air source heat pump

　　1, low temperature performance decline

　　2, frosting causes performance degradation

　　 There are shortcomings that are not terrible, there are always more methods than problems, so there are corresponding countermeasures for these two shortcomings.

　　 4. How to overcome the shortcomings of air source heat pumps?

　　 There are 5 measures to deal with the degradation of low temperature performance:

　　1, larger heat exchange area;

　　2, frequency conversion technology;

　　3, two-stage compression technology;

　　4, cascade compression technology;

　　5, the technology of air jet increasing enthalpy.

For the second problem-frosting performance degradation, there are 4 solutions:

　　1, larger heat exchange area-delay frosting;

　　2, reasonable fin heat exchanger design-delay frosting;

　　3, effective defrosting method mode-shorten defrosting time;

　　4, accurate defrosting entry and exit points-reduce heat loss.