The core problem of compressor oper
Principles and characteristics of heat recovery series air conditioning units
With the growth of China’s economic power and the continuous improvement of people’s material and cultural living standards; the rapid development of high-rise buildings, high air-tightness and high heat insulation affect people’s working and living environments, and people’s requirements for indoor air quality are becoming more and more serious. The higher you come, people are eager to have a healthy and comfortable indoor environment, especially after the SARS attack, people pay more and more attention to indoor air quality, and put forward higher requirements for the introduction of outdoor fresh air ventilation, but ventilation will inevitably be Bringing energy loss, the introduction of fresh air needs to consume more energy, so it is necessary to consider an effective energy-saving method to exchange heat between fresh air and exhaust air through a heat recovery device. The heat exchanger is a key device for air conditioning and waste heat recovery.
The main forms of heat recovery unit include runner total heat recovery, runner sensible heat recovery, plate total heat recovery, plate sensible heat recovery, heat pipe heat recovery, and glycol heat recovery.
The principle and characteristics of heat recovery
Ⅰ) The runner heat recovery device, inside is a runner that rotates at a constant speed/variable speed. It is made of aluminum foil or aluminum foil and a high-efficiency moisture absorber with high-tech technology, or made of special composite materials, assembled in one The box body that reverses the airflow without interfering with each other is driven by a belt driven by a transmission device.
The enthalpy value of the indoor exhaust air in winter is higher than that of the outdoor fresh air. When the exhaust air passes through the runner, the enthalpy value of the runner increases due to the energy exchange. When it runs to the fresh air side, it releases energy to the low enthalpy fresh air and the fresh air heats up. In summer, on the contrary, the fresh air temperature decreases. Due to the continuous rotation of the runner, the energy of the air on the high temperature side is constantly exchanged for the air on the low temperature side.
In the full heat type runner, humidity is also transferred. When there is a pressure difference between the water vapor partial pressures of the air on both sides, the water will be absorbed from the high side through the runner and released on the low side after rotation, thereby realizing latent heat exchange.
The characteristics of the runner heat recovery device: The equipment has a compact structure, a small footprint, and saves space; the heat recovery efficiency is high; the windward area of a single runner is large, and the resistance is small. It is widely used in heat recovery of large air volume air conditioning systems.
Ⅱ) The plate heat recovery device recovers sensible heat or total heat when there is a difference in temperature or partial pressure of water vapor between the two air streams on both sides of the partition. In the plate heat recovery device, two air streams flow through the heat exchanger in a cross flow. The partitions of the sensible heat exchanger are non-permeable materials with good thermal conductivity, generally aluminum materials. The total heat exchanger is a permeable air-to-air heat exchanger. The partition plate is made of processed materials with good heat and moisture permeability. The temperature (sensible heat) exchange mechanism is that when air of different temperatures flows on both sides of the medium, heat is exchanged by conduction.
The exchange of humidity (latent heat) in the total heat exchanger is carried out through the following two mechanisms:
① Humidity exchange is carried out through the partial pressure difference of water vapor on both sides of the medium.
②The water vapor on the high-humidity side is absorbed by the hygroscopic agent and discharged to the low-humidity side by the capillary action of the paper fibers.
Plate heat recovery device features: good sealing, low air mixing rate; high heat recovery efficiency; no moving parts, stable and reliable operation, low maintenance costs. It is widely used in the heat recovery of air conditioning systems.
Ⅲ) Heat pipe heat recovery device, first evacuated in the closed tube, and then filled with proper amount of working fluid in this state, heated at the lower end of the heat pipe, the working fluid absorbs heat and vaporizes into steam, and rises to the heat pipe under a slight pressure difference The upper end emits heat to the outside world and condenses into liquid. Under the action of gravity, the condensate returns to the heating section along the inner wall of the heat pipe, and is heated and vaporized again, so that the heat is continuously transferred from one end to the other end. Due to the phase change heat transfer, the thermal resistance in the heat pipe is very small.
The heat pipe is a heat transfer element that realizes heat transfer by the phase change of its internal liquid. It has the following characteristics:
⑴Each heat pipe is permanently sealed, there is no additional energy loss during heat transfer, no running parts, and high operational reliability.
⑵The structure of the heat pipe heat exchanger determines that it is a typical countercurrent heat exchange, and the heat pipe runs almost isothermally, so the heat pipe heat exchanger has high efficiency.
⑶The heat transfer of the hot and cold gas is carried out on the outer surface of the heat pipe to easily expand the heating area.
⑷The hot and cold gases are separated by partitions, and there is no leakage, so there is no cross-contamination problem.
⑸ Due to the wide fluid flow channel, the resistance loss is small.
⑹Each heat pipe is completely independent and easy to maintain.
⑺ From the perspective of environmental adaptability, waste heat recovery efficiency, pressure loss, blocking prevention, cleaning, and life span, heat pipe heat exchangers have unique advantages.
Ⅴ) The glycol heat recovery device uses the heat exchanger and glycol solution as the heat exchange medium to transfer the cold (heat) in the exhaust air to the glycol solution through the heat exchanger, reducing (increasing) ) The temperature of the glycol solution, and then the cooled (heated) glycol solution is transported to the heat exchanger on the fresh air side through the circulating pump to reduce (increase) the fresh air temperature, reduce the load of the system and the operation of the entire air conditioning system cost.
Glycol heat recovery device features: no cross-contamination, easy installation, small space restrictions, suitable for places with a long distance between air supply and exhaust.
