1. Rotary total heat exchanger
The surface of rotary heat exchanger is honeycomb, and a layer of adsorption material is coated as desiccant. Place the runner between the air ducts and divide it into two parts. The exhaust air from the air-conditioned room is discharged from one side, and the outdoor air enters from the other side in the opposite direction. In order to increase the heat exchange area, the wheel rotates slowly (1~12 rpm). Half of the wheel absorbs and stores heat from the hot air, and when it rotates to the other side, it releases heat to transfer it. The desiccant attached to the surface condenses the moisture from the air flow with high humidity, and then absorbs it through the desiccant. When it rotates to the other side, it releases the moisture into the air flow with low humidity, which transfers the latent heat.
baffles are arranged on both sides of the rotating body of the heat exchanger, so that fresh air and exhaust air flow in the opposite direction. The runner chip is made of special paper or aluminum foil, and its surface is coated with a hygroscopic coating to form a carrier for heat and moisture exchange. It rotates at a speed of 1-12r/min, and the cold heat in the exhaust air is first collected in the heat accumulator (runner core) and then transferred to the fresh air. The air passes through the heat accumulator at a flow rate of 2.5-3.5m/s, and the heat and moisture exchange is carried out by the temperature difference between the fresh air and the exhaust air and the steam partial pressure difference. Therefore, both sensible heat and latent heat can be recovered.
1) Function and scope of application of the runner heat exchanger
Scope of application of work energy
It has excellent moisture absorption performance, and can recover sensible heat and latent heat, and the efficiency can reach 7% (the wheel body coated with moisture absorption coating). For air conditioning systems with humidity requirements, such as textile mills, paper mills and some production workshops, there is no moisture absorption requirement. When the sensible heat is mainly recovered, the sensible heat recovery device should be used, and the surface. When the exhaust temperature is lower than the dew point, it is possible to absorb moisture and recover latent heat. Gymnasium, department store, industrial ventilation system
2) Main advantages and disadvantages of runner heat exchanger:
Advantages and disadvantages
1. It can recover sensible heat and latent heat. 1. The device is large, occupying more building area and space
2. There is a certain self purification in the process of reverse alternation of exhaust air and fresh air. 2. The nozzle position is fixed, and the flexibility of piping is poor
3. Through speed control, It can adapt to different indoor and outdoor air parameters. 3. It has transmission equipment, which consumes power by itself. 4. The recovery efficiency is high, which can reach 7-8%. 4. The pressure loss is large, and it is easy to get dirty and blocked. 5. It can be applied to the exhaust system at higher temperature. 5. There is leakage, which cannot completely avoid cross-contamination. 3. Factors affecting the efficiency of the runner heat exchanger:
A.
B. air filters need to be installed at the air inlet on both sides of the runner.
C. When designing, it is necessary to calculate and check whether frost and ice will appear on the runner; If necessary, an air preheater should be installed on the fresh air pipe, or a temperature automatic control device should be installed behind the heat recovery device. When the temperature reaches the frost point, a signal will be sent to close the fresh air valve or open the preheater.
D. Because the total heat exchanger runner needs power and increases the resistance, it increases the conveying power and investment. Therefore, the recovery effect must be calculated, and it can only be selected when the total energy consumption is significantly saved.
e. it is suitable for places where the exhaust air does not contain harmful or toxic substances.
2. Low-temperature heat pipe heat exchanger
In p>1942, American engineers put forward the heat pipe principle. In the early 196s, research and trial production began, and it was first used in spacecraft and nuclear reactors. In the 197s, as a heat energy recovery device in a brand-new air system, the heat pipe heat exchanger finally showed outstanding advantages in the HVAC industry. Heat pipe is a heat transfer element that realizes heat transfer by the phase change of liquid in itself. It has the following characteristics: (1) Each heat pipe is permanently sealed, and there is no extra energy loss during heat transfer, no running parts and high operation reliability. ⑵ The structure of 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. (3) It is easy to expand the heating area on the outer surface of the heat pipe due to the heat exchange between hot and cold gases. (4) Cold and hot gases are separated by partitions, and there is no leakage, so there is no cross-contamination problem. 5] Because the fluid flow channel is spacious, the resistance loss is small. [6] Each heat pipe is completely independent and easy to maintain. (7) From the comprehensive indicators of environmental adaptability, waste heat recovery efficiency, pressure loss, blockage prevention, cleaning and service life, the heat pipe heat exchanger is dominant.
working principle: the heat pipe consists of a shell, a wick and an end cover. The evacuated pipe is filled with appropriate working fluid, and then both ends are sealed. The heat pipe is both an evaporator and a condenser. One end of the heat flow is the evaporation section, and the working medium evaporates after absorbing heat, and flows to the other end, that is, the condensation section for exothermic liquefaction, and flows back to the evaporation section under the action of capillary force to automatically complete the cycle.
the heat pipe heat exchanger is assembled by a single heat pipe, and the evaporation section and the condensation section are separated by a partition plate in the middle. The heat pipe heat exchanger completes heat transfer by the phase change of the working medium in the heat pipe. Each heat pipe is an unpowered refrigeration cycle system, and its heat transfer speed is several thousand times to ten thousand times that of the same metal. When the temperature difference is .1℃, it has a thermal response. It was originally used in satellites to solve the uneven heating of the sunny side and the shady side, and it is one of the necessary equipment on satellites. Now, it is more and more widely used in the field of air conditioning and waste heat recovery. An expert from Waseda University in Japan said: "Japan pays special attention to energy conservation and environmental protection, and heat pipe technology has found a new way for energy conservation and environmental protection because of its efficient heat transfer." The heat pipe heat exchanger is introduced and selected in the HVAC design manual.
1) Main advantages and disadvantages of low-temperature heat pipe heat exchanger:
Advantages and disadvantages
1. Compact structure, large heat transfer area per unit volume 1. Only sensible heat can be recovered, but latent heat cannot be recovered
2. No rotating parts, no extra energy consumption 2. Fixed nozzle position, flexibility of missing pipes and pipes
3. Each heat pipe has its own heat exchange system, so it is not suitable for dirty plugging. Hot and cold fluids can be changed
5. When the temperature difference between cold and hot air streams is small, a certain recovery efficiency can be obtained
6. The temperature drop is very small, close to isothermal operation, and the heat exchange efficiency is high, 6-7%
7. The service life is long, more than 12 years
2) Design considerations:
A. Low temperature heat pipe.
B. the oncoming wind speed should be 1.5 ~ 3.5 m/s.
C. The partition plate between cold and hot ends adopts double-layer structure, which can prevent cross-contamination caused by air leakage.
D. heat exchangers can be installed vertically or horizontally, and several can be connected in parallel or in series.
e. when the moisture content of the airflow is large, (there is latent heat recovery at this time, which can be used as a surplus)
f. A condensate removal device should be designed.
g. when starting the heat exchanger, the cold and hot airflow should flow at the same time, or the cold airflow should flow first, and when stopping, the cold and hot airflow should be stopped at the same time, or the hot airflow should be stopped first.
the conclusion of Liaoning energy demonstration meeting on heat pipe heat exchanger is: "This device is a secondary heating device. In the first stage, KLS series low-temperature heat pipe heat exchanger is used to recover exhaust heat to preheat fresh air. The second stage adopts SRZ air heater commonly used in ventilation engineering, and the two stages are connected in series, which is novel in structure and practical in engineering. It is a new energy-saving air supply heating unit integrating central heating and ventilation. The exhaust waste heat recovery device used in this product is KLS heat pipe heat exchanger. This heat pipe heat exchanger has been appraised by the State Machinery Committee and the Beijing Municipal Science and Technology Commission. It is considered that this product has compact structure, stable performance and convenient operation and maintenance. More than 3 sets of this product have been produced, and users have responded well, so the core equipment of this unit is reliable. This product has remarkable energy-saving effect, and can recover 6% of exhaust heat, with a payback period of 1-2 years. At the same time, it can also reduce environmental pollution. Experts attending the meeting agreed that this product should be actively promoted and used in enterprises in our province, and accumulated experience in the use process will continue to improve and improve, which is conducive to the development of energy-saving work in our province. < P > Second, analysis of energy saving and economic benefits of low-temperature heat pipe heat exchanger: < P > According to the outdoor temperature of -19℃ and indoor temperature of 2℃ in Shenyang in winter, if the exhaust air volume is 3 cubic meters/h, the energy loss will be 37, kal/h. The heat that can be recovered by the heat pipe heat exchanger per hour is 222, Kal/h according to the efficiency of 6%.
1. Working principle of plate heat exchanger:
Special paper material or aluminum foil is used to assemble channels formed by the interval between upper and lower layers. Air inlet passes through odd-numbered channels, and air outlet passes through double-numbered channels, and heat is transferred through the contact between air and plate. The efficiency of air supply and exhaust is the highest when it is countercurrent, but when it is countercurrent, the material is stressed the most, and it is easy to blow through the exchanger. Therefore, cross-flow structure is often adopted, and when it is fully heated, the surface should be.
advantages and disadvantages of plate heat exchanger:
advantages and disadvantages
1. simple structure, safe operation 1. large equipment volume, occupying more building space
2. no transmission equipment, no power consumption 2. easy to get dirty and blocked, difficult to clean, and large resistance.
3. No intermediate heat medium is needed. 3. When the air volume is high, the plate heat exchanger is limited. 4. The equipment cost is low.
Attention should be paid when designing and selecting the plate heat exchanger:
i. It is only suitable for general air conditioning projects, and should not be selected when the exhaust air contains harmful components.
ii. Because of the large resistance loss, in order to utilize fresh air and reduce energy consumption in the transitional season, a bypass ventilation pipe should be designed beside the heat exchanger to allow fresh air to pass by.
iii. Air valves with good airtightness must be installed on the air pipes and bypass ventilation pipes connected with the heat exchanger.
Ⅳ. The installation position should be convenient for core replacement.